Historic Earthquakes

Magnitude 7.0 CENTRAL MEXICO
1999 June 15 20:42:05 UTC

Map of 3 earthquakes in the region

The June 15, 1999, magnitude 7.0 earthquake in CENTRAL MEXICO, occurred in the State of Puebla and was located about 20 km (13 mi) southeast of Tehuacan, and about 230 km (145 mi) east-southeast of Mexico City. It happened at 3:42 PM local time (CDT) and was felt thoughout southern Mexico.

 Date         Latitude      Longitude	Depth	 Magnitude
 1973 08 28    18.20N        96.60W      75 km    7.3 (Ms)
 1985 09 15    17.97N        97.16W      64 km    6.1 (Ms) 
 1999 06 15    18.41N        97.34W      80 km    7.0 (Mw)

This table shows the June 15 event in relation to two other similar earthquakes that hit this region (the magnitude and location of the June 15 quake may change slightly as additional data are received from other seismograph stations). None of these earthquakes is near the surface and therefore they were unable to make direct hits on population centers by surface faulting. Although earthquakes in this depth range of 60-80 km are capable of causing significant losses, these losses typically are much less than caused by the same sized earthquakes striking near the Earth's surface. Nevertheless, the large 1973 earthquake caused over 625 deaths, in Ciudad Serdan and in many locales in the States of Puebla and Veracruz. The very destructive, magnitude 8.1, 1985 Michoacan earthquake occurred far to the west of these earthquakes, at the Pacific coast of Mexico, and represents a different seismic source zone. The June 15 earthquake occurred well east of the Pacific coast and just south of the east-trending Trans-Mexican Volcanic Belt.

Today, seismologists can explain why most earthquakes occur in terms of plate tectonics. Here is a brief description for the tectonic setting and origin of the June 15 earthquake. The Cocos plate is moving northeastward and collides with the Pacific coast of Mexico (part of the North American plate). The Cocos plate moves beneath (subducts) coastal Mexico and leads to earthquakes such as the 1985 Michoacan event. The subduction of the Cocos plate continues to deepen and the earthquakes in the above table occurred within the subducting Cocos plate. These earthquakes probably were caused by the sinking of the Cocos plate. As the subduction of the Cocos plate continues to the northeast, it leads to formation of the Trans-Mexican Volcanic Belt (volcanoes typically form about 100 km above the surface of a subducting plate).