Slightly after noon local time (slightly after 6 pm GMT) on Tuesday 20 March 2012 the southern Mexican coast was shaken by an Earthquake felt as far away as Mexico City. The quake was centered 15 km east of the city of Ometepec, (180 km west of Acapulco), at a depth of about 20 km, and measured 7.4 on the Richter Scale, according to the United States Geological Survey. Mexican authorities are reporting no casualties at this time, although it is highly likely that a quake of this time will have caused fatalities or serious injuries. Local media are reporting damage to hundreds of homes in the Ometepec area.
Map showing the extent and severity of shaking felt across southern Mexico. USGS.
South Mexico lies on the boundary between the Cocos and North American Plates. The Cocos Plate is being subducted beneath the North American Plate in the Middle America Trench, off the south coast of Mexico, and passing under Mexico as it sinks into the Earth. This is not a smooth process, the plates stick together while pressure builds up, then move in sudden jerks, causing Earthquakes. This subduction zone also fuels a number of volcanoes in Mexico and Central America, fed by material from the Cocos Plate that has been melted by the heat of the Earth's interior and risen up through the overlying North American and Caribbean Plates as liquid magma.
Mexico has suffered some severely damaging Earthquakes in the past. In 2003 a magnitude 7.6 quake centered on Colima killed 29 people and made over 10 000 homeless. In 1995 a magnitude 8.0 quake, also near Colima, killed about 50 people and made over a thousand homeless. In 1985 a magnitude 8.0 in the Michoacan Region killed at least 9500 people and made over 100 000 homeless.