Category Archives: College of the Redwoods

M 7.0 south Atlantic Ocean

How exciting! This earthquake is on the other side of the Scotia plate from the earthquake swarm from last week.

This M7.0 earthquake appears to have slipped along a fault associated with the North Scotia Ridge (NSR). The NSR is mapped as a left-lateral transform fault (not a ridge, like it is named). There is not yet a moment tensor available, but I suspect this may be a left-lateral strike-slip earthquake.

Here is the USGS earthquake page.

Indeed, the moment tensor shows a possible left-lateral strike slip earthquake.

Here is a tectonic map of the region from here:

Here is a regional map with the epicenter in orange and historic earthquake epicenters in gray.

Here is a local map showing Modified Mercalli Intensity contours and historic earthquake epicenters.

Here is the USGS page showing the contributed moment tensors:

Mw 7.8 Earthquake in the Scotia Sea

We just got another large earthquake in this region, of magnitude 7.8. There were some changes in magnitudes and epicentral locations early on. It is still early and may change more. Earlier there was a M6.8 earthquake nearby, along with a couple ~M5. These earthquakes are probably occurring on a transform fault system that is connected on the east to the oceanic Scotia subduction zone.

This USGS fault data set is at a global scale and so may not account for the latest structural relations on a local scale. The magnetic anomaly data for the plates in this region are pretty well mapped in some places, but the complexities arise near this earthquake series, south of the east-west transform fault. I have also plotted the historic seismicity with IRIS’ earthquake viewer. Their plate boundary faults are better located than the USGS fault locations, in places.

The moment tensor (an indicator of the type of earthquake and sense of motion during the earthquake) shows a similar sense of motion on this fault as the M6.8 recorded earlier. Based on the mapped plate boundary faults in this area, I interpret this to be a left-lateral strike-slip earthquake, with slightly oblique motion suggesting transtension. The bathymetry also may slightly support a n-s fault with right lateral motion. The transform fault here is stepping left, so left-lateral slip would generate transtension (extension). It is equivocal without a better fault map or high resolution bathymetry. There is a fault-parallel basin that may be related to a possible left step over. There are a couple lines of higher resolution bathymetry about 50-75 km due west of the epicenter that does show some ~”n20e” structures (see figure below). moment tensor

Here is the USGS page.

Here is a map of the area. The epicenter is marked by a red starmap region

Here is the same map with historic earthquakes plotted. map region

Here is the IRIS map with historic earthquakes plotted. IRIS puts together learning moment educational products for many larger earthquakes. Here is the IRIS earthquake browser. map region

Here is a map scaled to the USGS Modified Mercalli intensity map. map region

Here is the USGS pager page, which helps us to rapidly evaluate potential infrastructure damages. map region

Here is a tide gage record from Paul Whitmore at the NOAA/NWS National Tsunami Warning Center. The tide gage is located on South Georgia Island. map region

Here is a figure from Lindeque et al., 2013 showing one tectonic model of this region (Marine Geology, V. 336, p 61-63). Their paper investigates the Cretaceous to Quaternary sedimentation history of the Weddel and Scotia seas. They use seismic stratigraphic profiles and sediment cores to evaluate the sources and timing of sedimentation. They interpret these sediments in terms of oceanographic circulation patterns that changed following the tectonic evolution of this margin. In the Cretaceous, the deep water gateway was closed and the subduction zone along southern Chile probably connected with the subduction zone off the Antarctic Peninsula. Here is a link to their paper. map region

Here is a map of the region from wiki commons http://commons.wikimedia.org/wiki/File:Scotia-sea.png. map region

Here is a map of the local area showing evidence for both e-w faulting (A) and ne-sw faulting (B). map region

Here is a video map showing seismic waves from this earthquake radiate through the seismic network in the US. (9.6 MB mp4) map region

Here is a great paper on the tectonic evolution of the western Scotia Sea.

Here is a great web page with tectonic reconstructions of this region.

