Moderately Deep Focus Earthquake in Colombia

There was a moderately deep focus extensional earthquake beneath Colombia today. Here is the USGS web page for this earthquake.
Here is a map that shows the epicenter as a green dot. Historic earthquake epicenters are plotted in grey. The USGS slab contours (the depth to the subduction zone fault, as estimated by Hayes et al. (2012) based on seismicity) show the slab to possibly be at about 200-300 km at the location of today’s earthquake. Unfortunately, their slab model does not extend to this region of Colombia. It is likely that today’s earthquake is in the downgoing slab (the Nazca plate) and is extensional due to bending of the slab, or due to slab pull (the plate that is deeper is going downwards due to its density, so it is pulling the slab down with it). Alternately, these may be due to the volcanism in this region.


This map is from the USGS here. I have placed the moment tensor on the map. There have been numerous earthquakes in this region (green epicenters) in the recent past.


This map shows the recent seismic activity in this region. These earthquakes, from the past year or so, align with the seismicity shown as green epicenters in the USGS map above.


Here is a map that shows the location of the cross sections below. These are from Moore and Twiss (1995) and were presented on this web site.


Cross Sections (Moore and Twiss, 1995):


Here is a paper that discusses the thermal control on subduction. They show how the slab is flat in this subduction zone.
Here is their tectonic setting map:


Here is a cross section in northern Columbia:


Here is their cross section where they present their models of different types of subduction zones. Their figure text: “Effect of subduction style on thermal regime and deformation in the upper plate. Note the increased viscous interplate coupling for fiat subduction and transfer of deformation inboard (to the backarc).”


References:

• Gutscher, M.-A., W. Spakman, H. Bijwaard, and E. R. Engdahl, 2000. Geodynamics of flat subduction: Seismicity and tomographic constraints from the Andean margin, Tectonics, 19(5), 814–833, doi:10.1029/1999TC001152.
• 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.
• Moores, E. M. & Twiss, R. J. 1995. Tectonics. ix + 415 pp. New York: W. H. Freeman.