Heim>The blog>2020>What is the San Andreas Fault?
22. June 2020
When we think of the next big earthquake, we think of the San Andreas Fault. The San Andreas Fault line formed about 30 million years ago when the North American Plate swallowed almost all of the Farallon Plate. Since then, the North American Plate has ground against the Pacific Plate at a boundary called the strike fault.
This fault is one of the largest faults in the world, stretching more than 800 miles from the Salton Sea to Cape Mendocino. It splits the state in two.San Diego,The angeland Big Sur are on the Pacific Plate.San Francisco, Sacramento and the Sierra Nevada lie on the North American Plate. The two plates are criss-crossed with dozens of active and passive seismic faults.
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Map of the San Andreas Fault Line
The San Andreas runs deep near and under some of California's most densely populated areas. The cities of Desert Hot Springs, San Bernardino, Wrightwood, Palmdale, Gorman, Frazier Park, Daly City, Point Reyes Station and Bodega Bay rest on the San Andreas Fault line.
Southern San Andreas bisects Los Angeles County along the north side of the San Gabriel Mountains. It can cause powerful earthquakes up to magnitude 8 that would affect populous communities in SoCal.
What kind of bug is the San Andreas?
A San Andreas earthquake would be classified as occurring on a strike fault. Strike-slip faults occur along the boundaries of tectonic plates sliding past one another.
A strike-slip is a vertical fracture in the Earth's crust that creates horizontal movement along the fault line. The rock walls move to the left relative to each other or to the right relative to each other. These perturbations are formed by horizontal compression.
- Motion along a strike fault is horizontal.
- Shear stress acts on the opposing blocks of earth.
- The fault surface is nearly vertical.
- Stress on the San Andreas Fault causes a right-hand movement
How would a major earthquake affect the San Andreas Fault?
USGS scenarios predict more than 1,800 deaths and 50,000 injuries from a major earthquake south of the San Andreas Fault. CoreLogic, a business analytics service, estimates that a rupture of the southern San Andreas Fault will endanger 3.5 million homes worth $289 billion in rebuilding.
Twelve years ago, seismologists modeled how the ground would shake at the southern San Andreas Fault. Engineers and social scientists used this information to estimate the effects of a hypothetical 7.8 magnitude quake to hit the Coachella Valley.
- The earthquake waves spread throughout the state of California, destroying older buildings, disrupting roads and severing power, telephone and water lines.
- Hundreds of fires start.
- Emergency services are hampered by the streets.
- Water, power and gas lines cross the San Andreas Fault in Los Angeles. They break during the quake and remain unfixed for months.
- Many retrofit homes and newer buildings survive the tremors, but many older homes are structurally unserviceable.
Video of the southern San Andreas earthquake scenario
Earthquake scenario in southern San Andreas
This portion of the San Andreas Fault has been identified as the most likely source of a very large earthquake in California. In this computer simulation created through a collaborative effort between theUnited States Geological Surveyand theSouthern California Earthquake Center, the 7.8 magnitude earthquake erupts 186 miles from Bombay Beach on the edge of the Salton Sea in the south to Lake Hughes northwest of Palmdale in the north.
watch the video
Is your home near the San Andreas Fault?
Scientists assume that the San Andreas fault line could cause a devastating earthquake in California2030. This fault has caused some of the largest single-magnitude earthquakes in California.
Most of California's population lives and works on the west side of the fault.
Do you live near the San Andreas Fault? Or near the network of 500 active California faults feeding into it?
Remember that the error is always moving about 2 inches per year. Find out about your home's earthquake risk with the CEA earthquakedisruption mapby county.
how to prepare for an earthquake
Although the San Andreas fault zone is the best studied in the world, nothing can prevent a major earthquake. The key to earthquake safety is preparation. While an earthquake safety kit will come in handy after an earthquake, nothing replaces the conversations you have with your family members before an earthquake.
Create an earthquake safety plan for you and your loved ones.
- Be sure to identify safe spots in each room of your home.
- Work outDrop, cover and holdwith every member of your household.
- Make or buy oneEarthquake Safety Set. Make sure water and snacks are available in every room in your home.
- Check out affordable Californiaearthquake insurance.
Consider a seismic retrofit, which involves strengthening your home's foundation to make it more resilient to shaking. CEA offers earthquake household insurancepremium discountsfor homes and RVs that have been retrofitted. Find out aboutSubsidies for retrofitsunder the Earthquake Brace & Bolt program and the CEA Brace & Bolt program.
Learn more about Brace+Bolt grants
Understand structural risks for your house
Learn more about the potentialgeological structural threatsto your home in the event of a major earthquake. The violent shaking from earthquakes can:
- break up the earth.
