San Jacinto Fault Zone - Earthquakes

Earthquakes

See also: List of earthquakes in California

February 9, 1890 earthquake

An early morning event measuring 6.3 occurred in northeast San Diego County that was reported with a maximum intensity of MM VI at all Southern Pacific stations between Pomona to Yuma, Arizona. The railroad line runs near both the San Andreas and San Jacinto fault traces northeast of Riverside, and through San Gorgonio Pass (near the Banning Fault). Since the event was felt equally at the railroad stations, Sanders and Kanamori submitted that the earthquake was most likely not a result of slip of any fault strand near the railroad, and that a more probable source of the event would be farther south along the SJFZ near Anza, though this contradicted the report from the 1995 Working Group on California Earthquake Probabilities, which placed the earthquake on the northernmost San Bernardino segment of the SJFZ. (33°4′N 116°30′W / 33.067°N 116.500°W / 33.067; -116.500)

May 28, 1892 earthquake

Another earthquake with an approximate magnitude of 6.5 occurred in the same region and delivered similar effects as the 1890 shock. Felt reports came from San Diego, Los Angeles, and Yuma, Arizona. Two shocks were reportedly felt at San Bernardino and Ontario at 3:15 and again at 3:20 am with the direction of the vibrations moving from east to west. The first shock was described as being very heavy and that it had broken dishes and stopped clocks. It is possible that it was an aftershock of the February 1892 Laguna Salada earthquake. (33°12′N 116°12′W / 33.2°N 116.20°W / 33.2; -116.20)

1899 San Jacinto earthquake

On December 25, with a maximum intensity of MM IX, this magnitude 6.6 earthquake destroyed San Jacinto and Hemet and six were killed by adobe walls that collapsed at Saboba (just east of San Jacinto). A 46 m (151 ft) fissure, which may have been surface rupture of the San Jacinto Fault, ran under a house that was severely damaged near Hemet. The effects of the early morning earthquake were severe. Not all the buildings in San Jacinto were completely destroyed by the thirty seconds of shaking, but most of the brick buildings' second floors were heavily damaged. (33°48′N 117°00′W / 33.8°N 117.0°W / 33.8; -117.0)

1918 San Jacinto earthquake

On April 21, a magnitude 6.6 earthquake caused major damage in the same area as the 1899 San Jacinto earthquake, with several injuries and one death occurring there. Many of the buildings in San Jacinto's business district were of poor construction and all but one frame building and one concrete building collapsed though high quality structures did not experience serious damage. Minor damage to other buildings within 160 kilometers (99 mi) of San Jacinto also occurred. Roadways and irrigation canals also sustained damage and small sand blows were seen on a farm near San Jacinto. (33°48′N 117°00′W / 33.8°N 117.0°W / 33.8; -117.0)

The earthquake occurred on a Sunday afternoon when most of the businesses in San Jacinto were closed and void of customers. According to a 1918 report by Sidney Townley, it was there in the business district that damage was the greatest, though Hemet was also severely damaged. The area was surveyed for three days about a week following the event, and Townley acknowledged that damage to chimneys, windows, and plaster walls occurred to buildings and structures within one hundred miles of San Jacinto, but not all locations with damage were surveyed. Some of the damage that was inspected included landslides, partially collapsed buildings, and damaged irrigation canals and roads. Ground cracks were observed near the banks of the San Jacinto river and sand blows were seen on a farm northwest of San Jacinto.

1923 North San Jacinto Fault earthquake

On July 23, a magnitude 6.0 earthquake damaged numerous buildings in the area surrounding San Bernardino and Redlands. The San Bernardino County Courthouse and Hall of Records was damaged beyond repair and was ultimately rebuilt. The large brick building housing the Patton State Hospital (also in San Bernardino) was closed then demolished because of the severe damage. No one was killed in the quake but two were critically injured. (34°00′N 117°18′W / 34.0°N 117.3°W / 34.0; -117.3)

1937 Terwilliger Valley earthquake

On March 25, a magnitude 5.9 earthquake occurred in San Diego County. Damage was limited as a result of the epicenter being located away from population centers, but some damage to chimneys and windows was found in Anza, Hemet, and Palm Springs. The maximum felt intensity was MM VI. (33°24′N 116°12′W / 33.4°N 116.2°W / 33.4; -116.2)

1942 Fish Creek Mountains earthquake

On October 21, a magnitude 6.0 event occurred near Borrego Valley. Landslides damaged a railroad bridge 19 kilometers (12 mi) north of Jacumba. Minor damage was also reported in several towns in the area and several aftershocks were felt. (33°00′N 116°00′W / 33.0°N 116.0°W / 33.0; -116.0)

