1968 Borrego Mountain Earthquake

A Look Back at Southern California’s Biggest Quake in Decades

As a resident of Borrego Springs, you know that living in southern California means living with the risk of earthquakes. Although you’ve probably felt your fair share of tremors over the years, there’s one quake that stands out in your memory: the Borrego Mountain earthquake of 1968.

A Seismic Event of Epic Proportions

On April 8, 1968, at 6:29 pm PST, the Borrego Mountain earthquake struck southern California with a magnitude of MW 6.5. The quake was caused by right-lateral strike-slip faulting, and its epicenter was located about 1 mile north of Ocotillo Wells, and 40 miles south of Indio. The earthquake occurred at a depth of 20 km and caused minor surface rupture along the Coyote Creek fault, which is a branch of the San Jacinto Fault Zone.

TYPE OF FAULTING:  right-lateral strike-slip
TIME: April 8, 1968 / 6:29 pm PST
LOCATION: 33° 09′ N, 116° 07.5′ W about 1.5 km (1 mile) north of Ocotillo Wells about 64 km (40 miles) south of Indio
MAGNITUDE: M _W  6.5

DEPTH: 20 km
SURFACE RUPTURE LENGTH: about 33 km
FAULT RUPTURED:  Coyote Creek fault  (a branch of the San Jacinto Fault Zone); others offset slightly

The Borrego Mountain Earthquake: Facts and Figures

The Borrego Mountain earthquake was the largest and most damaging quake to hit southern California since the Kern County earthquake 16 years earlier. The quake was felt as far away as Las Vegas, Fresno, and Yosemite Valley, and it caused damage across most of southern California. The surface rupture caused by the quake was approximately 33 km long, and it triggered small displacements along several faults in the region.

Damage and Destruction Across Southern California

The Borrego Mountain earthquake caused significant damage and disruption throughout southern California. Power lines were severed in San Diego County, plaster cracked in Los Angeles, and the Queen Mary in drydock at Long Beach rocked back and forth on its keel blocks for 5 minutes. Close to the epicenter, the quake caused landslides, hurling large boulders downslope and damaging campers’ vehicles at Anza-Borrego Desert State Park. The quake also caused minor surface rupture, cracking Highway 78 at Ocotillo Wells. In total, the earthquake caused millions of dollars in damage and left a lasting impact on the region.

Triggered Slip: An Intriguing Result of the Quake

One of the most intriguing features of the Borrego Mountain earthquake was the small displacements it caused along several faults in the region. These fresh breaks and displacements were not noticed immediately after the mainshock, but they were likely caused by the quake. These are probably among the first noted instances of triggered slip, and they continue to be studied by scientists and researchers today.

Remembering the Borrego Mountain Earthquake

The Borrego Mountain earthquake of 1968 was a seismic event that shook southern California to its core. Although it caused significant damage and disruption, it also led to new discoveries and insights into earthquake science. As a resident of Borrego Springs, it’s important to remember this event and to be prepared for future seismic activity. By staying informed and taking the necessary precautions, we can help ensure the safety and well-being of our community.