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2010.04.04 - El Mayor - Cucapah Earthquake

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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.

As of 10:30am PDT on Monday, April 5th, 2010, this is where things stand. The USGS has the earthquake at M 7.2 with a strike-slip mechanism, but with a normal-faulting component.  It seems to be on/near the Laguna Salada fault, though that has not been confirmed by observations of surface rupture, so we should not be associating it definitively with that fault.  Aftershocks extend to the US side of the border.  The Laguna Salada fault had an earthquake of similar size in 1892 (Hough and Elliot, 2004 BSSA).  We have made contact with colleagues across the border: Javier Gonzales is the contact for geodetic observations in Mexico, Victor Wong is the contact for seismological observations, and John Fletcher for geological observations.  All of these scientists are at CICESE.

As of 8:15pm PDT, Sunday, April 4th, 2010 this is where things stand. The USGS has the earthquake at M 7.2 with a strike-slip mechanism.  It seems to be on/near the Laguna Salada fault, which had an earthquake of similar size in 1892 (Hough and Elliot, 2004 BSSA).  Today's earthquake has been a bit challenging having happened on Easter Sunday and just across the border.  We have made contact with colleagues across the border, but it took awhile.  SCEC is gearing up for possible seismic, geodetic, and geologic fieldwork, but how it goes from here depends strongly on what we learn about what is possible to carry out in Mexico.  There also may be the issue that non-SCEC instruments are scattered far and wide: in Haiti and Chile.  Mike Oskin has made contact with John Fletcher at CICESE (Ensenada), who is headed out to the field tomorrow and is interested in collaborations.  I have also heard back from Carlos Valdes, who is head of the Mexican National Seismological Service.  I let him know that scientists here are interested and available to collaborate and that we should try to coordinate our response.  He has not yet managed to get throught to CICESE, but will be in touch with us tomorrow.

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Up to 2 cm of triggered slip on the SAF in the Mecca Hills reported by Ray Weldon who is currently in the field. So far this slip has been observed between Painted and Thermal Canyons. 4 images attached. IMG_3504.JPG919.3 KB