California's earthquake early warning system is getting a seismic upgrade, allowing residents to receive faster warnings about tremors from an upcoming megaquake.
The upgrade, also available in Oregon and Washington, will provide features important for Big One alerts.
The improvements could mean that, depending on where they are and where the earthquake starts, Californians would get an earlier, more accurate estimate of its size before the Earth starts shaking - for example, from a magnitude 7.8 earthquake Richter scale that begins on the San Andreas Fault near the Mexican border. border and rips the fault towards Los Angeles County.
The upgrade would also improve warnings for the Pacific Northwest and California's northern coast, which are threatened by tsunamis from earthquakes along the Cascadia subduction zone.
The US Geological Survey and its nonprofit partner EarthScope announced the improved system on Wednesday.
Read more: Japan and Mexico have early warning systems for earthquakes. How does California compare?
For the most powerful earthquakes, the improvements are going to be "very, very critical to help us get to the response faster - in terms of how big that event is," said Robert de Groot, one of the operational team leaders of the ShakeAlert system. USGS. .
For smaller earthquakes, the older system worked "perfectly well," De Groot said. But with larger earthquakes, their magnitude can be underestimated for quite some time, robbing residents of crucial information in the seconds before they feel the most destructive jolt.
Let's say an earthquake on the southern San Andreas Fault, which starts near the Mexican border, ends up being a magnitude 8, but the earliest estimate says it's a magnitude 6.5. The longer this underestimation is broadcast to phones, the less likely people are to take appropriate action.
"People would react differently - very differently - than if you said it was a magnitude 8," says David Mencin, vice president of data services for EarthScope, a nonprofit funded by the National Science Foundation, USGS and NASA that provides data supplies for the improved technology. early warning system.
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"The largest, most destructive earthquakes are the ones we really worry about," Mencin said. "This solves the problem of underestimating these quantities, which is critical."
One of the most famous underestimates came in 2011 with the epic magnitude 9.1 earthquake that caused a devastating tsunami off the east coast of Japan, killing around 18,000. An initial estimate put the earthquake's magnitude at 7.9, meaning the actual earthquake was as much as 63 times stronger in terms of energy released.
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That underestimation led to a misjudgment of tsunami heights - with some of the first detailed warnings incorrectly estimating that the tsunami would be lower than protective sea walls. And when communications were lost, a false sense of security was created, with many people never receiving accurate evacuation warnings.
If Japan had used GPS data, a more accurate earthquake magnitude could have been generated much faster, Mencin 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 a limited amount of vibration they can detect in a short time.
"Seismometers tend to become overwhelmed in earthquakes of magnitude 7 or greater. They can become 'saturated,'" Mencin said. During particularly severe shaking, the seismometers - essentially objects on a spring - begin to hit the wall of the instrument , which 'clips' the seismic signal and prevents it from quickly calculating magnitudes above a certain threshold.
Hundreds of GPS sensors on the Earth's surface are now coming to the rescue and are managed by EarthScope. Typically, these sensors track very slow movements, on the order of millimeters or less per year. That can illustrate the subtle tectonic plate action between large earthquakes, and illustrate how the Pacific plate, where LA is located, is moving northwestward relative to the North American plate, where the Mojave Desert is located.
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But a large earthquake involves significant, permanent ground movement, with one piece of land moving away from another, moving meters within seconds. In the Great San Francisco earthquake of 1906, land on one side of the San Andreas Fault was typically 8 feet (2.5 meters) beyond the other side, De Groot said.
And in the last major earthquake in southern San Andreas - which ruptured the fault between Monterey and San Bernardino counties in 1857 - the land on one side of the fault was generally tilted 10 feet from the other side . Both the 1857 and 1906 earthquakes had magnitudes of around magnitude 7.8.
In the largest of the 2019 Ridgecrest earthquakes, there was about 2 feet of rupture offset for the magnitude 7.1 quake, De Groot said.
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The initial 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 rupture along a fault line, GPS sensors measure the distance a block of land has traveled.
"What we can do with GPS is get a handle on how big that earthquake is likely to be - or could be," De Groot said. This means that the early warning system could realize that an earthquake was a magnitude 7 or higher a few seconds earlier than before.
Read more: California hasn't seen a catastrophic earthquake recently. But the 'silent' period will not last
It is important to know that the magnitude of an earthquake is not immediately visible. Earthquakes erupt at a rupture 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 further away from the start of an earthquake to be warned seconds in advance of the worst earthquake to come.
As for the San Andreas Fault, an earthquake that starts in the Salton Sea and ends at Mount San Gorgonio, about 80 miles away, would produce a magnitude 7.3 earthquake.
But an earthquake that ruptures the entire 340-mile length of southern San Andreas, ending in Monterey County, would trigger a magnitude 8.2 earthquake and send tremors across a much wider swath of Southern and Central California.
"As the earthquake gets bigger, it will be able to update that magnitude faster and with more accuracy," De Groot said of the GPS data, which will spread the early warnings to a wider region. "By adding the [GPS] data, you actually get an earlier insight into 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, like surgeons and dentists moving sharp tools close to patients, slowing trains to reduce the risk of derailment, opening fire station doors before they can be wedged shut and giving the public time to drop. cover and hold.
Depending on where people are, some may not get any warning before they feel the first tremor, known as the 'P wave'. But the goal is to provide a warning before the most damaging shaking - the 'S wave' - which comes later.
"What we really want to make people aware of is that they get the warning before the strongest vibrate," says De Groot.
Read more: Signs of past 'megaquakes' in California show danger from the Big One on the San Andreas Fault
By the end of 2025, the USGS's ShakeAlert - which is about 90% complete - is expected to have 1,675 seismic detection stations. EarthScope says another 1,000 of the nonprofit's GPS stations contribute data to the system.
EarthScope, the country's premier seismological and geodetic data facility, was recently created from the merger of UNAVCO, which owned a GPS data archive, and IRIS, which owned a seismic data archive.
The earthquake early warning system has become more popular in recent years as people become more accustomed to the warnings. During the widespread 4.6 magnitude earthquake in Malibu in February, some felt left out because they didn't get early warning.
Read more: Unshaken
The 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 of magnitude 4.5 or greater and the expected shaking intensity at the user's cell phone location is expected to be at least "weak" - level 3 on the modified Mercalli intensity scale, where it is felt quite noticeably by people indoors and can cause stationary motor vehicles to sway slightly or give the feeling of a truck passing by.
Higher magnitude 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 experience at least a "mild" shaking intensity. That's level 4 on the modified Mercalli intensity scale - a shaking intensity enough to rattle signs, windows and doors, and it can feel like a heavy truck crashing into a building.
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This story originally appeared in the Los Angeles Times.
