Imperial Valley, California
1915 June 23 03:59 UTC (local time June 22)
1915 June 23 04:56 UTC (local time June 22)
Magnitude 6.3 and 6.3
Two destructive earthquakes wrecked buildings, overturned chimneys, and knocked down walls in the Calexico-El Centro area. The second shock, which was as strong as the first, completed the destruction of the buildings that already were weakened. This shock killed six people in Mexicali, Mexico. A foreshock occurred at 03 50 UTC.
The area of heaviest property damage extended from Mexicali north to Calexico, El Centro, and Heber, where almost every brick and adobe building was damaged. Property loss, estimated at $900,000 for both Mexico and the United States, was due as much to the poor quality of construction as to the intensity of the earthquake. Damage at El Centro, the largest city in the Imperial Valley at this time, was estimated at $600,000. Property damage in Calexico, Heber, and Mexicali was almost as severe, but the rebuilding cost was less because the towns were much smaller than El Centro.
A few cracks formed in the alluvium parallel to the levees in the Imperial Valley, but the irrigation ditches were damaged only slightly, if at all. Many unstable banks of the Alamo and New Rivers slid into the water; cracks formed in the marshy bed of the New River northwest of El Centro. Residents about 25 km north of the mud volcanoes, which are west of Laguna de los Volcanes, Mexico (about 40 km south of Calexico), reported that columns of steam were seen rising from the vents for several days following the earthquakes and that occasional explosions were heard from that direction.
A foreshock occurred about 20 minutes before the first shock, and several aftershocks occurred through August 1915. The main earthquakes were felt north to Los Angeles and San Bernardino, east to Parker and Yuma, Arizona, and south at least to Ensenada, Mexico, and probably farther.
Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.