This study combines geodesy, seismology, and numerical models to elucidate the origin and nature of aseismic transients and their impact on seismic hazard in the Mexican state of Guerrero and in other subduction zones. The study area encompasses a ~200 km segment of the Cocos-North America plate boundary. The last great earthquake in the northwest section of region occurred in 1911. It has been estimated that if the Guerrero gap were to rupture, its magnitude would exceed Mw 8. GPS measurements have been critical in establishing the widespread existence of aseismic (transient) slip events in subduction zones. More recently, seismic tremor studies have been correlated with aseismic slip events. The seismic data have greater resolution of the location and propagation of transients, while GPS continues to constrain their moment release. Both geodesy and seismology will be needed to understand the source and periodicity of transients and how they relate to the mechanics of the subduction process throughout the earthquake cycle.
CU began the Guerrero GPS project in 1997 to measure/model crustal deformation rates and assess seismic hazard in the region. The National Autonomous University of Mexico (UNAM) faculty and students have been partners in this project since its inception. There are currently 10 GPS receivers operating in Guerrero as the result of this collaboration. Using these continuous GPS installations and earlier campaign data it has been demonstrated that three very large transients have occurred in Guerrero in the last decade. The PIs intend to improve and maintain GPS instrumentation, improve and distribute position estimates, and model the GPS data. Broadband seismic data will be collected in Guerrero by Caltech and UNAM during this project period, potentially allowing for tremor detection. A collaboration with a group at Harvard will allow comparison of geodetic and seismic observations with three-dimensional numerical models that includes temperature dependence, rate and state friction, and pore pressure effects.
