Updated Historic and Prehistoric Maps

I have updated a couple of these maps and include a figure from a recent presentation given by Roger Bilham at AGU (2011). Here was my original and first updated posts about this earthquake and here is my first compilation post.

Here is the regional map. I have added epicenter locations from Rajendran and Rajendran (2011). These, in some cases, do not coincide with the slip patches published by others. The Rajendran epicenter locations are probably the ones that may be incorrect. I compared where they placed the locations of cities and I found those to be largely incorrect.

Note how the region that has not ruptured since 1505 is immediately adjacent to the 2015 earthquake activity. Faults in this region possibly are experiencing an increase in stress following the earthquake. I will have to take a looksie at some analogous models (or run my own).

Here is an figure from Bilham, 2011. Note the southern terminus of the epicenters in the map below and compare this with the three proposed slip models in this cross section. Then, compare the magnitude estimates between these three different possibilities. It appears that Bilham et al. (2011) were quite cogent on their magnitude estimate.

Here is a local scaled map that shows the epicenters, the closest historic patches, and the city of Katmandu.


  • Bilham, R.G., Szeglia, W., Bali, B.S., Khan, A., Wahab, A., and Khan, F., 2011. Velocity Field in the NW Himalayan Syntaxis: Implications for Future Seismicity, Trans.. American Geophysical Union, Dec., 2011.
  • Rajendran, K and Rajendran, C.P_., 2011. Revisiting the earthquake sources in the Himalaya: Perspectives on past seismicity, Tectonophysics, v. 504, p. 75-78.

Posted in asia, Chemeketa Community College, education, geology, HSU, plate tectonics

Historic Earthquakes in the Himalayas

I have digitized some compilations of earthquake slip regions from a few papers and summarize these on the map below. The two main references are Bilham (blue; 2004) and Bettinelli et al. (orange; 2006). There are a couple of earthquakes that are differently plotted in these two publications (e.g. 1934 and 1950). This earthquake of 2015 appears to coincide with the region that slipped in 1833 and the western portion of the region that slipped in 1934. Here is my original page for this earthquake. Here is an post that I updated later in the day.

Here is a map from Bilham and Hough that shows the entire history for this convergent margin. This is more of a schematic view of these earthquake locations.

This is a space-time diagram for earthquakes along the Himalayan front (from Bilham and Wallace, 2005)

There have been trenches that led to the interpretation of the 1100 A.D. prehistoric earthquake. Here is the map from Lave et al. (2005) which shows the estimated MMI contours (ground shaking contours).

This map shows the area of the fault that seems to have slipped, with a fault length of approximately 150 km.

Here is the Global Earthquake Model map and space-time diagram (Berryman et al., 2014).

This is a cross section from the GEM report (Berryman et al., 2014). This shows Elevation, coupling coefficient, seismicity rate, temperature on the main Himalayan Thrust (MHT) HFT from Ader et al. (2012).

This shows today’s seismicity at a more local scale. The top map uses aerial imagery and the bottom map is overlain upon SRTM (Space Shuttle Topography Mission) data.

This is from a security camera and gives us an idea about the local duration of ground motions. Historic Slip patches are as in the above maps.


  • Ader, T., J.-­‐P. Avouac, J. Liu-­‐Zeng, H. Lyon-­‐Caen, L. Bollinger, J. Galetzka, J. Genrich, M. Thomas, K. Chanard, S. N. Sapkota, S. Rajaure, P. Shrestha, L. Ding, and M. Flouzat, 2012. Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard, J. Geophys. Res., 117, B04403, doi:10.1029/2011JB009071.
  • 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/.
  • 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
  • Bilham, R., 2004. Earthquakes in India and the Himalaya: tectonics, geodesy and history, Annals of Geophysics, v. 42, no. 2/3, p. 839-858.
  • Lavé, J., Yule, D., Sapkota, S., Basant, K., Madden, C., Attal, M., and Pandey, R., Evidence for a Great Medieval Earthquake (È1100 A.D.) in the Central Himalayas, Nepal, Science, vol. 307, p. 1,302-1,305.

