Category Archives: tsunami

Earthquake Report: Alaska

What a day. I started by waking up about 5:43 AM (about, heheh), which was 17 minutes before my alarm was set. I had a job interview at 8:30.

I went to the interview for a position working on tsunami geology. During the interview, everyone started getting phone calls and emails, there was an earthquake in Alaska. The main interviewer had to leave the interview to take a few calls. Pretty funny, before they left, they asked me what would I do. Perfect timing.

We all broke out our phones and started reviewing the early reports and hypothesizing. I thought this may be related to the earthquake in 2016, though that was much deeper.

Much has been written about this earthquake and I include tweets to summaries below in the social media section.

Today’s earthquake occurred along the convergent plate boundary in southern Alaska. This subduction zone fault is famous for the 1964 March 27 M = 9.2 megathrust earthquake. I describe this earthquake in more detail here.

During the 1964 earthquake, the downgoing Pacific plate slipped past the North America plate, including slip on “splay faults” (like the Patton fault, no relation, heheh). There was deformation along the seafloor that caused a transoceanic tsunami.

The Pacific plate has pre-existing zones of weakness related to fracture zones and spreading ridges where the plate formed and are offset. There was an earthquake in January 2016 that may have reactivated one of these fracture zones. This earthquake (M = 7.1) was very deep (~130 km), but still caused widespread damage.

There was also an earthquake associated with the faults in the Pacific plate, which is still having asftershocks, earlier this year. Here is my earthquake report for the 2018.01.24 M 7.9 earthquake. I prepared two update reports here and here.

Today’s earthquake was not on the megathrust fault interface and is extensional. I always have fun chatting with people new to subduction zones when we get to see an extensional earthquake at a convergent plate boundary. Because the earthquake was a normal earthquake (extensional) and it was rather deep, the possibility of a tsunami was quite small. However, there was a possibility that landslides could have triggered tsunami. However, these would be localized near the epicentral region.

The earthquake appears to have a depth of ~40 km and the USGS model for the megathrust fault (slab 2.0) shows the megathrust to be shallower than this earthquake. There are generally 2 ways that may explain the extensional earthquake: slab tension (the downgoing plate is pulling down on the slab, causing extension) or “bending moment” extension (as the plate bends downward, the top of the plate stretches out.

Below is my interpretive poster for this earthquake


I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 3.0 in one version.

I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab 2.0 contours plotted (Hayes, 2018), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault.li>

    Magnetic Anomalies

  • In the map below, I include a transparent overlay of the magnetic anomaly data from EMAG2 (Meyer et al., 2017). As oceanic crust is formed, it inherits the magnetic field at the time. At different points through time, the magnetic polarity (north vs. south) flips, the north pole becomes the south pole. These changes in polarity can be seen when measuring the magnetic field above oceanic plates. This is one of the fundamental evidences for plate spreading at oceanic spreading ridges (like the Gorda rise).
  • Regions with magnetic fields aligned like today’s magnetic polarity are colored red in the EMAG2 data, while reversed polarity regions are colored blue. Regions of intermediate magnetic field are colored light purple.
  • We can see the roughly east-west trends of these red and blue stripes. These lines are parallel to the ocean spreading ridges from where they were formed. The stripes disappear at the subduction zone because the oceanic crust with these anomalies is diving deep beneath the North America plate, so the magnetic anomalies from the overlying North America plate mask the evidence for the Pacific plate.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper left corner is a map of the plate boundary faults from IRIS, which shows seismicity with color representing depth. I place a blue star in the general location of today’s earthquake (same for other inset figures).
  • Below this map is a low-angle oblique view of the subduction zone.
  • In the lower right corner is a map that shows the isochrons (line of equal age) for the oceanic crust of the Pacific plate (Naugler and Wageman, 1973). Compare these lines with the magnetic anomalies in the main poster.
  • In the upper right corner is the USGS liquefaction susceptibility map which is now a standard map product for USGS earthquake pages (for earthquakes of sufficient size). There has been photos of road damage that appear to be the result of liquefaction induced slope failures. I presented this map product in my reports for the 2018.09.28 Sulawesi, Indonesia earthquake and tsunami.
  • Another new product from the USGS is an aftershock forecast. GNS (New Zealand) has been doing this for a while (I first noticed these following the 2016 Kaikoura earthquake). I prepared a table from their data that lists the potential number of earthquakes for different magnitudes for different time periods. These estimates are basically based on the empirical evidence that aftershock size and number decay with time.
  • Here is the map with a century’s seismicity plotted.

Other Report Pages

Some Relevant Discussion and Figures

  • Here is a map for the earthquakes of magnitude greater than or equal to M 7.0 between 1900 and 2016. This is the USGS query that I used to make this map. One may locate the USGS web pages for all the earthquakes on this map by following that link.

  • Here is a cross section showing the differences of vertical deformation between the coseismic (during the earthquake) and interseismic (between earthquakes).

  • Here is a figure recently published in the 5th International Conference of IGCP 588 by the Division of Geological and Geophysical Surveys, Dept. of Natural Resources, State of Alaska (State of Alaska, 2015). This is derived from a figure published originally by Plafker (1969). There is a cross section included that shows how the slip was distributed along upper plate faults (e.g. the Patton Bay and Middleton Island faults).

Below is an educational video from the USGS that presents material about subduction zones and the 1964 earthquake and tsunami in particular.
Youtube Source IRIS

mp4 file for downloading.

    Credits:

  • Animation & graphics by Jenda Johnson, geologist
  • Directed by Robert F. Butler, University of Portland
  • U.S. Geological Survey consultants: Robert C. Witter, Alaska Science Center Peter J. Haeussler, Alaska Science Center
  • Narrated by Roger Groom, Mount Tabor Middle School

Geologic Fundamentals

  • For more on the graphical representation of moment tensors and focal mechnisms, check this IRIS video out:
  • Here is a fantastic infographic from Frisch et al. (2011). This figure shows some examples of earthquakes in different plate tectonic settings, and what their fault plane solutions are. There is a cross section showing these focal mechanisms for a thrust or reverse earthquake. The upper right corner includes my favorite figure of all time. This shows the first motion (up or down) for each of the four quadrants. This figure also shows how the amplitude of the seismic waves are greatest (generally) in the middle of the quadrant and decrease to zero at the nodal planes (the boundary of each quadrant).

  • Here is another way to look at these beach balls.
  • There are three types of earthquakes, strike-slip, compressional (reverse or thrust, depending upon the dip of the fault), and extensional (normal). Here is are some animations of these three types of earthquake faults. The following three animations are from IRIS.
  • Strike Slip:

    Compressional:

    Extensional:

  • This is an image from the USGS that shows how, when an oceanic plate moves over a hotspot, the volcanoes formed over the hotspot form a series of volcanoes that increase in age in the direction of plate motion. The presumption is that the hotspot is stable and stays in one location. Torsvik et al. (2017) use various methods to evaluate why this is a false presumption for the Hawaii Hotspot.

  • A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)

  • Here is a map from Torsvik et al. (2017) that shows the age of volcanic rocks at different locations along the Hawaii-Emperor Seamount Chain.

  • Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.

Return to the Earthquake Reports page.

Earthquake Report: Sulawesi (Celebes), Indonesia

Well, around 3 AM my time (northeastern Pacific, northern CA) there was a sequence of earthquakes including a mainshock with a magnitude M = 7.5. This earthquake happened in a highly populated region of Indonesia.

This area of Indonesia is dominated by a left-lateral (sinistral) strike-slip plate boundary fault system. Sulawesi is bisected by the Palu-Kola / Matano fault system. These faults appear to be an extension of the Sorong fault, the sinistral strike-slip fault that cuts across the northern part of New Guinea.

There have been a few earthquakes along the Palu-Kola fault system that help inform us about the sense of motion across this fault, but most have maximum magnitudes mid M 6.

GPS and block modeling data suggest that the fault in this area has a slip rate of about 40 mm/yr (Socquet et al., 2006). However, analysis of offset stream channels provides evidence of a lower slip rate for the Holocene (last 12,000 years), a rate of about 35 mm/yr (Bellier et al., 2001). Given the short time period for GPS observations, the GPS rate may include postseismic motion earlier earthquakes, though these numbers are very close.

Using empirical relations for historic earthquakes compiled by Wells and Coppersmith (1994), Socquet et al. (2016) suggest that the Palu-Koro fault system could produce a magnitude M 7 earthquake once per century. However, studies of prehistoric earthquakes along this fault system suggest that, over the past 2000 years, this fault produces a magnitude M 7-8 earthquake every 700 years (Bellier et al., 2006). So, it appears that this is the characteristic earthquake we might expect along this fault.

Based on what we know about strike-slip fault earthquakes, the portions of the fault to the north and south of today’s sequence may have an increased amount of stress due to this earthquake. Stay tuned for a Temblor.net report about this earthquake where I discuss this further.

There are reports of a local tsunami with a run-up about 2 meters. However, the UNESCO Sea Level Monitoring Facility (website) does not show any tsunami observations on tide gage data in the region.

Most commonly, we associate tsunamigenic earthquakes with subduction zones and thrust faults because these are the types of earthquakes most likely to deform the seafloor, causing the entire water column to be lifted up. Strike-slip earthquakes can generate tsunami if there is sufficient submarine topography that gets offset during the earthquake. Also, if a strike-slip earthquake triggers a landslide, this could cause a tsunami. We will need to wait until people take a deeper look into this before we can make any conclusions about the tsunami and what may have caused it.

Did you feel this earthquake? If so, fill out the USGS “Did You Feel It?” form here. If not, why not? Probably because you were too far away. The closer to an earthquake, the more strong the shaking intensity and the larger chance of infrastructure damage (roads, houses, etc.). The USGS PAGER alert for this earthquake shows that there are ~282,000 people living in Palu, a city near the epicenter. The estimate for shaking intensity is a MMI VI, which could result in light damage for resistant structures and moderate damage for vulnerable structures. More about USGS PAGER alerts here. There exists a possibility that there were more than 100 fatalities from this earthquake.

UPDATE 2018.09.28 23:00

  • There have been tsunami waves recorded on a tide gage over 300 km to the south of the epicenter, at a site called Mumuju. Below is a map and a plot of water surface elevations from this source.


UPDATE 2018.09.29 07:00


I awakened this morning (my time, obviously) to find that there are over 380 reported deaths from this earthquake and tsunami. More on this later in the day (clouds are preparing to our and i need to put some of my stuff under tarps).

I prepared a report for Temblor where we present results of static coulomb stress modeling. Here is that report.

UPDATE 2018.09.29 10:45

Here is a (200 MB) video that I edited slightly. Download here. This was originally posted here.

UPDATE 2018.09.30 17:00

Below is my interpretive poster for this earthquake


I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M ≥ 6.0 in one version.

I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab 2.0 contours plotted (Hayes, 2018), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault.

