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Geodetic constraints on frictional properties and earthquake hazard in the Imperial Valley, Southern California

Impact:
We have used geodetic observations to infer in situ frictional properties on the Imperial Fault. We find that robust constraints on these properties require observations from all parts of the earthquake cycle. Our results are in good agreement with laboratory-derived values of the slip rate-dependence parameter (ab), for a reasonable range of assumptions. The inferred depth extent of shallow creep is ∼4 km, in close agreement with the seismically inferred depth of sediments, suggesting a compositional or pore fluid pressure control on the occurrence of stable creep. Our results also suggest that the Imperial Fault is not the only active plate boundary structure at the latitude of the U.S.-Mexico border. Geodetic evidence suggests that significant strain is accommodated by a subparallel fault located 10–20 km west of the Imperial Fault, which slips at a long-term rate comparable to that of the San Jacinto Fault to the north. If so, this fault represents a significant unmapped hazard to the U.S. and Mexican communities of El Centro, Calexico, Heber, and Mexicali.

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