A surface rupture was formed during the earthquake of , with a maximum recorded displacement of close to the border . The sense of movement along the rupture was almost pure strike-slip , with no vertical displacement seen . During the 1979 Imperial Valley earthquake the same section of the fault ruptured on the US side of the border , but this time there was no sign of rupture on the Mexican side . The displacement pattern of the two earthquakes was very similar on the US side , suggesting that the Imperial Fault slips in discrete patches . Two of these patches are thought to have ruptured in 1940 but only the northern one in 1979
1979 Imperial Valley earthquake
1979 Imperial Valley earthquake
1940 El Centro earthquake