    Magnetic Anomalies

  • In the map below, I include a transparent overlay of the magnetic anomaly data from EMAG2 (Meyer et al., 2017). As oceanic crust is formed, it inherits the magnetic field at the time. At different points through time, the magnetic polarity (north vs. south) flips, the north pole becomes the south pole. These changes in polarity can be seen when measuring the magnetic field above oceanic plates. This is one of the fundamental evidences for plate spreading at oceanic spreading ridges (like the Gorda rise).
  • Regions with magnetic fields aligned like today’s magnetic polarity are colored red in the EMAG2 data, while reversed polarity regions are colored blue. Regions of intermediate magnetic field are colored light purple.
  • We can see the roughly east-west trends of these red and blue stripes. These lines are parallel to the ocean spreading ridges from where they were formed. The stripes disappear at the subduction zone because the oceanic crust with these anomalies is diving deep beneath the Sunda plate (part of Eurasia), so the magnetic anomalies from the overlying Sunda plate mask the evidence for the Australia plate.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper left corner is a map from Bellier et al. (2016) that shows the plate boundary faults in the region. Relative senses of motion across these faults is shown as red arrows. The M 7.5 epicenter is shown as a blue star (as in other figures).
  • In the upper right corner is a larger scale map showing the strike-slip fautls that transect the island of Sulawesi, Indonesia (Bellier, et al., 2006)
  • In the lower right corner is a low angle oblique view of the subducting plates in this region (Hall, 2011). Note the orientation of the Sorong fault and the Sulawesi faults.
  • In the lower left corner is a large scale map showing detailed versions of these fault systems in Sulawesi. Earthquake fault mechanisms are plotted for historic earthquakes. Today’s M 7.5 occurred just to the north of the spatial extent of this map.
  • Here is the map with a month’s seismicity plotted.

  • Here is the map with a centuries worth of seismicity plotted.

Other Report Pages

Some Relevant Discussion and Figures

  • Here is the low angle oblique view of the plate boundaries in this region (Hall., 2011).

  • 3D cartoon of plate boundaries in the Molucca Sea region modified from Hall et al. (1995). Although seismicity identifies a number of plates there are no continuous boundaries, and the Cotobato, North Sulawesi and Philippine Trenches are all intraplate features. The apparent distinction between different crust types, such as Australian continental crust and oceanic crust of the Philippine and Molucca Sea, is partly a boundary inactive since the Early Miocene (east Sulawesi) and partly a younger but now probably inactive boundary of the Sorong Fault. The upper crust of this entire region is deforming in a much more continuous way than suggested by this cartoon.

  • Here is the map from Bellier et al. (2006) that shows the plate boundary faults, along with some other tectonic information.

  • Regional geodynamic sketch that presents the present day deformation model of Sulawesi area (after Beaudouin et al., 2003) and four main deformation systems around the Central Sulawesi block, highlighting the tectonic complexity of Sulawesi. Approximate location of the Central Sulawesi block rotation pole (P) [compatible with both GPS measurements (Walpersdorf et al., 1998a) and earthquake moment tensor analyses (Beaudouin et al., 2003)], as well as the major active structures are reported. Central Sulawesi Fault System (CSFS) is formed by the Palu–Koro and Matano faults. Arrows correspond to the compression and/or extension directions deduced from both inversion and moment tensor analyses of the focal mechanisms; arrow size being proportional to the deformation rate (e.g., Beaudouin et al., 2003).We also represent the focal mechanism provided by the Harvard CMT database [CMT data base, 2005] for the recent large earthquake (Mw=6.2; 2005/1/23; lat.=0.92° S; long.=120.10° E). The box indicates the approximate location of the Fig. 6 that corresponds to the geological map of the Palu basin region. The bottom inset shows the SE Asia and Sulawesi geodynamic frame where arrows represent the approximate Indo-Australian and Philippines plate motions relative to Eurasia.

  • The is the larger scale map showing the general layout of the strike-slip faults in Sulawesi (Bellier et al., 2006).

  • Sketch map of the Cenozoic Central Sulawesi fault system. ML represents the Matano Lake, and Leboni RFZ, the Leboni releasing fault zone that connects the Palu–Koro and Matano Faults. Triangles indicate faults with reverse component (triangles on the upthrown block). On this map are reported the fault kinematic measurement sites.

  • Here is a spectacular photo/sketch pair that demonstrates the excellent geomorphic evidence for this strike-slip fault (Bellier et al., 2006).The stream channels that flow down the alluvial fan in this photo are typical of the features that were used to evaluate the Holocene slip rate. There is a modest amount of vertical motion across this fault in places, causing the formation of basins like the Palu Palu Basin (a graben). The city of Palu is in the center of the Palu Palu Basin.

  • West-looking view of the Palu–Koro fault escarpment SSW of the Palu basin showing faceted spurs and a left-lateral offset of an alluvial fan. At the bottom, sketch of the photograph where white arrows point to the fault trace and black arrows point to the cumulate fan offset along the fault traces.

  • This map shows how Palu is situated relative to this fault system (Bellier et al., 2006).

  • Simplified geological map of the Palu domain (modified after Sukamto, 1973) where are reported the locations of fission-track samples. 1 — Holocene alluvial deposits; 2 — Quaternary coral reef terraces; 3 — Mio-quaternary molasses, 4 — Mio-quaternary granitic rocks and granodiorites, 5 — Middle to Upper Eocene Tinombo Formation metamorphism, 6 — Tinombo Formation magmatism, 7 and 8 — metamorphic bedrock (7 — Cretaceous Latimonjong Formation; 8 — Triassic-Jurassic Gumbasa Formation).

  • Some early GPS analysis was conducted by Waldpersdorf et al. (1998). Below is a map showing the location of these GPS observations relative tot he Palu-Koro fault.

  • The area of convergence of the Eurasian, Philippine and Australian plate is characterized by the Sula block motion. Active block boundaries are the North Sulawesi trench *(1)., the Palu-Koro (2), and the Matano (3) faults. The Palu transect is indicated buy the box, with a zoom presented in the inset. Furthermore, the two largest earthquakes (CMT) occurring during the observation period are indicated.

  • Here is a map that shows the GPS velocities as vectors in the region of Palu, Indonesia (Waldpersdorf et al., 1998).

  • Velocities of the Palu transect stations, with respect to the PALU station. Error ellipses correspond to formal uncertainties of the global solution with a confidence level of 90%.

  • Here are the Waldpersdorf et al. (1998) velocities plotted on a chart.

  • Transect station velocity components parallel to the fault, with the co-seismic deformation due to the Jan. 1996 earthquake removed. They are indicated in function of their distance to the fault. The dark grey line shows best model values (5.5 cm/yr total velocity, 12 km locking depth). Lighter grey lines correspond to locking depths of 8 and 16 km, marking an uncertainty of +-4 km.

  • Below are updated results from GPS and block model analyses from Socquet et al. (2006). Arrows are vectors that represent plate motion velocity in mm/yr (scale in upper right corner). Note how the velocities are different on either side of the Palu-Koro fault.

  • GPS velocities of Sulawesi and surrounding sites with respect to the Sunda Plate. Grey arrows belong to the Makassar Block, black arrows belong to the northern half of Sulawesi, and white arrows belong to non-Sulawesi sites (99% confidence ellipses). Numbers near the tips of the vectors give the rates in mm/yr. The main tectonic structures of the area are shown as well.

  • This map shows models plate motion velocities as informed by their block model.

  • Rotational part of the inferred velocity field in the Sulawesi area (relative to the Sunda Plate) as predicted by the Euler vectors of the best fit model (model 2). Error ellipses of predicted vectors show the 99% level of confidence. Also shown are poles of rotation and error ellipses (with respect to the Sunda Plate) from the best fit model. Curved arrows indicate the sense of rotation, and numbers indicate the rotation rate. MAKA, Makassar Block; MANA, Manado Block; ESUL, East Sula Block; NSUL, North Sula Block.

  • Here is a map that shows the plate boundary slip velocities as color (Socquet et al., 2006).

  • Best fit block model derived from both GPS and earthquakes slip vector azimuth data. Center: Observed (red) and calculated (green) velocities with respect to the Sunda Block (shown are 20% confidence ellipses, after GPS reweighting; see text). The slip rate deficit (mm/yr) for the faults included in the model is represented by a color bar. The profile of Figure 7 is located by the dashed black line. The black rectangles around Palu and Gorontalo faults localize the insets. Top right and bottom left insets show details of the measured and modeled velocities across the Gorontalo and Palu faults. The bottom right inset shows residual GPS velocities with respect to the model. The value of the coupling ratio, j, for the faults included in the model is represented by the color bar. Light blue dots represent the locations of the fault nodes where the coupling ratio is estimated. Nodes along the block boundaries are at the surface of the Earth, and the others are at depth along the fault plane. In this model, j is considered uniform along strike and depth for all the faults, except for Palu Fault and Minahassa Trench, where it is allowed to vary along strike.

  • This plot is similar to the one above, which shows how different GPS observations have different plate motion velocities relative to the faults in the area (Socquet et al., 2006).

  • Velocity profile across Makassar Trench, Palu Fault, and Gorontalo Fault (profile location in Figure 6) in Sunda reference frame. Observed GPS velocities are depicted by dots with 1-sigma uncertainty bars, while the predicted velocities are shown as curves. The profile normal component (approximately NNW) (i.e., the strike-slip component across the NW trending faults) is shown with black dots and solid line, while the profile-parallel component (normal or thrust component across the fault) is shown with grey dots and a dashed line. Where the profile crosses the faults and blocks is labeled.

  • Here are their results plotted on a map (Socquet et al., 2006).

  • (top) GPS velocities in Palu area relative to station WATA. STRM topography is used as background. (bottom) Four parallel elastic dislocations that fit best the velocities in the Palu fault zone. The fault-parallel component of the GPS velocities (with 1-sigma error bars) is plotted with respect to their distance to the main fault scarp, in the North Sula Block reference frame. The black curve represents the fault-parallel modeled velocity of the four strand model. For comparison, the fault-parallel modeled velocity predicted by the single fault model is also plotted (grey dashed curve). The location of the modeled dislocation is represented as vertical bars for each model (black and dashed grey lines, respectively).

  • Here is the fault map from Watkinson and Hall (2017).

  • Central Sulawesi overview digital elevation model (SRTM), CMT catalogue earthquakes, 35 km depth and structures that show geomorphic evidence of Quaternary tectonic activity. Rivers marked in white. Illumination from NE.

  • Here is another fantastic view of the geomorphology associated with the Palu-Koro fault (Watkinson and Hall, 2017). The hanging valley is evidence for normal displacement (extension) along this fault. Wine glass canyons are evidence for differential uplift.

  • (a) The Palu and Sapu valleys showing structures that with geomorphic evidence of Quaternary tectonic activity, plus topography and drainage. Mountain front sinuosity values in bold italic text. For location, see Figure 4. Major drainage basins for Salo Sapu and Salo Wuno are marked, separated by uplift at the western end of the Sapu valley fault system. (b) View of the Palu–Koro Fault scarp from the Palu valley, showing geomorphic evidence of Quaternary tectonic activity.

