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 descent into the mantle beneath Mexico. In the region of this earthquake, the Cocos plate moves approximately northeastwards at a rate of 60 mm/yr.

Image compiled by Earthquake-Report.com

Historically, there have been several significant earthquakes along the southern coast of Mexico. In 1932, a magnitude 8.4 thrust earthquake struck in the region of Jalisco, several hundred kilometers to the northwest of today’s event.

Seismic Hazard map shows the max. to expect ground acceleration along the coast – image courtesy USGS – Purple line : subduction trench / fault line, green line : transform fault

Magnitude 7 and Greater Earthquakes since 1900 – image courtesy USGS

On October 9, 1995 a magnitude 8.0 earthquake struck in the Colima-Jalisco region, killing at least 49 people and leaving 1,000 homeless.

The deadliest nearby earthquake occurred in the Michoacan region 470 km to the northwest of today’s event, on September 19, 1985. This magnitude 8.0 earthquake killed at least 9,500 people, injured about 30,000, and left 100,000 people homeless.

The 1985 Mexico City earthquake, a magnitude 8.0 earthquake that struck Mexico City on the early morning of 19 September 1985 at around 7:19 am (CST), caused the deaths of at least 10,000 people and serious damage to the greater Mexico City Area. The complete seismic event consisted of four quakes. A pre-event quake of magnitude 5.2 occurred on 28 May 1985. The main and most powerful shock occurred 19 September, followed by two aftershocks: one on 20 September 1985 of magnitude 7.5 and the fourth occurring seven months later on 30 April 1986 of magnitude 7.0. The quakes were located off the Mexican Pacific coast, more than 350 km away, but due to strength of the quake and the fact that Mexico City sits on an old lake-bed, Mexico City suffered major damage. The event caused between three and four billion USD in damage as 412 buildings collapsed and another 3,124 were seriously damaged in the city. While the number is in dispute, the most-often cited number of deaths is an estimated 10,000 people but experts agreed that it could be up to 40,000 (source : Wikipedia)

…

for more information, go to:   http://earthquake-report.com/2012/03/21/understanding-the-massive-march-20-mexico-earthquake/