Earthquake in Central Honshu!

David N Lindberg liked this post

This morning (my time) there was a large earthquake in central Honshu. Here is the USGS page for this earthquake. The earthquake hypocentral depth is shallow, giving rise to the likelihood of damage to infrastructure and people.

Here is a map of the region, showing the epicenter in orange, near Nangano. This earthquake occurred along the Itoigawa-Shizuoka Tectonic Line, a convergent plate boundary between the Eurasian/Amurian plate and the North America/Okhotsk plates. This earthquake is in the region where this fault zone flips vergence (in the south it dips to the southwest and to the north it dips to the northeast. This is where the Niigata-Kobe fold and thrust belt meets the mobile belt of the east margin of the Japan Sea.

This is the moment tensor, which is interesting in that it is not evidently parallel to the tectonic boundary of this region. The main tectonic boundary is complicated here and changes strike and also incorporates some strike slip faulting.

Here is an illustration showing the subduction zones and how they meet near Honshu. This image is from here.

This map shows the current tectonic configuration of this region, along with some inherited features from the tectonic past (e.g. green lines). This is from NUMO’s report: “Evaluating Site Suitability for a HLW Repository (Scientific Background and Practical Application of NUMO’s Siting Factors), NUMO-TR-04-04.”

Also from the NUMO report, this shows the Niigata-Kobe fold and thrust belt.

Here is the shaking intensity map as modeled using ground motion prediction equations (attenuation models).

Compare the above map with this one, which is generated by surveys from real people, not models.

Here is the attenuation plot, showing how the shaking intensity drops off with distance from the earthquake. Note how the real data (dots) match with the attenuation curve that was developed using seismicity in California, rather than the curve using central and eastern USA seismicity. Think about why you think this is.

Given the shallow depth for this earthquake, we can see that the PAGER estimate of damage is high.

Posted in geology, plate tectonics, subduction

Another Earthquake in the Molucca Sea

Dale Kramer, David N Lindberg liked this post

We just had another large earthquake in this region. Here is the USGS page for this M 6.5 earthquake. This earthquake hypocenter is much deeper than what we might expect for a subduction zone interface earthquake in this region. The M 7.1 earthquake from about a week ago was downdip of this earthquake (deeper along the subduction zone fault) than today’s earthquake. Here is my page on the M 7.1 earthquake.

This is a map of the region, showing the three largest magnitude earthquakes from the last couple of weeks.

Here is a generalized tectonic map showing how these plate boundaries are configured from here.

Here is a more detailed tectonic map with a cross section showing how these two opposing subduction zones are configured. This is from a Geological Society of America Special paper here.

Posted in College Redwoods, earthquake, education, geology, plate tectonics, subduction, tsunami

Earthquake along the Halmahera Arc

David N Lindberg, Dale Kramer liked this post

There was a Mw 7.1 thrust earthquake along the Halmahera Arc (a subduction zone) in the Molucca Sea, Indonesia. Here is the USGS web page for this earthquake. There was a small amplitude tsunami observed in the region of the earthquake: 9 cm at Jailolo, Indonesia (see map below). There was a M 7.5 earthquake to the south of this 2014/11/15 earthquake, also a thrust earthquake here is the USGS page.

This is a map that shows the epicenters on a global scale map.

This map shows the epicenters on a regional scale map.

This is the regional map with Modified Mercalli [shaking] Intensity Contours.

Here is a map I put together that shows the moment tensors for the largest magnitude earthquake and the largest magnitude aftershock. The plate boundaries have relative plate motion vectors. This is a region where there are two opposing ocean-ocean subduction zones. I edited this map since the plate boundaries plotted by USGS are in the incorrect location (the thin lines).

Here is a generalized tectonic map showing how these plate boundaries are configured from here.

Here is a more detailed tectonic map with a cross section showing how these two opposing subduction zones are configured. This is from a Geological Society of America Special paper here.

This earthquake was not located too close to land (i.e. people), so the probability of damage to people and their infrastructure was low (as evidenced by the pager report shown here). This can be downloaded from the USGS web page for this earthquake.

While the above maps of shaking intensity (MMI) are generated using models of ground shaking (GMPEs), this map shows the shaking intensity based upon peoples’ direct observations.

This plot shows the attenuation of ground motion with distance from the epicenter. The Ground Motion Prediction Equation (GMPE) models are plotted in orange and green. The orange model is based upon ground motion attenuation relations for the western US. The green model is based on relations for the eastern US. The western US is mostly accreted terrain, so this model matches the observational data (plotted as dots) probably because the Halmahera region is also composed of accreted terrain (albeit different from the western US).

