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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.

Earthquake Report: Laytonville (northern CA)!

This morning there was another earthquake in northern CA between the San Andreas (SAF) and Maacama faults (MF). This region has been active for the past few years, with earthquakes in the M 3-4 range. Most recently, there was a M 3.8 really close to today’s M 4.1. These earthquakes may indicate the possibility of an unmapped fault. There have been earthquakes in 2000, 2014, and 2015 that align along strike (of a possible fault that is sub-parallel to the SAF/MF systems). Here is the USGS website for today’s M 4.1 earthquake.

The San Andreas fault is a right-lateral strike-slip transform plate boundary between the Pacific and North America plates. The plate boundary is composed of faults that are parallel to sub-parallel to the SAF and extend from the west coast of CA to the Wasatch fault (WF) system in central Utah (the WF runs through Salt Lake City and is expressed by the mountain range on the east side of the basin that Salt Lake City is built within).

The three main faults in the region north of San Francisco are the SAF, the MF, and the Bartlett Springs fault (BSF). Here is a map that shows Saturday’s epicenter as a red star. I also place a graphical depiction of the USGS moment tensor for this earthquake. The SAF, MF, and BSF are all right lateral strike-slip fault systems. There are no active faults mapped in the region of Saturday’s epicenter, but I interpret this earthquake to have right-lateral slip. Without more seismicity or mapped faults to suggest otherwise, this is a reasonable interpretation.

Below I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I use the USGS Quaternary fault and fold database for the faults. I outlined the Vizcaino Block, which many interpret to be a prehistoric subduction zone accretionary prism from a time before the San Andreas existed.

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. Based on the moment tensor and my knowledge of the tectonics of this region, I interpret this earthquake to have had a right lateral strike slip motion along an east-west fault.

    I include some inset figures in the poster.

  • In the upper right corner I include a map from McLaughlin et al. (2012) that shows the regional faulting.
  • In the lower right corner I include generalized fault map of northern California from Wallace (1990).
  • In the lower left corner I include a map that shows the seismicity for this region since 1960, including earthquakes with magnitudes greater than or equal to M 1.5. I have labeled some of the significant earthquake swarms, with magnitudes ranging from M 3-4. Here is the USGS search that I used to create this map.
  • To the right of the seismicity 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 upper left 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.


  • Earlier this month (a couple days ago), there was an earthquake in this region. Below is my interpretive poster for that earthquake. Here is my Earthquake Report.

  • Earlier this year, there was an earthquake in this region. Below is my interpretive poster for that earthquake. Here is my Earthquake Report.

  • Last year there was an earthquake in this region. Below is my interpretive poster for that earthquake. Here is my Earthquake Report.

  • I place a map shows the configuration of faults in central (San Francisco) and northern (Point Delgada – Punta Gorda) CA (Wallace, 1990). Here is the caption for this map, that is on the lower left corner of my map. Below the citation is this map presented on its own.
  • Geologic sketch map of the northern Coast Ranges, central California, showing faults with Quaternary activity and basin deposits in northern section of the San Andreas fault system. Fault patterns are generalized, and only major faults are shown. Several Quaternary basins are fault bounded and aligned parallel to strike-slip faults, a relation most apparent along the Hayward-Rodgers Creek-Maacama fault trend.


  • About 75% of the relative plate motion is accommodated along the SAF and its synthetic sister faults in the northern CA region. The rest of the plate boundary motion is accommodated along the Eastern CA shear zone and Walker Lane, along with the Central Nevada Seismic Belt, and the Wasatch fault systems. In Northern CA, there is about 33-37 mm/yr strain accumulated on the SAF plate boundary system. About 18-25 mm/yr is on the SAF, 8-11 mm/yr on the MF, and 5-7 mm/yr on the Bartlett Springs fault system (Geist and Andrews, 2000).
  • Here is a map from McLaughlin et al. (2012) that shows the regional faulting. I include the figure caption as a blockquote below.

  • Maps showing the regional setting of the Rodgers Creek–Maacama fault system and the San Andreas fault in northern California. (A) The Maacama (MAFZ) and Rodgers Creek (RCFZ) fault zones and related faults (dark red) are compared to the San Andreas fault, former and present positions of the Mendocino Fracture Zone (MFZ; light red, offshore), and other structural features of northern California. Other faults east of the San Andreas fault that are part of the wide transform margin are collectively referred to as the East Bay fault system and include the Hayward and proto-Hayward fault zones (green) and the Calaveras (CF), Bartlett Springs, and several other faults (teal). Fold axes (dark blue) delineate features associated with compression along the northern and eastern sides of the Coast Ranges. Dashed brown line marks inferred location of the buried tip of an east-directed tectonic wedge system along the boundary between the Coast Ranges and Great Valley (Wentworth et al., 1984; Wentworth and Zoback, 1990). Dotted purple line shows the underthrust south edge of the Gorda–Juan de Fuca plate, based on gravity and aeromagnetic data (Jachens and Griscom, 1983). Late Cenozoic volcanic rocks are shown in pink; structural basins associated with strike-slip faulting and Sacramento Valley are shown in yellow. Motions of major fault blocks and plates relative to fi xed North America, from global positioning system and paleomagnetic studies (Argus and Gordon, 2001; Wells and Simpson, 2001; U.S. Geological Survey, 2010), shown with thick black arrows; circled numbers denote rate (in mm/yr). Restraining bend segment of the northern San Andreas fault is shown in orange; releasing bend segment is in light blue. Additional abbreviations: BMV—Burdell Mountain Volcanics; QSV—Quien Sabe Volcanics. (B) Simplifi ed map of color-coded faults in A, delineating the principal fault systems and zones referred to in this paper.

  • Here is the figure showing the evolution of the SAF since its inception about 29 Ma. I include the USGS figure caption below as a blockquote.

  • EVOLUTION OF THE SAN ANDREAS FAULT.

    This series of block diagrams shows how the subduction zone along the west coast of North America transformed into the San Andreas Fault from 30 million years ago to the present. Starting at 30 million years ago, the westward- moving North American Plate began to override the spreading ridge between the Farallon Plate and the Pacific Plate. This action divided the Farallon Plate into two smaller plates, the northern Juan de Fuca Plate (JdFP) and the southern Cocos Plate (CP). By 20 million years ago, two triple junctions began to migrate north and south along the western margin of the West Coast. (Triple junctions are intersections between three tectonic plates; shown as red triangles in the diagrams.) The change in plate configuration as the North American Plate began to encounter the Pacific Plate resulted in the formation of the San Andreas Fault. The northern Mendicino Triple Junction (M) migrated through the San Francisco Bay region roughly 12 to 5 million years ago and is presently located off the coast of northern California, roughly midway between San Francisco (SF) and Seattle (S). The Mendicino Triple Junction represents the intersection of the North American, Pacific, and Juan de Fuca Plates. The southern Rivera Triple Junction (R) is presently located in the Pacific Ocean between Baja California (BC) and Manzanillo, Mexico (MZ). Evidence of the migration of the Mendicino Triple Junction northward through the San Francisco Bay region is preserved as a series of volcanic centers that grow progressively younger toward the north. Volcanic rocks in the Hollister region are roughly 12 million years old whereas the volcanic rocks in the Sonoma-Clear Lake region north of San Francisco Bay range from only few million to as little as 10,000 years old. Both of these volcanic areas and older volcanic rocks in the region are offset by the modern regional fault system. (Image modified after original illustration by Irwin, 1990 and Stoffer, 2006.)

