Figure 1: Location of recent earthquakes (shown as red stars) in the northern Baja area; map provided by Dr. Sue Beck, Univ. of Arizona; the “beach balls” represent the type of motion associated with the earthquakes with black signifying compression, and white signifying tension; the yellow diamonds represent the location of the Arizona Broadband Network run by a consortium consisting of the Arizona Geological Survey, University of Arizona, Arizona State and Northern Arizona University.

el maYor CuCAPAH EARTHQUAKE
magnitude 7.2 earthquake
JERI J. YOUNG, AZGS RESEARCH GEOLOGIST

On April 4th, 2010, Baja California, Mexico shook violently from a Mw 7.2 earthquake that occurred  about 40 miles south of the U.S/Mexico border at a depth of approximately six miles (Figure 1).  In Mexacali, Mexico, there were two earthquake-related deaths, more than 200 injured, a city-wide power outage and substantial structural damage to some buildings.  The historic center of Calexico, California, was closed as a number of building were flagged with serious structural damage. 

The earthquake was felt hundreds of miles from its epicenter—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. In 1892, an event on this same fault produced an M 7.2 event.  In this region, plate movement 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.   

The US Geological Survey shake map, which integrates near-real time ground motion and shaking intensity, shows a NW-SE envelope of violent to severe shaking in the Laguna Salada basin west of the Cucapa 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 (Figure 2, below). 

There have been at least 708 aftershocks as of April 6th, most of which lie within a northwest-southeast trending 75 km long swath that parallels faults found in the area, and extends at least 6 miles north into the United States (Figure 3, below).   Foreshocks were recorded during the later part of March, including a moderate sized Mw 5.5 foreshock that occurred just minutes before the mainshock.

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 (Figures 4, below).  The April 4th Baja earthquake should be a reminder that ground-shaking associated with fault systems outside the state, and sometimes within the state, can occur in Arizona. 

Figure 2: Shake map produced by the U.S.G.S.; the Yuma area experienced moderate shaking, while Phoenix and other areas felt weak to light shaking; star represents the epicenter of the April 4th earthquake.

 

 

Figure 3: The April 4th, 2010 Sierra El Mayor main shock shown as red a blue star, aftershocks shown in red and foreshocks shown as blue circles;; earthquakes associated with the December 2009 series are shown in green and the remaining 2009 seismicity shown in black.  Large faults are represented as black lines; Image courtesy of the Southern California Seismic Network.

Figure 4: Seismogram from several Arizona seismometers.(From Global Seismology and Tectonics, Geosicences Dept, University of Arizona)

 

 

 

 

 

MORE PHOTOS of el mayor - cucapah earthquake

Photography by Danny Ashcraft (CEO Western CNC, Inc.) near Mexicali, Mexico

Photographs by Francisco Bernal (Mexican Section of the International Boundary and Water Commission - IBWC) near Mexicali, Mexico

 

 

 

ARTICLE AUTHOR:
Jeri J. Young
Research Geologist

Arizona Geological Survey
Phoenix, AZ
jeri.young@azgs.az.gov
















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