Posted in geology, plate tectonics, subduction, tsunami

Lassen Earthquake Swarm

There is currently an ongoing earthquake swarm in the region immediately south of Mt. Lassen. The largest magnitude is a M 3.9 (USGS). The California Volcano Observatory (CalVO) is monitoring these earthquakes. The earthquakes do not appear to be related to volcanism, but most likely related to the fault systems that strike through that area. These faults are an extension of the Walker Lane fault system, which is a sister of the San Andreas plate boundary. The Walker Lane fault system is a right lateral (dextral) fault system that extends the east side of the Sierra Nevada Mountains. We do not currently know how this part of the plate boundary ends, if it feeds into Cascadia, etc. We have some ideas, but I will leave this a mystery as many of these ideas are unpublished and I do not want to scoop anyone. There are no USGS active faults mapped in this region, but there has been earthquake activity in the Lake Almanor area in the last year or so (see map below from 5/23/13). This region may be an extension of the Butt Creek fault zone (the red faults directly to the southeast of this swarm.

Here is a map of the epicenters in the region of Mt. Lassen.

The CAVO is monitoring these earthquakes, but they clearly state this swarm is related to plate tectonics in the region and not volcanism. Here is a plot of seismicity for this region.

Here is the Did You Feel It map for the M 3.9 earthquake.

The M 3.9 earthquake has a focal mechanism that shows NE-SW extension.

Here is a primer for those who would like to understand focal mechanisms better (from the USGS.

Here is a map I made about some of these Almanor earthquakes.

Posted in College Redwoods, earthquake, education, geology, plate tectonics, San Andreas

Earthquake Swarm in NW Nevada!

There has been an earthquake swarm in northwest Nevada. There was also a swarm in this region last August. The largest magnitude EQ so far is a magnitude 4.6. Here is a magnitude 4.0 EQ that initiated my interest in posting about this swarm. These epicenters plot along the Warner Valley and Guano valley fault zones.

This map shows the recent EQs in orange, yellow, and white, in increasing age. The grey circles are part of the August 2014 swarm. The faults are from the USGS active fault and fold database.

Here is the extensional moment tensor for the magnitude 4.6 EQ:

Here is the extensional moment tensor for the magnitude 4.0 EQ:

Here is the shake map for the M 4.6 EQ:

Here is the shake map for the M 4.0 EQ:

Here is the USGS 2% probability of exceedance in 50 years map of peak ground acceleration. One can observe that this region of Nevada has a low probability of ground acceleration.

I will post more on this swarm later today. check back!

Posted in College Redwoods, earthquake, education, geology, plate tectonics

Earthquake in the Fiji Region!

There was a large earthquake in the Fiji region yesterday (Saturday my time). The epicenter is far from the major convergent plate boundary. Here is the USGS page for this earthquake.

Here is a map at the global scale. The epicenter is marked by a red circle, just South of Samoa and East of Fiji. This earthquake is related to the subduction zone associated with the Tonga Trench. The moment tensor shows an east-northeast striking compressional solution, due to principal axis compression in the n-nw/s-se direction. Prior to looking at the moment tensor, I was expecting to see an extensional solution at this depth. The cross section of seismicity is sourced from earthquakes designated by the purple line.

Here is a regional scale map showing the plate configuration.

This is a local scaled map showing the complexity of the spreading ridges and transform faults to the east of this earthquake swarm. The Modified Mercali Intensity Contour 3.5 is plotted as a light blue circle. Epicenters are plotted by color in relation to depth.

Here is the regional map showing the slab contours. The depth of this earthquake (434 km) is close to, but above, the slab depth (500 km). If one looks at the cross section of historic seismicity, it appears that the slab is possibly bending upwards. Perhaps there is some compression in the upper plate here, causing the compressional moment tensor.

Here is another view of the slab, generated using P-wave tomography. Doug Weins discusses his work in this region. “Red and blue colors denote slow and fast velocities, respectively, and the velocity perturbation scale is shown at the bottom.”

Interestingly, deep focus earthquakes take up ~66% of the deep earthquakes globally. From this paper, we can see that the slab contour may change strike in the region of yesterday’s earthquake.

Richards et al., 2011 also show bends in the downgoing slab. There is some controversy about the configuration of the slab in this region. They show a detached slab just above the main port (more Star Wars), above the main slab.