Posted in asia, Chemeketa Community College, collision, earthquake, education, geology, HSU, plate tectonics

Nepal Aftershock Region and Historic Earthquakes

Here is an updated map that shows the aftershocks following the devastating earthquake in Nepal. I have tentatively plotted the locations (epicenters) of some historic earthquakes in this region. Today’s earthquake ranks among the largest and approaches the size and devastation of the 1505 earthquake, that some consider the most devastating known earthquake in the region. Here is the post I made early this morning. After class (running late), I will post more material on the historic earthquakes in this region and some links to the human stories.

    Here are the two USGS webpages for the mainshock and the largest aftershock:

  • Mw 7.8 2015.04.25
  • Mw 6.6 2015.04.25

Here is the PAGER. The pager last night was not yet available. This is an estimate of the casualties to people and their belongings (roads, bldgs, etc. ). This is based upon the overlay analysis of two things. First there is a database that includes information abt the spatial distribution of the population and their infrastructure. Second, there is a numerical simulation of the ground shaking intensity. Just like how risk is the overlap of hazard with population, this estimate is the overlay of theses two analyses. Note the likelihood of an extremely large number of casualties. This is quite a devastating disaster.

Posted in asia, Chemeketa Community College, collision, earthquake, education, geology, HSU, plate tectonics

Earthquake in Nepal!

We just had a large earthquake in Nepal! The moment tensor shows that this is a thrust/reverse (originally it was solved as a strike slip) earthquake. I will need to do a little more investigating about this tomorrow. (I am running short on sleep and have an early flight in the morning). Here is the USGS website for this Mw 7.9 earthquake. This is still plotting as a shallow earthquake. Originally it was listed as a 7.5. This is a large earthquake, shallow, and compressional. There will possibly be many injured and many casualties from this earthquake. Smilie: :-(

Here is the map that I quickly put together. I have placed the moment tensor on the map. I have posted various tutorials about moment tensors on other earthquake posts, so will leave that out on this map.

This map shows the MMI contours with MMI VIII in nearest the epicenter.

Here is the USGS intensity map. The map uses the Modified Mercalli Intensity scale, which is largely based upon the qualitative observations by people just like you and me. The map below is generated using a numerical model to estimate the amount of ground motions from an earthquake given some assumptions about the crust nearby the earthquake (or, rather, the crust for the earthquakes used in the empirical relations used to create the model). These estimates are not direct observations, so the “Did You Feel It” map is better for people to learn about what the real ground motions, or shaking intensity, was for this earthquake.

Here is the current DYFI map, which should be updated over the next day as more people submit their observations to the web site.

This is a measure of how well the model used to create the intensity map above matches the DYFI map.

Posted in asia, Chemeketa Community College, education, geology, HSU, plate tectonics

Mendocino fault Earthquake

This sure looks like an earthquake on the Transform Plate Boundary fault system known as the Mendocino fault. I have plotted the moment tensor for this earthquake. The shaking intensity contours are plotted. Here is the USGS web page for this Mw 5.5 earthquake.

Posted in cascadia, Chemeketa Community College, earthquake, education, geology, HSU, humboldt, mendocino, plate tectonics

Earthquake near Taiwan

Marrissa Walker liked this post

Well, we just had a swarm of earthquakes with magnitudes near Taiwan. The USGS web pages for these earthquakes are here: M = 6.0, 6.1, and 6.4. This is a complicated tectonic region and there are many different and differing interpretations. Taiwan is at a location where a westward vergent subduction zone (Manila trench) comes from the South and an eastward vergent subduction zone comes from the north (Ryukyu trench). I am getting ready to head to class and then to Pasadena for a Seismological Society of America meeting, so I cannot fully describe the complexity right now. I will try to follow up later.

Here is a map that shows the three earthquake epicenters as they relate to these plate boundary faults.

Here is an oblique view of the plate configuration in this region. This is from Chang (2001).

Here is a great interpretation showing how the Island of Taiwan is being uplifted and exhumed. This is from Lin (2002).

Needless to say, this is an excellent map showing the complicated faulting of this region. This is from Theunissen et al. (2012).

Posted in Chemeketa Community College, education, geology, HSU, plate tectonics, subduction, tsunami

Earthquake in Crete

Semi Werner Francis liked this post

We just had a M = 6.0 earthquake in Crete. Here is the USGS web page for this earthquake.

