1978 Oaxaca earthquake

Along the west coast of Mexico, the Rivera, Cocos and Nazca Plate dives beneath the North American and Caribbean Plate in a process known as subduction. This occurs along the Middle America Trench which runs from Mexico down to Costa Rica for over 2,750 km. The subduction zone is a large thrust fault that has produced devastating earthquakes in human history. Subduction has also resulted in volcanic activity in central Mexico.

The earthquake ruptured an area of 5525 kilometer square along the boundary interface of the Cocos and North American Plates.[1] That particular segment has not produced any large earthquakes since 1928 and 1931 and thus considered a seismic gap. A major earthquake of magnitude 7.5 ± 2.5 was forecasted at that area in 1973.[2]

Maximum intensity in the Oaxaca area reached VIII (Severe) on the Mercalli intensity scale.

Nine people were killed, eight of those were from Mexico City one from Oaxaca. A few buildings in Mexico City had minor damage to it, this was contrary to the numerous newspaper reports that many buildings had collapsed. Eyewitness reported many buildings swaying during the earthquake. Two buildings, the Treasury Building and another owned by the Bank of Mexico suffered considerable damage to their external.[3]