The New Hebrides subduction zone dips to the east and turns into a transform fault just west of yesterdays earthquake. This map shows the profile for the above cross section from Richards et al. (2102)

This figure shows Richards et al. Figure 4, that displays their interpretation of how the plates came to be configured here. The Australia plate detached and collided with the Pacific slab about 4 million years ago.

Here is the USGS Open File poster for the region (Benz et al., 2010). Hypocenters are plotted as cross sections to show the geometry of the subducting slabs.


As one might expect, an earthquake at this depth, given this magnitude, would not generate strong ground motions at the surface. The pager, an estimate of human and infrastructural losses, reflects this low likelihood of damage.

Here is a primer about Focal Mechanisms from the USGS.

    References:

  • 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.
  • Benz, H.M., Herman, Matthew, Tarr, A.C., Furlong, K.P., Hayes, G.P., Villaseñor, Antonio, Dart, R.L., and Rhea, Susan, 2011, Seismicity of the Earth 1900–2010 eastern margin of the Australia plate: U.S. Geological Survey Open-File Report 2010–1083-I, scale 1:8,000,000.
  • Richards, S., Holm., R., Barber, G., 2011. When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region, Geology, v. 39, pp. 787-790.
  • Yu, W. and Wen, L., 2012. Deep-Focus Repeating Earthquakes in the Tonga–Fiji Subduction Zone, BSSA, v. 102, no. 4, pp. 1829-1849

Posted in College Redwoods, earthquake, education, geology, plate tectonics, subduction

Earthquake offshore of El Salvador!

Ian Pierce liked this post

We just had a large magnitude earthquake offshore of El Salvador. Here is the USGS web page for the earthquake. Based on the magnitude and depth, it is not expected to have triggered a tsunami that would reach the coast of CA, OR, nor WA.

Here is a map that shows the region. The epicenter is plotted in green (the initial depth was set at 70 km, so it plotted in green. the depth was updated to 40 km, so will plot in yellow in other maps.).

This map shows the historic earthquakes as grey circles. These earthquakes are largely associated with the subduction zone here, where the Cocos plate is subducting northeastwardly beneath the Carribean plate to form the Middle America trench.

This map shows the modeled intensity using the Modified Mercali Intensity Scale (MMI, a measure of the ground shaking). The MMI has a scale of I – XII.

This is the same map, zoomed in for a larger scale view of the area.

Here is a view of how the intensity attenuates (diminishes as the energy is absorbed by the earth’s crust) with distance from the earthquake. The blue dots are real data, with medians plotted as brown dots. One can see that there is considerable variation in the intensity for individual measurements. This can be due to a variety of reasons (variation in the earth’s crust, site conditions, etc.). The green and orange lines are model estimates of intensity attenuation given two models from Atkinson and Wald, 2007 (using Ground Motion Prediction Equations, GMPEs, based on regression through data from earthquakes in California and Central-Eastern US, respectively). The California regression seems to fit the data better than the Central/Eastern US model.

This map has the intensity plotted as contours, which allows one to see how the intensity varies across the region in relation to the geography and place names.

Based on the location, depth, and moment tensor shown below, I interpret this to be a normal earthquake. This earthquake is the result of extension in the downgoing plate, possibly from the bending (i.e. a bending moment normal fault).

This map shows the depth contours to the slab (the top of the downgoing Cocos plate). These slab contours were developed by Gavin Hayes who works at the USGS. Here is a web page that has links to the other slabs Hayes and his colleagues have developed. They are largely based on their interpretations of historic seismicity.

This is the pager (version 1) that shows modeled estimates of human and infrastructural damage from this earthquake. These pager estimates are revised as more seismological information is analyzed. The loss estimates assist aid agencies make plans on how much assustance they may need to send to the region (in the form of food, medical, money, etc.).

Here is the Did You Feel It map, showing observations based upon the DYFI survey tool. The results are plotted using the same color range for the MMI scale.

Here is the USGS poster for the tectonics of the region:

Here is a profile showing Ranero et al. (2003) interpretation of the structure of the subduction zone here. Look at the upper panel and note how the top of the slab bends downward. This causes extension that may be responsible for today’s earthquake. This is figure 8.14 from Mann et al., 2007.

Here is a map that shows preliminary tsunami wave height estimates from Here.

Here is a table of estimates for the tsunami wave height.

Here is a primer about Focal Mechanisms from the USGS.