    • Here is a map that shows the shaking potential for earthquakes in CA. This comes from the state of California here.
    • Earthquake shaking hazards are calculated by projecting earthquake rates based on earthquake history and fault slip rates, the same data used for calculating earthquake probabilities. New fault parameters have been developed for these calculations and are included in the report of the Working Group on California Earthquake Probabilities. Calculations of earthquake shaking hazard for California are part of a cooperative project between USGS and CGS, and are part of the National Seismic Hazard Maps. CGS Map Sheet 48 (revised 2008) shows potential seismic shaking based on National Seismic Hazard Map calculations plus amplification of seismic shaking due to the near surface soils.


      References

    • 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.
    • 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: Maule, Chile!

This morning there was a moderate sized earthquake along the megathrust in Chile. Here is the USGS website for this M 6.4 earthquake. Based upon the hypocentral depth, and the moment tensor, this appears to be along the megathrust fault (an “interface” event). This is a very seismically active region of the world, with a number of Great (M ≥ 8.0) earthquakes in recent years.

Below is my interpretive poster. I have plotted the epicenters (using the USGS earthquake feed kml) for the past 30 days with magnitudes 2.5 or greater, with color representing depth. I also include the slab depth contours from Hayes et al. (2012). These are the depth contours for the fault interface of the subduction zone. Today’s hypocentral depth is 90.8 km and the Hayes et al. (2012) slab contour in this region is between 80 and 100 km. I include the USGS moment tensor for this earthquake. I also plot the rupture length regions of historic earthquakes for this subduction zone in green (Beck et al., 1998). I present the patches for the 2010 and 2015 subduction zone earthquakes outlined in white dashed lines. Today’s earthquake happened in the region of the subduction zone that is “down-sip” from the 2010 earthquake. The 2010 earthquake would probably have loaded the fault in this region, so this M 6.4 earthquake may be related to the 2010 earthquake. However, it has been over 5 years since the 2010 earthquake. That being said, there are still aftershocks from the 2011 Tohoku-Oki earthquake (so it seems possible).

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. Based on the moment tensor and my knowledge of the tectonics of this region, I interpret this earthquake to have had a right lateral strike slip motion along an east-west fault.

    I include some inset figures in the poster.

  • In the upper left corner I place a cross section from Melnick et al. (2006). This shows the prehistoric earthquake history on the left and a cross section of the subduction zone on the right. This cross section is in the region of the 2010 subduction zone earthquake.
  • In the upper right corner I include the space-time diagram from Beck et al. (1998 ) showing the along strike length of prehistoric earthquakes in the central subduction zone. The map above shows these prehistoric rupture strike lengths as green lines (labeled with green labels). The 2015 earthquake series ruptured past the southern boundary of the 1943 earthquake and about 30% into the 1922 earthquake region. There is a small gap between the 2010 and 2015 earthquake series, which aligns with the Juan Fernandez Ridge (a fracture zone in the Nazca plate; von Huene et al., 1997; Rodrigo et al., 2014). This fracture zone appears to be a structural boundary to earthquake slip patches (subduction zone segmentation), at least for some earthquakes. Beck et al. (1998 ) show that possibly two earthquakes ruptured past this boundary (1730 A.D. and possibly 1647 A.D., though that is queried). This segment boundary appears to be rather persistent for the past ~500 years
  • In the lower right corner, I include a time-space diagram from Moernaut et al. (2010). This diagram extends further south than the Beck et al. (1998) figure.
  • In the lower left corner I include an inset map from the USGS Seismicity History poster for this region (Rhea et al., 2010). There are two seismicity cross sections here as well, with their locations plotted on the map. The USGS plot these hypocenters along these two cross sections and I include those.


  • In February of this year, there was a M 6.3 earthquake near the coast which caused considerable damage. Below is my interpretive poster for that earthquake and here is my report.

  • 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.

  • 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)

  • The September 2015 earthquake series inspired me to compile some information on the historic tsunami in this region. Here is my report on those tsunami. Below I present my figure and an animation that compares these three tsunami from 1960, 2010, and 2014.
  • These three maps use the same color scale. There is not yet a map with this scale for the 2015 tsunami, so we cannot yet make the comparison.

  • Here is an animation of these three tsunami from the US NWS Pacific Tsunami Warning Center (PTWC). This is the YouTube link.

  • Here is the cross section of the subduction zone just to the south of this 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 March 2015, there was some seismicity in this September/November 2015 earthquake slip region. I put together an earthquake report about those earthquake of magnitudes M = 5.0-5.3. I speculate that the 1922 earthquake region is a seismic gap. Note that this September/November 2015 earthquake region is along the southern portion of the seismic gap that I labeled on the map below. Dutchsinse can kiss my 4$$.
  • Here is a map that shows the recent swarm of ~M = 5 earthquakes. There are moment tensors for the earthquakes listed below, some recent historic subduction zone earthquakes. I placed the general along-strike distance for older historic earthquakes in green (and labeled their years). The largest earthquake ever recorded, the Mw = 9.5 Chile earthquake, had a slip patch that extends from the south of the map to just south of the 2010 earthquake swarm. The 2010 and 2014 earthquake swarm epicenters are plotted as colored circles, while most other historic earthquake epicenters are plotted as gray circles. Note how this March 2015 swarm is at the northern end of the 1922/11/11 M 8.3 earthquake. At the bottom of this page, I put a USGS graphic about what these moment tensor plots (beach balls) tell us about the earthquakes.

  • Hundreds of people died as a result of the 1922 earthquake. The USGS has more news reports about the 1922 earthquake here. There were also reports of a tsunami over 9 meters. So we know that this segment of the fault can produce large earthquakes and tsunami. However, it has been about a century since the last Great subduction zone earthquake in this region of the fault.

References:

Earthquake Report: Italy Update #1!

Here is an update to the #EarthquakeReport for the M 6.6 earthquake that hit Italy early this morning my time. Ironically, I was preparing a report for earthquakes in the western Pacific for my class when this M 6.6 earthquake hit and I did not notice the USGS email because I was so engaged with the western Pacific report. Here is the interpretive poster for that region over the past week or so.