- trigger landslides.
- Make loosely packed, water saturated soil liquid.
If your home was built before 1980, it may also be vulnerableserious structureDamage. with safety planning,strengthenoutside the home and your personal belongings andearthquake insurance, you have a better chance of surviving the next San Andreas breach.
Get a premium estimate now
Assessment of geological hazards near your home
Find out about the primarygeological hazardswhere you live could affect your home during an earthquake.
Your seismic hazard and seismic risk depend on the location of your home, the construction of your home, and the location of your home nearbyactive fault zonelike the San Andreas fault zone. Other factors to consider are:
- The population density in your community.
- building codes.
- your familyemergency preparedness.
Personal Preparedness Guidelines
Prepare your home BEFORE an earthquake. Reduce your risk of earthquake damage and injury from a San Andreas earthquake by identifying potential hazards to your home:
- Tall, heavy furniture that could fall over, such as bookcases, china cabinets, or modular wall units.
- Water heaters that don't match the code by being strapped down could break.
- Ovens and appliances that could move far enough to rupture gas or power lines.
- Hanging plants in heavy pots that could swing freely from hooks.
- Heavy picture frames or mirrors over a bed.
- Latches on kitchen cabinets or other cabinets that do not keep the door closed when shaken.
- Fragile or heavy items stored on high or open shelves.
- A masonry chimney that could crumble and fall through an unsupported roof.
- Flammable liquids such as paint or cleaning products that are safer in a garage or outside shed.
Is earthquake insurance worth it?
What if a devastating San Andreas earthquake hits your home and community?
- Severe earthquakes can cause major damage to the foundations, facades and roofs of houses. Older homes built on raised foundations before 1980 are particularly at risk if not retrofitted.
- Without residential earthquake insurance, you are responsible for all repair and/or rebuilding costs.
- Government disaster relief, when available, may only come in the form of a small grant or a limited loan that may only cover part of your repair costs and may have to be repaid.
- Without loss of use earthquake insurance — which covers coverage for your additional living expenses due to earthquake damage to your home — you would continue to pay your mortgage plus temporary rent while the repairs are being made.
watchcheap earthquake insurancelet you choose the cover that fits your budget. Our insurance rates are based on the latest science and research and are determined by several factors including the age of your home, its location near a fault, the type of foundation, type of construction and type of roof.
Discover the peace of mind—before the next San Andreas earthquake—that comes with making the wise financial decision to buy earthquake insurance in California.
Get a Free Estimate for Earthquake Insurance!
Don't be unprepared when the next San Andreas earthquake hits California! Get a free earthquake insurance estimate by using theCEA Premium Calculator.
Contact herinsurance agent todayto discuss policy options. CEA works with most California insurance companies. You don't have to wait for your home insurance renewal to sign up.
Get your free estimate for earthquake insurance
- USGS:The San Andreas Fault
- CalTech:San Andreas Fault Zone
- Corelogic:Fracturing Costs of the San Andreas Fault in Southern California
- Southern California Earthquake Center:Scenarios for the rupture of the San Andreas Fault
- Los Angeles Times: What would astrong earthquakeFeel like where you live
- LiveScience:Facts about the San Andreas earthquake
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What is actually the San Andreas Fault? ›
The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal).What is the San Andreas Fault and where is it? ›
The San Andreas Fault System, which crosses California from the Salton Sea in the south to Cape Mendocino in the north, is the boundary between the Pacific Plate (that includes the Pacific Ocean) and North American Plate (that includes North America).What will happen if San Andreas Fault breaks? ›
Narrator: Parts of the San Andreas Fault intersect with 39 gas and oil pipelines. This could rupture high-pressure gas lines, releasing gas into the air and igniting potentially deadly explosions. Stewart: So, if you have natural-gas lines that rupture, that's how you can get fire and explosions.How serious is the San Andreas Fault? ›
USGS regional scenarios anticipate 1800 deaths and 50,000 injuries in the event of a major San Andreas earthquake. More than 3 million homes could be damaged, at a reconstruction cost of $289 billion.Will the San Andreas Fault cause an earthquake? ›
Computer models show that the San Andreas fault is capable of producing earthquakes up to about magnitude 8.3. The fictional magnitude 9.6 that devastates San Francisco would be 90 times more intense overall than the largest earthquake possible (“only” a magnitude 8.3) on the San Andreas fault!