References:
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.
Mann, Paul, Robert D. Rogers, and Lisa Gahagan. “Overview of plate tectonic history and its unresolved tectonic problems.” Central America: Geology, resources and hazards 1 (2007): 201-237.
Ranero, C., Morgan, P., McIntosh, K. & Reichert, C.: Bending-related faulting and mantle serpentinization at the Middle America trench. Nature 425 (2003), pp.367–373.

Posted in College Redwoods, earthquake, education, geology, plate tectonics, subduction, tsunami

Earthquake near Guam!

Joe Magner liked this post

Last night (Pacific Time) there was a M 6.7 earthquake in the western Pacific near Guam. Here is the USGS page for the earthquake. The depth is about 137 km, so it is unlikely to generate a tsunami. Also, the depth reduces the likelihood of damage from ground shaking.

Here is a map showing the global tectonics. The epicenter is west of the Marianas Trench, which is formed by subduction of the Pacific plate beneath the Philippine plate. Note there is a spreading ridge east of the epicenter.

Here is a map showing the global tectonics along with the historic seismicity.

Here is a regional map showing the epicenter as it relates to Guam (the city Hagatna is labelled) and Saipan.

Here is a regional map showing the historic earthquakes.

This map shows the modeled Modified Mercalli Shaking Intensity (contours), along with the Did You Feel It results (colors on the islands). The MMI contours are generated by a computer model. The DYFI data are the results of observations made by real people.

This is the Moment Tensor from the USGS website. This shows that the earthquake is a “normal” earthquake, caused by extension in the Earth’s crust. Based on the location of this earthquake, it is probably located in the downgoing Pacific plate.

Here is a primer about Focal Mechanisms from the USGS.

This is the Pager Page, which shows the probability of damage to people and their infrastructure. These are generated by a computer model and are updated regularly following an earthquake as more seismological information is used to refine the earthquake shaking/intensity models. This one is version 2 and probably wont be updated.

Here is the regional tectonic map produced by the USGS. Historic earthquakes, tectonic plate boundaries, and downgoing plate slab contours are plotted.

Here is a map that shows the bathymetry (the shape and depths of the seafloor) in this region, as determined by Smith and Sandwell at Scripps Institute of Oceanography. Depth contours are 500 meters.

Here is a regional map showing the depth contours of the dowgoing Pacific plate, as generated by Gavin Hayes from the USGS.

References:
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.
Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997.

Posted in College Redwoods, earthquake, education, geology, plate tectonics, subduction, tsunami

Napa Earthquake Update

There have been a swarm of geologists running around Napa taking photos and documenting evidence from the earthquake swarm on Sunday. Here is my first post about this earthquake swarm, with the M 6.0 earthquake being the largest magnitude earthquake.

Mike Oskin and his students have been diligent in their reporting. Most of their observations have been posted to Oskin’s twitter account. Here is a google earth kmz file that Oskin posted to his twitter feed. They followed the surface trace of the fault, which is represented by the red line. There are notes and photos that are documented by yellow push pin icons. Here is a map with the epicenters of the swarm and the Oskin kmz observations overlain. Download the kmz to see the photos.

Here is the channel 2 photo database of damage.

Here I post a couple of the photos taken by Alex Moran. Many of them have Chad Trexler in them for scale. These are both posted on Oskin’s kmz file.

White Cliff Drive: Offset curb with tape measure for scale. Photo by Alex Morelan.

23 cm right lateral along Oak Rock Dr. Photo by Alex Morelan.

Here is an updated map showing all the aftershocks as of today at noon local time.

Here is a photo (Lori Dengler) of the seismograph as recorded in Van Matre Hall at Humboldt State University, Dept. of Geology.

This is a map from the California Geological Survey that shows the faults in the region.

Here is a kmz file of a map produced by Wesling and Hanson as part of their USGS NEHRP final report. Here is a map showing their map underlain by the USGS faults and the epicenter plots.

Here is a photo from the AP:

Here is a photo from SFGate:

Posted in College Redwoods, earthquake, education, geology, plate tectonics, San Andreas

Napa Earthquake!

Social media was abuzz today about the M 6.0 earthquake in Napa. Here is the USGS webpage for the M 6.1 earthquake. This earthquake, and the aftershocks, have epicenters that lie between the Rogers Creek and Green Valley fault systems. These two major fault systems are inboard/east of the San Andreas fault, each accommodating a portion of the Pacific-North America plate boundary relative motion rate. Today’s earthquake swarm appears to plot near the West Napa fault (WNF) and east of the Carneros fault (CF). The WNF is not mapped as far south as this earthquake swarm, but the fault system likely extends south, as possibly evidenced by today’s swarm.