This region has been experiencing a series of large earthquakes since August 2016, possibly culminating in this M 6.6 earthquake. These earthquakes may load adjacent faults in the region, so this may not be over. Given the series of earthquakes in the region further to the north (from 1916-1920), this may not be over. Stay tuned and stay safe!

The M 6.1 earthquake happened following the M 5.5 earthquake, so people had already been staying outside of their houses. This is thought to be why the casualty number was lower than expected for the M 6.1 earthquake. While the damage estimates are likely to be closer to the bar for both the M 6.1 and M 6.6 earthquakes, the casualty list is also thought to be lower for the M 6.6 earthquake for the same reason.

Below is a poster that shows epicenters from 2008 – 2016. I have included moment tensors for the largest megnitude earthquakes and outlined the region that has had earthquakes in the two periods (2009 & 2016). I also include the fault database from the Instituto Nazionale di Geofisica e Vulcanologia (the Database of Individual Seismogenic Sources, DISS v. 3.; DISS Working Group, 2015). There is a DISS legend to the right of the moment tensor legend. The Mt Vettore fault is considered a “Debated Seismogenic Source” in this database and is the blue fault line on the northern part of the 2016 rupture region.

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 tectonics of this region has many normal (extensional) faults, which explain the extensional moment tensor.

    I include some inset figures and maps.

  • In the upper left corner is a map that shows seismicity for this region on maps and cross sections (Boncio et al., 2004). I placed orange stars in the approximate location of the October, 2016 earthquakes. These earthquakes happen to appear right on the center of cross section b (the lowermost cross section on the right). It appears that these earthquakes are rupturing along the Mt. Vettore fault.
  • In the upper right corner I include a map and cross section compiled by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The map and cross section are from Pierantoni et al. (2013). The cross sectional focal mechanism is located in the approximate location on the cross section. Stars designate the epicentral locations for the recent seismicity on the map. This hypothesis for which structures these earthquakes are appearing on is consistent with my interpretation shown on the Boncio et al. (2004) map and cross section.
  • In the lower right corner is another map from INGV that shows the mapped faults in this region and the location of hte 2016.10.30 M 6.6 earthquake, along with other October 2016 seismicity. Observations of potential surface rupture have occurred in the region labeled “Surface faulting.”
  • In the lower left corner is another map from INGV that shows epicenters discriminated by time (August = blue, 72 hours = yeallow, 24 hours = orange, 1 hour = red). Note the overlap not seen in my main map. The local seismic network that INGV uses shows many more earthquakes than the global network contributing to the USGS database.
  • Along the base of the poster I include “USGS Did You Feel It?” maps for the 4 largest earthquakes plotted on this map.


  • Here are some views of the damage from news organizations.
  • BBC
  • BBC
  • BBC
  • As a remiinder, this region is in a seismically hazardous region of Italy. Here is the 10% probability of exceedance map (for 50 yrs) from INGV.

  • This is another view of the seismic hazard in Europe (Giardini et al., 2013).

  • Boncio et a. (2004) present a remarkable assessment of the seismic hazard in this region based on a 3-D model for seismogenic sources. I present some of their figures below. I include their original figure captions as blockquotes.
  • This map shows a detailed view of the normal faults in the region. Today’s earthquake is in the region shown in box 3, east of the Umbra Valley.

  • Digital elevation model of central Italy with active normal faults of the Umbria-Marche-Abruzzo Apennines and parameters of active stress tensors obtained by inversion of focal mechanisms of background microseismicity (1), aftershock sequences (2, 3, 4, 5) or striated active faults in seismic areas (6); stress data from Brozzetti and Lavecchia (1994), Boncio and Lavecchia (2000a) and Pace et al. (2002a); the stress axes are given as trend (first three numbers) and plunge (last two numbers).

  • This map shows an even more detailed and large scale view of the faults and seismicity in this region. Today’s earthquakes align to the north of Norcia, approximately along the cross section labeled “sec B.” The two cross sections are in the lower right part of the figure, with section B the lowermost cross section. Today’s earthquake may be on the AF2, the C-NFs (Colfiorito-Norcia fault systems), or MVf (Mt. Vettore fault). The AF2 fault is a proposed low angle detachment fault. These types of faults are controversial in that there are arguments about whether they are seismogenic or not. This year’s Pacific Cell Friends of the Pleistocene field trip in Panamint Valley presented research results that attempted to address this question. In Panamint Valley there are faults that have similar configurations as these faults in Italy.

  • Geological cross sections from seismic reflection profiles across the Gubbio, Gualdo T. and Colfiorito seismic areas (from Boncio et al., 1998; Boncio and Lavecchia, 2000b); epi- and hypocentral distribution of back-ground microseismicity recorded in the Umbria-Marche Apennines and rheological profiles (strength envelopes in critical stress difference, σ1–σ3) built for two different thermal contexts (50 and 40 mW/m2 surface heat flow, see Figure 3 for location); the depth of the brittle-plastic transition on rheological profiles is indicated by arrows; the used rheological parameters are indicated: crustal layering is from DSS data; A (empirical material constant), n (stress exponent) and E (activation energy) are creep parameters; ´ε = longitudinal strain rate (calculated by balancing of a regional geologic section; Figure 5 in Boncio et al., 2000); see text for further details.

  • This map shows a smaller scaled view (than the above figure) with focal mechanisms and cross sections (with structural interpretations). Hypocenters are also plotted on these cross sections. Today’s earthquakes are just south of cross section b. (earthquakes happened here in 1997)

  • Epicentres of the major seismic sequences of the last twenty years (Gubbio, 1984; Colfiorito, 1997; Norcia, 1979; Sangro, 1984) plus three small seismic sequences in the L’Aquila area (1992, 1994 and 1996); seismotectonic sections and rheological profiles built according to the local thermal context. The dashed line (sections ‘a’ and ‘b’) represents the AF low-angle extensional detachment; arrows in seismotectonic sections indicate the maximum depth-extent of the activated seismogenic faults as suggested by the best defined aftershock volume; rheological parameters as in Figure 7; in the southern Abruzzo area, creep strengths for geologic and geodetic longitudinal strain rates are compared (geologic strain rate calculated from data of Galadini and Galli, 2000; geodetic strain rate from D’Agostino et al., 2001); seismological data from Amato et al. (1998); Boncio (1998); Boncio et al. (2004); Cattaneo et al. (2000); De Luca et al. (2000); Deschamps et al. (1984); Ekstrom et al. (1998); Haessler et al. (1988); Harvard CMT database at www.seismology.harvard.edu.

Earthquake Report: Italy

Italy continues to shake following the Armatrice Earthquake series in August 2016. Here is my report for that series of earthquakes. Today’s earthquakes occurred along the northern end of the earthquakes that happened a few months ago.

    Today’s series started with a M 5.5, which was a foreshock to a M 6.1 earthquake. Here are the USGS websites for these two earthquakes. I plot the USGS moment tensors for each of these earthquakes on the interpretive poster below.