As such, recent predictions limit the possible maximum earthquake magnitude along the San Andreas fault system to 8.0, although with a 7% probability estimate that such an event could occur in Southern California in the next 30 years; over the same period, there is a 75% chance of a magnitude 7.0 event.What cities will the San Andreas Fault affect? ›
The San Andreas runs deep near and under some of California's most populated areas. The cities of Desert Hot Springs, San Bernardino, Wrightwood, Palmdale, Gorman, Frazier Park, Daly City, Point Reyes Station and Bodega Bay rest on the San Andreas fault line.What caused San Andreas Fault? ›
The San Andreas Fault System grew as a remnant of a oceanic crustal plate and a spreading ridge (like the Juan de Fuca Ridge) were subducted beneath the North American Plate as it moved west relative to the Pacific Plate.What is the biggest fault line in the world? ›
The San Andreas fault line in California is the longest in the world. It sits between the Pacific and North American plates and measures 1300kms.What year will the Big One hit? ›
The "Big One," a massive earthquake predicted to hit California along the San Andreas Fault, is expected to occur sometime in the next 100 years, and experts warn that climate change could make the already deadly event even worse.
What year will the San Andreas fault happen? ›
The threat of earthquakes extends across the entire San Francisco Bay region, and a major quake is likely before 2032.How long overdue is the San Andreas fault? ›
According to the U.S. Geological Survey, it is highly likely that some areas across the fault will experience a magnitude 6.7 earthquake in the next 30 years. In areas near the state boundary, it is nearly 100 percent likely to occur.How big will the big one be in California? ›
Southern California Is Due For A Big One
There's a 15% chance that Southern California will get hit by a 7.8 magnitude or larger quake sometime in the next three decades. That's 44 times more powerful than what we felt during the 1994 Northridge earthquake.
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.How bad will the big one be? ›
The 'Big One' is a hypothetical earthquake of magnitude ~8 or greater that is expected to happen along the SAF. Such a quake will produce devastation to human civilization within about 50-100 miles of the SAF quake zone, especially in urban areas like Palm Springs, Los Angeles and San Francisco.How does the San Andreas fault affect humans? ›
In one scenario produced by the United States Geological Survey, researchers found that a big quake along the San Andreas could kill 1,800 people, injure 55,000 and wreak $200 million in damage. It could take years, nearly a decade, for California to recover.Where will the Big One hit? ›
The Big One is what people call earthquakes of a magnitude 8 or higher. Scientists know that quakes of this size hit California semi-frequently, and study probability in order to understand the risks. We know the San Andreas Fault will strike again and significantly impact all civilization within a 50-100 mile radius.Can the San Andreas fault cause a tsunami? ›
The SAF is unlikely to produce tsunamis. This is because it is mostly on land and because it is a transform fault, the motion between plates being largely horizontal. Tsunami's are produced by vertical motions at an underwater fault and these are almost always associated with subduction zones.What cities in California are safest from earthquakes? ›
- 1) Sacramento. The state capital of California is an overall safe choice as it falls outside the major fault lines that follow the western coast. ...
- 2) Fresno. ...
- 3) San Diego. ...
- 4) Chico. ...
- 5) Redding. ...
- 6) Santa Barbara.
No, earthquakes of magnitude 10 or larger cannot happen. The magnitude of an earthquake is related to the length of the fault on which it occurs.
Is California going to break off? ›
No. The San Andreas Fault System, which crosses California from the Salton Sea in the south to Cape Mendocino in the north, is the boundary between two tectonic plates — the Pacific Plate and North American Plate.How often does the San Andreas Fault move? ›
San Andreas Fault Zone – The Big Picture
The relative motion between these two tectonic plates is 50 mm/yr (about 2 inches/yr), but that rate is distributed across all the faults that are part of the SAFZ.
While the San Andreas fault gets much of the attention, it's the Hayward fault that quake experts consider the most dangerous fault in America.What state has the most fault lines? ›
The seismic activity in California is widely known, and high-hazard areas cover large sections of the state, including the San Francisco Bay area, Los Angeles, and San Diego. The San Andreas Fault has caused some of the most notable earthquakes in recent memory.
Earth's biggest exposed fault
For nearly a century, scientists have been aware of a 4.47 mile-deep (7.2 km) oceanic abyss — known as the Weber Deep — located off the coast of eastern Indonesia in the Banda Sea. But until recently, they had been unable to explain how it got so deep.
