Earthquakes in California are common occurrences as the state is located in a major fault zone, known as the San Andreas Fault zone, which cuts across California and forms the tectonic boundary between the Pacific and the North American Plate boundary. There are many thousands of small earthquakes per year, most of them are so small that they are not felt. ^[1] California's complex and interesting landscape can be attributed to a network of faulting running underneath the state. The earliest reported earthquake in California was felt in 1769 by the exploring expedition about 30 miles southeast of Los Angeles. ^[2]

History

California has hundreds of active faults located throughout the state which sometimes produce large earthquakes. The most active fault in California is the San Jacinto Fault, which has produced large events on a regular basis throughout recent history. The first strong earthquake listed in earthquake annals for California occurred in the Los Angeles region in 1769, probably near the San Andreas Fault. ^[3] The historical record of major earthquakes affecting California includes basic seismologic data on the largest earthquakes occurring between 1769 and 1989. The forces that shaped the earth in the past are still occurring today, as best demonstrated by California's earthquakes.

Two of the most destructive earthquake in recent California history were the 1989 Loma Prieta earthquake, which affected the San Francisco bay area, ^[4], and the 1994 Northridge earthquake which hit the Greater Los Angeles area. ^[5] Both quakes caused widespread damage and deaths in their respective regions.

Preparedness

Today, there are ways to protect and prepare possible sites of earthquakes from severe damage, through the following processes: Earthquake engineering, Earthquake preparedness, Household seismic safety, Seismic retrofit (including special fasteners, materials, and techniques), Seismic hazard, Mitigation of seismic motion, and Earthquake prediction.

The United States Geological Survey (USGS) and California Institute of Technology (Caltech) provides public education to California. They hope to provide "public education about seismic hazards and methods of reducing or preventing seismic disaster damage. The California Earthquake Authority outlined the risks earthquakes pose to California and measures households can take to "Quake Safe their house. Putting Down Roots in Earthquake Country and Dare To Prepare are some of the Earthquake Readiness Campaigns.

Putting Down Roots in Earthquake Country

Is a popular 32-page earthquake science and preparedness handbook was first published in 1995 by the SCEC. ^[6]

Southern California

Each year the southern California area has about 10,000 earthquakes. Most of them are so small that they are not felt. Only several hundred are greater than magnitude 3.0, and only about 15-20 are greater than magnitude 4.0. ^[7]

The Great Southern California ShakeOut

The Great Southern California ShakeOut is based on a potential magnitude 7.8 earthquake on the southern San Andreas Fault— approximately 5,000 times larger than the magnitude 5.4 earthquake that shook southern California on July 29, 2008. ^[8] The question is not if but when southern California will be hit by a major earthquake, one so damaging that it will permanently change lives and livelihoods in the region. The magnitude 7.8 ShakeOut earthquake is modeled to cause about 2,800 deaths and $213 billion of economic losses.

Past Earthquakes in California

1857 Fort Tejon earthquake

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The Fort Tejon earthquake occurred at about 8:20 AM (Pacific time) on January 9, 1857. It ruptured the San Andreas Fault for a length of about 350 kilometers (225 miles), between Parkfield and San Bernardino. Displacement along the fault was as much as 9 meters (30 feet) in the Carrizo Plain but less along the Palmdale section of the fault, closest to Los Angeles. The amount of fault slip gives this earthquake a moment magnitude of 7.9, comparable to that of the 1906 San Francisco earthquake. Based on the (uncertain) distribution of foreshocks for this earthquake, it is assumed that the beginning of the fault rupture (the epicenter) was in the area between Parkfield and Cholame, about 60 miles northwest. Nevertheless, it is usually called the "Fort Tejon" earthquake because this was the location of the greatest damage, most of the area being unpopulated at the time.

1868 Hayward earthquake

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The 1868 Hayward earthquake was the last large earthquake to occur on the Hayward Fault Zone in the San Francisco Bay Area, California, United States. It caused significant damage throughout the region, and was known as the "Great San Francisco Earthquake" prior to the 1906 San Francisco earthquake and fire.^[9] The earthquake occurred at 7:53 AM on October 21, 1868. Its epicenter was likely located near Hayward, California, and its magnitude has been estimated to have been 6.8–7.0 on the Richter scale.

1872 Lone Pine earthquake

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The Great Lone Pine earthquake was one of the largest earthquakes to hit California in recorded history. The quake struck on March 26, 1872 and its epicenter was near Lone Pine, California in Owens Valley. The true size of this earthquake is not known, but historical evidence detailing the damage it caused in settlements and landforms near the epicenter, and the geographic extent to which noticeable movement was felt, leads researchers to estimate a Richter magnitude of 7.6 to 8 or greater — similar in size to the 1906 San Francisco earthquake.

