ShakeAlert Earthquake Warning App Recalibrates to Detect Smaller Temblors

Published : Thursday, August 15, 2019 | 5:00 AM

ShakeAlert, originally designed by scientists at Caltech and the U.S. Geological Survey in Pasadena as an early earthquake warning system for the West Coast, will soon be able to detect smaller earthquakes, officials announced Wednesday.

Los Angeles City Mayor Eric Garcetti said the system, which uses a mobile app, will alert users of earthquakes at magnitude 4.5 or larger starting the middle of this month. The previous threshold was magnitude 5.0.

Garcetti made the announcement Wednesday as he met with officials from Caltech and the USGS.

“What this means is simple – Angelenos will get more alerts about earthquakes,” Garcetti said at a press conference following the meeting.

The change in the threshold was apparently in response to complaints that the ShakeAlert system was not able to send out warnings about the powerful 4th of July earthquakes near Ridgecrest.

Officials said the system was designed to detect for the strongest earthquakes, but by the time the Ridgecrest shock waves hit Los Angeles they had dissapated in power and were below the magnitude 5.0 threshold, they said.

Lowering the threshold would also mean residents receiving more alerts through the app, which for some might be too many, they said.

“Our fear is that they will become desensitized to the alerts and not act to protect themselves in those instances when they really need to,” said Doug Given, earthquake early warning coordinator at USGS.

The ShakeAlert system has been in development since 2006. In 2011, Caltech, along with UC Berkeley and the University of Washington, received $6 million from the Gordon and Betty Moore Foundation for the research and development of the system.

In 2015, the USGS announced approximately $4 million in awards to Caltech, UC Berkeley, the University of Washington, and the University of Oregon for ShakeAlert’s expansion and improvement.

Currently, the ShakeAlert system’s infrastructures consist of hundreds of ground-motion sensors which compose the California Integrated Seismic Network – operated by Caltech in partnership with UC Berkeley, the USGS, and the State of California – and the Pacific Northwest Seismic Network, a similar regional network operated by the USGS, University of Washington, and the University of Oregon.

Over the past few years, ShakeAlert has detected thousands of earthquakes, including two that caused damage. It began sending alerts within four seconds of the beginning of the magnitude 5.1 La Habra earthquake in 2014, and gave users in Berkeley five seconds of warning before seismological waves arrived during the magnitude 6.0 South Napa earthquake, also in 2014.

At its epicenter in Kern County, the temblor on July 4 registered as a 6.4-magnitude quake. The shaking in Los Angeles was below 4.5, the USGS said.

The USGS added ShakeAlert provided 48 seconds of warning to Caltech’s seismology lab well before the shaking actually arrived in Pasadena.

For more information about the system, visit

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