Category Archives: Chemeketa Community College

Movies: Seismic Record of a Deep Izu-Bonin Earthquake

Scientists at the National Research Institute for Earth Science and Disaster Prevention have collected and processed seismic data from the High Sensitivity Seismograph Network Japan (Hi-net). They created movies of these data, in map view. Here is the page where they posted these movies. I have translated the text below to make it easier to read, but this is completely their work. I include links to the videos. The first movie shows long period seismic data and the second movie shows short period seismic data.

Here is a link to the USGS web page for this M 7.8 earthquake.

Here is a map that I put together that shows the mainshock, some aftershocks, and some triggered earthquakes.

I place the translated text in block quotes. The original text all comes from here.

Around 24 pm on May 30, 2015, 20:24, an earthquake of M 8.1 (by the Japan Meteorological Agency) has occurred in the Ogasawara Islands off the west coast. The earthquake, which occurred at a very deep place of about 680km, because scale is large, with observing the strong shaking of magnitude 5 [V] in Tokyo and Ogasawara Village and Kanagawa Prefecture Ninomiya Town, seismic intensity of one or more sway in all prefectures me was observed. In addition, long-period ground motion “around the Kanto region was also observed. Whether by this earthquake Japan archipelago is how the shaking, it was visualized using the observation data of NIED of high sensitivity seismograph network (Hi-net). Try compared the differences transmitted the way of waves of long period (wobbling and then shook) and short period waves (shaking was rattled).



Here is the link of the mp4 file (7 MB).

The Hi-net using seismic appropriate to be observed oscillation of period shorter than one second, but by correcting the characteristics of the seismometer and data acquisition system, of the wave that vibrates with a period several tens of seconds general features it is possible to also be considered . Here, by applying a band-pass (band-pass) filter to the waveform after the characteristic correction, we visualized how the transmitted seismic waves 25 to 50 seconds range. From around 20:25, you can confirm that wave that has spread from the epicenter to the longitudinal Japan to north-northwest. Initially, it is striped red and blue will continue to spread in concentric circles around the epicenter, from around 20:27, the shift has begun to occur in a stripe pattern at the center of the Japanese archipelago. From around 20:28, reflected by the underground, also joined the wave, which is thought to have through the refraction, etc., wave field shows the complex aspects.



Here is the link of the mp4 file (7 MB).

Through the Izu Islands from around 20:25 Kanto, amplitude is increased from the Tokai region coast, you can see that P wave (initial) has arrived. This wave, over a period of about 1 minute half, will continue to longitudinal the Japanese archipelago to Hokkaido northern tip. Over time and towards the West is seen how the amplitude ahead to decay than the East , but this is considered to reflect the region of the attenuation structure of the underground ( * )

Errata for Phantom Earthquakes: USGS

There have been a couple of reported earthquakes that have since been removed from the database. This happens when seismic waves are incorrectly interpreted by the computers, typically from the results of larger magnitude earthquakes. These large magnitude earthquakes can produce seismic waves that are easily interpreted to be local earthquakes in other locations. When people review the data, these errors are omitted. However, the phantom earthquakes are often submitted to the earthquake notification system prior to this removal. These deletions raise angst in the conspiracy theorists’ minds (we can only imagine what actually is in their minds, if much at all), suggesting that there is some global conspiracy to hide seismic data, for some nefarious reason. I cannot think of a single reason why someone might want to hide seismic data (well, maybe for nuclear testing). It would be difficult to really hide seismic data because there are so many unique and independent seismic networks, which publish their data online.

Sign up for the Earthquake Notification System here.

The USGS has posted information about these recent Phantom Earthquakes and the reasons behind their deletions. I paste the relevant information below, just in case there is a conspiracy that will later remove these words from the internets [sarcasm].

Here was the page for the M 5.1 Lewiston earthquake, which was the result of seismic waves travelling from the M 6.7 earthquake along the Alaska Peninsula. This is my first post about the M 6.7 earthquake and here is a post that I wrote that includes animations of historic seismicity in the region.

