Colima Mexico Earthquake

First Posting | Summary
Posting Date: January 22, 2003, 12:00:00 AM

A major earthquake struck Colima, Mexico on Tuesday, January 21, 2003, at about 8:06 p.m. local time (Wednesday, January 22, 02:06 UTC). The U. S. Geological Survey (USGS) initially estimated the moment magnitude to be 7.8, with a focal depth of about 20 miles (33 km). The National Seismological Center in Mexico City calculated a magnitude of 7.6. All estimates of depth and magnitude are preliminary at this point. The quake, which lasted 45 seconds, was centered about 30 miles (50 km) east-southeast of the port city of Manzanillo, and about 32 miles (51 km) south-southwest of the state capital, Colima City. The earthquake was felt across western and central Mexico and as far away as the capital, Mexico City, some 310 miles to the east. Preliminary indications suggest the earthquake occurred in a seismically active region at the juncture of three tectonic plates: the North American Plate to the northeast, the Rivera Plate to the northwest, and the Cocos Plate to the south. The USGS described the fault mechanism as a thrust due to the subduction of the Rivera and Cocos Plates under the North American. There have been several significant quakes in the region, most recently a magnitude 8.0 earthquake some 30 miles (50 km) to the northwest in 1995. Initial reports indicate that most of the damage occurred in the states of Colima, Michoacan, and Jalisco. Thus far, at least 24 people are reported dead and 175 injured, but those figures are expected to increase. In the hardest hit area, Colima City, portions of office buildings are reported to have collapsed, along with about 166 homes. Almost all the older, adobe homes in downtown Colima are reported to be in ruins. Adobe, which is a form of sun-dried brick made with straw and asphalt, is particularly vulnerable to ground shaking. Dozens of homes are reported to have collapsed in Guadalajara, Mexico’s second largest city and capital of Jalisco. While there was little significant damage in Mexico City, buildings swayed and fearful residents remembered the magnitude 8.1, Michoacán earthquake in 1985, which occurred about the same distance away, but which killed more than 10,000 people and destroyed more than 100,000 housing units. The AIR earthquake team is analyzing the available information in the early aftermath of this event and is currently running simulations based on that information. It is important to note that considerable uncertainty still exists with regard to the actual parameters of this event. AIR will continue to monitor events and will post additional information as appropriate.

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Posting Date: January 22, 2003, 12:00:00 AM