Upgrading California's earthquake early warning system

(TNS) – California's earthquake early warning system is getting a seismic upgrade, an upgrade that will allow residents to receive timely alerts about tremors from an upcoming massive earthquake.

The upgrade, also available in Oregon and Washington, will provide important features for “big order” warnings.

The improvements could mean that, depending on where they are and where the quake starts, Californians will get an earlier, more accurate estimate of the quake's size before the ground starts shaking — for example, from a 7.8-magnitude quake that starts on the San Andreas Fault near Mexico. Boundary and fault rupture towards Los Angeles County.

The upgrade would also improve warnings for the Pacific Northwest and the northern California coast, which are threatened by tsunamis triggered by earthquakes along the Cascadia subduction zone.

The USGS and its nonprofit partner EarthScope announced the updated system on Wednesday.

For the strongest earthquakes, improvements “become absolutely critical in helping us get to the answer faster — in terms of the magnitude of that event,” said Robert De Groot, an operations team leader for the USGS ShakeAlert system. .

For smaller earthquakes, the older system worked “perfectly well,” De Groot said. But in the case of larger earthquakes, their strength can be underestimated for some time, depriving residents of important information in the seconds before they feel the most devastating shaking.

Let's say an earthquake on the southern San Andreas Fault that started near the Mexican border ended up with a magnitude of 8, but the first estimate says it was a magnitude of 6.5. The longer this disdain for phones continues, the less likely people will be to take action.

“People will react differently — a lot differently — than if you said it had a magnitude of 8 on the Richter scale,” said David Mincin, vice president of data services at EarthScope, a nonprofit funded by the National Science Foundation, the U.S. Geological Survey and NASA that provides data to improve the environment. “. Early warning system.

“It's the larger, more destructive earthquakes that we're really concerned about,” Mincin said. “This solves the problem of minimizing those volumes, which is critical.”

One of the most famous underestimates came in 2011 when a 9.1-magnitude earthquake struck and triggered a devastating tsunami off the east coast of Japan, killing nearly 18,000 people. Initial estimates put the earthquake's magnitude at 7.9, meaning the actual earthquake was about 63 times stronger in terms of energy released.

This underestimation has led to miscalculations of tsunami heights – some of the first detailed alerts incorrectly estimated that the tsunami would be below the protective seawalls. When communications were cut, a false sense of security prevailed, as many people never received accurate warnings to evacuate.

If Japan had used GPS data, it would have been possible to generate a more accurate magnitude of the quake much more quickly, Mincin said.

The USGS West Coast Earthquake Early Warning System has long relied on hundreds of seismic sensors embedded in the ground. But there is only so much vibration they can detect in a short time.

“Seismographs tend to get fatigued in earthquakes of magnitude 7 or greater. They can start to saturate,” Mincin said. During particularly intense shaking, seismometers—essentially objects on a spring—begin to collide with the wall of the instrument, so the seismic signal is “clipped” and cannot calculate magnitudes quickly above a certain threshold.

Hundreds of ground-based GPS sensors powered by EarthScope are now coming to the rescue. Most of the time, these sensors track very slow motion, at a rate of millimeters or less per year. This could explain the movement of subtle tectonic plates between major earthquakes, showing how the Pacific Plate, where Los Angeles is located, is moving northwest relative to the North American Plate, where the Mojave Desert is located.

But in a large earthquake, there is a large and permanent movement of the ground, with one piece of ground shaking apart from another, moving yards in seconds. In the great San Francisco earthquake of 1906, the ground on one side of the San Andreas Fault generally buckled 8.5 feet from the other side, de Groot said.

In the last major earthquake south of the San Andreas — which ruptured the fault in 1857 between Monterey and San Bernardino counties — the ground on one side of the fault generally retreated by 10 feet compared to the other side. The earthquakes that occurred in 1857 and 1906 had a magnitude of about 7.8.

In the largest Ridgecrest earthquakes of 2019, there was a fault of about 2 feet that offset the 7.1 magnitude quake, De Groot said.

De Groot said the first calculation of the earthquake early warning system would still rely on seismic sensors, which measure ground speed and acceleration. Then, as the earthquake continues to rupture along the fault, GPS sensors will measure the distance a mass of earth has moved.

“What GPS allows us to do is recognize how big an earthquake is — or could get — sooner,” De Groot said. This means that the early warning system can recognize that an earthquake has a magnitude of 7, or higher, a few seconds earlier than before.

It is important to know that the size of an earthquake does not appear immediately. Earthquakes on a fault at the speed of sound rip through rock, which is slower than the speed of light in today's communications systems. This is the principle that allows people far from the beginning of an earthquake to have seconds of advance warning of the worst of the coming tremor.

On the San Andreas Fault, an earthquake that begins in the Salton Sea and ends at Mount San Gorgonio, about 80 miles away, would produce a magnitude 7.3 earthquake.

But an earthquake tearing through the entire 340-mile length of the southern San Andreas, ending in Monterey County, would create an 8.2-magnitude earthquake and shake a much wider area of ​​southern and central California.

“As the magnitude of the earthquake increases, it will be able to help update that magnitude more quickly and more accurately,” De Groot said of the GPS data that will spread early warnings to a larger area. “By adding in [GPS] “Data, you can actually get a sense of how strong an earthquake is much sooner.”

The net result “will translate into longer warning times for people who are likely to get alerts on their phones,” De Groot said. This would give people more time to take action, such as having surgeons and dentists move sharp instruments from nearby patients, allowing trains to slow to reduce the risk of derailment, and opening fire station doors before they are closed and giving the public time to get off. Cover and adhere.

Depending on where people are, some may not get warning before they feel the first vibration, which is known as a 'P wave'. But the goal is to give warning before the most damaging vibration — the “S wave” — occurs, which comes later.

“What we really want people to know is to get the alert before the strongest tremors,” De Groot said.

By the end of 2025, USGS's ShakeAlert — which is nearly 90% complete — is expected to have 1,675 seismic sensor stations. EarthScope says there are an additional 1,000 GPS stations operated by the nonprofit that contribute data to the system.

EarthScope, the country's main seismic and geodetic data facility, was recently created as a result of the merger of UNAVCO, which maintained an archive of GPS data, and IRIS, which maintained an archive of seismic data.

Earthquake early warning systems have become more popular in recent years as people become more accustomed to alerts. In the 4.6-magnitude earthquake that struck Malibu in February, some felt neglected when they did not receive early warning.

Alerts can be received by downloading the free MyShake app on iOS and Android. Android users are automatically subscribed to Android Earthquake alerts. These systems are set to sound an alarm when an earthquake is estimated to be 4.5 magnitude or higher, and the expected shaking intensity at the user's mobile location is expected to be at least “weak” – level 3 on the Modified Mercalli intensity scale, as felt by people inside Noticeably, motor vehicles may shake slightly or feel like a truck is passing.

Earthquakes of greater magnitude — magnitude 5 and above — will send users a wireless emergency alert, similar to an Amber Alert, if they are in a location expected to receive at least “mild” shaking intensity. This is level 4 on the Modified Mercalli intensity scale – the force of the vibration is enough to shake dishes, windows and doors, and it can feel like a heavy truck crashing into a building.

This story originally appeared in the Los Angeles Times.

©2024 Los Angeles Times. Visit latimes.com. Distributed by Tribune Content Agency, LLC.

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