Here was my post about this earthquake. This happened at a time when I needed to go to sleep, so I was putting off from posting a more detailed accounting until the next day. Of course, when I awoke the next day, it was deleted… So I had little to post about. This is the link to the USGS for this earthquake.

This is the pager alert (which is also an automated product):

Here is the “Did You Feel It?” map, with no reports (should be no surprise, since there was no earthquake).

Here is the Modified Mercalli Intensity shake map, showing that people would have felt it if it had happened (and probably would have reported it!).

Here is what the USGS states about these earthquakes:

Commentary for Multiple “Phantom Events” in California – posted June 2, 2015

Automated notification systems are a convenient and often essential component of modern life. The USGS has invested heavily in developing automated systems that provide the public with timely and accurate earthquake information. On rare occasions the Earth throws a curveball and on May 29th and 30th, the USGS issued multiple alerts for false earthquakes in Northern California. The first, a M5.1 near Lewiston, CA, was distributed on Friday. More false alerts were distributed on Saturday, including a M5.5 near Ukiah and M4.7 near San Simeon.

These erroneous earthquake notifications were created by the seismic waves from large, distant earthquakes. On Friday, a M6.7 earthquake occurred at a depth of approximately 60 km, 111 km off of Chirikof Island, Alaska. It was this earthquake that fooled the automatic processing of the Northern California Seismic System to issue the first false alert. Just 28 hours later, a M7.8 earthquake off of Japan with a depth of more than 660 km – the deepest earthquake of its size to have occurred during our history of recording – spawned two more phantom events in Northern California.

Large earthquakes have created challenges for regional seismic monitoring in the past. This problem is particularly acute for deep earthquakes as they generate very impulsive seismic waves which may be misinterpreted as a local earthquake. The USGS and its partners have developed a number of methods to stop or screen these events from being distributed on the Web and through such mechanisms as the Earthquake Notification Service. The USGS will be implementing changes to improve the system and minimize the chances of this occurring in the future.

The erroneous events were deleted quickly by a duty seismologist. Unfortunately, a problem with the distribution software prevented the delete messages from being transmitted to recipients of the Earthquake Notification Service. The inability to transmit the information about the false events to the users of the Earthquake Notification Service caused significant confusion and the USGS regrets the problems caused by this failure. USGS staff have identified the problem in the distribution software and fixed it.

Errata for “Phantom Events” in Central and Northern California resulting from the M6.7 Alaska Earthquake on 2015-05-29 07:00:29 UTC

Strong earthquakes generate seismic waves that spread across the entire globe. When the earthquakes are deep, the distant recordings are quite impulsive and are often mistakenly identified by automated systems as local earthquakes. On 2015/05/29 07:00 UTC, a 60 km-deep M6.7 earthquake occurred offshore of Chirikof Island, Alaska and swept across the seismic networks in northern California. The automatic earthquake detection systems recognized the arrival of seismic energy but misinterpreted it as several earthquakes, including an M 5.1 event occurring near Lewiston, rather than one large distant event. These “phantom events” were automatically released for public distribution on the Web and through the Earthquake Notification Service. All “phantom events” were cancelled by the duty seismologist within 15 minutes.

Blanco Fracture Zone: 2000 – 2015 Seismicity Animation

I put together an animation that includes the seismicity from 1/1/2000 until 6/1/2015 for the region near the Blanco fracture zone, with earthquake magnitudes greater than or equal to M = 5.0. The map here shows all these epicenters, with the moment tensors for earthquakes of M = 6 or more (plus the two largest earthquakes from today’s swarm). This is the search that I used for the earthquakes plotted in the map and animations below. Here is the page that I posted regarding the beginning of this swarm. Here is a post from some earthquakes last year along the BFZ.

Earthquake epicenters are plotted with the depth designated by color and the magnitude depicted by the size of the circle. These are all fairly shallow earthquakes at depths suitable for oceanic lithosphere.