This is an interesting region tectonically. The convergence of the Africa-India-Australia plates northwards towards the Eurasian plate runs from west of Europe, through the Middle East, through the Himalayas, out east towards the north side of Australia. As this large convergent plate boundary passes through these regions, it makes bends and these bends make the plate boundary have all the different types of faults (convergent, divergent, and strike-slip).

The plate boundary in the Crete-Greece-Turkey region is debated in the literature. There are different interpretations about what the faults are doing in this region. I will post a couple different maps below showing these different interpretations. (They probably are not all correct, but there may be tectonic “truths” in each of them.)

Here is a map that I put together that shows a simplified version of the plate boundary, showing one interpretation that favors some obliquity to the plate boundary on the eastern side of this map. I have placed the USGS moment tensor to show that this earthquake has a strike-slip sense of motion. I do not know which of the two fault plane solutions is correct, due to the wide range of different tectonic maps of this region. Before today, I did not know much about this area (just a general understanding of some of it). I love when these earthquakes happen because it gives me a change to learn about the different interpretations around the world…

I have placed the two options for the two fault plane solutions (right-lateral or left-lateral). Remember, when you are on one side of a strike-slip fault and you are looking across the fault to your friend, if they move to your right (and you move to their right, from their perspective), you are looking across a right-lateral (dextral) strike-slip fault. The obliquity of the plate boundary here is depicted as a right-lateral (oblique) plate boundary fault. Based upon this, I suspect that the fault is not the ~east-west striking left-lateral fault solution, but the ~north-south striking right-lateral fault solution. I may be wrong and someone who works in this area could correct me.

This is the USGS Intensity map that uses the Modified Mercalli Intensity Scale. It looks like this earthquake was felt across a broad region. Based upon the “Did You Feel It” map (composed of reports from real people, compared to this MMI map that is merely based upon a model), the MMI map is pretty good.

Here is a map that I found on the internets. It is from a Geological Society of America paper, but I cannot tell which (when I click on “take me to the page,” I get the log in page and it does not have any author information.) We can see their interpretation about how this plate boundary is more compressional on the west and transform on the east (at the Pliny and Strabo trenches). While there is conflict about the details, each map shares the sense of motion for the obliquity of the plate boundary here (right-lateral).

Here is another version from the Corith Rift Laboratory. This also shows right-lateral motion in this region.

Here is yet another map, also from a GSA paper. This one shows that there are a series of thrust faults, some with differing vergence (the direction that a thrust fault goes in when going from deep in the earth upwards to the surface). In my interpretation map above, the fault dips to the north, so is southward vergent.

Posted in Chemeketa Community College, earthquake, education, europe, geology, HSU, plate tectonics, subduction, Transform

Earthquake in the Baldwin Hills (Los Angeles)

Well, there was quite a buzz on social media following this small magnitude earthquake today. Here is the USGS web page for this Mw 3.3 earthquake. The earthquake appears to be related to the Newport-Inglewood fault system and the epicenter shows it to have happened in the Baldwin Hills region (I thought that this earthquake might have some obliquity, or some compressional motion on it).

Below is a map that I put together for this earthquake. I have highlighted several other significant earthquakes in the region as well (1971, 1994, 2014). The focal mechanism for the Mw 3.3 is plotted in orange and white. There is an explanatory legend for interpreting focal mechanism and moment tensor plots (in the upper left corner). These graphical solutions provide two potential fault orientations and it takes someone to interpret which fault is the correct solution (with data or simply a fault map of the region). I place a semi-transparent generic b&w focal mechanism to show the sense of motion on the Newport-Inglewood fault zone in the region of this earthquake. The NI fault system is a right-lateral strike-slip fault system that runs sub-parallel to the similarly right-lateral strike-slip San Andreas transform plate boundary fault system.

