M 5.8 - 12km N of Delta, B.C., MX

Tectonic Summary

The northern Baja California earthquake of December 30, 2009, occurred on the principal plate boundary 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 45 mm/y. The principal plate boundary in northern Baja California consists of a series of northwest-trending strike-slip (transform) faults that are separated by pull-apart basins. The faults are distinct from, but parallel to, the San Andreas fault.

The December 30 main-shock occurred near the southeastern end of a strike-slip segment of the plate boundary that coincides with the Imperial fault, and the focal-mechanism of the earthquake is consistent with the shock having occurred on the Imperial fault. To the south of the region of the earthquake, the principal plate boundary changes from the Imperial fault to the strike-slip Cerro Prieto fault, which is sub-parallel to the Imperial fault but offset from it to the southwest. The pull-apart basin between the two northwest-trending strike-slip faults is a region of high heat flow and frequent earthquakes. Earthquakes having magnitudes as high as 7.1 have been historically recorded from the section of the Pacific/North American plate boundary on which the December 30, 2009, earthquake occurred.