    Here is the list of the earthquakes with moment tensors plotted in the above maps (with links to the USGS websites for those earthquakes):

  • 2000/06/02 M 6.0
  • 2003/01/16 M 6.3
  • 2008/01/10 M 6.3
  • 2012/04/12 M 6.0
  • 2015/06/01 M 5.8
  • 2015/06/01 M 5.9
    Here are some files that are outputs from that USGS search above.

  • csv file
  • kml file (not animated)
  • kml file (animated)

VIDEOS

    Here are links to the video files (it might be easier to download them and view them remotely as the files are large).

  • First Animation (20 mb mp4 file)
  • Second Animation (10 mb mp4 file)

Here is the first animation that first adds the epicenters through time (beginning with the oldest earthquakes), then removes them through time (beginning with the oldest earthquakes).

Here is the second animation that uses a one-year moving window. This way, one year after an earthquake is plotted, it is removed from the plot. This animation is good to see the spatiotemporal variation of seismicity along the BFZ.

Late addition:
Here is a seismogram from Gold Mountain Washington. Thanks for posting this Pacific Northwest Seismic Network fb page. Here is the page that it came from.

Blanco Fracture Zone Earthquakes!

This morning we had three earthquakes related to the Blanco fracture zone, a transform (shear) plate boundary. These earthquakes occurred quite a bit north of the bathymetric expression of the BFZ (though the M 5.8 is actually plotting closer to the BFZ this morning), similar to the seismicity earlier this year to the southeast of today’s swarm. Here is a post regarding the seismicity along the BFZ in April 2015.

Here is a map showing these earthquakes, with moment tensors plotted for the M 5.8 and M 5.5 earthquakes. I include an inset map showing the plate configuration based upon the Nelson et al. (2004) and Chaytor et al. (2004) papers (I modified it). I also include a cross section of the subduction zone, as it is configured in-between earthquakes (interseismic) and during earthquakes (coseismic), modified from Plafker (1972).


Here is a version of the CSZ map alone (Chaytor et al., 2004; Nelson et al., 2004).

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

Here is a map showing the BFZ seismicity from April 2015.

Historic Seismicity Animations: Izu-Bonin, Mariana: 1940 – 2015

Following up on the seismicity in the western Pacific, I put together a couple animations. My post about the deep mainshock (magnitude M = 7.8 ) is here. My second post has some aftershocks plotted (and some foreshocks), as well as a little more about this series of earthquakes.

Here are a couple animations that show the seismicity in the western Pacific for the time span of 1940 through the end of May, 2015. These earthquakes were downloaded from the USGS NEIC using the html based query, using this search. The diameter relates to earthquake magnitude and the color represents the depth. These earthquakes have magnitudes greater than or equal to M = 7 and span the period from 1940 through May 2015.

I also have placed an overlay of the oceanic crustal age that I downloaded from here: Les SVT dans l’académie de Versailles. Color represents age. The ichrons have 5 Ma spacing.

Here is a screenshot showing all earthquakes included in the following animations.

1940 – 2015 with no moving window. Link to the file here.

1940 – 2015 with 5 year moving window. Link to the file here.

Also, here is another cross section in the same region as the M 7.8 earthquake. This is from the USGS poster about the seismicity in this region (Rhea. This legend for this cross section is here.

Here is the cross section. Note again, how this M 7.8 earthquake does not fit the existing slab model.

    References

  • Rhea, S., Tarr, A.C., Hayes, G., Villaseñor, A., and Benz, H.M., 2010, Seismicity of the Earth 1900-2007, Japan and vicinity: U.S. Geological Survey Open-File Report 2010-1083-D, 1 map sheet, scale 1:5,000,000.

Triggered Earthquakes: Izu-Bonin

Well, we had a large magnitude earthquake (M = 6.2) triggered by the M 7.8 deep earthquake along the Izu-Bonin Trench. Here is my post from yesterday. Note the triggered earthquake is in a region where there were earthquakes about 2 weeks prior to the M 7.8. These “foreshocks” (not really foreshocks since they are on different faults) are thrust or reverse earthquakes (the result of compression from the convergent plate boundary). The M 7.8 and triggered M 6.2 are, instead, normal earthquakes (the result of extension).

