The Rivera Plate is believed to have separated from the Cocos Plate
located to its southeast about 5–10 million years ago. Seismicity and tomography images show that the Rivera plate dips at 40° beneath the forearc region and then dips ~70° beneath the Trans-Mexican Volcanic Belt
. The subduction of the Rivera Plate under the North American Plate, in the Mid-American Trench, has been the cause of the strongest earthquakes in the history of Mexico, including the largest earthquake in Mexico during the 20th century which occurred on June 3, 1932 in the state of Jalisco
. The quake had a magnitude of 8.2 with a magnitude 7.8 aftershock, both of which caused widespread casualties and damage.