  • In this case, we can see how the river meanders are controlled by the fault. Places where stream offsets were used to measure slip rate are also shown (Watkinson and Hall, 2017).

  • Evidence of a cross-basin fault system within the Palu valley Quaternary fill. (a) Overview ASTER digital elevation model draped with ESRI imagery layer. Illumination from NW. Palu River channels traced from six separate images from 2003 to 2015. Inset shows fault pattern developed in an analogue model of a releasing bend, modified after Wu et al. (2009), reflected and rotated to mimic the Palu valley. Sidewall faults and cross-basin fault system are highlighted in the model and on the satellite imagery. (b, c) Laterally confined meander belts, interpreted as representing minor subsidence within the cross-basin fault system. (d) Laterally confined river channels directly along-strike from a Palu–Koro Fault strand seen to offset alluvial fans in the south of the valley. (c, d, e) showESRI imagery.

Geologic Fundamentals

  • For more on the graphical representation of moment tensors and focal mechnisms, check this IRIS video out:
  • Here is a fantastic infographic from Frisch et al. (2011). This figure shows some examples of earthquakes in different plate tectonic settings, and what their fault plane solutions are. There is a cross section showing these focal mechanisms for a thrust or reverse earthquake. The upper right corner includes my favorite figure of all time. This shows the first motion (up or down) for each of the four quadrants. This figure also shows how the amplitude of the seismic waves are greatest (generally) in the middle of the quadrant and decrease to zero at the nodal planes (the boundary of each quadrant).

  • Here is another way to look at these beach balls.
  • There are three types of earthquakes, strike-slip, compressional (reverse or thrust, depending upon the dip of the fault), and extensional (normal). Here is are some animations of these three types of earthquake faults. The following three animations are from IRIS.
  • Strike Slip:

    Compressional:

    Extensional:

  • This is an image from the USGS that shows how, when an oceanic plate moves over a hotspot, the volcanoes formed over the hotspot form a series of volcanoes that increase in age in the direction of plate motion. The presumption is that the hotspot is stable and stays in one location. Torsvik et al. (2017) use various methods to evaluate why this is a false presumption for the Hawaii Hotspot.

  • A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The geologic ages of the oldest volcano on each island (Ma = millions of years ago) are progressively older to the northwest, consistent with the hot spot model for the origin of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from image of Joel E. Robinson, USGS, in “This Dynamic Planet” map of Simkin and others, 2006.)

  • Here is a map from Torsvik et al. (2017) that shows the age of volcanic rocks at different locations along the Hawaii-Emperor Seamount Chain.

  • Hawaiian-Emperor Chain. White dots are the locations of radiometrically dated seamounts, atolls and islands, based on compilations of Doubrovine et al. and O’Connor et al. Features encircled with larger white circles are discussed in the text and Fig. 2. Marine gravity anomaly map is from Sandwell and Smith.

    References:

  • Bellier, O., Sebrier, M., Beaudouin, T., Villenueve, M., Braucher, R., Bourles, D., Siame, L., Putranto, E., and Pratomo, I., 2001. High slip rate for a low seismicity along the Palu-Koro active fault in central Sulawesi (Indonesia) in Terra Nova, v. 13, No. 6, p. 463-470
  • Bellier, O., Sebrier, M., Seward, D., Beaudouin, T., Villenueve, M., and Putranto, E., 2006. Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia) uin Tectonophysics, v. 413, p. 201-220, doi:10.1016/j.tecto.2005.10.036
  • Hall, R., 2011. Australia-SE Asia collision: plate tectonics and crustal flow in Geological Society, London, Special Publications 2011; v. 355; p. 75-109 doi: 10.1144/SP355.5
  • Hayes, G., 2018, Slab2 – A Comprehensive Subduction Zone Geometry Model: U.S. Geological Survey data release, https://doi.org/10.5066/F7PV6JNV.
  • Meyer, B., Saltus, R., Chulliat, a., 2017. EMAG2: Earth Magnetic Anomaly Grid (2-arc-minute resolution) Version 3. National Centers for Environmental Information, NOAA. Model. doi:10.7289/V5H70CVX
  • Socquet, A., W. Simons, C. Vigny, R. McCaffrey, C. Subarya, D. Sarsito, B. Ambrosius, and W. Spakman (2006), Microblock rotations and fault coupling in SE Asia triple junction (Sulawesi, Indonesia) from GPS and earthquake slip vector data, J. Geophys. Res., 111, B08409, doi:10.1029/2005JB003963.
  • Watkinson, I.M. and Hall, R., 2017. Fault systems of the eastern Indonesian triple junction: evaluation of Quaternary activity and implications for seismic hazards in Cummins, P. R. &Meilano, I. (eds) Geohazards in Indonesia: Earth Science for Disaster Risk Reduction, Geological Society, London, Special Publications, v. 441, https://doi.org/10.1144/SP441.8,
  • Walpersdorf, A., Rangin, C., and Vigny, C., 1998. GPS compared to long-term geologic motion of the north arm of Sulawesi in EPSL, v. 159, p. 47-55
  • Zahirovic, S., Seton, M., and Müller, R.D., 2014. The Cretaceous and Cenozoic tectonic evolution of Southeast Asia in Solid Earth, v. 5, p. 227-273, doi:10.5194/se-5-227-2014

Good Friday Earthquake 27 March 1964

In March of 1964, plate tectonics was still a hotly debated topic at scientific meetings worldwide. Some people still do not accept this theory (some Russian geologists favor alternative hypotheses; Shevchenko et al., 2006). At the time, there was some debate about whether the M 9.2 earthquake (the 2nd largest earthquake recorded with modern seismometers) was from a strike-slip or from a revers/thrust earthquake. Plafker and his colleagues found the evidence to put that debate to rest (see USGS video below).

I have prepared a new map showing the 1964 earthquake in context to the plate boundary using the same methods I have been using for my other earthquake reports. I also found a focal mechanism for this M 9.2 earthquake and included this on the map (Stauder and Bollinger, 1966).

    Here is the USGS website for this earthquake.

  • 1964.03.27 M 9.2

Below is my interpretive poster for this earthquake.

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include a focal mechanism for the M 9.2 earthquake determined by Stauder and Bollinger (1966). I include the USGS epicenters for earthquakes with magnitudes M ≥ 7.0.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth of the M 5.5 plots this close to the location of the fault as mapped by Hayes et al. (2012).

    I include some inset figures in the poster.

  • In the upper left corner I include two maps from the USGS, both using the MMI scale of shaking intensity mentioned above. The map on the left is the USGS Shakemap. This is a map that shows an estimate of how strongly the ground would shake during this earthquake. This is based upon a numerical model using Ground Motion Prediction Equations (GMPE), which are empirical relations between fault types, earthquake magnitude, distance from the fault, and shaking intensity. The map on the right is based upon peoples’ direct observations. Below each map are plots that show how these models demonstrate that the MMI attenuates (diminishes) with distance. The lines are the empirical relations. The dots are the data points.
  • To the right of those maps and figures is a map produced by Dr. Peter Haeussler from the USGS Alaska Science Center (pheuslr at usgs.gov) that shows the historic earthquakes along the Aleutian-Alaska subduction zone.
  • In the lower right corner I include an inset map from the USGS Seismicity History poster for this region (Benz et al., 2011). There is one seismicity cross section with its locations plotted on the map. The USGS plot these hypocenters along this cross section E-E’ (in green).
  • In the upper right corner, I include a figure that shows the measurements of uplift and subsidence observed by Plafker and his colleagues following the earthquake (Plafker, 1969). This is shown in map view and as a cross section.


Below is an educational video from the USGS that presents material about subduction zones and the 1964 earthquake and tsunami in particular.
Youtube Source IRIS

mp4 file for downloading.

    Credits:

  • Animation & graphics by Jenda Johnson, geologist
  • Directed by Robert F. Butler, University of Portland
  • U.S. Geological Survey consultants: Robert C. Witter, Alaska Science Center Peter J. Haeussler, Alaska Science Center
  • Narrated by Roger Groom, Mount Tabor Middle School

This is a map from Haeussler et al. (2014). The region in red shows the area that subsided and the area in blue shows the region that uplifted during the earthquake. These regions were originally measured in the field by George Plafker and published in several documents, including this USGS Professional Paper (Plafker, 1969).


Here is a cross section showing the differences of vertical deformation between the coseismic (during the earthquake) and interseismic (between earthquakes).


This figure, from Atwater et al. (2005) shows the earthquake deformation cycle and includes the aspect that the uplift deformation of the seafloor can cause a tsunami.


Here is a figure recently published in the 5th International Conference of IGCP 588 by the Division of Geological and Geophysical Surveys, Dept. of Natural Resources, State of Alaska (State of Alaska, 2015). This is derived from a figure published originally by Plafker (1969). There is a cross section included that shows how the slip was distributed along upper plate faults (e.g. the Patton Bay and Middleton Island faults).


Here is a graphic showing the sediment-stratigraphic evidence of earthquakes in Cascadia, but the analogy works for Alaska also. Atwater et al., 2005. There are 3 panels on the left, showing times of (1) prior to earthquake, (2) several years following the earthquake, and (3) centuries after the earthquake. Before the earthquake, the ground is sufficiently above sea level that trees can grow without fear of being inundated with salt water. During the earthquake, the ground subsides (lowers) so that the area is now inundated during high tides. The salt water kills the trees and other plants. Tidal sediment (like mud) starts to be deposited above the pre-earthquake ground surface. This sediment has organisms within it that reflect the tidal environment. Eventually, the sediment builds up and the crust deforms interseismically until the ground surface is again above sea level. Now plants that can survive in this environment start growing again. There are stumps and tree snags that were rooted in the pre-earthquake soil that can be used to estimate the age of the earthquake using radiocarbon age determinations. The tree snags form “ghost forests.


This is a photo that I took along the Seward HWY 1, that runs east of Anchorage along the Turnagain Arm. I attended the 2014 Seismological Society of America Meeting that was located in Anchorage to commemorate the anniversary of the Good Friday Earthquake. This is a ghost forest of trees that perished as a result of coseismic subsidence during the earthquake. Copyright Jason R. Patton (2014). This region subsided coseismically during the 1964 earthquake. Here are some photos from the paleoseismology field trip. (Please contact me for a higher resolution version of this image: quakejay at gmail.com)


Here is the USGS shakemap for this earthquake. The USGS used a fault model, delineated as black rectangles, to model ground shaking at the surface. The color scale refers to the Modified Mercalli Intensity scale, shown at the bottom.


http://earthjay.com/earthquakes/19640327_alaska/intensity.jpg

There is a great USGS Open File Report that summarizes the tectonics of Alaska and the Aleutian Islands (Benz et al., 2011). I include a section of their poster here. Below is the map legend.




Most recently, there was an earthquake along the Alaska Peninsula, a M 7.1 on 2016.01.24. Here is my earthquake report for this earthquake. Here is a map for the earthquakes of magnitude greater than or equal to M 7.0 between 1900 and today. This is the USGS query that I used to make this map. One may locate the USGS web pages for all the earthquakes on this map by following that link.