Here is one of their maps:

Adobe Software

https://www.adobe.com/cfusion/entitlement/index.cfm?e=cs2_downloads&loc=en

In an enormous act of charity, Adobe has just offered their outdated CS2 suite of products for free. This includes Photoshop and Illustrator. I know a lot of geo students are using illustrator for their projects so this is a great opportunity. CS2 is an older version but it still works great for generating strat columns and doesn’t cost $200; plus, it runs better on slower machines. These all have registration disabled and have full functionality. Now only if they made a decent GIS program!…

They did this a few months ago by accident and disabled downloading immediately, but after an overwhelming number of downloads and support they decided it was good for their business model to get people hooked on their products. The software is widely pirated already so they would rather have people using legitimate copies instead of downloading sketchy pirated copies.

Here is the link!

M 7.3 offshore Honshu Japan

Extensional earthquake in Pacific plate “up-dip” of the 11 March 2011 Tohoku-Oki earthquake.

Here is the USGS page.

Here is the moment tensor:
M7.3 Honshu

Here is a map of the epicenter and Japan:
M7.3 Honshu

Here is a map of the epicenter and Japan with historic seismicity (dominated by 2011):
M7.3 Honshu

Here is a zoomed in map of the epicenter and Japan with the “did you feel it” overlay on land:
M7.3 Honshu

Here is a zoomed in map of the epicenter and Japan with the Intensity Contours plotted:
M7.3 Honshu

Here is the usgs map for the region:
M7.3 Honshu

Here is the moment tensor page:
M7.3 Honshu

Here is the PAGER page:
M7.3 Honshu

Hookton Slough Coring

Tom Leroy and I went to my old coring site 01-BR-05 to make sure it was usable as a field trip stop for my class. We will be going here this coming Wednesday. Thanks Tom for helping me out.

I will write more about these cores and what our interpretations are after the field trip. I want the class to come up with their own interpretations. I have a few photos of the core we collected today.

This is an overall view of the 3rd core section down. This core samples sediment of approximately 1 meter in length. This core sampled sediment from approximately 1.8 to 2.8 meters. Up is to the left. The base of the core includes blue-gray silty-clay, overlain by an organic rich brown muddy peat, overlain by a clean mud and then a series of muddy sand and sandy mud layers, which is finally overlain by some more mud. Some of the mud has darker grey layers.

Here is an overall view of the middle of the core.01-BR-05

Here is a “zoom in” of the middle of the core.01-BR-05

Here is a map of the regional tectonics.01-BR-05

Alaska Earthquakes

The 1964 Great Alaska Earthquake occurred on Good Friday, March 27th. It and rocked the state with strong ground shaking for 4.5 minutes. At magnitude 9.2, it was the second largest quake ever recorded by seismometers.

This animation shows the underlying causes of that earthquake, and tells how research done on the ground deformation contributed to confirmation of early theories of plate tectonics.

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.

Errata: 1) Fourth Ave., not Fourth St. 2) After 2min48sec the epicenter was shifted N. Should be ESE of that, closer to Prince William Sound. Apologies from animator.

Youtube Source IRIS

WMV file for downloading.

EQ title page

M 7.1 Phillipines 2013.10.15

Fairly big earthquake. Sounds like it has caused some damage. Looks like a thrust or reverse earthquake, USGS poses the fault is in the Sunda crust. Fairly deep earthquake, but this is continental crust i believe, so might not be too deep after all.

Here is the USGS moment tensor page
Mw = 7.2 Philippines

Here is a map that shows the epicenter as it relates to the general plate tectonics of the region. the Philippine plate is subducting westward beneath the Sunda plate, part of the Eurasia plate. The island of Sumatra is on the western side of this plate, where the India-Australia plate subducts northeasterly to form the Java, Sumatra, and Andaman subduction zones.

Mw = 7.2 Philippines

Here is the same map with historic earthquakes plotted. Note how they outline the plate boundaries.

Mw = 7.2 Philippines

Here is a map zoomed into the region.

Mw = 7.2 Philippines

Here is the same map with shaking intensity plotted.

