USGS experts predict when magnitude 7.5 earthquake could hit Bay Area

So, what are the chances of a bigger quake hitting the Bay Area? And how bad could it be?

ByStephanie Sierra KGO logo

Wednesday, October 26, 2022

USGS experts predict when magnitude 7.5 quake could hit Bay Area

As the MyShake app was put to the test during the 5.1 earthquake near San Jose, experts also discuss when a 7.5 quake could rock the Bay Area.

SAN JOSE, Calif. -- Emergency alerts were sent out seconds before the 5.1 magnitude earthquake hit east of San Jose Tuesday. Did you get one?

The state rolled out an app called MyShake in 2019 to warn people with an alert on their cellphone before the ground starts shaking. Professor Richard Allen is a director of the UC Berkeley Seismology lab where the app was developed.

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"We will study pretty hard the feedback we get from people," Allen said. "Are we alerting the right group of people? Do we need to alert a wider area?"

The warnings are managed through a system run by the US Geological Survey and the California Dept. of Emergency Services. Allen says the technology has been in the works for over the past decade, but has only been in the market for a few years.

"A magnitude 5 is not a huge earthquake, we don't expect much damage if any damage at all," Allen said. "We need to be ready for much larger earthquakes than this."

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Seismologist Dr. Lucy Jones says aftershocks possible on Calaveras fault, following 5.1 quake in San Jose.

So, what are the chances of a bigger quake hitting the Bay Area? And how bad could it be?

"It's a real threat that we all have to be prepared for," USGS scientist and earthquake consultant Ross Stein. "We're always worried about the possibility of a magnitude 7 quake."

Stein explains the 5.1 magnitude quake hit along the Calaveras fault Tuesday - one of the most "lethal" faults. He says a big portion of the Bay Area could be at highest risk.

"The Calaveras fault connects to the Hayward fault, creating one very long fault, which if ruptured together could create a magnitude 7.5 earthquake," said Stein. "Occurring on the most populated corridor of the Bay Area... from Oakland, to Hayward, to San Jose, to Morgan Hill."

VIDEO: Cal students were taking quake exam when 5.1 temblor hit near SJ

Students at UC Berkeley were the middle of taking an earthquake exam when the 5.1 temblor struck the Bay Area.

The Bay Area has been a training ground for earthquake alert systems. Stein says the best alert on record is around a 10 second warning.

"Can we create a system that gives us more than 10 seconds? Probably not. Because for the shaking to be really strong, it needs to be really close. If it's really close, the seismic wave is going to arrive really soon with respect to our ability to identify that wave," Stein said.

But scientists at USGS have indicated new research is underway to advance that.

"In which we don't just use seismometers in the ground that are dedicated to earthquake early warning, but everybody's cellphones. There will always be more cellphones in the San Andreas Fault than seismometers. And we can harness those into the network ultimately to create a more powerful warning," said Stein.

The timeliness and accuracy of these alerts will be crucial for the next big earthquake. To put it in perspective, the shaking is ten times strong with a magnitude 6 earthquake, and 100 times stronger with a magnitude 7 earthquake, according to scientists at UC Berkeley.

Click here for the latest stories and videos about earthquakes here in the Bay Area and around the world, and click here for more information on disaster preparedness.

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