Poster of the Gulf of California Earthquake of 03 August 2009 - Magnitude 6.9

Tectonic Summary

The Gulf of California earthquakes of August 3, 2009, occurred in the plate boundary region between the North America and Pacific plate. At the latitude of the earthquake, the Pacific plate moves northwest with respect to the North America plate at about 45 mm/y. The plate boundary beneath the Gulf consists of a series of transform faults separated by small spreading centers or pull-apart basins: earthquakes occur as the result of strike-slip faulting and normal faulting. The seismographically recorded radiation pattern of the main shock of August 3, 18:00 UTC, implies that the shock occurred as the result of strike-slip faulting, but the earthquake has not yet been associated with a specific geologically mapped fault. The largest historically recorded shocks from the Gulf of California have had magnitudes of about 7.

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