Here is an interesting map from Atwater et al., 2001. This figure shows how the estuarine setting in Portage, Alaska (along Turnagain Arm, southeast of Anchorage) had recovered its ground surface elevation in a short time following the earthquake. Within a decade, the region that had coseismically subsided was supporting a meadow with shrubs. By 1980, a spruce tree was growing here. This recovery was largely due to sedimentation, but an unreconciled amount of postseismic tectonic uplift contributed also. I include their figure caption as a blockquote.


(A and B) Tectonic setting of the 1964 Alaska earthquake. Subsidence from Plafker (1969). (C) Postearthquake deposits and their geologic setting in the early 1970s. (D–F) Area around Portage outlined in C, showing the landscape two years before the earthquake (D), two years after the earthquake (E), and nine years after the earthquake (F). In F, location of benchmark P 73 is from http://www.ngs.noaa.gov/cgi-bin/ds2.prl and the Seward (D-6) SE 7.5-minute quadrangle, provisional edition of 1984.

    Here is the tsunami forecast animation from the National Tsunami Warning Center. Below the animation, I include their caption as a blockquote. This includes information about the earthquake and the formation of the warning center.

  • Here is a link to the file for the embedded video below (22 MB 720 mp4)
  • Here is a link to the higher resolution file for the embedded video below (44 MB 1080 mp4)
  • At 5:36 pm on Friday, March 27, 1964 (28 March, 03:36Z UTC) the largest earthquake ever measured in North America, and the second-largest recorded anywhere, struck 40 miles west of Valdez, Alaska in Prince William Sound with a moment magnitude we now know to be 9.2. Almost an hour and a half later the Honolulu Magnetic and Seismic Observatory (later renamed the Pacific Tsunami Warning Center, or PTWC) was able to issue its first “tidal wave advisory” that noted that a tsunami was possible and that it could arrive in the Hawaiian Islands five hours later. Upon learning of a tsunami observation in Kodiak Island, Alaska, an hour and a half later the Honolulu Observatory issued a formal “tidal wave/seismic sea-wave warning” cautioning that damage was possible in Hawaii and throughout the Pacific Ocean but that it was not possible to predict the intensity of the tsunami. The earthquake did in fact generate a tsunami that killed 124 people (106 in Alaska, 13 in California, and 5 in Oregon) and caused about $2.3 billion (2016 dollars) in property loss all along the Pacific coast of North America from Alaska to southern California and in Hawaii. The greatest wave heights were in Alaska at over 67 m or 220 ft. and waves almost 10 m or 32 ft high struck British Columbia, Canada. In the “lower 48” waves as high as 4.5 m or 15 ft. struck Washington, as high as 3.7 m or 12 ft. struck Oregon, and as high as 4.8 m or over 15 ft. struck California. Waves of similar size struck Hawaii at nearly 5 m or over 16 ft. high. Waves over 1 m or 3 ft. high also struck Mexico, Chile, and even New Zealand.
  • As part of its response to this event the United States government created a second tsunami warning facility in 1967 at the Palmer Observatory, Alaska–now called the National Tsunami Warning Center (NTWC, http://ntwc.arh.noaa.gov/ )–to help mitigate future tsunami threats to Alaska, Canada, and the U.S. Mainland.
  • Today, more than 50 years since the Great Alaska Earthquake, PTWC and NTWC issue tsunami warnings in minutes, not hours, after a major earthquake occurs, and will also forecast how large any resulting tsunami will be as it is still crossing the ocean. PTWC can also create an animation of a historical tsunami with the same tool that it uses to determine tsunami hazards in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they travel through the world’s oceans one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).
  • Toward the end of this simulated 24 hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” are hit by larger waves than those to either side of it.

References:

Earthquake Report: EOTD Chile M 8.8 2010.02.27

Earthquake of the Day: 2010.02.27 M 8.8 Maule, Chile.

There was an earthquake with a magnitude of M 8.8 on this day in 2010. I have prepared an interpretive poster that shows the extent of ground shaking modeled for this earthquake. The attenuation relations (how the ground shaking diminishes with distance from the rutpure) generally match the ground shaking reports on the USGS “Did You Feel It?” web page.

I also include other material on the poster, including information about the 1960 M 9.5 Chile earthquake, which is the largest that we have ever recorded on modern seismologic instruments. Below are the USGS web pages for these two earthquakes.

Below is my interpretive poster for this earthquake.


I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend).

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary. Most of the recent seismicity in this region is associated with convergence along the New Britain trench or the South Solomon trench.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012).

    I include some inset figures in the poster.

  • In the upper right corner, I include a time-space diagram from Moernaut et al. (2010).
  • In the upper left corner I include an inset map from the USGS Seismicity History poster for this region (Rhea et al., 2010). There is one seismicity cross section with its locations plotted on the map. The USGS plot these hypocenters along this cross section and I include that below (with the legend).
  • In the lower right corner are the MMI intensity maps for the two earthquakes listed above: 1960 M 9.5 & 2010 M 8.8. Note these are at different map scales.


Here is a version that includes the MMI contours for the 1960 earthquake as well.


  • Here is a great figure from Lin et al. (2013) that shows the tectonic context of the 2010 Maule earthquake. On the map are plotted extents of historic earthquakes along this convergent plate margin. On the right is a large scale map showing the active magmatic arc volcanoes associated with this subduction zone. Finally, there is a cross section showing where the coseismic slip and postseismic slip occurred. I include the figure captions as blockquote.

  • (a) Regional tectonic map showing slab isodepth contours (blue lines) [Cahill and Isacks, 1992], M>=4 earthquakes from the National Earthquake Information Center catalog between 1976 and 2011 (yellow circles for depths less than 50 km, and blue circles for depths greater than 50 km), active volcanoes (red triangles), and the approximate extent of large megathrust earthquakes during the past hundred years (red ellipses) modified from Campos et al. [2002]. The large white vector represents the direction of Nazca Plate with respect to stable South America [Kendrick et al., 2003]. (b) Simplified seismo-tectonic map of the study area. Major Quaternary faults are modified after Melnick et al. [2009] (black lines). The Neogene Deformation Front is modified from Folguera et al. [2004]. The west-vergent thrust fault that bounds the west of the Andes between 32 and 38S is modified from Melnick et al. [2009]. (c) Schematic cross-section along line A–A0 (Figure 1b), modified from Folguera and Ramos [2009]. The upper bound of the coseismic slip coincides with the boundary between the frontal accretionary prism and the paleo-accretionary prism [Contreras-Reyes et al., 2010], whereas the contact between the coseismic and postseismic patch is from this study. The thick solid red line and dashed red line on top of the slab represent the approximate coseismic and postseismic plus interseismic slip section of the subduction interface. The thin red and grey lines within the overriding plate are active and inactive structures in the retroarc, modified from Folguera and Ramos [2009]. The red dashed line underneath the Andean Block represents the regional décollement. Background seismicity is from the TIPTEQ catalog, recorded between November 2004 and October 2005 [Rietbrock et al., 2005; Haberland et al., 2009].

  • Below are some figures from Moreno et al. (2011) that show estimates of locking along the plate interface in this region. I include the figure captions as blockquote.
  • The first figure shows how the region of today’s earthquake is in an area of higher locking.

  • a) Optimal distribution of locking rate in the plate interface. Predicted interseismic velocities and GPS vectors corrected by the postseismic signals are shown by green and blue arrows, respectively. b) Tradeoff curve for a broad range of the smoothing parameter (β). The optimal value for β is 0.0095 located at the inflection of the curve.

  • This second figure shows the moment released during historic earthquakes and the moment accumulated due to seismogenic locking along the megathrust.

  • a) Latitudinal distribution of the coseismic moment (Mc) released by the 1960 Valdivia (Moreno et al., 2009) (red line) and 2010 Maule (Tong et al., 2010) (blue line) earthquakes, and of accumulated deficit of moment (Md) due to interseismic locking of the plate interface 50 (orange line) and 300 (gray line) years after the 1960 earthquake, respectively. The range of errors of the Md rate is depicted by dashed lines. High rate of Md was found in the earthquake rupture boundary, where slip deficit accumulated since 1835 seems to be not completely released by the 2010 Maule earthquake. b) Schematic map showing the deformation processes that control the observed deformation in the southern Andes and the similarity between coseismic and locking patches. Blue and red contours denote the coseismic slip for the 2010 Maule (Tong et al., 2010) and 1960 Valdivia (Moreno et al., 2009) earthquakes, respectively. Patches with locking degree over 0.75 are shown by brown shaded areas. The 1960 earthquake (red star) nucleated in the segment boundary, area that appears to be highly locked at present. The 2011 Mw 7.1 aftershock (gray) may indicate that stress has been transmitted to the southern limit of the Arauco peninsula.

  • Here is a figure from Moreno et al. (2010) that shows the seismogenic locking for the region that includes the 2010 earthquake (shown with a focal mechanism from the M 8.8 earthquake. The figure caption is included below in blockquote.

  • Tectonic setting of the study area, data, observations and results. a, Shaded relief map of the Andean subduction zone in South- Central Chile. Earthquake segmentation along the margin is indicated by ellipses that enclose the approximate rupture areas of historic earthquakes (updated from refs 4–6). The inset shows the location of panel a (rectangle) relative to the South American continent. b, Compilation of GPS-observed surface velocities (1996–2008) with respect to stable South America before the 2010 Maule earthquake (for references see online-only Methods). Ellipses attached to the arrows represent 95% confidence limits. c, GPS 1 FEM modelled interface locking (fraction of plate convergence) distribution along the Andean subduction zone megathrust in the decade before the 2010 Maule earthquake. The epicentre (white star, USGS NEIC) and focal mechanism (beach ball, GCMT, http://www.globalcmt.org) of the 2010 Maule earthquake are shown in panels a and c.

  • This is also from Moreno et al. (2010) and shows the relations between different parts of the earthquake cycle. Recall these parts are the interseismic (between earthquakes), coseismic (during the earthquake), preseismic (before the earthquake), and postseismic (after the earthquake). The postseismic phase can last days to decades.

  • Relationship [sic] between pre, co- and postseismic deformation patterns. a, Coseismic slip distribution during the 2010 (blue contours; USGS slip model26) and 1960 (green contours; from ref. 30) earthquakes overlain onto pre-seismic locking pattern (red shading $0.75), as well as early (during the first 48 h post-shock) M$5 aftershock locations (the grey circle sizes scale with magnitude; GEOFON data29). b, Histograms of early (first 48 h; total number of events, 80) and late (first 3 months; total number of events, 168) aftershock density along a north–south profile (GEOFON data29, M$5). c, Residual slip deficits since 1835 as observed after the 2010 earthquake along a north–south profile (left column, based on the USGS slip model26). The middle and right columns show the effects on slip deficit of overlapping twentieth-century earthquakes (the black lines are polynomial fits to the data). Coloured data points and dates indicate earthquakes by year of occurrence.

