GPS Investigations in the Jalisco region, Mexico

These investigations are a collaboration among la Universidad Nacional Autonoma de Mexico, Caltech, the University of Wisconsin, and the University of California at Berkeley. The project is 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 in March 1996, January - February 1997, February 1998, March 1999, and February 2000. 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. We will continue to monitor this network periodically through 2003 in order to establish the nature of any post-seismic slip and in order to quantify 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. Recent collaborators on this project are from the University of Guadalajara and Proteccion Civil of the State of Jalisco.

The earliest results from the network were discussed in the Ph.D. thesis of Tim Melbourne, of Caltech. The latest results from this network are the subject of a Ph.D. thesis by Wallis Hutton of the University of Wisconsin.

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.