The San Andreas Fault is at the highest level of pressure in 1,000 years and what it means

New research finds that the San Andreas and San Jacinto fault systems are in a “critically loaded” state, with stress levels that could support large, multi-fault earthquakes near major California cities.

Tectonic stress along Southern California’s San Andreas and San Jacinto fault systems has reached — and in some areas exceeded — the highest levels seen in the past 1,000 years, according to new research by geoscientists at the University of Hawaii at Mānoa.

The system does not show signs of imminent rupture, researchers say, but is operating under unusually high pressure in a long-period seismic cycle that can support large earthquakes, including multi-fault events.

The study, published in the journal Geophysical Research: Solid Earth, suggests that the area is in a “critical loading state”, with pressure building across multiple fault segments. One key area of ​​focus is the Cajon Corridor, a junction between two fault systems that may act as an “earthquake gateway,” either preventing fractures from crossing between faults or allowing them to link into one larger event.

The system is under intense stress more than 160 years since the last major rupture, said lead author Lillian Burkhard, a researcher affiliated with the Institute of Geophysics and Planetary Science at the University of Hawaii and a scientist at the University of Bern.

“Currently, with pressure reaching historically high levels across the region and more than 160 years having passed since the last major rupture, the system is in a critical state,” Burkhard said.

Researchers say a rupture involving both fault systems could be much more damaging than an earthquake triggered by a single fault due to its size and proximity to major population centers, including Los Angeles, San Bernardino, Riverside and the Coachella Valley.

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Can the San Andreas Fault break completely?

The San Andreas Fault is not a fault that could “split” and drop part of California away from the continent. It’s a sliding plate boundary, meaning the Pacific plate and North American plate are sliding past each other horizontally, not pulling apart, according to the USGS.

Therefore, even in a very large earthquake, what occurs is lateral movement along the fault, not disintegration of the land mass. Parts of California can suddenly move by feet or even dozens of feet during a major rupture, but both sides remain part of the same crustal system.

There are other tectonic places on Earth where continents break up and eventually form new oceans — such as the East African Rift, which is in the process of splitting into two tectonic plates — but the San Andreas system isn’t one of them. It is a sliding boundary, where plates slide past each other instead of apart.

However, over millions of years, continued movement along the fault could gradually bring Los Angeles and San Francisco closer together, geological models suggest.

What would happen if the San Andreas Fault ruptured?

Surface rupture occurs when movement along a fault deep within the Earth penetrates to the surface. According to the Pacific Northwest Seismic Network, it is one of the clearest physical expressions of an earthquake, showing permanent deformation as two sides of a fault slide over each other.

Most earthquakes do not produce surface rupture, according to the USGS. Some faults do not reach the surface, and even when they do, rupture does not always propagate all the way to the top during a given event.

When surface rupture occurs, it can produce either horizontal or vertical displacements, depending on the type of fault. Strike-slip faults, such as the San Andreas Fault, usually cause horizontal displacement, while strike-slip faults can produce vertical displacement. Some earthquakes involve a combination of both.

In the case of a large rupture, strong shaking can last from tens of seconds to more than a minute. The most severe damage may occur near a fault and in areas built on soft or water-saturated soil, which can amplify vibration and increase the risk of liquefaction. Scientists point out that infrastructure built across active faults is particularly vulnerable, as surface rupture can directly offset roads, buildings and other structures that extend across the fault’s footprint.

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San Andreas Fault Map What causes earthquakes?

The Earth consists of four layers: the inner core, outer core, mantle, and crust. The crust and the top of the mantle form another region called the lithosphere, which acts like the skin surrounding the Earth’s surface.

However, the lithosphere is not one piece, but is divided into puzzle-like pieces called tectonic plates, according to the USGS. These parts of the lithosphere are not stationary and move slowly.

When tectonic plates move close to each other, they sometimes collide or collide. This puts pressure on the edges of the plates. When the pressure becomes too great, it creates cracks called “flaws.” The point where these faults move against each other is called the ‘fault line’.

When there is a lot of friction between fault lines, energy is suddenly released, creating seismic waves that cause an earthquake.

Why are earthquakes so common in California?

California lies along the border between two huge tectonic plates – the Pacific Plate and the North American Plate. These plates are constantly moving, sliding past each other at different speeds.

The state is also home to more than 500 active faults, according to geologists, making it one of the most earthquake-prone areas in the United States. The most famous is the San Andreas Fault, a system about 800 miles long that runs through much of the state and forms the primary boundary between the two plates.

Other major fault systems include the Hayward Fault in the Bay Area, the Calaveras Fault in central California, and the San Jacinto and Elsinore Fault in Southern California.

But earthquakes are not limited to Earth. Many of them occur offshore, including near the Mendocino Triple Junction, where the Pacific, North American, and Gorda plates meet. This intersection creates one of the most seismically active marine areas along the West Coast.

Can earthquakes be predicted?

Earthquakes cannot be predicted. Neither the USGS nor scientists have predicted a major earthquake, and there is no expectation that this will change in the near future.

What is California’s earthquake early warning system?

California’s earthquake early warning system uses seismic sensors, ground motion monitoring, and alert technology to deliver warnings to people via cell phones before the strongest tremor arrives, according to the official website.

Officials say even a short warning can allow people to take preventative actions such as “drop, cover and wait” or putting devices and systems in safe mode. In some cases, alerts may arrive as soon as shaking begins or after the earthquake has already passed, especially for those closest to the epicenter.

The system is delivered through multiple channels, including Android Earthquake alerts, wireless emergency alerts, and the MyShake app.

Developed by the UC Berkeley Seismic Laboratory, MyShake is a free smartphone app that issues audio and visual warnings for earthquakes that typically have a magnitude of 4.5 or greater, or when weak shaking is expected. It is available on iPhone and Android, as well as select computer platforms.

What to do during an earthquake

An evergreen classic box that pairs well with any earthquake story.

Get down on your hands and knees. Cover your head and neck under sturdy furniture if possible. Wait until the shaking stops. Stay indoors unless you are near a known coastal tsunami hazard area. Stay alert. Get weather alerts via text message

Brandy d covers. Addison reports weather conditions across the United States as a Weather Connect correspondent for the USA TODAY Network. She can be reached at [email protected].

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