  • This figure shows the results of analyses from Lin et al. (2013) where they estimate the spatial variation in postseismic slip associated with the 201 M 8.8 Maule earthquake. They used GPS observations along the upper plate to estimate how the fault continued to slip after the main earthquake.

  • Comparison of the postseismic slip model between the 1st and 488th day constrained by (a) horizontal GPS observations only, (b) all three components of GPS observations, and (c) three component GPS observations plus InSAR data. The coseismic slip model is of 2.5 m contour intervals (gray lines). (d) The same afterslip model as Figure 9c. Red dots are aftershocks [Rietbrock et al., 2012]. Black triangles represent the location of GPS stations. A is the afterslip downdip of the coseismic slip patch, with the black arrows indicating the along-strike extent. B and C correspond to two regions of afterslip that bound the southern and northern end of the coseismic slip patch. D is a deep slip patch that may reflect some tropospheric errors in the Andes.

  • Here is the space-time diagram from Moernaut et al., 2010. I include their figure caption below in blockquote.

  • Fig.: Setting and historical earthquakes in South-Central Chile. Data derived from Barrientos (2007); Campos et al. (2002); Melnick et al.(2009)

  • Here is the cross section of the subduction zone just to the south of the Sept/Nov 2015 swarm (Melnick et al., 2006). Below I include the text from the Melnick et al. (2006) figure caption as block text.

  • (A) Seismotectonic segments, rupture zones of historical subduction earthquakes, and main tectonic features of the south-central Andean convergent margin. Earthquakes were compiled from Lomnitz (1970, 2004), Kelleher (1972), Comte et al. (1986), Cifuentes (1989), Beck et al. (1998 ), and Campos et al. (2002). Nazca plate and trench are from Bangs and Cande (1997) and Tebbens and Cande (1997). Maximum extension of glaciers is from Rabassa and Clapperton (1990). F.Z.—fracture zone. (B) Regional morphotectonic units, Quaternary faults, and location of the study area. Trench and slope have been interpreted from multibeam bathymetry and seismic-reflection profiles (Reichert et al., 2002). (C) Profile of the offshore Chile margin at ~37°S, indicated by thick stippled line on the map and based on seismic-reflection profiles SO161-24 and ENAP-017. Integrated Seismological experiment in the Southern Andes (ISSA) local network seismicity (Bohm et al., 2002) is shown by dots; focal mechanism is from Bruhn (2003). Updip limit of seismogenic coupling zone from heat-fl ow measurements (Grevemeyer et al., 2003). Basal accretion of trench sediments from sandbox models (Lohrmann, 2002; Glodny et al., 2005). Convergence parameters from Somoza (1998 ).

  • In September through November of 2015, there was a M 8.3 earthquake further to the north. Below is my interpretive poster for that earthquake and here is my report, where I discuss the relations between the 2010, 2015, and other historic earthquakes in this region. Here is my report from September.

  • Here is a space time diagram from Beck et al. (1998 ). The 2015 earthquake occurs in the region of the 1943 and 1880 earthquakes. I updated this figure to show the latitudinal extent of the 2010 and 2015 earthquakes.

References:

Earthquake Report: 1700 Cascadia subduction zone 317 year commemoration

Today (possibly tonight at about 9 PM) is the birthday of the last known Cascadia subduction zone (CSZ) earthquake. There is some evidence that there have been more recent CSZ earthquakes (e.g. late 19th century in southern OR / northern CA), but they were not near full margin ruptures (where the entire fault, or most of it, slipped during the earthquake).

I have been posting material about the CSZ for the past couple of years here and below are some prior Anniversary posts, as well as Earthquake Reports sorted according to their region along the CSZ. Below I present some of the material included in those prior reports (to help bring it all together), but I have prepared a new map for today’s report as well.


On this evening, 317 years ago, the Cascadia subduction zone fault ruptured as a margin wide earthquake. I here commemorate this birthday with some figures that are in two USGS open source professional papers. The Atwater et al. (2005) paper discusses how we came to the conclusion that this last full margin earthquake happened on January 26, 1700 at about 9 PM (there may have been other large magnitude earthquakes in Cascadia in the 19th century). The Goldfinger et al. (2012) paper discusses how we have concluded that the records from terrestrial paleoseismology are correlable and how we think that the margin may have ruptured in the past (rupture patch sizes and timing). The reference list is extensive and this is but a tiny snapshot of what we have learned about Cascadia subduction zone earthquakes. Brian Atwater and his colleagues have updated the Orphan Tsunami and produced a second edition available here for download and here for hard copy purchase (I have a hard copy).

Here is a map of the Cascadia subduction zone, modified from Nelson et al. (2006). The Juan de Fuca and Gorda plates subduct norteastwardly beneath the North America plate at rates ranging from 29- to 45-mm/yr. Sites where evidence of past earthquakes (paleoseismology) are denoted by white dots. Where there is also evidence for past CSZ tsunami, there are black dots. These paleoseismology sites are labeled (e.g. Humboldt Bay). Some submarine paleoseismology core sites are also shown as grey dots. The two main spreading ridges are not labeled, but the northern one is the Juan de Fuca ridge (where oceanic crust is formed for the Juan de Fuca plate) and the southern one is the Gorda rise (where the oceanic crust is formed for the Gorda plate).


Today I prepared this new map showing the results of shakemap scenario model prepared by the USGS. I prepared this map using data that can be downloaded from the USGS website here. Shakemaps show what we think might happen during an earthquake, specifically showing how strongly the ground might shake. There are different measures of this, which include Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Modified Mercalli Intensity (MMI). More background information about the shakemap program at the USGS can be found here. One thing that all of these measures share is that they show that there is a diminishing of ground shaking with distance from the earthquake. This means that the further from the earthquake, the less strongly the shaking will be felt. This can be seen on the maps below. The USGS prepares shakemaps for all earthquakes with sufficiently large magnitudes (i.e. we don’t need shakemaps for earthquakes of magnitude M = 1.5). An archive of these USGS shakemaps can be found here. All the scenario USGS shakemaps can be found here.

I chose to use the MMI representation of ground shaking because it is most easily comparable for people to understand. This is because MMI scale is designed based upon relations between ground shaking intensity and observations that people are able to make (e.g. how strongly they felt the earthquake, how much objects in their residences or places of business responded, how much buildings were damaged, etc.).

The MMI ground motion model is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. More on the MMI scale can be found here and here.


Here is the USGS version of this map. The outline of the fault that was used to generate the ground motions that these maps are based upon is outlined in black.


I prepared an end of the year summary for earthquakes along the CSZ. Below is my map from this Earthquake Report.

  • Here is the map where I show the epicenters as circles with colors designating the age. I also plot the USGS moment tensors for each earthquake, with arrows showing the sense of motion for each earthquake.
  • I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • In some cases, I am able to interpret the sense of motion for strike-slip earthquakes. In other cases, I do not know enough to be able to make this interpretation (so I plot both solutions).

    I include some inset figures in the poster.

  • In the upper left corner is a map of the Cascadia subduction zone (CSZ) and regional tectonic plate boundary faults. This is modified from several sources (Chaytor et al., 2004; Nelson et al., 2004)
  • Below the CSZ map is an illustration modified from Plafker (1972). This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. Today’s earthquake did not occur along the CSZ, so did not produce crustal deformation like this. However, it is useful to know this when studying the CSZ.
  • To the lower right of the Cascadia map and cross section is a map showing the latest version of the Uniform California Earthquake Rupture Forecast (UCERF). Let it be known that this is not really a forecast, and this name was poorly chosen. People cannot forecast earthquakes. However, it is still useful. The faults are colored vs. their likelihood of rupturing. More can be found about UCERF here. Note that the San Andreas fault, and her two sister faults (Maacama and Bartlett Springs), are orange-red.
  • To the upper right of the Cascadia map and cross section is a map showing the shaking intensities based upon the USGS Shakemap model. Earthquake Scenarios describe the expected ground motions and effects of specific hypothetical large earthquakes. The color scale is the same as found on many of my #EarthquakeReport interpretive posters, the Modified Mercalli Intensity Scale (MMI). The latest version of this map is here.
  • In the upper right corner I include generalized fault map of northern California from Wallace (1990).
  • To the left of the Wallace (1990) map is a figure that shows the evolution of the San Andreas fault system since 30 million years ago (Ma). This is a figure from the USGS here.
  • In the lower right corner I include the Earthquake Shaking Potential map from the state of California. This is a probabilistic seismic hazard map, basically a map that shows the likelihood that there will be shaking of a given amount over a period of time. More can be found from the California Geological Survey here. I place a yellow star in the approximate location of today’s earthquake.


This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. We also can see how a subduction zone generates a tsunami. Atwater et al., 2005.


Here is a version of the CSZ cross section alone (Plafker, 1972).


Here is an animation produced by the folks at Cal Tech following the 2004 Sumatra-Andaman subduction zone earthquake. I have several posts about that earthquake here and here. One may learn more about this animation, as well as download this animation here.

Here is a graphic showing the sediment-stratigraphic evidence of earthquakes in Cascadia. Atwater et al., 2005. There are 3 panels on the left, showing times of (1) prior to earthquake, (2) several years following the earthquake, and (3) centuries after the earthquake. Before the earthquake, the ground is sufficiently above sea level that trees can grow without fear of being inundated with salt water. During the earthquake, the ground subsides (lowers) so that the area is now inundated during high tides. The salt water kills the trees and other plants. Tidal sediment (like mud) starts to be deposited above the pre-earthquake ground surface. This sediment has organisms within it that reflect the tidal environment. Eventually, the sediment builds up and the crust deforms interseismically until the ground surface is again above sea level. Now plants that can survive in this environment start growing again. There are stumps and tree snags that were rooted in the pre-earthquake soil that can be used to estimate the age of the earthquake using radiocarbon age determinations. The tree snags form “ghost forests.


Here is a photo of the ghost forest, created from coseismic subsidence during the Jan. 26, 1700 Cascadia subduction zone earthquake. Atwater et al., 2005.


Here is a photo I took in Alaska, where there was a subduction zone earthquake in 1964. These tree snags were living trees prior to the earthquake and remain to remind us of the earthquake hazards along subduction zones.


This shows how a tsunami deposit may be preserved in the sediment stratigraphy following a subduction zone earthquake, like in Cascadia. Atwater et al., 2005. If there is a source of sediment to be transported by a tsunami, it will come along for the ride and possibly be deposited upon the pre-earthquake ground surface. Following the earthquake, tidal sediment is deposited above the tsunami transported sediment. Sometimes plants that were growing prior to the earthquake get entombed within the tsunami deposit.


The NOAA/NWS/Pacific Tsunami Warning Center has updated their animation of the simulation of the 1700 “Orphan Tsunami.”

Source: Nathan C. Becker, Ph.D. nathan.becker at noaa.gov


Below are some links and embedded videos.

