LA ShakeAlert App Changed to Alert Users on Small Quakes

PASADENA, Calif. (CN) – An app designed to give users advance warning of an earthquake recently received an important update, after failing to warn Southern California residents of a magnitude 7.1 earthquake in July.

This photo provided by Adam Graehl shows food that fell from shelves on the floor at the Stater Bros. on China Lake Blvd., in Ridgecrest, Calif., on July 4, 2019. It was the strongest earthquake in 20 years, hitting a large swath of Southern California and parts of Nevada, rattling nerves on the July 4th holiday and causing injuries and damage in a town near the epicenter, followed by a swarm of aftershocks. (Adam Graehl via AP)

Officials called the series of earthquakes in the Kern County town of Ridgecrest a wake-up call for everyone, while geologists designing the early-warning app called it the first real-world test run.

On Wednesday, the California Institute of Technology, U.S. Geological Survey and LA officials announced the ShakeAlertLA app will now send out alerts for light temblors, lowering the threshold from the previous setting.

The tradeoff? Users can expect five times more notifications for “light” earthquakes.

Two major earthquakes rocked Ridgecrest, about 125 miles northeast of Los Angeles, over the Fourth of July holiday, with quakes of 6.4 and 7.1 – and thousands of smaller aftershocks – over a two-day period. Because of the distance from the epicenter, those quakes only registered as “light” shaking – less than a magnitude 5 – on the early warning system in Los Angeles and users did not receive alerts on their cellphones.

Los Angeles Mayor Eric Garcetti said the app has been updated to give warning when shaking equivalent to magnitude 4.5 is expected.

“Now the application has been updated to notify users when they can expect some trembling from earthquakes in their region, even if the shaking is expected to not cause any damage,” said Garcetti.

More than 800,000 people have downloaded the app since it was first launched in December 2018. The app corresponds with the ShakeAlert early-warning system maintained by multiple organizations, including the U.S. Geological Survey.

The system is based on ground-motion sensors and data gathered at centers along the West Coast and also alerts emergency officials and other institutions.

Geophysicist Doug Givens of the U.S. Geological Survey said the Ridgecrest quakes did not register for an alert by design, because while the trembling might have been felt by people in the region there was minimal damage overall.

He cautioned the update will come more alerts, which people tend to ignore in their busy lives.

“Our fear is they’ll become desensitized to the alerts and not act to protect themselves in those instances where they really do need to,” said Givens. “In the system we have more work to do. Improve the performance of the system and the app. We have a lot to learn about people and their response to emergency information.”

Approximately 300,000 users downloaded the ShakeAlertLA app after last month’s earthquakes in Ridgecrest, Garcetti said.

The two largest Ridgecrest quakes were the strongest to hit the region in two decades.

Days after a 7.1 earthquake struck Searles Valley, California, a U.S Geological Survey crew scanning the area photographed huge swaths of surface rupture. (Ben Brooks / USGS)
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