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Magnitude 7.4 Earthquake Strikes Oaxaca, Mexico

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The ShakeMap showing shaking intensities for the March 20 earthquake

A magnitude-7.4 earthquake struck in the Mexican state of Oaxaca Tuesday, March 20, 2012, at 12:02 p.m., local time at the epicenter. It was followed by a subsequent M-5.1 earthquake at 12:35 p.m. local time.

The earthquake occurred at a depth of 12 miles (20 km) and caused moderate shaking in Acapulco and Oaxaca. As of 3:13p.m. ET, the National Oceanic and Atmospheric Administration has issued no warning of tsunami activity.

The current version of the USGS Prompt Assessment of Global Earthquakes for Response (PAGER) estimate is that economic losses are most likely to be in the $10-100 million range, and fatalities are equally likely to be in the 10-100 range.

The earthquake struck in the southwestern part of Mexico between Acapulco and Oaxaca. As of this writing, 859 people in 144 cities throughout Mexico and the surrounding region had responded on the USGS Did You Feel It? website.

History of strong earthquakes

Mexico is one of the most tectonically active countries in the world, and it experiences frequent significant earthquakes. This earthquake is a reminder of the many seismic events that Mexico has experienced in the recent past.

  • The most recent significant earthquake to strike Oaxaca was a M-6.5 that struck on Tuesday, February 12, 2008.
  • The most recent significant earthquake to strike Mexico was a M-7.2 that struck in Baja California on Sunday, April 4, 2010. There were two confirmed fatalities and 233 injured in the Mexicali area.
  • In September 1985, an earthquake measuring 8.1 on the Richter scale and centered in the subduction zone off Acapulco killed more than 4,000 people in Mexico City, more than 300 kilometers away.
A Map showing Did You Feel It? responses

Did You Feel It? Individuals report on the intensity of shaking

Tectonics of this earthquake

The March 20, 2012 earthquake occurred as a result of thrust-faulting on or near the plate boundary interface between the Cocos and North America plates. The focal mechanism and depth of the earthquake are consistent with its occurrence on the subduction zone interface between these plates, approximately 100 km northeast of the Middle America Trench, where the Cocos plate begins its decent into the mantle beneath Mexico. In the region of this earthquake, the Cocos plate moves approximately northeastwards at a rate of 60 mm/yr.

For the most recent information on this earthquake, maps, and scientific and technical information, visit Magnitude 7.4 – Oaxaca, Mexico.