California‘s earthquake early warning system is receiving a seismic upgrade, one that will allow residents to receive more timely alerts about shaking from an incoming megaquake.
The update, also available in Oregon and Washington, will provide important features for warnings about the “Big One.”
The 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 ground begins to shake (for example, of a magnitude 7.8 earthquake that begins on the San Andreas Fault, near the Mexican coast). border and breaks the fault into Los Angeles County.
The update would also improve warnings for the Pacific Northwest and the northern California coast, which are threatened by tsunamis caused by earthquakes along the Cascadia subduction zone.
The U.S. Geological Survey and its nonprofit partner EarthScope announced the updated system Wednesday.
For more powerful earthquakes, the improvements “become very, very critical in helping us get to the response faster, in terms of how big that event is,” said Robert de Groot, one of the team’s operations team leaders. USGS ShakeAlert system. .
For smaller earthquakes, the older system worked “perfectly well,” de Groot said. But with larger earthquakes, the magnitude could be underestimated for quite some time, depriving residents of crucial information in the seconds before they feel the most destructive tremor.
Say an earthquake on the southern San Andreas Fault that starts near the Mexican border ends up being magnitude 8, but the earliest estimate says it’s magnitude 6.5. The longer that underestimation is transmitted to 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 at EarthScope, a nonprofit organization funded by the National Science Foundation, the USGS and NASA providing data for improvement. early warning system.
“The larger, more destructive earthquakes are the ones we’re really concerned about,” Mencin said. “This solves the problem of underestimating those magnitudes, which is critical.”
One of the most famous underestimations occurred in 2011, with the epic magnitude 9.1 earthquake that triggered a devastating tsunami off the eastern coast of Japan, leaving approximately 18,000 dead. An initial estimate put the earthquake’s magnitude at 7.9, meaning the actual quake was a staggering 63 times stronger in terms of energy released.
That underestimation led to a miscalculation of the tsunami’s height: some of the first detailed warnings wrongly estimated that the tsunami would be lower than the protective walls. And when communications were cut, a false sense of security set in, and many people never received 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 are a limited number of tremors they can detect in a short time.
“Seismometers tend to be overloaded with earthquakes of magnitude 7 or larger. They can start to ‘saturate,’” Mencin said. During particularly intense shaking, seismometers (basically objects on a spring) begin to hit the wall of the instrument, so the seismic signal becomes “clipped” and cannot quickly calculate magnitudes above a certain threshold.
Now hundreds of GPS sensors on the Earth’s surface and managed by EarthScope come to the rescue. Most of the time, these sensors track very slow movements, on the order of millimeters or less per year. This can illustrate the subtle action of plate tectonics between large earthquakes, illustrating how the Pacific plate, where Los Angeles is located, is shifting northwest relative to the North American plate, where the Mojave Desert is located. .
But in a major earthquake, there is considerable and permanent ground movement, where one piece of land separates from the other, moving yards in seconds. In the great San Francisco earthquake of 1906, the ground on one side of the San Andreas Fault generally became stuck 8.5 feet beyond the other, De Groot said.
And in the last great southern San Andreas earthquake, which ruptured the fault in 1857 between Monterey and San Bernardino counties, the ground on one side of the fault generally shook 10 feet relative to the other side. Both the 1857 and 1906 earthquakes had a magnitude of around 7.8.
In the largest of the Ridgecrest earthquakes in 2019, there was about 2 feet of fault offset for the magnitude 7.1 earthquake, De Groot said.
The first calculation of the earthquake early warning system will continue to be based on seismic sensors, which measure ground speed and acceleration, De Groot said. Then, as an earthquake continues to strike along a fault, GPS sensors will measure the distance a block of earth has moved.
“What GPS allows us to do is know how big that earthquake is getting (or could be) sooner,” De Groot said. That means the early warning system could realize that an earthquake was magnitude 7, or larger, a few seconds earlier than before.
It is important to know that the magnitude of an earthquake does not appear instantly. Earthquakes explode on a fault at the speed of sound through rock, which is slower than the speed of light of today’s telecommunications systems. This is the principle that allows people furthest from the start of an earthquake to receive seconds’ advance warning of the worst shaking to come.
On the San Andreas Fault, an earthquake that begins to rupture in the Salton Sea and ends at Mount San Gorgonio, approximately 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 one that ruptures the entire 340-mile length of the southern San Andreas, ending in Monterey County, would create a magnitude 8.2 earthquake and produce shaking across a much wider swath of southern and central California.
A rupture of 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 earthquake grows in size, it will be able to help update that magnitude more quickly and with greater precision,” De Groot said of the GPS data, which will spread early warnings to a larger region. “By adding the (GPS) data, you can tell more quickly how big the earthquake really is.”
The net result “will translate into longer alert times for people who could potentially receive alerts on their phones,” De Groot said. That would give people more time to take action, such as having surgeons and dentists move sharp tools from nearby patients, allowing trains to slow down to reduce the risk of derailment, opening fire station doors before they can be closed and gives the public time to get off. Cover up and hold on.
Depending on where people are, some may not receive a warning before feeling the first tremor, which is known as a “P wave.” But the goal is to provide a warning before the most damaging tremor occurs: the “S wave,” which arrives later.
“What we really want people to know is to be alerted before the strongest shaking,” De Groot said.
By the end of 2025, USGS ShakeAlert, which is about 90% complete, is expected to have 1,675 seismic detection stations. EarthScope says an additional 1,000 GPS stations managed by the nonprofit are contributing data to the system.
EarthScope, the country’s premier seismological and geodetic data facility, was recently formed as a result of the merger of UNAVCO, which had a GPS data archive, and IRIS, which had a seismic data archive.
The earthquake early warning system has become more popular in recent years as people become more accustomed to the alerts. In the magnitude 4.6 earthquake that was widely felt in Malibu in February, some felt left out by not receiving early warning.
Alerts can be received by downloading the free MyShake app on iOS and Android. Android users automatically subscribe to Android earthquake alerts. Those systems are configured to sound an alarm when an earthquake is estimated to be magnitude 4.5 or higher and the expected intensity of the shaking at the location of the user’s cell phone is expected to be at least “weak”: level 3 in the Modified Mercalli Intensity Scale, where People who are indoors feel it quite noticeably and may slightly sway motor vehicles or feel as if a truck is passing by.
Stronger earthquakes (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 “light” shaking intensity. That’s level 4 on the Modified Mercalli Intensity Scale: The intensity of the shaking is enough to rattle dishes, windows and doors, and it can feel like a heavy truck hitting a building.
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