  • 2016.10.26 M 5.5 Italy
  • 2016.10.26 M 6.1 Italy

This earthquake is north of the region that had an M 6.3 earthquake in 2009 that led to an interesting (putting it nicely) interaction between scientists, public employees/politicians, and the legal system. Basically, several seismologists were sentenced to prison. More on this is found online, for example, here and here.

Below is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. 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. There is a legend for MMI intensities in the upper part of the interpretive poster below.

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 tectonics of this region has many normal (extensional) faults, which explain the extensional moment tensor. However, I do not know enough of this region to interpret is this is an east or west dipping fault that ruptured (depends upon which side of which basin experience this earthquake; see below).

    I include some inset figures and maps.

  • In the lower right corner I include the Rapid Assessment of an Earthquake’s Impact (PAGER) report. More on the PAGER program can be found here. An explanation of a PAGER report can be found here. PAGER reports are modeled estimates of damage. On the top is a histogram showing estimated casualties and on the right is an estimate of possible economic losses. This PAGER report suggests that there will be quite a bit of damage from this earthquake (and casualties). This earthquake has a high probability of damage to people and their belongings.
  • Above that I show the Seismic Hazard for Europe as prepared by the SHARE Consortium (Giardini et al., 2013).
  • In the upper left corner I include a basic tectonic map of this region (Woudloper, 2009). Maps with local (larger) scale have much more detailed views of the faulting.
  • In the lower left corner is a map showing the faulting mapped in the region surrounding and including Italy (Billi et al., 2006). There is a convergent plate boundary along the eastern part of Italy (part of the Alpide belt, a convergent boundary that extends from the Straits of Gibraltar to Australia). This fault system dips westward and is onshore in the south, but extends offshore into the Adriatic Sea in central-northern Italy. In the central part of Italy is a series of north-northwest striking extensional faults. It is these extensional (normal) faults that are responsible for the damaging seismicity in this region of central Italy. This includes the 1915, 1997, 2009, and 2016 earthquakes.
  • To the right of the Billi et al. (2006) fault map is a plot showing the seismicity from the last year. Today’s earthquakes are plotted as orange circles and the epicenters from August are plotted as gray circles.


  • Bonio et a. (2004) present a remarkable assessment of the seismic hazard in this region based on a 3-D model for seismogenic sources. I present some of their figures below. I include their original figure captions as blockquotes.
  • This map shows a detailed view of the normal faults in the region. Today’s earthquake is in the region showin in box 3, east of the Umbra Valley.

  • Digital elevation model of central Italy with active normal faults of the Umbria-Marche-Abruzzo Apennines and parameters of active stress tensors obtained by inversion of focal mechanisms of background microseismicity (1), aftershock sequences (2, 3, 4, 5) or striated active faults in seismic areas (6); stress data from Brozzetti and Lavecchia (1994), Boncio and Lavecchia (2000a) and Pace et al. (2002a); the stress axes are given as trend (first three numbers) and plunge (last two numbers).

  • This map shows an even more detailed and large scale view of the faults and seismicity in this region. Today’s earthquakes align to the north of Norcia, approximately along the cross section labeled “sec B.” The two cross sections are in the lower right part of the figure, with section B the lowermost cross section. Today’s earthquake may be on the AF2, the C-NFs (Colfiorito-Norcia fault systems), or MVf (Mt. Vettore fault). The AF2 fault is a proposed low angle detachment fault. These types of faults are controversial in that there are arguments about whether they are seismogenic or not. This year’s Pacific Cell Friends of the Pleistocene field trip in Panamint Valley presented research results that attempted to address this question. In Panamint Valley there are faults that have similar configurations as these faults in Italy.

  • Geological cross sections from seismic reflection profiles across the Gubbio, Gualdo T. and Colfiorito seismic areas (from Boncio et al., 1998; Boncio and Lavecchia, 2000b); epi- and hypocentral distribution of back-ground microseismicity recorded in the Umbria-Marche Apennines and rheological profiles (strength envelopes in critical stress difference, σ1–σ3) built for two different thermal contexts (50 and 40 mW/m2 surface heat flow, see Figure 3 for location); the depth of the brittle-plastic transition on rheological profiles is indicated by arrows; the used rheological parameters are indicated: crustal layering is from DSS data; A (empirical material constant), n (stress exponent) and E (activation energy) are creep parameters; ´ε = longitudinal strain rate (calculated by balancing of a regional geologic section; Figure 5 in Boncio et al., 2000); see text for further details.

  • This map shows a smaller scaled view (than the above figure) with focal mechanisms and cross sections (with structural interpretations). Hypocenters are also plotted on these cross sections. Today’s earthquakes are just south of cross section b. (earthquakes happened here in 1997)

  • Epicentres of the major seismic sequences of the last twenty years (Gubbio, 1984; Colfiorito, 1997; Norcia, 1979; Sangro, 1984) plus three small seismic sequences in the L’Aquila area (1992, 1994 and 1996); seismotectonic sections and rheological profiles built according to the local thermal context. The dashed line (sections ‘a’ and ‘b’) represents the AF low-angle extensional detachment; arrows in seismotectonic sections indicate the maximum depth-extent of the activated seismogenic faults as suggested by the best defined aftershock volume; rheological parameters as in Figure 7; in the southern Abruzzo area, creep strengths for geologic and geodetic longitudinal strain rates are compared (geologic strain rate calculated from data of Galadini and Galli, 2000; geodetic strain rate from D’Agostino et al., 2001); seismological data from Amato et al. (1998); Boncio (1998); Boncio et al. (2004); Cattaneo et al. (2000); De Luca et al. (2000); Deschamps et al. (1984); Ekstrom et al. (1998); Haessler et al. (1988); Harvard CMT database at www.seismology.harvard.edu.

  • Here is a poster that shows the seismic hazard for Europe (Giardini et al., 2013).

  • This is the PAGER alert for the M 6.1 earthquake.

  • Here is a more detailed seismic hazard map for Italy (Stucchi et al., 2011). This shows the median PGA (Peak Ground Acceleration, units of g where g = 9.8 m/s2) that has a 10% probability of exceedance (PE) in the next 50 years. This model assumes a Vs30 greater than 800 m/s. Vs is the average seismic velocity in the upper 30 meters. Vs30 is a proxy used for global to regional estimates of seismic hazard.I include their original figure captions as blockquote.

  • The seismic hazard map showing the PGA distribution with 10% probability of exceedance in 50 years, computed on hard ground (VS30 > 800 m=s).

Earthquake Report: South Bismarck Sea

There was a moderately deep earthquake in the South Bismarck Sea last night. Here is the USGS website for this earthquake. This earthquake has an exentional earthquake. Here, the Solomon Sea plate subducts northward beneath the South Bismarck plate to form the New Britain trench (a subduction zone). There is a tear in the downgoing Solomon Sea plate, with the South Solomon Trench formed where the Solomon Sea plate is subducting northeastwardly beneath the Pacific plate. The subduction zones have different strikes due to this.