I also placed a semi-transparent focal mechanism plot over the San Andreas fault in the upper right corner of the map. The faults are from the USGS fault and fold database (this and other google ™ kml files are freely online here). The red faults are faults that have ruptured historically. The red portion of the San Andreas fault shows the southern limit of the 1857 M 7.9 earthquake. The other red fault in this region is from the surface rupture of the 1971 Sylmar earthquake. Here is the USGS web page for the Sylmar earthquake. This earthquake ruptured through a hospital and led to several deaths. Due to this catastrophe, the Alquist-Priolo law was passed so that people won’t build hospitals (and other buildings) across earthquake faults. There is lots more on the A-P law, but I will leave that for another post.

I also plot the epicenter of the 1994 Northridge earthquake. Here is the USGS web page for this earthquake. This earthquake ruptured a blind thrust fault in the San Ferndando Valley Basin. Since there was no surface rupture, there is no red fault line. This fault was not known of prior to the earthquake (mostly because it was blind, it did not reach the ground surface). This earthquake led to a new search for fault hazards that had previously been under appreciated.

Finally, I plot the La Brea Mw 5.1 earthquake epicenter. Here is the USGS web page for this earthquake. This earthquake was particularly well responded to in the southland and on social media. My family lives within blocks of the epicenter and the children of the house were very jittery for each aftershock. I have posted about this earthquake before here, here, here, and here. The Southern Earthquake Research Center produced some educational material about this earthquake and I posted their animations here and here.

In the lower left corner is a map from Carena and Suppe (2002), which shows the focal mechanisms for the 1994 and 1971 earthquakes. There also is a plot of the map view for their 3-D fault mapping investigation (what their 2002 paper is about). If you want to learn about how that fault was located, read that paper!

This is a map showing the response from people who felt the earthquake. Even though it was a small earthquake, it was felt over a broad area. This map uses the Modified Mercalli Intensity scale. This is an assessment of the shaking intensity (different from earthquake magnitude, which relates to the amount of energy released during the earthquake).

In comparison, here is the “Did you Feel It” map for the 1971 and 1994 earthquakes, respectively.


This plot shows how the energy attenuates with distance from the epicenter of the Mw 3.3 earthquake.

Also, for comparison, here are the attenuation plots for these two other earthquakes.




  • Carena, S. and Suppe, J., 2002. Three-dimensional imaging of active structures using earthquake aftershocks: the Northridge thrust, California: Journal of Structural Geology, v. 24, p. 887-904.

Posted in Chemeketa Community College, earthquake, education, geology, HSU, los angeles, plate tectonics, Transform

Blanco fracture zone strikes again

The Blanco fracture zone (BFZ) is a transform plate boundary that connects the Juan de Fuca ridge with the Gorda rise spreading centers. This active fault zone consists of numerous right-lateral (dextral) faults. There is some debate as to how far east the BFZ extends beyond the Gorda rise (some pose it extends far past the trench and ambient noise tomographic data supports this interpretation; Porritt et al., 2011). I remember a colleague of mine who once adamantly stated that there is no evidence for the extension of the BFZ eastwards past the megathrust fault tip. However, they were working on faulting in the North America plate along coastal Oregon, so their view was limited (compared to the plot I share below). However, this colleague made this statement a decade before the Porritt et al. (2011) data were to be published.

There were two Mw 4.2 earthquakes associated with this plate boundary fault system in the past week. I plot the moment tensors for these earthquakes (USGS pages: 4/7/15 and 4/11/15) in this map below. I also have placed the relative plate motions as arrows, labeled the plates, and placed a transparent focal mechanism plot above the BFZ showing the general sense of motion across this plate boundary. There have been several earthquakes along the Mendocino fault recently and I write about them 1/2015 here and 4/2015 here.

Here is a map of the CSZ that shows the orientation and configuration of these left-lateral strike-slip faults within the Gorda plate (modified from Chaytor et al., 2004 and Nelson et al., 2006).

Tomography is a technique that uses data collected from different locations to determine the structure of some interior phenomenon. Or, from Merriam Webster: a method of producing a three-dimensional image of the internal structures of a solid object (as the human body or the earth) by the observation and recording of the differences in the effects on the passage of waves of energy impinging on those structures. CT scans, or CAT scans (Computed Tomography of X-Rays), are an example that most people are familiar with. X-Rays are sent through a part of one’s body at different angles. The measurements of these X-Rays are compared with each other (cross-correlated) to produce the 3-D image of the interior of that body part.

