California’s earthquake early warning system is undergoing a seismic upgrade, which will allow residents to receive faster alerts of shaking caused by an impending megaquake.
The upgrade, also available in Oregon and Washington, will provide important functionality for “Big One” warnings.
These improvements could mean that, depending on where they are and where the earthquake begins, Californians would receive an earlier, more accurate estimate of the magnitude before the earth begins to shake – for example from A magnitude 7.8 earthquake begins on the San Andreas Fault near the Mexican border. border and breaks the fault towards Los Angeles County.
The upgrade would also improve alerts for the Pacific Northwest and the northern California coast, which are threatened by tsunamis from earthquakes along the Cascadia subduction zone.
The U.S. Geological Survey and its nonprofit partner EarthScope announced the system upgrade Wednesday.
For the strongest earthquakes, the enhancements “become very, very critical in helping us get a response more quickly – in terms of the magnitude of the event,” said Robert de Groot, one of the USGS ShakeAlert system operations team leaders. .
For small earthquakes, the old system worked “perfectly well,” De Groot said. But with larger earthquakes, the magnitude could be underestimated for some time, depriving residents of crucial information seconds before they feel the most destructive jolt.
Let’s say an earthquake on the southern San Andreas Fault that starts near the Mexican border ends up being a magnitude 8, but the first estimate says it’s a magnitude 6.5 . The longer this underestimation lasts on phones, the less likely people are to take appropriate action.
“People would react differently — very differently — than if you said it was magnitude 8,” said David Mencin, vice president of data services for EarthScope, a nonprofit funded by the National Science Foundation, USGS and NASA which provides data for improvement. early warning system.
“The biggest, most destructive earthquakes are the ones that really worry us,” Mencin said. “This solves the problem of underestimating these magnitudes, which is critical.”
One of the most famous underestimates occurred in 2011 with the epic 9.1 magnitude earthquake that triggered a devastating tsunami off Japan’s east coast, killing around 18,000 people. An initial estimate put the earthquake’s magnitude at 7.9, meaning the actual earthquake was 63 times more powerful in terms of energy released.
This underestimation led to a misjudgment of tsunami heights – with some of the first detailed warnings incorrectly estimating that the tsunami would be lower than the protective seawalls. And when communications were cut off, a false sense of security set in, with many people never receiving accurate evacuation alerts.
If Japan had used GPS data, a more accurate magnitude of the earthquake could have been generated much more quickly, Mencin said.
The USGS West Coast Earthquake Early Warning System has long relied on hundreds of seismic sensors embedded in the ground. But there’s only a limited amount of shaking they can detect in a short time.
“Seismometers tend to be overwhelmed by earthquakes of magnitude 7 or greater. They can start to get ‘saturated,’” Mencin said. During particularly intense shaking, seismometers – essentially objects on a spring – start hitting the wall of the instrument, so the seismic signal is “clipped” and cannot quickly calculate magnitudes above a certain threshold.
Hundreds of GPS sensors installed on the Earth’s surface and managed by EarthScope are now coming to the rescue. Most of the time, these sensors track very slow movements, on the order of a few millimeters or less per year. This can illustrate the subtle action of tectonic plates between major earthquakes, illustrating how the Pacific Plate, where Los Angeles is located, is moving northwest relative to the North American Plate, where the desert is located. from Mojave.
But during a major earthquake, there is considerable and permanent ground movement, where one patch of land moves away from another, moving several meters in a matter of seconds. During the Great San Francisco Earthquake of 1906, land on one side of the San Andreas Fault typically got stuck 8.5 feet on the other, De Groot said.
And in the last big South San Andreas earthquake — which ruptured the fault in 1857 between Monterey and San Bernardino counties — landfall on one side of the fault typically lurched 10 feet per relation to the other side. The earthquakes of 1857 and 1906 had a magnitude of approximately 7.8.
During Ridgecrest’s largest earthquake in 2019, there was about 2 feet of fault offset for the 7.1 magnitude quake, De Groot said.
The first calculation of the earthquake early warning system will still rely on seismic sensors, which measure ground speed and acceleration, De Groot said. Then, as an earthquake continues to propagate along a fault, GPS sensors will measure how far a block of earth travels.
“What GPS allows us to do is get a sense of how big this earthquake was – or could be – sooner,” De Groot said. This means that the early warning system could realize that an earthquake was of magnitude 7 or greater a few seconds earlier than before.
It is important to know that the magnitude of an earthquake does not appear instantly. Earthquakes erupt on a fault at the speed of sound through rock, which is slower than the speed of light in today’s telecommunications systems. This is the principle that allows people furthest away from the start of an earthquake to be warned a few seconds in advance of the worst tremors to come.
On the San Andreas Fault, an earthquake that begins ruptured at the Salton Sea and ends at Mt. San Gorgonio, about 80 miles away, would produce a magnitude 7.3 earthquake.
A rupture of the San Andreas Fault between the Salton Sea and Mount San Gorgonio could produce a magnitude 7.3 earthquake.
(Angélica Quintero / Los Angeles Times)
But an earthquake that shatters the entire 340-mile length of the southern San Andreas, ending in Monterey County, would create a magnitude 8.2 earthquake and produce shaking over a much wider swath of the southern and central from California.
A rupture along the entire 340-mile length of the southern San Andreas Fault between Monterey County and the Salton Sea would produce a magnitude 8.2 earthquake.
(Angélica Quintero / Los Angeles Times)
“As the size of the earthquake increases, it will be able to update that magnitude faster and more accurately,” De Groot said of the GPS data, which will broadcast early warnings to a wider region. vast. “By adding the (GPS) data, you get an earlier idea of the true magnitude of the earthquake.”
The net result “will result in longer warning times for people who may receive alerts on their phones,” De Groot said. This would give people more time to act, such as surgeons and dentists moving sharp tools closer to patients, allowing trains to slow down to reduce the risk of derailment, opening fire station doors before they can be blocked and give the public time to descend, cover and hold on.
Depending on where people are, some may not receive warning until they feel the first jolt, known as a “P wave.” But the goal is to give a warning before the most damaging shock occurs – the “S wave” – which will occur later.
“What we really want to let people know is that they be alerted before the The Strongest trembling,” De Groot said.
By the end of 2025, the USGS ShakeAlert program, approximately 90% complete, is expected to have 1,675 seismic detection stations. EarthScope says an additional 1,000 GPS stations run by the nonprofit organization contribute data to the system.
EarthScope, the country’s main seismological and geodetic data center, was recently established through the merger of UNAVCO, which held GPS data archives, and IRIS, which held seismic data archives.
The earthquake early warning system has become more popular in recent years as people become accustomed to the alerts. During the widely felt 4.6 magnitude earthquake in Malibu in February, some felt left out when they didn’t 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 configured to sound an alarm when an earthquake is estimated to be 4.5 magnitude or greater and the expected shaking intensity at the user’s cell phone location is expected to be at least “small » – level 3 on the Modified Mercalli Intensity Scale, where it is felt very visibly by people inside and may slightly shake stationary motor vehicles or give the impression that a truck passes.
Larger earthquakes – magnitude 5 and above – will send users a wireless emergency alert, similar to an Amber Alert, if they are in a location where earthquakes are expected. there is at least an intensity of “light” shaking. This is Level 4 on the Modified Mercalli Intensity Scale: enough shaking intensity to shake dishes, windows and doors, and may feel like a heavy truck hitting a building.
