California Earthquake Risk Map & Faults By County

North Coast

Counties: Del Norte, Humboldt, Lake, Mendocino

• The Cascadia Subduction Zone stretches underneath the Humboldt-Del Norte county region, extending from Cape Mendocino all the way up through the Pacific Northwest.
• This fault zone is capable of generating a magnitude 9 (or larger) earthquake on average every 500 years. The last such event was in 1700.
• Scientists report that partial ruptures on the southern half of the Cascadia Seismic Zone (which extends into Northern California) have historically generated earthquakes with magnitude 8 or greater.
• Recently, on Dec. 20th, 2022, a magnitude 6.4 quake struck a few miles off the coast of Humboldt County, followed by at least a dozen smaller aftershocks.
• Very large earthquakes occurring close to the coast could cause damaging levels of ground shaking and tsunami waves.  
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 76% probability of one or more magnitude 7.0 earthquakes striking Northern California is based on a 30-year period, beginning in 2014.

Shasta Cascade

Counties: Butte, Glenn, Lassen, Modoc, Plumas, Shasta, Sierra, Siskiyou, Tehama, Trinity

• The Trinity Mountains, Modoc Plateau, Shasta and Lassen peaks were created by geologic forces that are still shaping the landscape. In addition to volcanoes, this is also earthquake country.
• The Modoc Plateau has both active volcanoes and faults. 
• Much of the north-eastern part of the state is actively stretching apart, creating numerous faults, all capable of producing earthquakes. 
• Very large earthquakes that occur closer to the Northern California coast could cause damaging levels of ground shaking here too. Even moderate shaking can damage seismically-vulnerable structures and trigger landslides that could quickly block roads and highways.
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 76% probability of one or more magnitude 7.0 earthquakes striking Northern California is based on a 30-year period, beginning in 2014.

Greater Bay Area

Counties: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, Sonoma

What is the Earthquake Risk in San Francisco

• The greater San Francisco Bay Area has a high likelihood of future damaging earthquakes as it straddles the San Andreas fault system—the major geologic boundary between the North American and Pacific tectonic plates.
• The main trace of the San Andreas fault runs through much of the State of California, including the Santa Cruz Mountains, up the San Francisco Peninsula, and along the Marin and Sonoma County coasts.
• The Calaveras and Hayward faults extend up the east side of the San Francisco Bay. These and several other major faults in the region are part of the San Andreas fault system and can cause damaging earthquakes, like the 1989 Loma Prieta earthquake. 
• Scientists predict that within a 30-year period (beginning in 2014), there’s a 51 percent chance that the San Francisco region specifically will experience one or more magnitude-7.0 or greater earthquakes. And there’s a 98% chance of one or more magnitude-6.0 or greater quakes hitting the Bay Area in that same timeframe. 
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.
• Learn more about if a seismic retrofit worth it in San Francisco

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 76% probability of one or more magnitude 7.0 earthquakes striking Northern California is based on a 30-year period, beginning in 2014.

Delta, Sierra and Greater Sacramento Areas

Counties: Alpine, Amador, Calaveras, Colusa, El Dorado, Nevada, Placer, Sacramento, San Joaquin, Stanislaus, Sutter, Tuolumne, Yolo, Yuba 

• The Delta region and the Sierra Nevada are known for their natural scenery and historic landmarks, but like the rest of the state, this is earthquake country. The mountains and the valley have been shaped by repeated earthquakes on faults in the region.
• Moderate earthquakes have occurred in the high Sierra, the foothills and in the Central Valley. These occurred on active faults found in wide zones along the crest of the Sierra Nevada, through Lake Tahoe, along the foothills, and in the western Sacramento Valley.
• Large quakes from distant faults such as those in the San Francisco Bay Area or east of the Sierra Nevada can also cause significant damage to homes, businesses, and communities, especially in areas where water levels are high in soft soils that can settle unevenly during shaking. 
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides. 

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 76% probability of one or more magnitude 7.0 earthquakes striking Northern California is based on a 30-year period, beginning in 2014.

Central Coast

Counties: Monterey, San Benito, San Luis Obispo, Santa Barbara, Santa Cruz

• This region has a long history of damaging earthquakes. Large earthquakes will occur along the San Andreas fault system—the major geologic boundary between the North American and Pacific tectonic plates—which traverses much of the State of California. 
• The main trace of the San Andreas fault runs up through the Carrizo Plain and the Diablo range of the central coast region before shifting slightly westward into the Santa Cruz Mountains as it continues northward.
• The San Gregorio fault is another major part of the system. It generally follows the coast, just offshore. These and numerous other faults are capable of damaging earthquakes, similar to the 1906 San Francisco and 1989 Loma Prieta earthquakes.
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move sideways on gentle slopes. Landslides are likely in the mountains and on steep hillsides.

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Southern California is based on a 30-year period, beginning in 2014.