I have included a cross section on the map (also include this below). The cross section B-B’ is in a great location compared to the M 7.8. Note the purple line, as this coincides with the B-B’ cross section on seismicity in the inset figure. I placed a red circle on the inset, approximately where the M 7.8 hypocenter would plot. This M 7.8 is the deepest earthquake in this part of the subduction zone, but on cross section E-E’ shows an earthquake with a similar hypocentral depth. I also show where the 1944 M 8.1 Tonankai and 1946 M 8.3 Nankai subduction zone earthquakes are.


    Here are the USGS web sites for the earthquakes with moment tensors plotted on the above map.

  • 2015.05.10 M 5.3
  • 2015.05.10 M 5.6
  • 2015.05.30 M 6.2
  • 2015.05.30 M 7.8

Something that is interesting, possibly, is that the M 7.8 earthquake is at a much deeper position than is suggested by the slab model from Hayes et al. (2012). Based upon these slab contours (the depth contours for where the subduction zone fault may be, based upon seismicity), the slab is at a depth of 200-220 km in the region of the M 7.8 earthquake, yet this earthquake has a USGS hypocentral depth of 677 km. These slab contours are free to download and then they can be plotted in Google Earth (or ArcGIS). However, if we examine the cross section on the inset figure (or below), we will see that the M 7.8 fits well with the earlier seismicity. Perhaps the Hayes et al. (2012) slab model could be updated for this subduction zone.

The M 7.8 was felt broadly in Japan.

This shows how the seismic energy attenuates (diminishes) with distance from the earthquake. Note how the observations are at such a great distance.

Here is the cross section figure that is an inset on the above map. This comes from Dr. Matt Fouch from Arizona State University. Here is some text from the wiki page.
“Map view of bathymetry and seismicity in the IBM subduction zone using the earthquake catalog of Engdahl, van der Hilst & Buland 1998. Circles denote epicentral locations; lighter circles represent shallower events, darker circles represent deeper events. Black lines denote cross sectional areas depicted in 6 profiles on right, organized from N to S. Black circles represent hypocentral locations in volume ~60 km to each side of the lines shown on the map at left. Large variations in slab dip and maximum depth of seismicity are apparent. Distance along each section is measured from the magmatic arc.”
“B) Central Izu Bonin region. Slab dip is nearly vertical; seismicity tapers off from ~100 km to ~325 km but increases in rate and extends horizontally around 500 km, and terminates at ~550 km.”

    References:

  • Engdahl, E.R.; van der Hilst, R.D.; Buland, R., 1998. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination. Bulletin of the Seismological Society of America 88: 722–743.
  • Hayes, G. P., D. J. Wald, and R. L. Johnson (2012), Slab1.0: A three-dimensional model of global subduction zone geometries, J. Geophys. Res., 117, B01302, doi:10.1029/2011JB008524

Earthquake along the Alaska Penninsula!

We just had an earthquake along the Alaska Peninsula. The magnitude is currently set at 6.7 on the USGS website. The Peninsula is a volcanic arc that forms as a result of the subduction of the Pacific plate beneath the North America plate. The second largest earthquake ever recorded by seismometers occurred on March 27, 1964, known as the Good Friday Earthquake. I have posted some material about this earthquake.

Here is an early map showing the epicenter of the Mw = 6.7 earthquake. This earthquake has an oblique strike-slip moment tensor fault plane solution. Based upon the block rotation in the forearc to the west, I suspect that this may be a N-S right-lateral earthquake.

    Here are a couple pages that discuss the Good Friday Earthquake and the general tectonic setting along this plate boundary.

  • 1964 Earthquake Before and After Photo Tour
  • 1964 Earthquake Seismic Wave Propagation Animation
  • June 2013 M 7.9 Rat Islands Earthquake. This page also has some cool animations from the Rat Island Earthquake and tectonic maps of the Aleutian Islands.

Here is a graphic showing what a forearc sliver might look like (from GSA).

