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GPS in Jalisco, Mexico

These investigations involved collaboration among la Universidad Nacional Autonoma de Mexico, Caltech, the University of Wisconsin, and the University of California at Berkeley, with more recent partnerships including the University of Guadalajara, Proteccion Civil del Estado de Jalisco, and the Colima Volcano Observatory. The project was supported by the US National Science Foundation. We set up a regional GPS network in the states of Jalisco and Colima, Mexico, and first measured it in spring 1995 in order to monitor deformation of the North America plate over the subducting Rivera plate. In October 1995, there was a magnitude 8 earthquake in the subduction zone beneath the GPS network. We reoccupied this GPS network the week after the earthquake, in October 1995, as well as periodically thereafter. Comparison of the results from before and after the earthquake show up to nearly 1 meter of co-seismic displacement at one of our coastal sites (Chamela). The distribution of deformation due to the earthquake shows that the slip on the fault zone was entirely offshore during the event, and was thus anomalously shallow.  One major result of this study was also that considerable post-seismic displacement took place after the mainshock, but it occurred on the part of the plate interface that was deeper and had not slipped coseismically.

We continued to monitor this network periodically in order to quantify the post-seismic slip and in order to evaluate the deformation going on in the continental rift systems surrounding the Jalisco Block. In Feb. 2000 we also established and occupied some more campaign-style sites in order to densify the network coverage near the coast.  The long-term monitoring of the subduction zone was interrupted by another subduction zone earthquake in January 2003.  Our subsequent study of the aftershock data from this earthquake was able to resolve previously unknown details concerning the dips of the Cocos and Rivera slabs in this region.  Through the period from 2005 to 2010 many of the campaign GPS sites were converted to continuous stations now being operated by our Mexican colleagues.

The earliest results from the network were discussed in the Ph.D. thesis and related publications by Tim Melbourne, of Caltech. The later results from this network were the subject of a Ph.D. thesis and related publications by Wallis Hutton of the University of Wisconsin and an MS thesis and published article by Stuart Schmitt of the University of Wisconsin.  Our most recent results include two papers published in PAGEOPH in 2010 (Andrews et al. and Selvans et al), one of which was a chapter in the PhD thesis of Michelle Selvans (Caltech PhD 2011).

This project was funded by the US National Science Foundation.

Here is the image showing the coseismic displacement vectors at our sites, with the largest having a 3D length of 980 mm. This is from the paper by Melbourne et al., GRL, 1997.