In the map below I plot the epicenters of earthquakes from the past 30 days of magnitude greater than M = 2.5. The epicenters have colors representing depth in km. The USGS plate boundaries are plotted vs color. The USGS modeled estimate for ground shaking is plotted with contours of equal ground shaking using the Modified Mercalli Intensity (MMI) scale. 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 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.

I also 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.

Today’s earthquake has an hypocentral depth of ~445 km, while the slab depth estimate from Hayes et al. (2013) is 480 km. This is a pretty good match, so the earthquake is possibly above the slab interface. However, if the earthquake is below the slab, then we can explain the moment tensor as a northwest-southeast extensional earthquake possibly due to either bending in the upper part of the downgoing Solomon sea plate or due to tension within the slab. I suppose that, if this earthquake were above the slab, then perhaps the fault was bending up at this point, causing extension in the lower part of the over-riding South Bismarck plate. This seems unlikely, so the earthquake is probably in the Solomon Sea plate.

    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.
  • In the lower right corner a figure from Oregon State University, which are based upon Hamilton (1979). “Tectonic microplates of the Melanesian region. Arrows show net plate motion relative to the Australian Plate.” This is from Johnson, 1976.


    • In earlier earthquake reports, I discussed seismicity from 2000-2015 here. The seismicity on the west of this region appears aligned with north-south shortening along the New Britain trench, while seismicity on the east of this region appears aligned with more east-west shortening. Here is a map that I put together where I show these two tectonic domains with the seismicity from this time period (today’s earthquakes are not plotted on this map, but one may see where they might plot).

    • 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.

    • Here is the slab interpretation for the New Britain region from Holm and Richards, 2013. Note the tear in the slab where the New Britain and South Solomon trenches intersect. This feeds into the tectonic domains discussed in my map above and also here. I include the figure caption below as a blockquote.

    • 3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.

    • This map shows plate velocities and euler poles for different blocks. Note the counterclockwise motion of the plate that underlies the Solomon Sea (Baldwin et al., 2012). I include the figure caption below as a blockquote.

    • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

    • This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). The New Britain region is in the map near the A and B sections. I include the figure caption below as a blockquote.

    • Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.

Earthquake Report: Oklahoma!

Oklahoma is OK! Albeit a little shaken up. Early this morning there was an earthquake that started off their Labor Day Weekend. Here is the USGS website for this M 5.6 earthquake. There have been earthquakes of similar magnitude in OK in 1952 and 2011.

Below is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. 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. This earthquake could be either a northeast striking left lateral earthquake or a northwest striking left-lateral strike-slip earthquake. Based upon the seismicity for this region of the past week or so, it appears aligned along a northwest trend.

    I include some inset figures.

  • In the upper right corner is a plot showing “Did You Feel It?” (DYFI) responses for two earthquakes. This shows how earthquakes on the west coast attenuate faster than earthquakes on the east coast. Basically, on the west coast, due to the geology there, seismic waves are absorbed by the Earth with distance. While, on the east coast, they do so to a lesser degree. The result is that earthquakes on the east coast are felt from a greater distance than those on the west coast. This comparison is for between the 2004.09.28 M 6.0 Parkfield Earthquake in California and the 2011.08.23 M 5.8 Mineral Virginia Earthquake.
  • In the lower right corner is an isoseismal map from the 1952 Oklahoma earthquake. The black lines are isoseismal lines, which means that along those lines, there were ground motions of equal intensity. The scale used on this map is similar (but different from) the MMI scale discussed above and plotted on the main map.
  • In the lower left corner are two panels. The upper panel is a map that shows the responses from “DYFI?” reports. When this map was made, there were 51,680 responses. The lower panel shows how ground motions attenuate with distance, based upon these DYFI reports. The small blue dots are individual reports. The large blue and red dots are the mean and median intensity, respectively. The green line is based upon a Ground Motion Prediction Equation (GMPE) numerical model. GMPE models are empirical relations developed using thousands of earthquake seismologic observations. This model is based upon earthquakes from the central and eastern USA.
  • To the right of those panels are two shaking intensity maps. These maps are generated using the GMPE models. The map on the left is from this 2016.09.03 M 5.6 earthquake. The map on the right is from the 2011.11.06 M 5.6 earthquake.


    I created an animation showing the uptake in seismicity in this region in the past decade or so. This animation shows seismicity from 1974 through this morning. I queried the USGS earthquake website extending the date range to 1900, but the earliest earthquake records for this region are in 1974. This increased seismicity has made Oklahoma the new earthquake capital of the lower 48 (Alaska is the earthquake king up north and Puerto Rico wins an award for number of earthquakes per unit area, down south). The increased seismicity, has been linked to the injection of waste water into the ground. Individual earthquakes are difficult to link to individual actions. However, when waste water injection is halted, seismicity is reduced. Do not confuse waste water injection with fracking. Sure, the waste water comes from the fracking industry, but the induced seismicity is largely from the waste water injection. There is some induced seismicity from fracking, but it is typically of much smaller magnitude than that for induced seismicity resulting from waste water injection.

  • First I show a map with all the earthquakes shown in the animation, then I present the animation. The map and animation include the MMI contours from today’s M 5.6 earthquake.

  • Here is a link to the embedded video below (3 MB mp4)
    Here is a plot showing the cumulative moment release from earthquakes. This shows the large increase in potentially induced seismicity in this region. This plot comes from Daniel McNamara (USGS).


    Here is a map from the USGS link above that shows seismicity since 1980. There are polygons drawn where these earthquakes are suggested to be induced by humans.



UPDATES:

    Update: 2016.09.03 14:30 PST

  • Steve Hicks, from the University of Liverpool, (@seismo_steve) used some published faults from OK, compared to the epicenters of the 2011 Prague and 2016 Pawnee earthquakes, to interpret the fault plane solution for the moment tensors. This is a reasonable interpretation, given the fault maps. However, I remember doing this for the 2012 earthquakes offshore Sumatra.

  • Daniel McNamara, from the USGS, (@DanielMcNamara) later plotted the aftershocks. These aftershocks appear to align along a possible fault that is oblique to some of the previously mapped faults. Perhaps this is a better interpretation.

Earthquake Report: New Britain!

We just had an earthquake in the New Britain region of the equatorial Pacific. Here is the USGS website for this M 6.7 earthquake. This is a very interesting earthquake for this region because it is very deep.

Below is my interpretive poster for this earthquake. This map shows the slab contours (an estimate of the subduction zone plate interface). These contours are estimated by Hayes et al., (2012). The hypocentral depth is 499.1 km, which is deeper than the slab depth according to Hayes et al. (2012), which is about 220 km. This earthquake is clearly in one of the downgoing slabs of this region. I include several figures below that present various interpretations of the different oceanic slabs in this region.