Here is a map from Krutikov et al. 2008 (Active Tectonics and Seismic Potential of Alaska, Geophysical Monograph Series 179 Copyright 2008 by the American Geophysical Union. 10.1029/179GM07)
Note that there are blocks that are rotating to accomodate the oblique convergence. There are also margin parallel strike slip faults that bound these blocks. These faults are in the upper plate, but may impart localized strain to the lower plate, resulting in strike slip motion on the lower plate (my arm waving part of this). Note how the upper plate strike-slip faults have the same sense of motion as these deeper earthquakes.

This map shows the region with historic earthquakes extending back to 1960, of magnitude 6,0 and larger. The largest circle in the upper right part of the map is the epicenter for the Good Friday Earthquake.

Here is a map that shows the regional extent of the 1964 earthquake. Regions of coseismic uplift/subsidence are delineated by blue/red polygons.

This shows a cross section of a subduction zone through the two main parts of the earthquake cycle. The interseismic part (inbetween earthquakes) and the coseismic part (during earthquakes). This was developed by George Plafker and published in his 1972 paper on the Good Friday Earthquake.

Here is a map showing the historic earthquakes along this subduction zone. This is from Peter J. Haeussler, USGS, Alaska Science Center.

These are leveling data from the earthquake cycle along the subduction zone in southeastern Japan.

Here is a video that discusses the 1964 earthquake.

Youtube Source IRIS

WMV file for downloading.

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
Maps from Google Earth. Video from US Army Corps of Engineers. Tsunami animation from National Oceanic & Atmospheric Administration (NOAA). Photographs from US Geological Survey.

    References:

  • Hyndman and Wang, 1995
  • Plafker, 1972

Mid Atlantic Ridge Plate Boundary

In the past week, there have been a few earthquakes along the Mid Atlantic Ridge (MAR) and some associated fracture zones. The Mid Atlantic Ridge is a divergent plate boundary. As the plates move apart, the asthenosphere is decompressed and magma rises to the surface to create new oceanic lithosphere. The youngest oceanic crust is along these oceanic spreading centers/ridges. When these spreading ridges are offset laterally, transform plate boundaries called fracture zones form. The MAR has many fracture zones.

Here is a map showing the southern swarm is related to the spreading center and that the seismicity in the north is strike-slip motion on a fault probably related to a fracture zone, possibly the Vernadsky or Bogdanov fracture zones (looks like it is on a fracture zone between these two, but I am uncertain about which fz is which). The southern earthquake magnitude M = 6.3 moment tensor for the spreading ridge earthquake is extensional, consistent with being related to a divergent plate boundary (orange arrows). This spreading ridge is between the St. Helena and Hotspur fracture zones. The northern earthquake magnitude M = 5.1 moment tensor matches what we would expect for a fracture zone in this region (green arrows). I found these fracture zones labeled on a couple maps (Bonatti et al., 2010 and online from Woods Hole, and the USGS earthquake maps).

Click on the map to be able to read the labels for the fracture zones.

    Here are the USGS web pages for the three largest magnitude earthquakes in the above map:

  • 2015.05.24 M 5.1 northern earthquake
  • 2015.05.24 M 6.3 southern mainshock
  • 2015.05.25 M 5.2 southern aftershock

Nepal (Gorkha) Earthquake: USGS Slip Models

The USGS has processed an inversion of the seismic data for a slip model for the Mw 7.3 earthquake. I have rubbersheeted their fault plane solution, as well as the solution for the Mw 7.8 earthquake for comparison. Please find them below. Here are the links to the USGS web pages for the Mw 7.8 Finite Fault Plane Solution and the Mw 7.3 Finite Fault Plane Solution. The methods that the USGS uses to invert the seismic data are included on those pages. I list their references below.

Mw 7.8 Earthquake Finite Fault Plane Solution from the USGS.

Mw 7.3 Earthquake Finite Fault Plane Solution.

