Hybrid Measurements of Crustal Deformation in Guerrero, Mexico

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Recent improvements in our understanding of the physics and rheology of fault slip suggest that predictive modeling of fault displacement may be possible in the near future. Such models require observational constraints from both geodesy and seismology, and ideally the observations should encompass time scales greater than that of the earthquake cycle. Working collaboratively with UNAM (National Autonomous University of Mexico), the University of Colorado is developing an integrated model of megathrust fault slip, using data from the state of Guerrero, Mexico. The study area encompasses a ~100 km segment of the Cocos-North America plate boundary with more than 5 m of seismic slip deficit. The geodetic data suggest that significant transient, aseismic slip recently occurred on the Guerrero subduction interface. This poses a fundamental question: does the seismic slip deficit (or "seismic gap") in Guerrero represent a very mature accumulation of plate boundary strain? Or, does the subduction megathrust in Guerrero relieve most of its strain accumulation aseismically? In other words, does transient motion in Guerrero translate to a higher seismic hazard, or a lower hazard, than on other megathrusts? This question is being addressed via a combination of data collection and modeling. The Guerrero gap is being monitored continuously with GPS receivers operated by CU and UNAM. These GPS data are combined to estimate positions on a daily basis and are used as input to the models. The GPS receivers are also being operated at higher rates, 5 Hz, so that higher rate positions can be estimated during earthquakes and combined with seismic data also being collected in Guerrero.