  • Here is the yt link for the embedded video below.
  • Here is the mp4 link for the embedded video below. (2160p 145 mb mp4)
  • Here is the mp4 link for the embedded video below. (1080p 145 mb mp4)
  • Here is the text associated with this animation:

    Just before midnight on January 27, 1700 a tsunami struck the coasts of Japan without warning since no one in Japan felt the earthquake that must have caused it. Nearly 300 years later scientists and historians in Japan and the United States solved the mystery of what caused this “orphan tsunami” through careful analysis of historical records in Japan as well as oral histories of Native Americans, sediment deposits, and ghost forests of drowned trees in the Pacific Northwest of North America, a region also known as Cascadia. They learned that this geologically active region, the Cascadia Subduction Zone, not only hosts erupting volcanoes but also produces megathrust earthquakes capable of generating devastating, ocean-crossing tsunamis. By comparing the tree rings of dead trees with those still living they could tell when the last of these great earthquakes struck the region. The trees all died in the winter of 1699-1700 when the coasts of northern California, Oregon, and Washington suddenly dropped 1-2 m (3-6 ft.), flooding them with seawater. That much motion over such a large area requires a very large earthquake to explain it—perhaps as large as 9.2 magnitude, comparable to the Great Alaska Earthquake of 1964. Such an earthquake would have ruptured the earth along the entire length of the 1000 km (600 mi) -long fault of the Cascadia Subduction Zone and severe shaking could have lasted for 5 minutes or longer. Its tsunami would cross the Pacific Ocean and reach Japan in about 9 hours, so the earthquake must have occurred around 9 o’clock at night in Cascadia on January 26, 1700 (05:00 January 27 UTC).

    The Pacific Tsunami Warning Center (PTWC) can create an animation of a historical tsunami like this one using the same too that they use for determining tsunami hazard in real time for any tsunami today: the Real-Time Forecasting of Tsunamis (RIFT) forecast model. The RIFT model takes earthquake information as input and calculates how the waves move through the world’s oceans, predicting their speed, wavelength, and amplitude. This animation shows these values through the simulated motion of the waves and as they race around the globe one can also see the distance between successive wave crests (wavelength) as well as their height (half-amplitude) indicated by their color. More importantly, the model also shows what happens when these tsunami waves strike land, the very information that PTWC needs to issue tsunami hazard guidance for impacted coastlines. From the beginning the animation shows all coastlines covered by colored points. These are initially a blue color like the undisturbed ocean to indicate normal sea level, but as the tsunami waves reach them they will change color to represent the height of the waves coming ashore, and often these values are higher than they were in the deeper waters offshore. The color scheme is based on PTWC’s warning criteria, with blue-to-green representing no hazard (less than 30 cm or ~1 ft.), yellow-to-orange indicating low hazard with a stay-off-the-beach recommendation (30 to 100 cm or ~1 to 3 ft.), light red-to-bright red indicating significant hazard requiring evacuation (1 to 3 m or ~3 to 10 ft.), and dark red indicating a severe hazard possibly requiring a second-tier evacuation (greater than 3 m or ~10 ft.).

    Toward the end of this simulated 24-hours of activity the wave animation will transition to the “energy map” of a mathematical surface representing the maximum rise in sea-level on the open ocean caused by the tsunami, a pattern that indicates that the kinetic energy of the tsunami was not distributed evenly across the oceans but instead forms a highly directional “beam” such that the tsunami was far more severe in the middle of the “beam” of energy than on its sides. This pattern also generally correlates to the coastal impacts; note how those coastlines directly in the “beam” have a much higher impact than those to either side of it.

    Offshore, Goldfinger and others (from the 1960’s into the 21st Century, see references in Goldfinger et al., 2012) collected cores in the deep sea. These cores contain submarine landslide deposits (called turbidites). These turbidites are thought to have been deposited as a result of strong ground shaking from large magnitude earthquakes. Goldfinger et al. (2012) compile their research in the USGS professional paper. This map shows where the cores are located.


    Here is an example of how these “seismoturbidites” have been correlated. The correlations are the basis for the interpretation that these submarine landslides were triggered by Cascadia subduction zone earthquakes. This correlation figure demonstrates how well these turbidites have been correlated. Goldfinger et al., 2012.


    This map shows the various possible prehistoric earthquake rupture regions (patches) for the past 10,000 years. Goldfinger et al., 2012. These rupture scenarios have been adopted by the USGS hazards team that determines the seismic hazards for the USA.


    Here is an update of this plot given new correlations from recent work (Goldfinger et al., 2016).


    Here is a plot showing the earthquakes in a linear timescale.


    I combined the plot above into another figure that includes all the recurrence intervals and segment lengths in a single figure. This is modified from Goldfinger et al. (2012).


Earthquake Report: 2016 Summary Cascadia

Here I summarize the seismicity for Cascadia in 2016. I limit this summary to earthquakes with magnitude greater than or equal to M 4.0. I reported on all but two of these earthquakes. I put this together a couple weeks ago, but wanted to wait to post until the new year (just in case that there was another earthquake to include).

I prepared a 2016 annual summary for Earth here.

    I include summaries of my earthquake reports in sorted into three categories. One may also search for earthquakes that may not have made it into these summary pages (use the search tool).

  • Magnitude
  • Region
  • Year

Earthquake Summary Poster (2016)

  • Here is the map where I show the epicenters as circles with colors designating the age. I also plot the USGS moment tensors for each earthquake, with arrows showing the sense of motion for each earthquake.
  • I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • In some cases, I am able to interpret the sense of motion for strike-slip earthquakes. In other cases, I do not know enough to be able to make this interpretation (so I plot both solutions).

    I include some inset figures in the poster.

  • In the upper left corner is a map of the Cascadia subduction zone (CSZ) and regional tectonic plate boundary faults. This is modified from several sources (Chaytor et al., 2004; Nelson et al., 2004)
  • Below the CSZ map is an illustration modified from Plafker (1972). This figure shows how a subduction zone deforms between (interseismic) and during (coseismic) earthquakes. Today’s earthquake did not occur along the CSZ, so did not produce crustal deformation like this. However, it is useful to know this when studying the CSZ.
  • To the lower right of the Cascadia map and cross section is a map showing the latest version of the Uniform California Earthquake Rupture Forecast (UCERF). Let it be known that this is not really a forecast, and this name was poorly chosen. People cannot forecast earthquakes. However, it is still useful. The faults are colored vs. their likelihood of rupturing. More can be found about UCERF here. Note that the San Andreas fault, and her two sister faults (Maacama and Bartlett Springs), are orange-red.
  • To the upper right of the Cascadia map and cross section is a map showing the shaking intensities based upon the USGS Shakemap model. Earthquake Scenarios describe the expected ground motions and effects of specific hypothetical large earthquakes. The color scale is the same as found on many of my #EarthquakeReport interpretive posters, the Modified Mercalli Intensity Scale (MMI). The latest version of this map is here.
  • In the upper right corner I include generalized fault map of northern California from Wallace (1990).
  • To the left of the Wallace (1990) map is a figure that shows the evolution of the San Andreas fault system since 30 million years ago (Ma). This is a figure from the USGS here.
  • In the lower right corner I include the Earthquake Shaking Potential map from the state of California. This is a probabilistic seismic hazard map, basically a map that shows the likelihood that there will be shaking of a given amount over a period of time. More can be found from the California Geological Survey here. I place a yellow star in the approximate location of today’s earthquake.



    Cascadia subduction zone: General Overview

  • Cascadia’s 315th Anniversary 2015.01.26
  • Cascadia’s 316th Anniversary 2016.01.26
  • Earthquake Information about the CSZ 2015.10.08


The big player this year was an M 6.5 along the Mendocino fault on 2016.12.08. Here I present an inventory of 8 earthquakes with M ≥ 5.0. There are a few additional earthquakes with smaller magnitudes that are of particular interest.

Please visit the #EarthquakeReport pages for more information about the figures that I include in the Earthquake Report interpretive posters below.


    References

  • Atwater, B.F., Musumi-Rokkaku, S., Satake, K., Tsuju, Y., Eueda, K., and Yamaguchi, D.K., 2005. The Orphan Tsunami of 1700—Japanese Clues to a Parent Earthquake in North America, USGS Professional Paper 1707, USGS, Reston, VA, 144 pp.
  • Chaytor, J.D., Goldfinger, C., Dziak, R.P., and Fox, C.G., 2004. Active deformation of the Gorda plate: Constraining deformation models with new geophysical data: Geology v. 32, p. 353-356.
  • Dengler, L.A., Moley, K.M., McPherson, R.C., Pasyanos, M., Dewey, J.W., and Murray, M., 1995. The September 1, 1994 Mendocino Fault Earthquake, California Geology, Marc/April 1995, p. 43-53.
  • Geist, E.L. and Andrews D.J., 2000. Slip rates on San Francisco Bay area faults from anelastic deformation of the continental lithosphere, Journal of Geophysical Research, v. 105, no. B11, p. 25,543-25,552.
  • Irwin, W.P., 1990. Quaternary deformation, in Wallace, R.E. (ed.), 1990, The San Andreas Fault system, California: U.S. Geological Survey Professional Paper 1515, online at: http://pubs.usgs.gov/pp/1990/1515/
  • McLaughlin, R.J., Sarna-Wojcicki, A.M., Wagner, D.L., Fleck, R.J., Langenheim, V.E., Jachens, R.C., Clahan, K., and Allen, J.R., 2012. Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California in Geosphere, v. 8, no. 2., p. 342-373.
  • Nelson, A.R., Asquith, A.C., and Grant, W.C., 2004. Great Earthquakes and Tsunamis of the Past 2000 Years at the Salmon River Estuary, Central Oregon Coast, USA: Bulletin of the Seismological Society of America, Vol. 94, No. 4, pp. 1276–1292
  • Rollins, J.C. and Stein, R.S., 2010. Coulomb stress interactions among M ≥ 5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fault Zone, Cascadia subduction zone, and northern San Andreas Fault: Journal of Geophysical Research, v. 115, B12306, doi:10.1029/2009JB007117, 2010.
  • Stoffer, P.W., 2006, Where’s the San Andreas Fault? A guidebook to tracing the fault on public lands in the San Francisco Bay region: U.S. Geological Survey General Interest Publication 16, 123 p., online at http://pubs.usgs.gov/gip/2006/16/
  • Wallace, Robert E., ed., 1990, The San Andreas fault system, California: U.S. Geological Survey Professional Paper 1515, 283 p. [http://pubs.usgs.gov/pp/1988/1434/].

Earthquake Report: 2016 Summary

Here I summarize the global seismicity for 2016. I limit this summary to earthquakes with magnitude greater than or equal to M 7.0. I reported on all but two of these earthquakes. There were no earthquakes as large as an M 8.0 for the entire year of 2016. However, we had an inventory of 17 earthquakes with M ≥ 7.0. Here is the 2015 Earthquake Summary Page. I initially prepared this a couple weeks ago, but wanted to wait until January 1 before I presented it. Good thing I waited as there was an earthquake in Chile on 12/25 and a swarm in Nevada on 12/28. Happy New Year! Waiting to post this was challenging, sort of like waiting to open wrapped holiday gifts.