Here is their original map for the Mw 7.8 earthquake:

Here is their original map for the Mw 7.3 earthquake:

Here are the slip models:

Mw 7.8 earthquake:

Mw 7.3 earthquake:

    References:

  • Bassin, C., Laske, G. and Masters, G., 2000. The Current Limits of Resolution for Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.
  • Ji, C., Wald, D.J., and Helmberger, D.V., 2002. Source description of the 1999 Hector Mine, California earthquake; Part I: Wavelet domain inversion theory and resolution analysis, Bull. Seism. Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.
  • Ji, C., Helmberger, D. V., Wald, D. J., and Ma, K. F., 2003. Slip history and dynamic implications of the 1999 Chi-Chi, Taiwan, earthquake, J Geophys Res-Sol Ea, 108(B9).
  • Shao, G. F., Li, X. Y., Ji, C., and Maeda, T., 2011. Focal mechanism and slip history of the 2011 M-w 9.1 off the Pacific coast of Tohoku Earthquake, constrained with teleseismic body and surface waves, Earth Planets Space, 63(7), 559-564.

Large Aftershock in Nepal: 2nd Update

Well, there have been a few more aftershocks over night… Here is my first post about these aftershocks (I provide more links to the USGS web sites). Plus, the USGS has inverted the seismic data to estimate a fault plane (with estimated slip on the fault). They also updated their shaking intensity maps and PAGER estimates to reflect results of modeling slip and ground motions upon this fault plane. Below I plot the new Modified Mercalli Intensity data (in red, not the typical MMI color scale). I also include the Hough and Bilham (2008 ) slip model for the 1934 earthquake. It appears as though this 2015 swarm overlaps slightly with the 1934 slip patch (less so than the other two 1934 slip patches). Previously I had plotted other historic earthquakes on a regional map.

I digitized the outline of the USGS fault model and present this outline on this map. Here is the fault model with seismicity plotted…

Here is an updated regional map that incorporates Hough and Bilham (2008 ) and today’s seismicity. The historic and prehistoric earthquake slip patches are also shown. The three other data sets now include Bilham (2004), Bettinelli et al (2006), and Berryman et al. (2009). I provide information about how I compiled these data sets on this page.

Here is the USGS fault plane solution.

The PAGER [Version 3] estimate has also increased the estimated casualties. This does not include potential casualties from the landslides that will fail during the soon coming monsoon season.

Here is the updated DYFI map.

Here is the associated updated attenuation relations plot. I spend more time explaining these two figures in my prior post here.

This is the prior attenuation plot for comparison.

For another comparison, here are the two MMI intensity maps. The first one was based on an automated numerical attenuation model. The lower one is based upon the finite fault inversion.



12:15 PM PST:
Here is an update of the seismicity…

2:30 PM PST:
Here are two visualizations of the seismic waves as they propagate through the Earth. These are records from the USArray Transportable Array. Your tax dollars at work, unless congress defunds these projects. This first video shows vertical motion as red and blue.


This second video shows horizontal motion with magnitude and direction.

    References:

  • Bilham, R., Gaur, V.K., Molnar, P., 2001. Himalayan Seismic Hazard, Science, v. 293, p/ 1,442-1,444.
  • Bilham, R., 2004. Earthquakes in India and the Himalaya: tectonics, geodesy and history, Annals of Geophysics, v. 42, no. 2/3, p. 839-858.
  • Bettinelli, P., Avouac, J-P., Flouzat, M., Jouanne, F., Bollinger, L., Willis, P., and Chikitrar, G.R., 2006. Plate motion of India and interseismic strain in the Nepal Himalaya from GPS and DORIS measurements, Journal of Geodesy, v. 80, p. 567-589
  • Berryman, K., Ries, W., Litchfield, N. (2014) The Himalayan Frontal Thrust: Attributes for seismic hazard Version 1.0, December 2014, GEM Faulted Earth Project, available from http://www.nexus.globalquakemodel.org/.
  • Hough, S.E. and Bilham, R., 2008. Site response of the Ganges basin inferred from re-evaluated macroseismic observations from the 1897 Shillong, 1905 Kangra, and 1934 Nepal earthquakes, Journal of Earth System Sciences, v. 117, S2, November 2008, p. 773-782.