Here is a map showing the faults in the San Francisco bay area. Epicenters from today’s swarm appear in the center of the map as orange dots. The largest dot is the M 6.0 epicenter. There is also a swarm of earthquakes to the northwest, just south of Clear Lake. These are related to the geothermal activity in the Geysers region. Faults are plotted with color representing the relative age of the most recent movement. Younger to older = red, orange, yellow, blue.

The faults in this region are mostly related to the strike-slip (transform) relative motion along the San Andreas fault system. Faults are sub-parallel to the SAF system and have a similar sense of motion as the SAF (right lateral, or dextral). Here is a moment tensor that shows two possible fault plane interpretations (either northwest striking right lateral or northeast striking left lateral). Given that the SAF is nw striking right lateral, the most reasonable interpretation of this moment tensor is nw striking right lateral.

This map shows the results of the USGS “did you feel it?” survey. I hope everyone who felt this earthquake filled out a form. Please do so here if you have not yet done so. The colors represent the Modified Mercalli Intensity Scale (MMI scale; a measure of the shaking intensity based upon observations people make about how strongly the earthquake shook).

This is a map showing an estimate of ground shaking (MMI scale) based upon computer modeling.

This is a map also showing the simulated intensity as MMI contours.

Here is a map showing the regional faulting in the area, along with the Sonoma Volcanics Wagner et al., 2011. These volcanic units represent the passage of the Mendocino triple junction through the bay area (~8-14 millions of years ago). The Carneros and West Napa faults are labeled CF and WNF respectively. There are plate motion arrows along the major faults reminding us that the relative motion of these faults is right lateral.

Here is a map that shows the swarm epicenters as they relate to the local geography. Napa Valley is to the north. The Carneros fault is not plotted since it is not part of the USGS fault and fold database (Dr. Rich Koehler reminded me that the USGS database is a Quaternary database, so it is probably because the CF has not displaced Quaternary age geologic units). The WNF fault system is mapped as yellow and blue lines along the western boundary of Napa Valley.

Here is another map from the Wagner et al., 2011 paper. This map shows how the CF and WNF systems relate to each other.Just south of the word “Napa,” the WNF lines stop at the edge of the Tertiary volcanics that are mapped in pink. South of that, the geology is mapped as Cenozoic sedimentary deposits. It is possible that the WNF continues south, but has not been found to displace the geologic units in that area.

Here is the USGS PAGER page that shows an automated estimate of damage to people and infrastructure. This is useful for govt. agencies who may be responsible to plan evacuations and assistance to internally displaced people.

Here is a map that shows the historic ruptures along the SAF and inboard fault systems (Smith and Sandwell, 2006). The GVF shows a rupture in 1858 and 1864. The Rogers Creek/Maacama fault sustem shows a rupture in 1898. The Hayward fault ruptured in 1868.

This is a map that shows the earthquake probabilities for the faults in the SF Bay area. This is part of the 2008 Uniform California Earthquake Rupture Forecast (UCERF). Compiled by USGS, Southern California Earthquake Center (SCEC), and the California Geological Survey (CGS), with support from the California Earthquake Authority. Here is a 10 MB high resolution version of the map. Here is a short document that discusses the Hayward fault earthquake of 1868 and what we might expect on the HF in the future.

Here is a photo database of damage from this earthquake.

Here is a summary of observations made by the media.

Here is a photo gallery documenting damage from the earthquake.

Here is a great summary of this earthquake swarm.

Here is a link to a video taken from a drone.

Smith, B. R., and D. T. Sandwell (2006), A model of the earthquake cycle along the San Andreas Fault System for the past
1000 years, J. Geophys. Res., 111, B01405, doi:10.1029/2005JB003703.

Wagner, D. L.; Saucedo, G. J.; Clahan, K. B.; Fleck, R. J.; Langenheim, V. E.; McLaughlin, R. J.; Sarna-Wojcicki, A. M.; Allen, J. R.; Deino, A. L., 2011. Geology, geochronology, and paleogeography of the southern Sonoma volcanic field and adjacent areas, northern San Francisco Bay region, California, Geosphere, 7: 658 – 683

Posted in College Redwoods, earthquake, education, geology, plate tectonics, San Andreas