On November 29, 1978, a moment magnitude 7.7–7.8 earthquake struck off the coast of the southern Mexican state Oaxaca.

The subduction zone is a large thrust fault that has produced devastating earthquakes in human history.

The earthquake ruptured an area of 5,525 km3 along with the boundary interface of the Cocos and North American plates.

[3] The earthquake ruptured about 80 percent of the segment designated a seismic gap and produced slip of 1.48 m (4 ft 10 in).

The other was the 5.9 magnitude 1975 Oroville earthquake in California, both due to irregular seismic activities in the area before the main shock.