I prepared a 2016 annual summary for the Cascadia region here.

    I include summaries of my earthquake reports in sorted into three categories. One may also search for earthquakes that may not have made it into these summary pages (use the search tool).

  • Magnitude
  • Region
  • Year

Earthquake Summary Poster (2016)

  • Here is the map where I show the epicenters as circles with colors designating the age. I also plot the USGS moment tensors for each earthquake, with arrows showing the sense of motion for each earthquake.
  • I placed a moment tensor / focal mechanism legend in the lower left corner of the map. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
  • In some cases, I am able to interpret the sense of motion for strike-slip earthquakes. In other cases, I do not know enough to be able to make this interpretation (so I plot both solutions).

  • Compare with last year’s summary poster. Here is the 2015 Earthquake Summary Page. Note how the subduction zones in the southwestern Pacific are highly active in both 2015 and 2016.

    2016 Highlights from others

  • Here is a summary showing a running total and mean of earthquakes for different magnitude ranges. This came from Chris Rowan @Allochthonous.

  • Here is a summary showing the epicenters from earthquakes in 2016 with symbol sorted vs. magnitude. This came from Susan Hough @SeismoSue.


ALL Earthquake Reports – 2016

Earthquake Report: Solomons!

Yesterday there began a swarm of seismic activity along the southern Solomon trench. What began with a M 7.8 earthquake on 2016.12.08, there have been many aftershocks including a M 6.9 this morning (my time).

Below is my interpretive poster for this earthquake.


I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I also plot the moment tensor and rupture slip patch for the 2007.04.01 M 8.1 subduction zone tsunamigenic earthquake.

  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely. The moment tensor shows northeast-southwest compression, perpendicular to the convergence at this plate boundary. Most of the recent seismicity in this region is associated with convergence along the New Britain trench or the South Solomon trench.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012). So, the earthquake is either in the downgoing slab, or in the upper plate and a result of the seismogenic locked plate transferring the shear strain from a fracture zone in the downgoing plate to the upper plate.
  • Here are the USGS web pages for the larger magnitude earthquakes.
  • 2016.12.08 17:38 M 7.8
  • 2016.12.08 18:03 M 5.6
  • 2016.12.08 21:48 M 5.5
  • 2016.12.08 21:56 M 6.5
  • 2016.12.09 19:10 M 6.9
  • 2016.12.09 17:38 M 5.5
  • 2016.12.09 21:38 M 5.8
  • 2016.12.09 23:39 M 5.6
  • I include some inset figures.

  • In the upper right corner is a generalized tectonic map of the region from Holm et al., 2015. This map shows the major plate boundary faults including the New Britain trench (NBT), one of the main culprits for recent seismicity of this region.
  • To the left of this map is the USGS fault plane solution. This figure shows their model results with color representing the spatial variation in earthquake fault slip for this M 7.8 earthquake. This model is calibrated using seismologic observations. The MMI contours reflect the rectangular fault plane used in their model. Smaller earthquake are modeled using a point source (imagine an hypocenter as a source instead of a rectangular fault slip source). These point source MMI contours are generally more circular looking (except where they intersect topography or regions with bedrock that might amplify seismic waves).
  • Below the Holm et al. (2015) map is a map that shows the region of this subduction zone that ruptured in 2007 (USGS, 2007). This M 8.1 earthquake caused a damaging tsunami. Here is the USGS website for this earthquake.
  • In the lower left corner is another generalized tectonic map of the region from Benz et al., 201. This map shows historic seismicity for this region. Earthquake epicenters are colored to represent depth and sized to represent magnitude. There is a yellow star located approximately in the location of today’s M 7.8. This earthquake has a similar down-dip distance as the 2007.04.01 M 8.1 earthquake (the large red dot labeled 2007 near the intersection of the Woodlark Spreading Center and the South Solomon Trench). The 2007 earthquake generated a large damaging tsunami. I include the cross section that shows hypocentral depths for earthquakes in the region between the 2007 April and 2016 December earthquakes.


  • This is an image of the HSU Baby Benioff seismograph showing the M 7.8 earthquake.


  • This swarm of earthquake may be the result of a a static coulomb stress change along the subduction fault as imparted by the strike-slip earthquakes from mid-May of 2015. There is a transform plate boundary connecting the southern South Solomon Trench with the northern New Hebrides Trench. There were three earthquakes with upper M 6 magnitudes. These were left lateral strike slip faults that may have increased the stress along the subduction zone faults to the east and west of these earthquakes. This current swarm of earthquakes may be in the region of increased stress, but I have not modeled this myself (too much other stuff to do right now). There is no way to know what the state of stress along these subduction zone faults was prior to the May 2007 earthquakes, but for there to be static triggering like this, the fault would need to be at a high state of stress.
    • Here are the USGS web pages for the three largest earthquakes in this May 2007 series:

    • 2015.05.20 Mw 6.8
    • 2015.05.22 Mw 6.9
    • 2015.05.22 Mw 6.8
  • Here is a map that I put together. I plot the epicenters of the earthquakes, along with the moment tensors for the three largest magnitude earthquakes. I also place a transparent focal mechanism over the swarm, showing the sense of motion for this plate boundary fault. More is presented in my Earthquake Report for this May 2007 series.
  • I also note that these three largest earthquakes happen in a time order from east to west, unzipping the fault over three +- days. I label them in order (1, 2, 3) and place an orange arrow depicting this temporal relation). Very cool!

  • In addition, there was a subduction zone earthquake to the north of the current swarm. There was a M 6.0 in 2016.09.14. Here is my report for that earthquake. Below is my interpretive poster for that earthquake. This was a much smaller earthquake, but still may have contributed slightly. Coulomb modeling might help, but that would only produce estimates of stress change.

  • In 2015 November, there was a strike slip earthquake even further to the north. It seems improbable that this earthquake would have directly affected the fault to encourage rupture for the current swarm. Here is my Earthquake Report for the November earthquake.


Background Figures

  • Here is the generalized tectonic map of the region from Holm et al., 2015. I include the figure caption below as a blockquote.

  • Tectonic setting and mineral deposits of eastern Papua New Guinea and Solomon Islands. The modern arc setting related to formation of the mineral deposits comprises, from west to east, the West Bismarck arc, the New Britain arc, the Tabar-Lihir-Tanga-Feni Chain and the Solomon arc, associated with north-dipping subduction/underthrusting at the Ramu-Markham fault zone, New Britain trench and San Cristobal trench respectively. Arrows denote plate motion direction of the Australian and Pacific plates. Filled triangles denote active subduction. Outlined triangles denote slow or extinct subduction. NBP: North Bismarck plate; SBP: South Bismarck plate; AT: Adelbert Terrane; FT: Finisterre Terrane; RMF: Ramu-Markham fault zone; NBT: New Britain trench.


Background Videos

  • I put together an animation that shows the seismicity for this region from 1900-2016 for earthquakes with magnitude of M ≥ 6.5. Here is the USGS query I used to search for these data used in this animation. I show the location of the Benz et al. (2011) cross section E-E’ as a yellow line on the main map.
  • In this animation, I include some figures from the interpretive poster above. I also include a tectonic map based upon Hamilton (1979). Music is from copyright free music online and is entitled “Sub Strut.” Above the video I present a map showing all the earthquakes presented in the video.
  • Here is a link to the embedded video below (5 MB mp4)

    In this region, there was a subduction zone earthquake that generated ground deformation and a tsunami on 2007.04.10. Below is some information about that earthquake and tsunami.

  • Here is a map from the USGS that shows the rupture area of the 2007 earthquake with a hashed polygon. The epicenter is shown as a red dot. The USGS preliminary analysis of the tsunami is here. I include their text as a blockquote below.

  • The M=8.1 earthquake that occurred in the Solomon Islands on April 1, 2007 (UTC), was located along the Solomon Islands subduction zone, part of the Pacific “Ring of Fire”. A subduction zone is a type of plate tectonic boundary where one plate is pulled (subducted) beneath another plate. For most subduction zones that make up the western half of the Ring of Fire, the Pacific plate is being subducted beneath local plates. In this case, however, the Pacific plate is the overriding or upper plate. There are three plates being subducted along the Solomon Islands subduction zone: the Solomon Sea plate, the Woodlark plate, and the Australian plate (see figure below). A spreading center separates the Woodlark and Australian plates. More detailed information on the plate tectonics of this region can be found in Tregoning and others (1998) and Bird (2003).

  • I put together this map to show how the New Britain and Solomon trenches meet. Earthquakes along the New Britain trench have principal stress aligned perpendicular to the New Britain trench and earthquakes along the Solomon trench have principal stresses aligned perpendicular to the Solomon trench due to strain partitioning in the upper plate. I provide more links and explanations about these earthquakes on this page.


Below are some Earthquake Reports for this region of the western Pacific


Earthquake Report: Japan!

While I was returning from my research cruise offshore of New Zealand, there was an earthquake offshore of Japan in the region of the 2011.01.11 M 9.0 Tohoku-Oki Earthquake. Japan is one of the most seismically active regions on Earth. Below is a series of earthquake reports for the region of Japan. Here is the USGS website for this M 6.9 earthquake.

Here is my interpretive poster for the extensional earthquake that is in the upper North America plate. This earthquake has a shallow depth and produced a small tsunami run-up. I include two versions: (1) the first one has seismicity from the past 30 days and (2) the second one includes earthquakes with magnitudes M ≥ 5.5. The second map is useful to view the aftershock region of the 2011.03.11 M 9.0 earthquake. The M 9.0 Tohoku-Oki Earthquake was a subduction zone earthquake, while this M 6.9 earthquake is a shallow depth extensional earthquake. I label the location of the 1944 Tonanki and 1946 Nankai subduction zone earthquakes (both M 8.1). These earthquakes spawned decades of research that continues until this day. I discuss the recurrence of earthquakes in this region of Japan in my earthquake report here.

I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.

I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.

I include the slab contours plotted (Hayes et al., 2012), which are contours that represent the depth to the subduction zone fault. These are mostly based upon seismicity. The depths of the earthquakes have considerable error and do not all occur along the subduction zone faults, so these slab contours are simply the best estimate for the location of the fault. The hypocentral depth plots this close to the location of the fault as mapped by Hayes et al. (2012). So, the earthquake is either in the downgoing slab, or in the upper plate and a result of the seismogenic locked plate transferring the shear strain from a fracture zone in the downgoing plate to the upper plate.

    Inset Figures

    I include some inset figures. Here is some information about them. Below I include the original figures with the figure captions as blockquotes.

  • In the upper right corner is a map showing the tectonics of the region (Kurikami et al., 2009). I include this map below.
  • In the lower right corner is a figure from the USGS that shows seismicity along the subduction zone that forms the Japan trench.
  • To the left of the cross section shows a low angle oblique view of the plate configuration in this region (from AGU).
  • In the upper left corner is a comparison of the USGS “Did You Feel It?” report maps. The map on the right is from the M 9.0 Tohoku-Oki earthquake and the map on the left is from this M 6.9 earthquake.