1906 San Francisco earthquake

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The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, CA and the coast of Northern California at 5:12 A.M. on Wednesday, April 18, 1906.^[10] The most widely-accepted estimate for the magnitude of the earthquake is a moment magnitude (M_w) of 7.8; however, other values have been proposed, from 7.7 to as high as 8.25.^[11] The main shock epicenter occurred offshore about 2 miles (3 km) from the city, near Mussel Rock. It ruptured along the San Andreas Fault both northward and southward for a total of 296 miles (477 km).^[12] Shaking was felt from Oregon to Los Angeles, and inland as far as central Nevada. The earthquake and resulting fire is remembered as one of the worst natural disasters in the history of the United States. The death toll from the earthquake and resulting fire, estimated to be above 3,000,^[13] is the greatest loss of life from a natural disaster in California's history. The economic impact has been compared with the more recent Hurricane Katrina.^[14]

1933 Long Beach earthquake

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The Long Beach earthquake of 1933 took place on March 10, 1933 at 17:55 PST (March 11, 01:55 UTC), with a magnitude of 6.4, causing widespread damage to buildings throughout Southern California. The epicenter was offshore, southeast of Long Beach on the Newport-Inglewood Fault. Forty million dollars property damage resulted, and 115 lives were lost. Many of these fatalities occurred as people ran out of buildings and were hit by falling debris.

1952 Kern County earthquake

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The 1952 Kern County earthquake occurred on July 21, 1952 in Kern County, California, with a magnitude of 7.3M_w. It was the largest earthquake to strike Southern California since the 1857 Fort Tejon earthquake and the 1872 Lone Pine earthquake, causing immense and widespread damage. The mainshock killed 12 people, injured 18 and caused over $50 million in property damage.

1971 San Fernando earthquake

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The 1971 San Fernando earthquake (also known as Sylmar earthquake) struck the San Fernando Valley near Sylmar at 6:00:55 a.m. PST on February 9 1971, with a magnitude of 6.6.^[15] There are various names for this earthquake. Seismologists call it the San Fernando earthquake. USGS 'Sylmar Quake' or 'Sylmar earthquake' is the name initially given to the event by local media outlets.

1983 Coalinga earthquake

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The 1983 Coalinga earthquake occurred on May 2, 1983 at exactly 23:42 UTC in Coalinga, California. The earthquake recorded 6.5 on the Richter scale. The earthquake was caused by creep along the San Andreas Fault.^[16] The Coalinga earthquake was felt from the Los Angeles area north to Susanville (Lassen County) and from the coast east to western Nevada. Through July 31, more than 5,000 aftershocks were recorded, of which 894 had a magnitude of 2.5 or larger. Most of the larger magnitude shocks were felt in Coalinga.

1987 Whittier Narrows earthquake

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The Whittier Narrows earthquake struck the southern San Gabriel Valley and surrounding communities of southern California at 7:42 a.m. (Pacific Daylight Time) on October 1, 1987. The magnitude 5.9 earthquake was originally assigned a magnitude of 6.0 but was revised a few days later when additional data became available. Its epicenter was actually in the town of Rosemead, California, at a depth of 11 km.

1989 Loma Prieta earthquake

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The Loma Prieta earthquake, also known as the Quake of '89 and the World Series Quake, was a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989 at 5:04 p.m. local time. Caused by a slip along the San Andreas Fault, the earthquake lasted approximately 15 seconds and measured 6.9 on the moment magnitude scale (surface-wave magnitude 7.1).^[17] The quake killed 63 people throughout northern California, injured 3,757 people and left some 8,000^[18] to 12,000 people homeless.^[19]

The earthquake occurred during the warm-up for the third game of the 1989 World Series, coincidentally featuring both of the Bay Area's Major League Baseball teams, the Oakland Athletics and the San Francisco Giants. This was the first major earthquake in America to be broadcast on live television.

1992 Landers earthquake

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The 1992 Landers Earthquake was a magnitude 7.3 earthquake on June 28, 1992 in California's Yucca Valley, near the town of Landers, California.^[20] The quake was described at the time as the largest earthquake to have occurred in the contiguous United States in 40 years.^[21]

1992 Big Bear earthquake

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The 1992 Big Bear earthquake was an earthquake that occurred on 28 June 1992 in Big Bear Lake, California, with a magnitude of 6.4. This earthquake occurred three hours after the 7.3 magnitude Landers earthquake, also in California. The closely-timed occurrence of these earthquakes is an often-cited example of a regional earthquake sequence.^[22]

1994 Northridge Earthquake

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The Northridge earthquake occurred on January 17 1994 at 4:31 AM Pacific Standard Time in Reseda, a neighborhood in the city of Los Angeles, California, lasting for about 20 seconds.^[23] The earthquake had a "strong" moment magnitude of 6.7, but the ground acceleration was one of the highest ever instrumentally recorded in an urban area in North America.^[24] Seventy-two deaths were attributed to the earthquake, with more than 9,000 injured. In addition, the earthquake caused an estimated $20 billion in damage, making it one of the costliest natural disasters in U.S. history.^[25]

1995 Ridgecrest Earthquake

The area, associated with the Eastern California Shear Zone (ECSZ), has experienced numerous earthquake swarms in the past (groups of several thousand quakes under magnitude 6.0 or so) often with no obvious mainshock. The 1995 Ridgecrest earthquake sequence started on August 17, when a Template:Dn 5.5 quake, centered 18 kilometers north of the town of Ridgecrest, shook the area and spawned over 2,500 aftershocks over the course of the following five weeks. Then, on September 20, 1995, the second large quake struck the area: it measured magnitude 6.0, and was at that time the largest earthquake to hit southern California since the January 17, 1994 Northridge earthquake.