List of earthquakes in 2023.
|Strongest magnitude||7.8 Mw Turkey|
|Deadliest||7.8 Mw Turkey 55,191 deaths|
|Number by magnitude|
Worldwide the probability that an earthquake will be followed within 3 days by a large earthquake nearby is somewhere just over 6%. In California, that probability is about 6%. This means that there is about a 94% chance that any earthquake will NOT be a foreshock.Will there be small earthquakes before a Big One? ›
Previously, scientists observed that only half of all moderate quakes had precursor smaller events. Now, this new study of earthquakes in Southern California of at least magnitude 4 between 2008 and 2017 finds that at least 72% of them had earlier, smaller quakes.How likely is a big earthquake in California? ›
More than 99% chance that one or more M6. 7 or greater earthquakes will strike somewhere in California. 75% chance one or more M7. 0 or greater earthquakes will strike Southern California.What is the strongest earthquake to ever hit the United States? ›
Prince William Sound Alaska (March 28, 1964) — 9.2
The Great Alaska earthquake or the Good Friday Earthquake as it's also called, is the most powerful earthquake to have occurred in the United States, and the second most powerful earthquake on record in the world.
What would happen if a 9.0 earthquake hit California? ›
If a 9.0 earthquake were to strike along California's sparsely populated North Coast, it would have a catastrophic ripple effect. A giant tsunami created by the quake would wash away coastal towns, destroy U.S. 101 and cause $70 billion in damage over a large swath of the Pacific coast.What do people say will happen to California if the Big One hits? ›
1,800 people will die. 1,600 fires will ignite and most of those will be large fires. 750 people will be trapped inside buildings with complete collapse. 270,000 people will be immediately displaced from their homes.What will happen to San Francisco when the Big One hits? ›
SAN FRANCISCO, CA — The "big one," a powerful earthquake that could devastate California at any moment, will likely kill thousands of people and topple buildings, crumble bridges and roads, sever water lines and ignite numerous fires.What is the largest earthquake in California history? ›
|7.9||Jan. 9, 1857||Fort Tejon|
|7.8||April 18, 1906||San Francisco|
|7.4||Mar. 26, 1872||Owens Valley|
|7.4||Nov. 8, 1980||W. of Eureka*|
On November 8, 1980, a magnitude 7.0 (ML) earthquake, known as the Gorda Basin or Humboldt earthquake, occurred off the coast of Humboldt County. Six people were injured, and aftershocks were felt for days. The earthquake was felt in parts of California, Oregon and Nevada.Can California fall into the ocean if an earthquake is large enough? ›
For those of us who live in inland areas of Southern California, the myth persists that in a strong quake, our homes could end up as beachfront property. Not so. According to the Earthquake Country Alliance, the motion of the plates will not make portions of California fall into the ocean.Why is the San Andreas Fault located where it is in California? ›
What Is It? Scientists have learned that the Earth's crust is fractured into a series of "plates" that have been moving very slowly over the Earth's surface for millions of years. Two of these moving plates meet in western California; the boundary between them is the San Andreas fault.What states are San Andreas Fault? ›
San Andreas Fault Line Map
It divides California into two in which San Diego, Los Angeles, and Big Sur are on the Pacific Plate, whereas Sacramento, San Francisco, and the Sierra Nevada are on the North American Plate.
The San Andreas fault southeast of San Bernardino has not experienced a major earthquake in the historical record, and paleoseismic investigations of this reach of the fault suggests it last ruptured in the late 17th Century.What parts of California will be affected by the Big One? ›
The 'Big One' is a hypothetical earthquake of magnitude ~8 or greater that is expected to happen along the SAF. Such a quake will produce devastation to human civilization within about 50-100 miles of the SAF quake zone, especially in urban areas like Palm Springs, Los Angeles and San Francisco.
How does the San Andreas Fault affect humans? ›
In one scenario produced by the United States Geological Survey, researchers found that a big quake along the San Andreas could kill 1,800 people, injure 55,000 and wreak $200 million in damage. It could take years, nearly a decade, for California to recover.What year will the San Andreas Fault happen? ›
The threat of earthquakes extends across the entire San Francisco Bay region, and a major quake is likely before 2032.How far down does the San Andreas fault go? ›
The entire San Andreas fault system is more than 800 miles long and extends to depths of at least 10 miles within the Earth. In detail, the fault is a complex zone of crushed and broken rock from a few hundred feet to a mile wide.What was the worlds worst earthquake? ›
The 1960 Valdivia earthquake and tsunami (Spanish: Terremoto de Valdivia) or the Great Chilean earthquake (Gran terremoto de Chile) on 22 May 1960 was the most powerful earthquake ever recorded.What is the biggest threat to California? ›
A new study has found that California faces the existential threat of a megaflood due to climate change. California had been a state for scarcely a decade and was home to fewer than 500,000 people when it was hammered in the winter of 1861-62 by the most powerful series of rainstorms in recorded history.