Then the 3-D data can be sub-sampled into slices in order to evaluate the structure in more detail, at specific locations. Here is an example showing two “slices” from Wikipedia Commons:

Here is an example of a 3-D CT “volume” showing the tip of a finger, also from Wikipedia Commons. “Rotating image of Optical Coherence Tomography (OCT) tomogram of a fingertip, depicting stratum corneum (~500µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. At the bottom are superficial parts of the dermis. Sweatducts are clearly visible.”

I use CT data to look at sediment cores. Others use seismic waves to look at the interior structure of Earth. Porritt et al. (2011) use Ambient Noise Tomography (ANT) to look at the interior structure of the Cascadia subduction zone region. Porritt et al. (2011) use low amplitude seismic “noise” present at all seismic stations that is generated from a wide range of sources like waves and wind along shorelines to local man-made activities such as cars, trucks, and trains. These seismic data are known as “Ambient Noise”, noise in the background. By cross correlating long time series between stations, the common signal is retrieved while the incoherent energy cancels out. This leaves a signal that reveals information about seismic velocity between the two seismometers. By making measurements on these signals and using an array of stations for many ray paths, a three-dimensional image of the subsurface shear velocity can be determined.

Here is a vertical cross section, running North-South, of the Earth materials in the Cascadia subduction zone. They plot a histogram (a) of the percent of non volcanic tremor also plotted N-S (from Boyarko and Brudzinski, 2010). The topography is plotted also (b). Then they plot the “relative shear velocity structure along a profile where the slab is at 30 km depth (profile location shown in d). Vertical lines on profile at 43°N and 46.7°N indicate the tremor segmentation bounds of Brudzinski and Allen (2007) with the names and recurrence interval given. The horizontal line is the top of the ocean crust from Audet et al. (2010). Also labeled are the slab sections corresponding to the Gorda, Southern Juan de Fuca (S. JdF) and Northern Juan de Fuca (N. JdF).” Based upon the differences in position of the Gorda and S. JDF plates, we can see why I interpret these data to support the hypothesis that the Blanco fracture zone extends east past the Cascadia subduction zone fault tip. dVs% is the deviation of S-wave seismic velocity from some value. Blue colors represent Earth materials with high S-wave velocities and red colors represent Earth materials with low S-Wave velocities. Siletizia and the Klamath Mountains are regions of high seismic velocity in the upper North America plate. The propagation velocity of the waves depends on density and elasticity of Earth’s materials. Velocity tends to increase with depth, and ranges from approximately 2 to 8 km/s in the Earth’s crust up to 13 km/s in the deep mantle (Shearer, 1999).

Here is a primer for those that want to learn about moment tensors (MT) and focal mechanisms (FM). While MT and FM are determined differently, their graphical depiction is analogous. Here is the USGS web page that describes the figure below in detail. Here is the USGS web page that describes how a moment tensor is determined.


  • Audet, P., Bostock, M.G., Boyarko, D.C., Brudzinski, M.R., Allen, R.M., 2010. Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip. J. Geophys. Res. 115, B00A16. doi:10.1029/2008JB006053.
  • Boyarko, D.C., Brudzinski, M.R., 2010. Spatial and temporal patterns of nonvolcanic tremor along the southern Cascadia subduction zone. J. Geophys. Res. 115, B00A22. doi:10.1029/2008JB006064.
  • Brudzinski, M., Allen, R.M., 2007. Segmentation in episodic tremor and slip all along Cascadia. Geology 35 (10), 907–910. doi:10.1130/G23740A.1.
  • Chaytor, J.D., Goldfinger, C., Dziak, R.P., and Fox, C.G., 2004. Active deformation of the Gorda plate: Constraining deformation models with new geophysical data: Geology v. 32, p. 353-356.
  • Nelson, A.R., Kelsey, H.M., and Witter, R.C., 2006. Great earthquakes of variable magnitude at the Cascadia subduction zone: Quaternary Research, doi:10.1016/j.yqres.2006.02.009, p. 354-365.
  • Porritt, R.W., Allen, R.M., Boyarko, D.C., Brudzinski, M.R., 2011. Investigation of Cascadia segmentation with ambient noise tomography. Earth and Planetary Science Letters 309, 67-76.
  • Shearer, P.M. 1999. Introduction to seismology. Cambridge Univ. Press, 1999, isbn 0 521 669 53 7

