April 21, 1918 Earthquake: San Jacinto, Hemet, California, United States

1918 April 22. Riverside County. San Jacinto and Hemet suffered heavy damage. Only one new concrete and one frame building remained standing in the business section of San Jacinto after the shock. The buildings wrecked were brick or artificial stone of poor construction, or old frame buildings. Concrete, substantial frame, and well constructed brick buildings were not damaged seriously. Property loss in the two places was in excess of $200,000. If the shock had occurred during business hours, instead of on Sunday afternoon, the loss of life would have been considerable. Numerous lengthwise cracks were found in the road between the two towns named, and concrete irrigation canals were broken in a number of places.

Damage corresponding to intensity VI and VII also occurred at Redlands, Riverside, and San Bernardino, and as far away as Los Angeles the intensity was a high V. The disturbance was most intense along about 10 miles of the San Jacinto Fault in the vicinity of San Jacinto. Roads in the epicentral area were closed to travel by slides, and one automobile was carried off the road by a slide. Because of the extreme dryness of the ground, great clouds of dust arose from the mountains. Changes occurred in the water flow and springs either increased or decreased their output. A number of sand or mud craterlets were formed. In the region of the San Jacinto Fault southeast of Hemet, the dry earth surface in places was broken up as though by a harrow. The shock was felt as far northwest as Fresno and Los Olivos, Santa Barbara County, east into Arizona, and undoubtedly a considerable distance into Mexico. Magnitude 6.8. There was a strong aftershock on April 22 near 08:00 that brought down tottering walls, and other shocks continued for weeks, the strongest occurring on June 6. (reference #1128)

LOCATION: 33° 45' N, 116° 53' W near the town of San Jacinto about 112 km (70 miles) ESE of Los Angeles MAGNITUDE: roughly ML6.8. While the damage caused by the San Jacinto earthquake of 1918 was high, its timing was fortunate, and kept the number of fatalities and injuries low. Most of the damage caused by the quake occurred in the business districts of the towns of San Jacinto and Hemet, where large masonry structures collapsed in the shaking. Luckily, the quake struck on a Sunday afternoon, when the business districts were empty. Still, as it was, several people were injured and one death was reported. Two miners were trapped in a mine near Winchester, but were eventually rescued, uninjured. In another display of amazingly good fortune, two men in an automobile were swept off a road by a landslide, and would have rolled several hundred feet down a hillside had they not been stopped by a large tree, before they had moved far very off the road at all. The shaking cracked the ground, concrete roads, and concrete irrigating canals, but none of the cracks left behind were thought to represent actually surface rupture, though in one place, the alignment of a road was said to be off by about 7.5 centimeters (3 inches). Landslides, as mentioned above, were triggered, and the road from Hemet to Idyllwild was blocked in several places. Huge boulders rolled down nearby slopes. The flow rates of several springs in the area were altered, and it is claimed that the temperature of nearby hot springs changed. Sand craters were formed on one farm, and an area near Blackburn Ranch seemed to have "sunk" roughly one meter during the quake. The earthquake caused minor damage outside the San Jacinto area, as well, and was felt as far away as Taft (west of Bakersfield), Seligman (Arizona), and Baja California. (reference #13509)

1918-04-21 22:32:30.35 UTC, 33.762 N 116.972 W, magnitude 6.7 Mw. (reference #10476, v.10)