Central Valley South

Counties: Fresno, Kern, Kings, Madera, Mariposa, Merced, Tulare

• Like all of California, the Central Valley—which is ringed by faults—is earthquake country. Shaking can begin suddenly but have lasting impacts. 
• The San Andreas fault system is to the west, the Garlock fault is to the south and the faults of the Sierra Nevada are to the east.
• The San Andreas fault system is the major geologic boundary between the North American and Pacific tectonic plates and passes through much of the state. It will create the biggest earthquakes—as big as magnitude 8—that will disrupt the whole region. But smaller magnitude earthquakes can also cause damaging levels of ground shaking.
• A study by the U.S. Geological Survey indicates that a portion of the San Andreas fault near Tejon Pass could be overdue for a major earthquake. Earthquakes occur about every hundred years on average, along this section of the fault, with the last major earthquake occurring in 1857: the magnitude 7.9 Fort Tejon quake.
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Southern California is based on a 30-year period, beginning in 2014.

Inyo/Mono

Counties: Inyo, Mono

• Like all of California, this is earthquake country! Residents of these counties have experienced shaking from Nevada earthquakes, as well.  
• The region has been fashioned by tremendous geologic forces, from the incredible steep slope of Mt. Whitney to the vast Owens Valley in Inyo County. 
• The Eastern California Shear Zone (ECSZ), a region of increased seismic activity, runs from the Gulf of California through the Mojave Desert-Death Valley and into Nevada. It is part of the tectonic boundary between the Pacific and North American plates.  
• Active faults at the base of the Sierra Nevada mountain range and within the basins to the east have caused damaging earthquakes in the past, such as the 1872 Owens Valley earthquake. 
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides. 

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Southern California is based on a 30-year period, beginning in 2014.

Southern California Coast

Counties: Los Angeles, Ventura, Orange County

Los Angeles Earthquake Prediction - What is LA's Risk of a Quake?

• Many of the mountains, and some of the valleys, in Southern California were formed by movement within the San Andreas fault system—the tectonic boundary between the Pacific and North American tectonic plates.
• The San Andreas fault is the primary feature of the system and the longest fault in California, slicing through Los Angeles County along the north side of the San Gabriel Mountains. It can cause powerful earthquakes—as big as magnitude 8.
• A study by the U.S. Geological Survey indicates that a portion of the San Andreas fault near Tejon Pass could be overdue for a major earthquake. Along this section of the fault, earthquakes occur about every hundred years on average. The last major earthquake occurring in 1857: the magnitude 7.9 Fort Tejon quake.
• There are over a hundred smaller active faults in the region that can cause damaging earthquakes like the Northridge earthquake in 1994, such as the Raymond fault, the Santa Monica fault, the Hollywood fault, the Newport-Inglewood fault, and the San Jacinto and Elsinore faults.
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.
• See why you should you be considering a seismic retrofit in Los Angeles

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Southern California is based on a 30-year period, beginning in 2014.

Inland Southern California

Counties: Imperial, Riverside, San Bernardino

• Inland Southern California has scenic mountains, valleys, and deserts – all shaped by the tremendous geologic forces within the  San Andreas fault system. This tectonic boundary between the Pacific and North American tectonic plates is still very much active today and reminds us often that we live in earthquake country. 
• The San Andreas fault is the primary feature of the system and the longest fault in California that can cause powerful earthquakes—as big as magnitude 8. 
• A large part of the region’s population lives within 50 miles of the San Andreas fault and could be exposed to very strong levels of ground shaking in a major earthquake.  
• Many other faults, such as the San Jacinto fault, create smaller, yet more frequent earthquakes. 
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides. 

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Northern California is based on a 30-year period, beginning in 2014.

San Diego

County: San Diego

What is the Earthquake Risk in San Diego?

• Like all of California, San Diego is earthquake country. Many of the mountains, and some of the valleys, in Southern California were formed by the San Andreas fault system—the tectonic boundary between the Pacific and North American tectonic plates—which runs to the east of San Diego County from the Gulf of California up through the Salton Sea and into the Los Angeles region.
• The San Andreas fault is the longest fault in California and can cause powerful earthquakes—as big as magnitude 8—that can still generate strong shaking levels in San Diego. 
• The Rose Canyon fault runs along the coast and beneath downtown San Diego. Geologists say this is the biggest earthquake threat to San Diego, capable of earthquakes of magnitude 6.9.
• The Elsinore and San Jacinto faults cut through East County and can also generate moderately-sized but potentially damaging earthquakes. 
• Soils in lowland areas away from major faults may be subject to liquefaction. Houses on liquefied soil may settle or even move laterally on gentle slopes. Landslides are possible on steep hillsides.
• See why it is worth it to earthquake retrofit a home in San Diego

How to Strengthen Your House

See the USGS interactive fault map to learn more about faults in this area

*The 75% probability of one or more magnitude 7.0 earthquakes striking Southern California is based on a 30-year period, beginning in 2014.