  • Here is the upper figure showing the tectonic setting (Kurikami et al., 2009). I include their figure caption as a blockquote.

  • Active faults in southwest Japan from the Active Fault Research Centre’s active fault database (http://www.aist.go.jp/RIODB/activefault/cgi-bin/index.cgi). The faults are color coded by sense of movement (green = dextral; blue = normal, red = reverse, yellow = sinistral).

  • Here is another figure showing the tectonic setting (Kurikami et al., 2009). I include their figure caption as a blockquote.

  • Current tectonic situation of Japan and key tectonic features.

  • The upper slope of the accretionary prism for this part of the subduction zone that forms the Japan trench has well developed normal faults. Tsuji et al. (2013) present seismic reflection profiles that for this region. I present their figure and include their figure citation below as a blockquote. The first figure is a map showing the locations of the cross sections and the locations of sites with direct observations of sea floor surface displacements (surface ruptures).

  • Index maps for the 2011 Tohoku-oki earthquake in the Japan Trench (JCG, JAMSTEC, 2011). (a) Blue and white contour lines are subsidence and uplift, respectively, estimated from tsunami inversion (Fujii et al., 2011), with contour intervals of 0.5 m (subsidence) and 1.0 m (uplift).Blue arrows indicate dynamic seafloor displacements observed at seafloor observatories (Kido et al., 2011; Sato et al., 2011). Red lines are locations of seismic profiles (SR101, MY101, and MY102) shown in Fig. 2. Stars indicate diving sites and are labeled with dive numbers of pre-earthquake observations (blue numerals) and post-earthquake observations in 2011 (red numerals) and in 2012 (orange numerals). Background heatflow values measured before the 2011 earthquake are displayed as colored dots (Yamano et al.,2008; Kimura et al., 2012). (b) Enlarged map around the diving sites, corresponding to the yellow rectangle in panel (a). Red dashed lines indicate seafloor traces of normal faults (i.e.,ridge structures). Yellow dashed lines indicate estimated locations of the backstop interface. The white dashed line indicates the boundary of the area of significant seafloor uplift (49 m uplift)and also the tsunami generation area (Fujii et al., 011), corresponding to the reddish-brown area in panel (a). Observations made during the post-earthquake dives are described in panel(b).


    Reflection seismic profiles obtained in the central part of tsunami source area(line MY102 in panels f–h), at its northern edge (line MY101 in panels c–e), and its outside (line SR101 in panels a,b). Original profiles of (a) line SR101, (c) line MY101, and (f) line MY102. Composite seismic reflection profiles with geological interpretations of(b) line SR101,(d) line MY101, and (g) line MY102 (Tsuji et al.,2011). Red arrows in panel (d) and (g) indicate seafloor displacements (Ito et al.,2011; Kido et al.,2011; Sato et al.,2011). Enlarged profiles around (e) Site 2W on line MY101, and (h) Site 3W on line MY102.

  • Here is a figure from Tsuji et al. (2013) that shows some images of the seafloor. These show views of ruptured sea floor.

  • (a) Diving tracks on seafloor bathymetry at Site 2W. Stars indicate locations of seafloor photographs displayed in panels (b)–(f). (b) Photograph of an open fissure representative of those commonly observed after the earthquake. (d) An open fissure was observed during post-earthquake observations where (c) no fissure had been before the earthquake.(g,h) Photographs taken in (g) 2011 and (h) 2012 showing the heat flow measurements being made at the same location by SAHF probe.


    (a) Diving tracks on seafloor bathymetry at Site 1E. The white dashed line indicates the location of the interpreted fault. Stars indicate locations of seafloor images displayed in panels(b)–(f).(b) Photograph of an open fissure representative of those commonly observed after the earthquake. (d) Open fissure seen during post-earthquake observations where (c) a clam colony (1 m wide) was observed before the earthquake. (e,f) Photographs taken in (e) 2011 and (f) 2012,showing the heatflow measurements at the same location by SAHF probe. (g) Dive track on seafloor bathymetry at Site 3E. The star indicates the location of (h) a seafloor photograph showing a steep cliff.

  • Here is an explanation for the extension generated during the 2011 earthquake.

  • Schematic images of coseismic fault ruptures and the tsunami generation model (a) at the northern edge (and outside) and (b) in the central part of the tsunami source area. Soft slope sediments covering the continental crust are not shown in these images. (a) Collapse of the continental framework occurred mainly at the backstop interface north of the large tsunami source area. (b) Anelastic deformation around the normal fault allowed large extension of the overriding plate in the tsunami source area.

  • These are some observations posted by the Pacific Tsunami Warning Center.

Earthquake Report: New Zealand Post # 01

This is the first of several posts about a complex earthquake series that happened along the northern end of the South Island in New Zealand. I was at sea on the R/V Tangaroa collecting piston cores offshore along the Hikurangi subduction zone this month. While I was at sea, there was a large earthquake, probably along one of the upper plate faults in this region. I present a simple interpretive poster below and will follow up with several more posts as I find more time between my other responsibilities (I have been gone at sea for two weeks, so I have lots of catch up work to do). This earthquake series is in a complicated part of the Earth where a subduction plate boundary turns into a transform plate boundary. There was a tsunami warning for the nearby coasts, but not for a global tsunami.

Geonet is a website in New Zealand that is a collaboration between the Earthquake Commission and GNS Science. Here is the website at Geonet where one can find the most up to date observations and interpretations about this M 7.8 Kaikoura Earthquake series.

  • Below is a map that I prepared that shows the earthquakes (magnitude M ≥ 2.5) for the month of November as green circles (diameter represents earthquake magnitude). I also plot earthquakes with magnitudes M ≥ 5.5 from the period of 1950-2016. These are from the USGS NEIC, so the regional network run in New Zealand may have a larger number of earthquakes. I present two maps, one with a 250 m resolution bathymetric grid as a base and one with a Google Earth satellite based map as a base. This is not an official GNS nor NIWZ figure, but they were major supporters of the TAN163 cruise that I participated on, so we can attribute the core data to these organizations.
  • I placed the moment tensors for the larger earthquakes during this time period since the M 7.8 earthquake. The main earthquake is a compressional earthquake, probably on an upper plate fault. The M 7.8 earthquake triggered slip on other thrusts and some strike-slip faults in the region. Surface deformation measured using Interferometric Synthetic Aperture Radar (INSAR) is localized, supporting the upper plate rupture interpretation. Slip on the thrust during the 7.8 is estimated to be about 10 meters, which is also the maximum slip on some of the strike-slip fault systems. There have been some excellent photographs of the fault rupture (I will include these in a later post). Most of the large earthquakes are strike-slip, but there are some connecting faults that show thrust mechanisms. I also show the regions of different faults that have been observed to have surface ruptures.
  • After the earthquake, we changed our plans to conduct some post-earthquake response analyses. We collected additional cores to search for sedimentary evidence of the M 7.8 earthquake. We also collected sub-bottom profile and bathymetric data to search for seafloor exposed fault rupture. The cores we collected for our general study are shown as red cross-dots. The cores we collected as the earthquake are plotted as yellow cross-dots.
  • I also include the shaking intensity contours on the map. These use the Modified Mercalli Intensity Scale (MMI; see the legend on the map). This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations. The MMI is a qualitative measure of shaking intensity. More on the MMI scale can be found here and here. This is based upon a computer model estimate of ground motions, different from the “Did You Feel It?” estimate of ground motions that is actually based on real observations.
  • I placed a moment tensor / focal mechanism legend on the poster. There is more material from the USGS web sites about moment tensors and focal mechanisms (the beach ball symbols). Both moment tensors and focal mechanisms are solutions to seismologic data that reveal two possible interpretations for fault orientation and sense of motion. One must use other information, like the regional tectonics, to interpret which of the two possibilities is more likely.
    • Inset Figures

      I include some inset figures. Here is some information about them. Below I include the original figures with the figure captions as blockquotes.

    • In the upper right corner is a map from NIWA (Phil Barnes). This map shows some of the major faults in this region. I placed the observed fault offsets on this map as orange lines. This map is on the NIWA website, but I will find the Barnes publication this came from and post that in a follow up web page.
    • In the lower right corner is a map from Geological and Nuclear Sciences (GNS) in Māori: Te Pū Ao. This map shows the regional faults and where there have been observations of surface rupture. The coseismic (during the earthquake) Global Positioning System (GPS) observations. Earthquakes are also plotted.
    • To the left of that is a figure from the Geospatial Information Authority of Japan (GSI). This is a summary figure showing modeled uplift as compared to InSAR analysis results. Note how localized the deformation is. I will present and discuss the analyses that went into this figure in a follow-up report.
    • To the left of that is a generalized tectonic map of the region.



    Here are the USGS websites for the large earthquakes plotted in the map above.

  • 20161113 M 7.8 11:02 USGS
  • 20161113 M 6.5 11:32 USGS
  • 20161113 M 6.1 11:52 USGS
  • 20161113 M 6.2 13:31 USGS
  • 20161113 M 5.7 19:28 USGS
  • 20161114 M 6.5 00:34 USGS
  • 20161114 M 5.4 01:30 USGS
  • 20161114 M 5.8 06:47 USGS
  • 20161115 M 5.4 01:34 USGS
  • 20161115 M 5.4 06:30 USGS
  • 20161118 M 5.1 14:22 USGS
  • 20161122 M 5.9 00:19 USGS
  • 20161122 M 5.3 00:19 USGS
  • 20161122 M 5.0 19:38 USGS
  • Here is an image of the seismograph as recorded by the Humboldt State University, Department of Geology, Baby Benioff seismometer.

  • Here is the USGS Seismicity of the Earth map for this region (Benz et al., 2010). Click on the map for the pdf of this report (66 MB pdf). Here is 10 MB jpg file.

  • Initial recon overflights report that there have been over 100,000 landslides from this earthquake. Below is a map that shows a different analysis that people are conducting. There will be more.

  • Here is one of the early InSAR results from COMET. I will present more of these is a follow-up report.

  • Here is a cool comparison animated gif showing before and after the earthquake. This is an animated gif showing photos taken by Casey Miln and Andrew Spencer.

  • Casey Miln

  • Andrew Spencer

    Videos

  • Here is a video of the Kekerengu fault rupture. This is the yt link for the embedded video below. Here is an mp4 link.
  • Here is a video of the Papatea fault rupture. This is the yt link for the embedded video below. Here is an mp4 link.
  • Here is a video of the Papatea fault and uplifted coast. This is the yt link for the embedded video below.
  • Here is a video of the earthquake and aftershocks. This is the yt link for the embedded video below.
  • Here is a video showing a simulation of the M 7.8 Kaikoura earthquake. This is the yt link for the embedded video below.
  • Here is a video of the road to Kaikoura. This is the yt link for the embedded video below.