Monthly Archives: May 2014

Panama Aftershocks Reveal Likely Fault Solution

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All rightee… We have a number of aftershocks that are lighting up the potential fault that ruptured a couple days ago. Here is my page for this earthquake. Here is the USGS page.
The aftershocks are aligned with the north-south transform fault system (named the Colba Ridge) that separates the Cocos plate to the West and the Nazca plate to the East. Here is the local map with historic epicenters in gray and the mainshock and aftershock epicenters plotted as orange circles. Note that many of the historic epicenters also align along this fracture zone.


Here is a map with only the recent epicenters in orange.


Here is an updated moment tensor (Mwb). With these aftershocks, we can better interpret this as rupture on a N-S striking right-lateral fault.

There are 5 moment tensors on the USGS page. For those looking for a refresher on focal mechanisms, here is the USGS page that describes them.

Here is the USGS poster that describes the historic seismicity and plate tectonic setting.


Here is a more comprehensive view of the local and regional tectonics in this region. This is a compilation by Harley M. Benz and others.

1964 Earthquake Animation

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Here is a simulation of the 1964 earthquake. I found this posted online on livescience (they do not typically provide a link to the original content, but repost without attribution) but here is the source. Carl is  an assistant professor of geophysics at the University of Alaska Fairbanks  at the Geophysical Institute (GI)  and the Department of Geology and Geophysics 

Earthquake offshore Panama

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Good sized earthquake offshore Panama! Here is the USGS page.
This is probably an earthquake on an oblique high angle reverse fault, based on this early moment tensor. The hypocentral depth is pretty shallow too.

This looks related to the seismicity that plots along the North-South transform fault system that separates the Cocos and Nazca plates. However, it is near a triple junction and could be related to the East-West transform fault, or the subduction zone that strikes to the northwest. Very interesting.
Here is a regional map showing historic epicenters in grey. Today'[s earthquake is plotted in orange.


Here is a local map showing the same historic quakes, just zoomed in more.


This shows that the shaking was probably felt throughout coastal Panama.


Here is the USGS regional tectonic map:


Here is the PAGER report, that indeed shows there were many people who probably felt this earthquake.

Update Commentary on the OSO Slide: Scott Burns

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Scott Burns, emeritus at Portland State and a student of Peter Birkeland, wrote an excellent article about the OSO Slide. I made a few animations and armchair interpretations about this slide shortly after it happened (here).
Scott discusses the geologic history and how heavy rainfall was a likely co-conspirator that led to the triggering of this horribly destructive landslide. Here is the article.
This is a general location map:

Here is an animation from David George and Dick Iverson at the USGS:

As a reminder, here is a map showing the historic landslides in the area:


Here is the geologic mapping done at the 1:24,000 scale published by the Washington State Department of Natural Resources. Click on the map below to see the entire map. Below is a clip of the map in the region of the OSO Landslide of 2014. Click here to see this inset map in a new browser window. Note the location of a dotted strike slip fault in the region of the OSO slide.

1964 Great Alaska Earthquake: Before and After Photos

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I just got back from a great Seismological Society Meeting in Anchorage, Alaska. The meeting was held there in part to celebrate the 50th anniversary of the 1964 Great Alaska Earthquake. I will post more online in the coming week. I present here a couple maps below, as well as a link to the USGS open file report that shows before and after photos in Anchorage.
Here is a map that shows the regional extent of the 1964 earthquake. Regions of coseismic uplift/subsidence are delineated by blue/red polygons.

Here is a map that shows the extent of historic earthquakes in southern Alaska. This is from a USGS open file report.

Here is a link to the USGS open file report. Click on the image to get the 12 MB pdf.