The magnitude 7.2 El Mayor - Cucapah earthquake of Sunday April 4th 2010, occurred in northern Baja California, approximately 40 miles south of the Mexico-USA border at shallow depth along the principal plate boundary between the North American and Pacific plates. This is an area with a high level of historical seismicity, and also it has recently been seismically active, though this is the largest event to strike in this area since 1892. The 4 April earthquake appears to have been larger than the M 6.9 earthquake in 1940 or any of the early 20th century events (e.g., 1915 and 1934) in this region of northern Baja California. See full summary by USGS.

From Greg Beroza:

As of 8:15pm PDT on Monday, April 5th, 2010, the earthquake has been christened the Sierra El Mayor earthquake. SCEC geologists and geodesists are in the field now, to be followed tomorrow (Tuesday, April 6th) by seismologists. Surface rupture appears to extend across Highway 2, south of the border.  Ken Hudnut is coordinating an airborne reconnaisance of surface rupture tomorrow that will provide important constraints on the distribution of faulting.