1999 Hector Mine earthquake

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The 1999 Hector Mine earthquake was a magnitude 7.1 earthquake that occurred on October 16 1999 at 2:46:44 PDT 47 Miles ESE of Barstow, California. The earthquake occurred in a remote part of the Mojave Desert, inside the Twentynine Palms marine corps base. Its name comes from a nearby quarry named Hector Mine, which is located 22 kilometres (14 mi) northwest of the epicenter.

The earthquake was so strong that it was felt for 20–30 seconds in Las Vegas, Nevada. Many people were awakened in Las Vegas, with many reporting dizziness or trouble walking. Reports were filed as far north as Carson City, Nevada, where one woman reported waking up, hearing chimes in her house ringing. It was also felt to the southwest in Los Angeles.

2000 - 2009 Earthquakes

This section documents past events. This section may need to be updated.

2003 San Simeon earthquake

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The 2003 San Simeon Earthquake was a magnitude 6.5 earthquake on the Central Coast of California, about 7 miles northeast of San Simeon. It occurred at 11:15 PST (19:15 UTC) on December 22, 2003. The earthquake probably occurred on the Oceanic fault zone in the Santa Lucia Mountains. It was caused by reverse faulting and propagated southeast from the hypocenter for 12 miles (19 km).

2007 Alum Rock earthquake

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The 2007 Alum Rock earthquake occurred on October 30, 2007 at approximately 8:04 p.m. PDT (October 31, 3:04 a.m. UTC)^[26] in the San Jose area in California. It measured 5.6 on the moment magnitude scale and had a depth of 5.7 miles.^[27]

2008 Chino Hills earthquake

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The 2008 Chino Hills earthquake occurred at 11:42:15 am PDT (18:42:15 UTC) on July 29, 2008, in Southern California.^[28] The epicenter of the magnitude 5.4 earthquake was in Chino Hills, approximately 28 miles (45 km) east-southeast of downtown Los Angeles.^[28] Though no lives were lost during the earthquake, it caused considerable damage in numerous structures throughout the area and caused some amusement park facilities to shut down their rides. The earthquake led to increased discussion regarding the possibility of a stronger earthquake.

2009 Inglewood earthquake

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The 2009 Inglewood earthquake occurred on May 17, 2009 at 8:39:36 pm PDT (May 18, 2009 at 3:39:36 UTC), in Southern California.^[29] The earthquake was originally listed as a magnitude 5.0 but it was later downgraded to a magnitude 4.7. As of 1400 UTC, no reports of serious damage or injury were made. ^[30] The epicenter of the earthquake was located in the city of Inglewood immediately west of the Morningside High School campus and approximately ten miles (16 km) southwest of downtown Los Angeles at a depth of 13.5 km. The shaking was felt as far away as San Diego and Palm Springs and was likely felt within a 100 mile (160 km) radius according to the USGS; the distance of both of those cities from the epicenter support the theory.^[31]

There have been reports of broken windows in Long Beach. KCAL 9 showed live news video of a Long Beach street with broken glass and debris in the middle. Also South Bay Galleria had broken windows, falling ceiling tiles in the AMC theater, and one report of a movie screen falling. Two days later, a light earthquake occurred at 3:49:11 PM (PDT) on Tuesday, May 19, 2009. The magnitude 4.0 event occurred 2 km (1 miles) NNE (33 degrees) of Hawthorne, CA. The hypocentral depth is 15 km (10 miles).

Seismological data centers

California

• Southern California Earthquake Data Center
• The Southern California Earthquake Center (SCEC)
• Putting Down Roots in Earthquake Country An Earthquake Science and Preparedness Handbook produced by SCEC
• Recent earthquakes in California and Nevada
• Incorporated Research Institutions for Seismology (IRIS), earthquake database and software
• IRIS Seismic Monitor - world map of recent earthquakes
• SeismoArchives - seismogram archives of significant earthquakes of the world
• UCSD Broadband Seismic Data Collection Center - small localized broadband seismic network monitoring the San Jacinto and San Andreas fault zones, located in Southern California

See also

References

External links

• U.S. Geological Survey, Menlo Park Northern California - USGS
• University of California, Berkeley Northern California - UCB
• U.S. Geological Survey, Pasadena Southern California - USGS
• California Institute of Technology Southern California - Caltech
• University of California, San Diego Southern California - UCSD