The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the U.S. state of California. It forms part of the tectonic boundary between the Pacific plate and the North American plate. Traditionally, for scientific purposes, the fault has been classified into three main segments, each with different characteristics and a different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm per year.
The White Wolf Fault is a fault in southern California, located along the northwestern transition of the Tejon Hills and Tehachapi Mountains with the San Joaquin Valley. It is north of the intersection of the San Andreas Fault and the Garlock Fault, and roughly parallel with the latter. It is classed as a reverse fault with a left lateral (sinistral) component.
The San Jacinto Fault Zone (SJFZ) is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area. Together they relieve the majority of the stress between the Pacific and North American tectonic plates.
The 2010 Baja California earthquake occurred on April 4 with a moment magnitude of 7.2 and a maximum Mercalli intensity of VII. The shock originated at south of Guadalupe Victoria, Baja California, Mexico.
The Imperial Fault Zone is a system of geological faults located in Imperial County in the Southern California region, and adjacent Baja California state in Mexico. It cuts across the border between the United States and Mexico.
Cerro Prieto is a volcano located approximately 29 km (18 mi) SSE of Mexicali in the Mexican state of Baja California. The volcano lies astride a spreading center associated with the East Pacific Rise. This spreading center is also responsible for a large geothermal field, which has been harnessed to generate electric power by the Cerro Prieto Geothermal Power Station.
The 1940 El Centro earthquake occurred at 21:35 Pacific Standard Time on May 18 in the Imperial Valley in southeastern Southern California near the international border of the United States and Mexico. It had a moment magnitude of 6.9 and a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. It was the first major earthquake to be recorded by a strong-motion seismograph located next to a fault rupture. The earthquake was characterized as a typical moderate-sized destructive event with a complex energy release signature. It was the strongest recorded earthquake in the Imperial Valley, causing widespread damage to irrigation systems and killing nine people.
The Salton Trough is an active tectonic pull-apart basin, or graben. It lies within the Imperial, Riverside, and San Diego counties of southeastern California and extends south of the Mexico–United States border into the state of Baja California.
The 1892 Laguna Salada earthquake occurred at . It had an estimated moment magnitude of 7.1–7.2 and a maximum perceived intensity of VIII (Severe). The shock was centered near the Mexico–United States border and takes its name from a large dry lake bed in Baja California, Mexico. There were no reported casualties, but the event affected the then largely-uninhabited areas of northern Mexico and Southern California.
The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Daylight Time on 15 October just south of the Mexico–United States border. It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California. The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at US$30 million. The irrigation systems in the Imperial Valley were badly affected, but no deaths occurred. It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier.
The 1979 Coyote Lake earthquake occurred at on August 6 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. The shock occurred on the Calaveras Fault near Coyote Lake in Santa Clara County, California and resulted in a number of injuries, including some that required hospitalization. Most of the $500,000 in damage that was caused was non-structural, but several businesses were closed for repairs. Data from numerous strong motion instruments was used to determine the type, depth, and extent of slip. A non-destructive aftershock sequence that lasted throughout the remainder of the month was of interest to seismologists, especially with regard to fault creep, and following the event local governments evaluated their response to the incident.
The 1918 San Jacinto earthquake occurred in extreme eastern San Diego County in Southern California on April 21 at . The shock had a moment magnitude of 6.7 and a maximum Mercalli intensity of IX (Violent). Several injuries and one death occurred with total losses estimated to be $200,000.
Lake Cahuilla was a prehistoric lake in California and northern Mexico. Located in the Coachella and Imperial valleys, it covered surface areas of 5,700 km2 (2,200 sq mi) to a height of 12 m (39 ft) above sea level during the Holocene. During earlier stages of the Pleistocene, the lake reached even higher elevations, up to 31–52 m (102–171 ft) above sea level. During the Holocene most of the water came from the Colorado River with little contribution from local runoff; in the Pleistocene local runoff was higher and it is possible that Lake Cahuilla was supported solely from local water sources during the Wisconsin glaciation. The lake overflowed close to Cerro Prieto into the Rio Hardy, eventually draining into the Gulf of California.
The Salton Buttes are a group of volcanoes in Southern California, on the Salton Sea. They consist of a 7-kilometer (4.3 mi)-long row of five lava domes, named Mullet Island, North Red Hill, Obsidian Butte, Rock Hill and South Red Hill. They are closely associated with a fumarolic field and a geothermal field, and there is evidence of buried volcanoes underground. In pre-modern times Obsidian Butte was an important regional source of obsidian.
The 1981 Westmorland earthquake occurred at 05:09 Pacific Daylight Time on April 26. The moderate strike-slip shock took place in the Imperial Valley of Southern California, just north of the Mexico–United States border. No injuries or deaths occurred, but damage was estimated at $1–3 million. With a Mercalli intensity of VII, this was one of fifteen intensity VII or greater shocks in the Imperial Valley that were observed in the 20th century up until April 1981. The region experiences large stand-alone events and earthquake swarms due to its position in an area of complex conditions where faulting transitions from strike-slip movement to the north and divergence to the south.
The 1987 Superstition Hills earthquake affected the Imperial Valley of California and Baja California on November 24, nearly 12 hours after a 6.0 foreshock, called the Elmore Ranch earthquake. The mainshock, measuring 6.5, struck at 17:54 PST, along the Superstition Hills segment of the San Jacinto Fault Zone. The earthquake generated a 27 km (17 mi) surface rupture with additional postseismic slip continuing for a year.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST in the geologically active Salton Trough of Southern California. The Salton Trough represents a pull-apart basin formed by movements along major faults. This region is dominated by major strike-slip faults one of them being the San Jacinto Fault which produced the 1968 earthquake. The mainshock's epicenter was near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). The zone of surface rupture was assigned a maximum Modified Mercalli intensity (MMI) of VII.
The 1899 San Jacinto earthquake occurred on Christmas morning at 04:25 local time in Southern California. The estimated moment magnitude 6.7 earthquake had an epicenter located 10 miles southeast of San Jacinto. The earthquake had a maximum Mercalli intensity of IX (Violent). Severe damage occurred, amounting to US$50,000, as well as six fatalities.
The 1915 Imperial Valley earthquakes were two destructive shocks centered near El Centro, California on June 22. The earthquakes measured 6.25 and occurred nearly one hour apart at 19:59 and 20:57 PST. Both shocks were assigned VIII (Severe) on the Modified Mercalli intensity scale. Heavy damage occurred in the areas of Mexicali and El Centro, amounting to $900,000. At least six people were killed in the earthquakes.