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 northwest-southeast tension. If this is due to slab tension, then the slab would be dipping to the northwest, or the southeast. This tension may also be due to some form of bending in the slab, but it is difficult to tell given these limited data. Most of the recent seismicity in this region is associated with convergence along the New Britain trench or the South Solomon trench.

    I include some inset figures.

  • In the top of the poster are two figures from Oregon State University, which are based upon Hamilton (1979). “Tectonic microplates of the Melanesian region. Arrows show net plate motion relative to the Australian Plate.” To the right of the map is a cross section showing how the Solomon Sea plate is subducting beneath New Britain. This is from Johnson, 1976.
  • In the lower left corner is another 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.
  • In the upper right corner are two figures from Holm and Richards (2013). The panel on the left shows (a) a plan view of the downgoing slab relative to islands in this region, (b) and (c) oblique views of the downgoing oceanic lithosphere of the Solomon Sea plate. Their paper discusses the back-arc spreading in the Bismarck Sea. They use hypocenter data to construct this 3-D model of the slab. On the right is a forecast of how the slab will be consumed along these subduction zones in the future.
  • In the lower right corner, I include a map that shows the Modified Mercalli Intensity Contours from this earthquake. I include this map further down on this page and have some explanations about what the Modified Mercalli Intensity (MMI) scale is.


  • Here is the localized map that shows the MMI contours. 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 have posted material about the recent and near recent (decadal) seismicity in the past:

  • Here is a post regarding the foreshocks. 2015.05.03
  • Here is a post summarizing the seismicity since 2000 AD. 2015.03.29
  • Here is a post comparing the New Britain region with the adjacent Bougainville region. 2015.03.30
  • This is a map showing the seismicity of this region since 2000 A.D.

  • Earlier, I discussed seismicity from 2000-2015 here. The seismicity on the west of this region appears aligned with north-south shortening along the New Britain trench, while seismicity on the east of this region appears aligned with more east-west shortening. Here is a map that I put together where I show these two tectonic domains with the seismicity from this time period (today’s earthquakes are not plotted on this map, but one may see where they might plot).

  • 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.

  • Here is the slab interpretation for the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.

  • 3-D model of the Solomon slab comprising the subducted Solomon Sea plate, and associated crust of the Woodlark Basin and Australian plate subducted at the New Britain and San Cristobal trenches. Depth is in kilometres; the top surface of the slab is contoured at 20 km intervals from the Earth’s surface (black) to termination of slabrelated seismicity at approximately 550 km depth (light brown). Red line indicates the locations of the Ramu-Markham Fault (RMF)–New Britain trench (NBT)–San Cristobal trench (SCT); other major structures are removed for clarity; NB, New Britain; NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; TLTF, Tabar–Lihir–Tanga–Feni arc. See text for details.

  • Here are the forward models for the slab in the New Britain region from Holm and Richards, 2013. I include the figure caption below as a blockquote.

  • Forward tectonic reconstruction of progressive arc collision and accretion of New Britain to the Papua New Guinea margin. (a) Schematic forward reconstruction of New Britain relative to Papua New Guinea assuming continued northward motion of the Australian plate and clockwise rotation of the South Bismarck plate. (b) Cross-sections illustrate a conceptual interpretation of collision between New Britain and Papua New Guinea.

  • This map shows plate velocities and euler poles for different blocks. Note the counterclockwise motion of the plate that underlies the Solomon Sea (Baldwin et al., 2012). I include the figure caption below as a blockquote.

  • Tectonic maps of the New Guinea region. (a) Seismicity, volcanoes, and plate motion vectors. Plate motion vectors relative to the Australian plate are surface velocity models based on GPS data, fault slip rates, and earthquake focal mechanisms (UNAVCO, http://jules.unavco.org/Voyager/Earth). Earthquake data are sourced from the International Seismological Center EHB Bulletin (http://www.isc.ac.uk); data represent events from January 1994 through January 2009 with constrained focal depths. Background image is generated from http://www.geomapapp.org. Abbreviations: AB, Arafura Basin; AT, Aure Trough; AyT, Ayu Trough; BA, Banda arc; BSSL, Bismarck Sea seismic lineation; BH, Bird’s Head; BT, Banda Trench; BTFZ, Bewani-Torricelli fault zone; DD, Dayman Dome; DEI, D’Entrecasteaux Islands; FP, Fly Platform; GOP, Gulf of Papua; HP, Huon peninsula; LA, Louisiade Archipelago; LFZ, Lowlands fault zone; MaT, Manus Trench; ML, Mt. Lamington; MT, Mt. Trafalgar; MuT, Mussau Trough; MV, Mt. Victory; MTB, Mamberamo thrust belt; MVF, Managalase Plateau volcanic field; NBT, New Britain Trench; NBA, New Britain arc; NF, Nubara fault; NGT, New Guinea Trench; OJP, Ontong Java Plateau; OSF, Owen Stanley fault zone; PFTB, Papuan fold-and-thrust belt; PP, Papuan peninsula; PRi, Pocklington Rise; PT, Pocklington Trough; RMF, Ramu-Markham fault; SST, South Solomons Trench; SA, Solomon arc; SFZ, Sorong fault zone; ST, Seram Trench; TFZ, Tarera-Aiduna fault zone; TJ, AUS-WDKPAC triple junction; TL, Tasman line; TT, Trobriand Trough;WD, Weber Deep;WB, Woodlark Basin;WFTB, Western (Irian) fold-and-thrust belt; WR,Woodlark Rift; WRi, Woodlark Rise; WTB, Weyland thrust; YFZ, Yapen fault zone.White box indicates the location shown in Figure 3. (b) Map of plates, microplates, and tectonic blocks and elements of the New Guinea region. Tectonic elements modified after Hill & Hall (2003). Abbreviations: ADB, Adelbert block; AOB, April ultramafics; AUS, Australian plate; BHB, Bird’s Head block; CM, Cyclops Mountains; CWB, Cendrawasih block; CAR, Caroline microplate; EMD, Ertsberg Mining District; FA, Finisterre arc; IOB, Irian ophiolite belt; KBB, Kubor & Bena blocks (including Bena Bena terrane); LFTB, Lengguru fold-and-thrust belt; MA, Mapenduma anticline; MB, Mamberamo Basin block; MO, Marum ophiolite belt; MHS, Manus hotspot; NBS, North Bismarck plate; NGH, New Guinea highlands block; NNG, Northern New Guinea block; OKT, Ok Tedi mining district; PAC, Pacific plate; PIC, Porgera intrusive complex; PSP, Philippine Sea plate; PUB, Papuan Ultramafic Belt ophiolite; SB, Sepik Basin block; SDB, Sunda block; SBS, South Bismarck plate; SIB, Solomon Islands block; WP, Wandamen peninsula; WDK, Woodlark microplate; YQ, Yeleme quarries.

