El Mayor - Cucapah Earthquake
On April 4th, 2010, an Mw 7.2 earthquake shook Baja California, Mexico, violently. Authorities in Mexacali, Mexico reported two earthquake-related deaths and more than 200 injured. Mexacali experienced a short-lived, city-wide power outage and substantial structural damage to some buildings. The historic center of nearby Calexico, California, was closed for days as a number of buildings were flagged with serious structural damage.
The earthquake was felt as far north as Santa Barbara, California, and as far east as Scottsdale, Arizona.
According to the US Geological Survey, the main shock coincides with the southeast segment of the Laguna Salada fault.
The US Geological Survey shake map shows a NW-SE envelope of violent to severe shaking in the Laguna Salada basin west of the Cucapah Mountains. Very strong to strong shaking was observed as far north as El Centro, California, with strong to moderate shaking extending east to Yuma, Arizona. People throughout southern and central Arizona reported feeling the ground shake and observed sloshing swimming pools and shaking objects in and outside of their homes.
By 6 April, more than 708 aftershocks occurred, mostly within a northwest-southeast trending 75 km long swath that parallels nearby faults and extends at least 6 miles north into the United States. (See the Southern California Seismic Network image below showing aftershocks of the El Mayor-Cucapah earthquake.) Foreshocks were recorded during the later part of March, including a moderate sized Mw 5.5 foreshock, presaging the Mw 7.2 event.
Broadband seismometers of the Arizona Integrated Seismic Network (AISN), a consortium comprising the Arizona Geological University, Arizona State University, Northern Arizona University, and University of Arizona recorded the large temblor.
Historical Events: In 1892, the Laguna Salada fault produced an M 7.2 event. Mueller and Rockwell (1995) estimate about 3-mm of vertical displacement annually along the fault, and 1,000 to 2,000 year of repose between large magnitude earthquakes.
Plate motion occurs along a series of northwest trending strike-slip faults that parallel the San Andreas fault system to the north. The Pacific Plate is moving approximately 45 mm per year to the northwest with respect to the North American plate.
References:
Mueller, K.J. and Rockwell, T.K., 1995, Late Quaternary activity of the Laguna Salada fault in northern Baja California, Mexico. Geological Society of America, v. 107, no. 1, p. 8-18.
USGS Earthquake Hazards Program. http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/ci14607652/
Southern California Seismic Network. http://www.scsn.org/
Photograph by Francisco Bernal (Mexican Section of the International Boundary and Water Commission - IBWC) near Mexicali, Mexico.