The 2010 Baja California earthquake (also known as 2010 Easter earthquake, 2010 Sierra El Mayor earthquake, or 2010 El Mayor – Cucapah earthquake) occurred on April 4 (Easter Sunday) with a moment magnitude of 7.2 and a maximum Mercalli intensity of VII (Very strong). The shock originated at (3:40:41 PM PDT) south of Guadalupe Victoria, Baja California, Mexico.
The 89-second quake was widely felt throughout northwest Mexico and southern California. It was also the strongest to rock southern California in at least 18 years (since the M 7.3 1992 Landers earthquake), if not longer: the next most recent comparable earthquake—the 1952 Kern County earthquake (M 7.3)—was 58 years earlier. Each of these earthquakes had a similar magnitude, and was also felt across a large swath of North America. Most of the damage occurred in the twin cities of Mexicali and Calexico on the Mexico–United States border.
Geology
The quake originally was believed to have occurred on the Laguna Salada Fault, which is about to long and straddles the California–Baja California border. The active Laguna Salada Fault ruptured in February 1892 with an estimated 7.2 earthquake.
By the distribution of aftershocks and using radar interferometry, the main shock rupture was found to have occurred on a previously unmapped fault in the Cucapah Mountains and beneath the Colorado River Delta. This fault line was named the Indiviso Fault, after the nearby town of El Indiviso. A liquefaction zone bounded by the Cerro Prieto Fault and the Laguna Salada Fault was observed.
Timeline
Foreshocks
Mexicali, El Centro, San Diego, Ensenada, and Tijuana are situated in a very active seismic zone and surrounded by important faults. An earthquake of such magnitude had been expected around the fault situated in the southeast of Mexicali. Before the 7.2 earthquake occurred, the surrounding area had been seismically active in 2009. Several foreshocks began from April 1, 2010, with magnitudes of 3 and 4.
Mainshock
The earthquake measured 7.2 on the moment magnitude scale that started south of Guadalupe Victoria, Baja California, at a depth of . It occurred at 22:40 UTC (1540 local time) on Easter Sunday, April 4, 2010, and it is said to have lasted about a minute and 29 seconds. Since the earthquake occurred on this day, it has been also called the Easter Sunday earthquake. Intensity VII (Very strong) shaking was felt in Calexico, Imperial, El Centro, and Heber. Intensity VI (Strong) shaking was felt in the Imperial Valley towns of Ocotillo, Calipatria, Brawley, and Holtville.
The April 4 quake was the second largest earthquake in Baja California history after the 1892 Laguna Salada earthquake at a magnitude of 7.2–7.8 on the Richter magnitude scale, and was well recorded in Southern California, especially in the Imperial valley.
Aftershocks
Four aftershocks with a magnitude of at least 5 have been reported; one at a magnitude of 5.2, one at 5.4, one at 5.1, and one at a magnitude of 5.7, all four within one hour. Additionally, a 5.3 aftershock hit the region very close to the mainshock epicenter on April 8, at approximately 9:44 AM local time. There have been at least nine large aftershocks in total.
By six hours after the earthquake, more than 90 aftershocks or triggered earthquakes between magnitude 3.0 and 5.1 were recorded in northern Baja California and Southern California. This included a magnitude 3 event off the coast of Malibu, California. By the early hours of the following morning, scientists had measured 100 aftershocks.
Pat Abbott, a professor emeritus of geology at San Diego State University, said, "Any quake of this size seems to pass some kind of threshold where it's large enough to disturb or trigger other faults. In cases like this, that often means increasing stress on other faults, which makes them more prone to movement. The energy seems to be moving northward toward the San Andreas Fault. I don't want to anthropomorphize, but it's like this quake was goading the San Andreas." It remains to be seen how the San Andreas Fault was affected by these temblors. The southern section of the San Andreas Fault worries scientists, because it has not ruptured in more than 300 years. The region also includes other faults, including the Imperial Fault Zone.
In the early morning hours of April 10, 2010, an aftershock measuring magnitude 4.4 was felt throughout most of Southern California and Baja California. It was said to have lasted about ten seconds. No injuries or damage were reported. Another aftershock measuring a similar magnitude struck Southern California on the morning of April 11.