  • This figure incorporates cross sections and map views of various parts of the regional tectonics (Baldwin et al., 2012). The New Britain region is in the map near the A and B sections. I include the figure caption below as a blockquote.

  • Oblique block diagram of New Guinea from the northeast with schematic cross sections showing the present-day plate tectonic setting. Digital elevation model was generated from http://www.geomapapp.org. Oceanic crust in tectonic cross sections is shown by thick black-and-white hatched lines, with arrows indicating active subduction; thick gray-and-white hatched lines indicate uncertain former subduction. Continental crust, transitional continental crust, and arc-related crust are shown without pattern. Representative geologic cross sections across parts of slices C and D are marked with transparent red ovals and within slices B and E are shown by dotted lines. (i ) Cross section of the Papuan peninsula and D’Entrecasteaux Islands modified from Little et al. (2011), showing the obducted ophiolite belt due to collision of the Australian (AUS) plate with an arc in the Paleogene, with later Pliocene extension and exhumation to form the D’Entrecasteaux Islands. (ii ) Cross section of the Papuan peninsula after Davies & Jaques (1984) shows the Papuan ophiolite thrust over metamorphic rocks of AUS margin affinity. (iii ) Across the Papuan mainland, the cross section after Crowhurst et al. (1996) shows the obducted Marum ophiolite and complex folding and thrusting due to collision of the Melanesian arc (the Adelbert, Finisterre, and Huon blocks) in the Late Miocene to recent. (iv) Across the Bird’s Head, the cross section after Bailly et al. (2009) illustrates deformation in the Lengguru fold-and-thrust belt as a result of Late Miocene–Early Pliocene northeast-southwest shortening, followed by Late Pliocene–Quaternary extension. Abbreviations as in Figure 2, in addition to NI, New Ireland; SI, Solomon Islands; SS, Solomon Sea; (U)HP, (ultra)high-pressure.

Earthquake Report: Burma!

Well, there was an earthquake about 6 hours ago in Burma. This M 6.8 earthquake was rather deep, which is good for the residents of that area (the ground motions diminish with distance from the earthquake hypocenter). Here is the USGS website for this earthquake. This M 6.8 earthquake is possibly soled in the convergent plate boundary thrust fault at the base of the Indo-Burmese Wedge (see maps below). While this M 6.8 earthquake probably won’t result in a large number of casualties, there are reports of damage to buildings and temples. Some live updates on damage in this area are posted here.

Below is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. 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 some inset figures and maps. I also post some of these figures below, along with their original figure captions.

  • In the upper right corner I include the Rapid Assessment of an Earthquake’s Impact (PAGER) report. More on the PAGER program can be found here. An explanation of a PAGER report can be found here. PAGER reports are modeled estimates of damage. On the top is a histogram showing estimated casualties and on the right is an estimate of possible economic losses. This PAGER report suggests that there will be quite a bit of damage from this earthquake (and casualties).
  • In the lower right corner, is a map from Maurin and Rangin (2009) that shows the regional tectonics at a larger scale.
  • In the lower left corner is a map that shows an estimate of the ground motions from a hypothetical earthquake of this magnitude in this location. This shows the shaking intensity and uses the MMI scale mentioned above. The plot to the right shows the reported MMI intensity data as they relate to two plots of modeled estimates (the orange and green lines). These green dots are from the USGS “Did You Feel It?” reports compared to the estimates of ground shaking from Ground Motion Prediction Equation (GMPE) estimates. The relations between ground shaking and distance to an earthquake are also known as attenuation relations as the ground motions diminish (get attenuated) with distance from the earthquake.
  • In the upper left corner is a map from Wang et al. (2014) that shows even more details about the faulting in the Indo-Burmese Wedge (IBW) shown in the Maurin and Rangin (2009) map. To the right of this map is a cross section (c-c’ shown on the map) that shows an east-west transect of earthquake hypocenters (Wang et al., 2014).

Here is the Curray (2005) plate tectonic map.


Here is a map from Maurin and Rangin (2009) that shows the regional tectonics at a larger scale. They show how the Burma and Sunda plates are configured, along with the major plate boundary faults and tectonic features (ninetyeast ridge). The plate motion vectors for India vs Sunda (I/S) and India vs Burma (I/B) are shown in the middle of the map. Note the Sunda trench is a subduction zone, and the IBW is also a zone of convergence. There is still some debate about the sense of motion of the plate boundary between these two systems. This map shows it as strike slip, though there is evidence that this region slipped as a subduction zone (not strike-slip) during the 2004 Sumatra-Andaman subduction zone earthquake. I include their figure caption as a blockquote below.


Structural fabric of the Bay of Bengal with its present kinematic setting. Shaded background is the gravity map from Sandwell and Smith [1997]. Fractures and magnetic anomalies in black color are from Desa et al.[2006]. Dashed black lines are inferred oceanic fracture zones which directions are deduced from Desa et al. in the Bay of Bengal and from the gravity map east of the 90E Ridge. We have flagged particularly the 90E and the 85E ridges (thick black lines). Gray arrow shows the Indo-Burmese Wedge (indicated as a white and blue hatched area) growth direction discussed in this paper. For kinematics, black arrows show the motion of the India Plate with respect to the Burma Plate and to the Sunda Plate (I/B and I/S, respectively). The Eurasia, Burma, and Sunda plates are represented in green, blue, and red, respectively.

Wang et al. (2014) also have a very detailed map showing historic earthquakes along the major fault systems in this region. They also interpret the plate boundary into different sections, with different ratios of convergence:shear. I include their figure caption as a blockquote below.


Simplified neotectonic map of the Myanmar region. Black lines encompass the six neotectonic domains that we have defined. Green and Yellow dots show epicenters of the major twentieth century earthquakes (source: Engdahl and Villasenor [2002]). Green and yellow beach balls are focal mechanisms of significant modern earthquakes (source: GCMT database since 1976). Pink arrows show the relative plate motion between the Indian and Burma plates modified from several plate motion models [Kreemer et al., 2003a; Socquet et al., 2006; DeMets et al., 2010]. The major faults west of the eastern Himalayan syntax are adapted from Leloup et al. [1995] and Tapponnier et al. [2001]. Yellow triangle shows the uncertainty of Indian-Burma plate-motion direction.

Here is a map from Wang et al. (2014) that shows even more details about the faulting in the IBW. Today’s fault occurred nearby the CMf label. I include their figure caption as a blockquote below. Wang et al. (2014) found evidence for active faulting in the form of shutter ridges and an offset alluvial fan. Shutter ridges are mountain ridges that get offset during a strike-slip earthquake and look like window shutters. This geologic evidence is consistent with the moment tensor from today’s earthquake. There is a cross section (C-C’) that is plotted at about 22 degrees North (we can compare this with the Maurin and Rangin (2009) cross section if we like).


