The Strength of Strike-Slip Faults: Space-Geodetic Constraints for a Ridge-Transtensional System in the Gulf of California

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This project is a space-geodetic study of the Ballenas Transform Fault in the Gulf of California, which is part of the North America-Pacific plate boundary. The research team will acquire campaign GPS and interferometric synthetic aperture radar data and use finite element modeling methods to study the accumulation and release of tectonic strain to test for crustal strength variations along the fault. Strength variations are expected because the heat flow varies with distance from two incipient mid-ocean ridge basins in the north and south, and because of significant variations in crustal structure on both sides of the fault (undeformed Baja California versus the Gulf of California extensional province). The fault, situated in a oceanic channel, affords a special opportunity to study strength variation for because: 1) the transform fault has a very high slip rate of approximately 46 mm/yr; 2) the fault accommodates the entire North America-Pacific plate relative motion without any other strike-slip faults in its vicinity and therefore no overlapping strain patterns; 3) the August 2009 magnitude 6.9 earthquake and its regular earthquake repeat time (every 55 years) allows for a clear definition of the state of the fault within the earthquake cycle which is very important for models of the strain accumulation.This study has important implications for seismic hazard estimates for all major transform faults such as the San Andreas Fault system in California further to the north. Seismic hazard estimates are commonly based on models that ignore strength variations. This study will provide new data on how crustal strength variations affect strain accumulation.