by California’s earthquake early warning system is getting a seismic upgrade that will allow residents to receive more timely warnings of tremors from an incoming major earthquake.
The upgrade, also available in Oregon and Washington, will provide features important for warnings about the “Big One.”
The improvements could mean that, depending on where they are and where the shaking starts, Californians could get an earlier and more accurate estimate of magnitude before the earth starts shaking – say from a magnitude earthquake 7.8 which starts on the San Andreas fault near Mexico. border and the fault will rupture towards Los Angeles County.
The upgrade would also improve warnings for the Pacific Northwest and the North Coast of California, which are threatened by tsunamis from earthquakes along the Cascadia subduction zone.
The US Geological Survey and its nonprofit partner EarthScope announced the upgraded system on Wednesday.
Read more: Japan and Mexico have earthquake early warning systems. How does California compare?
For the most powerful earthquakes, the improvements “become very critical to help us find the answer faster – in terms of how big that event is,” said Robert de Groot, one of the operational team leaders The USGS ShakeAlert system. .
For smaller earthquakes, the older system worked “perfectly,” De Groot said. But with larger tremors, the magnitude could be underestimated for quite some time, robbing residents of vital information in the seconds before they feel the most damaging tremors.
Let’s say a magnitude 8 earthquake hits the southern San Andreas fault that starts near the Mexican border, but the earliest estimate says it’s a magnitude 6.5. The longer the low estimate is broadcast on phones, the less likely people are to take appropriate action.
“People would act differently — much differently — than if you said it was a size 8,” said David Mencin, vice president of data services for EarthScope, a nonprofit funded by the National Science Foundation, USGS and NASA is providing data for enhanced humans. early warning system.
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“The biggest, most destructive earthquakes are the ones we’re really worried about,” Mencin said. “This solves the problem of underestimating those amounts, which is critical.”
One of the most famous underestimations came in 2011 with the epic 9.1 magnitude earthquake that triggered a devastating tsunami off the east coast of Japan, leaving an estimated 18,000 dead. An initial estimate put the magnitude of the quake at 7.9, meaning the actual earthquake was 63 times stronger in terms of energy release.
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That underestimation led to a misjudgment of the height of the tsunami – with some of the first detailed warnings erroneously estimating that the tsunami would be lower than the protective sea walls. And when communications were cut off, 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 quake could have been generated much more quickly, Mencin said.
The USGS earthquake early warning system on the West Coast has long relied on hundreds of seismic sensors embedded in the ground. But there are only so many tremors they can detect in a short amount of time.
“Seismometers tend to get overwhelmed for earthquakes of magnitude 7 and above. They can start to get ‘saturated,'” Mencin said. During a very intense shaking, the seismometers – basically things on a spring – start hitting the wall of the instrument, so the seismic signal becomes “clipped” and cannot quickly calculate magnitudes above a certain threshold .
Now coming to the rescue are hundreds of GPS sensors on the Earth’s surface and run by EarthScope. Most of the time, these sensors track very slow movement, on the order of a millimeter or less per year. That can indicate subtle tectonic plate action between major earthquakes, showing how the Pacific plate, where LA is located, is moving northwest relative to the North American plate, where the Mojave Desert is located situated.
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But in a large earthquake, there is significant permanent ground motion, where one piece of land moves away from the other, moving yards in seconds. In the great San Francisco earthquake of 1906, land on one side of the San Andreas fault was generally jammed 8.5 feet over the other side, De Groot said.
And in the last major earthquake in the southern San Andreas – the fault ruptured in 1857 between Monterey and San Bernardino counties – ground on one side of the fault generally rose 10 feet compared to the other. Both the 1857 and 1906 earthquakes were around magnitude 7.8.
In the largest of the 2019 Ridgecrest earthquakes, the magnitude 7.1 quake had about 2 feet of fault offset, De Groot said.
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The first calculation of the earthquake early warning system will still rely on seismic sensors, which measure ground velocity and acceleration, De Groot said. Then, as an earthquake continues to rip along a fault, GPS sensors will measure how far a block of land has moved.
“What GPS allows us to do is to get a handle on how big that earthquake is getting – or could be – earlier,” said De Groot. That means the early warning system could detect a magnitude 7 or higher quake a few seconds earlier than before.
Read more: California has not seen a catastrophic earthquake recently. But there won’t be a ‘quiet’ period
It is important to know that the magnitude of an earthquake is not immediately apparent. Quakes rupture 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 further away from the start of an earthquake to get a second advance of the worst shaking to come.
On the San Andreas fault, a magnitude 7.3 earthquake would produce an earthquake if an earthquake rupture starts at the Salton Sea and ends at the San Gorgonio Strand, about 80 miles away.
But one that ruptures the entire 340-mile length of the southern San Andreas, which ends in Monterey County, would create a magnitude 8.2 earthquake and shake a much wider swath of Southern and Central California.
“As the earthquake increases in size, it will be able to help update that size faster and with greater accuracy,” said De Groot about the GPS data, which will spread the early warnings to a larger region. “By entering the [GPS] data, you get a handle on how big the earthquake really is sooner.”
The net result “will translate into longer warning times for people who could get alerts on their phones,” De Groot said. That would give people more time to take action, such as surgeons and dentists moving sharp instruments from nearby patients, allowing trains to slow down to reduce the risk of derailment, opening firehouse doors before they can be closed and giving time to the community to fall, cover and hold on.
Depending on where people are, some may not get a warning before they feel the first tremor, known as the “P wave.” But the goal is to warn before the most damaging shock – the “S wave” – that comes later.
“What we really want to inform people is to get the warning before the the strongest shaking,” said De Groot.
Read more: Signs of past ‘mega-quakes’ in California point to danger on Great San Andreas fault
By the end of 2025, the USGS ShakeAlert is estimated to have 1,675 seismic detection stations – which is about 90% complete. EarthScope says the nonprofit is running an additional 1,000 GPS stations adding data to the system.
EarthScope, the nation’s leading seismological and geodetic data facility, was recently formed as a merger of UNAVCO, which had an archive for GPS data, and IRIS, which had an archive of seismic data.
The earthquake early warning system has become more popular in recent years as people become accustomed to the alerts. In February when a magnitude-4.6 earthquake was widely felt in Malibu, some felt left out when they did not receive early warning.
Read more: No shaking
The alerts can be accessed by downloading the free MyShake app on iOS and Android. Android users are automatically subscribed to Android Earthquake Alerts. Those systems are set to sound an alarm when an earthquake of magnitude 4.5 or greater is predicted and the expected shaking intensity at the user’s mobile phone location is estimated to be at least “weak” — level 3 on the Modified Intensity Scale Mercalli, where people inside feel it significantly and motor vehicles may be standing a little rock or feel that a truck is passing by.
Stronger earthquakes – magnitude 5 and above – will send users a wireless emergency alert, such as an Amber Alert, if they are present that are expected to have at least “light” shaking intensity. That’s level 4 on the Mercalli Altered Intensity Scale – shaking with enough intensity to shake dishes, windows and doors, and it can feel like a heavy truck hitting a building.
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This story originally appeared in the Los Angeles Times.