Mw = 7.2 Philippines

Here are the PAGER data (estimates for the amount of people or fiscal damage).

Mw = 7.2 Philippines

Here is the PAGER map (estimates for the amount of people or fiscal damage).

Mw = 7.2 Philippines

Mw 5.0 Trinidad 2013.10.11

All right! That was exciting and a little bit scary. Most all earthquakes scare me because I recognize they might get bigger or trigger a bigger one.

This earthquake is most likely on a northeast striking strike-slip fault in the downgoing Gorda plate. The GP is caught in a vice between the older and stronger North America and Pacific plates.

Here is the USGS page: http://earthquake.usgs.gov/earthquakes/eventpage/nc72086051#summary

Here is the moment tensor
Mw = 5 Trinidad Moment Tensor

Here is the seismogrpaph at HSU (photo credit Lori Dengler)
Mw = 5 Trinidad Moment Tensor

Mw = 5 Trinidad Map

Here is a map I made in google earth showing historic earthquakes. Note the larger gray circle to the northeast of today’s earthquake. That is the 1980 Mw = 7.2 earthquake that caused extensive damage in Humboldt County (knocking the bridge partly down on hwy 101 near CR). Today’s earthquake appears to be along the same fault system that ruptured in 1980:

Mw = 5 Trinidad Map

Here is the seismogrpaph at Jacoby Creek (data credit Lori Dengler). The vertical lines are six seconds apart.
Mw = 5 Trinidad Moment Tensor

Here is a map that Chris Rollins used in his 2010 paper. It shows historic seismicity in this region, including the 1980 swarm.
Mw = 5 Trinidad Rollins

Here is a map that I made in google earth that shows the shaking intensity (Modified Mercalli Intensity Scale).
Mw = 5 Trinidad Rollins

Here is a map that I made in google earth that shows the % Peak Ground Acceleration (% of g, where g is defined as 9.8 m/s^2).
Mw = 5 Trinidad Rollins

These are the models for tectonic deformation within the Gorda plate as presented by Jason Chaytor in 2004.
Mw = 5 Trinidad Chaytor

Here is the SCEC page: http://www.data.scec.org/recenteqs/Quakes/nc72086051.html

Here are the seismologic information:
Mw = 5 Trinidad NCSS Seismo

Here is the SCEC map I went to before it showed up on the USGS page. Note that no magnitude had been assigned yet:
Mw = 5 Trinidad Moment Tensor

M7.7 Earthquake in Pakistan

A very large earthquake in Pakistan today!

As a result of collision of the Arabia plate into the Eurasia plate, thrust faults formed in Pakistan. This collision zone is the same basic convergence region that extends from Java/Sumatra, up through Burma, across India (creating the Himalaya), through the middle east, into the Mediterranean creating the Alps.
Here is the moment tensor for this earthquake, showing the oblique mechanism.
M=7.7 Pakistan Moment Tensor

Here is a map with the epicenter plotted in google earth.
M=7.7 Pakistan

Here is a map with the Modified Mercalli Intensity Contours plotted in google earth.
M=7.7 Pakistan

Here is a map with the MMI intensity (USGS shakemap color overlay) and Peak Ground Acceleration Contours plotted in google earth.
M=7.7 Pakistan

Here is the USGS page: http://earthquake.usgs.gov/earthquakes/eventpage/usb000jyiv#summary

Here is the USGS map for the region:
http://earthjay.com/earthquakes/20130924_pakistan/middleeast_tsum.jpg

Here is the USGS page for the loss estimates below: http://earthquake.usgs.gov/earthquakes/eventpage/usb000jyiv#pager

Here is the estimate of fatalities for this earthquake:
http://earthjay.com/earthquakes/20130924_pakistan/alertfatal.jpg

Here is the estimate of economic loss for this earthquake:
http://earthjay.com/earthquakes/20130924_pakistan/alertecon.jpg

Here is the estimate of “exposure” for this earthquake:
http://earthjay.com/earthquakes/20130924_pakistan/pakistan_78_table_population_exposure_20130924_0850.PNG