CEA - What is the San Andreas Fault? (2023)

FAQs

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).

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).

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.

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.

Earthquake Science

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

1. California

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The threat of earthquakes extends across the entire San Francisco Bay region, and a major quake is likely before 2032.

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.

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.

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.