Below is my poster for this and the earlier earthquakes. There is a legend that shows how moment tensors can be interpreted. Moment tensors are graphical solutions of seismic data that show two possible fault plane solutions. One must use local tectonics, along with other data, to be able to interpret which of the two possible solutions is correct. The legend shows how these two solutions are oriented for each example (Normal\/Extensional, Thrust\/Compressional, and Strike-Slip\/Shear). There is more about moment tensors<\/a> and focal mechanisms<\/a> at the USGS.
\nSiqueiros, Rivera, and Orozco were the “Tres Grandes,” 20th century political activists in Mexico who led the muralist movement. Their murals have inspired, and continue to inspire, political activists globally (as well as the Mexican muralism movement). Check out more about them here<\/a>. I am fascinated that there are fracture zones named for Siqueiros and Rivera in this region.<\/p>\n\nI include some inset figures.<\/p>\n
\nBased upon the location of the Clipperton fracture zone compared with the M 6.6 epicenter, I interpret this earthquake to have left-lateral slip on a strike-slip fault. The cool part about this earthquake suite is that there are examples of all types of earthquakes (extensional, compressional, and shear). The 4\/15 M 6.1 appears to possibly have triggered the 4\/25 & 4\/27 M 5.6 and M 5.8 earthquakes. Then, two days later, we had the M 6.6 earthquake. This earthquake is too far to be affected by changes in coulomb stress, however it sure seems like it is more than a coincidence. I have not run a coulomb stress modeling analysis, but this is just based upon modeling others have done in different regions. While the earthquakes along the Middle America Trench (MAT) would have resulted in the Cocos plate extending slightly to the northeast, and that there is the Tehuantepec fracture zone that appears to bend and link the Clipperton fracture zone to the region near the MAT (so we want to link these earthquakes), there probably is no linkage.
\nThe red-orange-yellow lines are slab contour lines from Hayes et al.<\/a> (2012). These lines are a best estimate for the depth to the subduction zone fault. These are based largely upon seismicity and there is currently an effort to update these contours to integrate other data types. The hypocentral depth for this earthquake is consistent with being along the subduction zone interface.
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\n![\"\"](\"http:\/\/earthjay.com\/earthquakes\/20160429_EPR\/20160429_EPR_interpretation.jpg\")
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\nFor more on the graphical representation of moment tensors and focal mechnisms, check this IRIS<\/a> video out:
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