The Victoria, Mexico, Earthquake of June 9, 1980

Abstract

The Victoria earthquake of June 9, 1980 (ML = 6.1 ), occurred in the Mexicali Valley near the trace of the Cerro Prieto fault with a focal mechanism consisting of a dextral strike-slip motion on a vertical fault. We present results from an analysis of local data concerning ground surface effects, epicenter locations, and focal mechanisms of the main shock and its aftershock activity. A field reconnaissance showed no clear ground surface displacement related to the main shock. The aftershocks occurred northwest of the main shock epicenter, in a few clusters at or near the northwest end of the Cerro Prieto fault. There was some aftershock activity north of the Cerro Prieto fault tip and towards the southeast end of the Imperial fault. Only a few aftershocks were located near the main shock; they occurred during the first few hours after the main event. The aftershock activity was mainly located between 3 and 8 km in depth, beneath the thick overlying sediments. The average depth of the aftershocks generally decreases to the northwest, away from the main epicenter which is at a depth of about 9 km. Composite focal mechanisms of the aftershocks show a right-lateral strike-slip motion on a vertical plane striking N45°W for the cluster near the main shock epicenter, and normal faulting for the cluster at the northwest end of the Cerro Prieto fault. Two small tightly clustered earthquake swarms occurred a few hours before the main shock.