Figure 6. (a) Active faults and anticlines of the Dhaka domain superimposed on SRTM topography. Most of the active anticlines lie within 120 km of the deformation front. Red lines are structures that we interpret to be active. Black lines are structures that we consider to be inactive. CT = Comilla Tract. White boxes contain the dates and magnitudes of earthquakes mentioned in the text. CMf = Churachandpur-Mao fault; SM = St. Martin’s island antilcline; Da = Dakshin Nila anticline; M= Maheshkhali anticline; J = Jaldi anticline; P = Patiya anticline; Si = Sitakund anticline; SW= Sandwip anticline; L = Lalmai anticline; H = Habiganj anticline; R = Rashidpur anticline; F = Fenchunganj anticline; Ha = Hararganj anticline; Pa = Patharia anticline. (b) Profile from SRTM topography of Sandwip Island.

Here is the Wang et al. (2014) cross section. I include their figure caption as a blockquote below.


Schematic cross sections through two domains of the northern Sunda megathrust show the geometry of the megathrust and hanging wall structures. Symbols as in Figure 18. (a) The megathrust along the Dhaka domain dips very shallowly and has secondary active thrust faults within 120 km of the deformation front. See Figures 2 and 6 for profile location.

Here is a different cross section that shows how they interpret this plate boundary to have an oblique sense of motion (it is a subduction zone with some strike slip motion). Typically, these different senses of motion would be partitioned into different fault systems (read about forearc sliver faults, like the Sumatra fault. I mention this in my report about the earthquakes in the Andaman Sea from 2015.07.02). This cross section is further to the south than the one on the interpretation map above. I include their figure caption as a blockquote below.


Present cross section based on industrial multichannel seismics and field observations. The seismicity from USGS catalog and Engdahl [2002] is represented as black dots. Focal mechanisms from Global CMT (http://www.globalcmt.org/CMTsearch.html) catalog are also represented.

    For the January 2016 earthquake, Jascha Polet made these two figures:

  • Here is a cross section that shows seismicity for this region. The earthquakes are plotted as focal mechanisms. This comes from Jacha Polet, Professor of Geophysics at Cal Poly Pomona.

  • Here is a map showing the seismicity and focal mechanisms, also from Jacha Polet.

Earthquake Report: Italy!

There was a M 6.2 earthquake in Italy tonight. Here is the USGS website for today’s earthquake. There is lots of information about the tectonics of this region. I can hardly do justice to all the people who have worked here. It seems like every route I take for more information, I get 10 more publications.

This earthquake is north of the region that had an M 6.3 earthquake in 2009 that led to an interesting (putting it nicely) interaction between scientists, public employees/politicians, and the legal system. Basically, several seismologists were sentenced to prison. More on this is found online, for example, here and here.

Below is my interpretive map that shows the epicenter, along with the shaking intensity contours. These contours use the Modified Mercalli Intensity (MMI) scale. 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. The tectonics of this region has many normal (extensional) faults, which explain the extensional moment tensor. However, I do not know enough of this region to interpret is this is an east or west dipping fault that ruptured (depends upon which side of which basin experience this earthquake; see below).

    I include some inset figures and maps.

  • In the upper right corner I include the Rapid Assessment of an Earthquake’s Impact (PAGER) report. More on the PAGER program can be found here. An explanation of a PAGER report can be found here. PAGER reports are modeled estimates of damage. On the top is a histogram showing estimated casualties and on the right is an estimate of possible economic losses. This PAGER report suggests that there will be quite a bit of damage from this earthquake (and casualties).
  • Below that I show the USGS plot of “Did You Feel It?” reports compared to the estimates of ground shaking from Ground Motion Prediction Equation (GMPE) estimates. The relations between ground shaking and distance to an earthquake are also known as attenuation relations as the ground motions diminish (get attenuated) with distance from the earthquake.
  • To the left of the PAGER report I include a basic tectonic map of this region. Maps with local (larger) scale have much more detailed views of the faulting.
  • In the lower left corner is a map showing a series of earthquake swarms that occurred between 1916 and 1920, rupturing across the Apennines in northern Italy. This is just to the north of tonight’s M 6.2 earthquake. It is interesting as Baize posted on twitter some accounts of this earthquake series on twitter yesterday. There is another map showing greater detail of the 1916 swarm.


I also plot a moment tensor from an earthquake in the western Mediterranean from 2016.01.24 in the above map. Here is my Earthquake Report for that seismicity and below is the map from that report.


In late 2015 (2015.11.17) there was a M 6.5 earthquake along a fault related to the terminus of the North Anatolian fault system in western Greece. Here is my earthquake report for that seismicity and below is my map from that report. Below this first map is another map that shows some aftershocks.


Here is an updated map that shows a couple more aftershocks, at a large (local) scale. I have included the moment tensors for the two largest aftershocks.


For more on the graphical representation of moment tensors and focal mechanisms, check this IRIS video out:

    Here are some observations made by others.

  • Susan Hough (USGS) asked people tonight what they thought about explaining why the “DYFI” reports seemed too small compared to the GMPE model predictions. So far, I am unsatisfied with the answers. Looking at the plot from the 2009 M 6.3 earthquake, the region’s low population density would not appear to explain this discrepancy. Perhaps it is because today’s earthquake happened at night time, so maybe people have not yet reported yet. Below I include these GMPE/DYFI plots for both 2016.08.24 M 6.2 and 2009.04.06 M 6.3 earthquakes. Interesting that the DYFI reports for the 2009 earthquake also have higher MMI values, in general, than the 2016 earthquake. The difference between a M 6.2 and > 6.3 earthquake is about 3 times (a M 6.3 releases about 3 times as much energy as a M 6.2 earthquake), but these maps seem much more different than that. I plot the DYFI maps below the attenuation plots.
  • 2016.08.24

  • 2009.04.06

  • 2016.08.24

  • 2009.04.06

  • David Schwartz (USGS) noted that tonight’s earthquake is “between the 1997 Assisi aftershock zone and the north end of the 2009 l’aquila rupture” and may be a “foreshock to a 1915-like Fucino rupture.” So we need to look at these two earthquakes to learn more about what Schwartz is talking about. Here is a web post about an INQUA workshop held in “Pescina, to commemorate the centenary of the 13/1/1915 M7 Fucino Earthquake.” This was posted by Stephanie Baize who is also on twitter. Follow him to learn more about tonight’s earthquake. There is a great paper that discusses the 1915 earthquake sequence that Schwartz was talking about here (Galadini and Galli, 1999). A more recent paper also discusses the faulting in this region (Palumbo et al., 2004).
    Here are some other maps that might help. (well, one so far)

  • This Billi et al. (2006) map shows some of these west dipping normal faults in central Italy, just south of the Apennines.

  • There are some excellent maps and figures from a study from 2004 (Boncio et al, 2004). This material was posted on twitter here.