Posted in cascadia, Chemeketa Community College, earthquake, education, geology, HSU, humboldt, mendocino, oregon, plate tectonics, subduction, Transform

Mendocino fault earthquake

Kellie Townsend, Sandy Patton liked this post

We had a small magnitude earthquake “today” along the Mendocino fault system approximately 150 km west of Cape Mendocino. Here is the USGS web page for the Mw 4.8 earthquake. Based upon the tectonic setting, the hypocentral depth, and the moment tensor, I interpret this to be a right-lateral (dextral) strike-slip fault earthquake.

The Mendocino fault is a transform plate boundary that is formed by the strike-slip motion between the Pacific plate to the south and the Gorda plate to the north.

In this map below, I label a number of other significant earthquakes in this Mendocino triple junction region. Another historic right-lateral earthquake on the Mendocino fault system was in 1994. There was a series of earthquakes possibly along the easternmost section of the Mendocino fault system in late January 2015, here is my post about that earthquake series.

The Gorda and Juan de Fuca plates subduct beneath the North America plate to form the Cascadia subduction zone fault system. In 1992 there was a swarm of earthquakes with the magnitude Mw 7.2 Mainshock on 4/25. Initially this earthquake was interpreted to have been on the Cascadia subduction zone (CSZ). The moment tensor shows a compressional mechanism. However the two largest aftershocks on 4/26/1992 (Mw 6.5 and Mw 6.7), had strike-slip moment tensors. These two aftershocks align on what may be the eastern extension of the Mendocino fault.

There have been several series of intra-plate earthquakes in the Gorda plate. Two main shocks that I plot of this type of earthquake are the 1980 (Mw 7.2) and 2005 (Mw 7.2) earthquakes. I place orange lines approximately where the faults are that ruptured in 1980 and 2005. These are also plotted in the Rollins and Stein (2010) figure below. The Gorda plate is being deformed due to compression between the Pacific plate to the south and the Juan de Fuca plate to the north. Due to this north-south compression, the plate is deforming internally so that normal faults that formed at the spreading center (the Gorda Rise) are reactivated as left-lateral strike-slip faults. In 2014, there was another swarm of left-lateral earthquakes in the Gorda plate. I posted some material about the Gorda plate setting on this page.

Here is a map of the CSZ that shows the orientation and configuration of these left-lateral strike-slip faults within the Gorda plate (modified from Nelson et al., 2006).

Here is a map from Rollins and Stein, showing their interpretations of different historic earthquakes in the region. This was published in response to the January 2010 Gorda plate earthquake. The faults are from Chaytor et al. (2004). The 1980, 1992, 1994, 2005, and 2010 earthquakes are plotted and labeled. I did not mention the 2010 earthquake, but it most likely was just like 1980 and 2005, a left-lateral strike-slip earthquake on a northeast striking fault.

Here is a primer for those that want to learn about moment tensors (MT) and focal mechanisms (FM). While MT and FM are determined differently, their graphical depiction is analogous. Here is the USGS web page that describes the figure below in detail. Here is the USGS web page that describes how a moment tensor is determined.


  • Chaytor, J.D., Goldfinger, C., Dziak, R.P., and Fox, C.G., 2004. Active deformation of the Gorda plate: Constraining deformation models with new geophysical data: Geology v. 32, p. 353-356.
  • Nelson, A.R., Kelsey, H.M., and Witter, R.C., 2006. Great earthquakes of variable magnitude at the Cascadia subduction zone: Quaternary Research, doi:10.1016/j.yqres.2006.02.009, p. 354-365.
  • Rollins, J.C. and Stein, R.S., 2010. Coulomb stress interactions among M ≥ 5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fault Zone, Cascadia subduction zone, and northern San Andreas Fault: Journal of Geophysical Research, v. 115, B12306, doi:10.1029/2009JB007117, 2010.

Posted in cascadia, Chemeketa Community College, College Redwoods, earthquake, education, geology, HSU, mendocino, plate tectonics, San Andreas, subduction, Transform