1954 Arroyo Salada earthquake

On March 19, an early morning magnitude 6.2 earthquake rattled much of southern California. Damage included broken water pipes, cracked walls and swimming pools, and broken windows. The earthquake was felt over a wide area including western Arizona and southwestern Nevada. Several aftershocks followed with the strongest occurring later the same day. The event occurred at 2 am local time and was described as two separate motions that took place within 10–15 seconds. Though the quake was reportedly felt in adjacent states the Kern County Sheriff stated that the rolling movements were not felt there. Kern County was the scene of the 1952 Kern County earthquake. (33°18′N 116°12′W / 33.3°N 116.2°W / 33.3; -116.2)

1968 Borrego Mountain earthquake

On April 9, a magnitude 6.4 M_L earthquake with a maximum perceived intensity of MM VII hit the extreme eastern San Diego County area and created a 31 km (19 mi) surface break along the Coyote Creek Fault. California State Route 78 was damaged with cracks near Ocotillo Wells and large boulders blocked the Montezuma-Borrego Springs Highway. Other rockslides occurred at Palm Canyon and Split Mountain in Anza-Borrego Desert State Park. One house was split apart in Ocotillo Wells with one bedroom becoming detached from the rest of the home. The mainshock was felt in Arizona and Nevada and the largest aftershock damaged a theater's walls in Calexico near the United States - Mexico border.

According to a report in the Los Angeles Times, this was the strongest earthquake to affect southern California since the Tehachapi earthquake fifteen years earlier. Taller buildings swayed in both Los Angeles and San Diego and power outages affected numerous areas, primarily in the cities of Imperial Valley. Power failures along with disruption to telephone service caused problems in the Hemet Valley area, and smaller power outages in Los Angeles and Orange Counties also occurred. A brick wall collapsed at a laundromat in Westmorland (in the El Centro Metropolitan Area) but no one was injured, and in the seaside neighborhoods of San Diego county several hundred windows were broken. Charles Richter, a Caltech seismologist, stated that the earthquake was centered near Ocotillo Wells about 120 mi (190 km) southeast of Los Angeles. The mainshock occurred at 6:28 pm and aftershocks continued through the evening, but were tapering off by 10 pm. (33°12′N 116°06′W / 33.2°N 116.1°W / 33.2; -116.1)

1987 Superstition Hills and Elmore Ranch earthquakes

See also: Brawley Seismic Zone

Two earthquakes in late November caused property damage totaling three million in Imperial County. The two events were separated by eleven hours and were located in the western Imperial Valley on the Superstition Hills Fault and a previously unknown fault. Damage in Westmoreland, Imperial, and El Centro consisted of collapsed chimneys, broken windows, and damaged highways. The Worthington Road bridge, at the New River, failed due to liquefaction and at the Desert Test Range Control Center, water tanks toppled into the building and other equipment crashed through a window. Activities were suspended there for several days due to the damage. The Southern California Irrigation District estimated damage to be $600,000 – $750,000. The initial shock produced a small amount of deformation in the canal's liner while the second main shock caused considerable damage to thousands of feet of canal lining in the northwest section of the valley.

Several foreshocks preceded the main shocks and a series of aftershocks included two in the range of magnitude five. On the Mexican side of the border, 50 injuries and two deaths were reported, and 44 were treated for their injuries in California. According to the spokesperson for the state of Baja California, a motor vehicle accident east of Mexicali that claimed the lives of a mother and her four year old son was blamed on the earthquake. Thomas H. Heaton, a USGS seismologist, stated that the faults in the area are difficult to track down because of the sediment deposited in the valley, which had been an intermittent drainage basin of the Colorado River.

The Superstition Hills fault (SHF) lies between the Coyote Creek fault that ruptured during the 1968 event and the Imperial Fault that ruptured during the 1940 El Centro earthquake and the 1979 Imperial Valley earthquake. To the northeast are several cross faults that trend northeast. One of these faults ruptured during a large aftershock of the 1979 event and another slipped as the smaller of the two shocks during the November 1987 sequence. The first shock (on what became known as the Elmore Ranch fault) measured 6.2 M_s and the shock 11.4 hours later on the SHF measured 6.6 M_s. (33°06′N 115°48′W / 33.1°N 115.8°W / 33.1; -115.8 & 33°00′N 115°48′W / 33.0°N 115.8°W / 33.0; -115.8)