When Should We Issue Earthquake Warnings? It’s Complicated.
Seismologists need help from social scientists to know how people respond to earthquake alerts
By Ula Chrobak
When back-to-back earthquakes shook Southern California in July, residents of Los Angeles were frustrated; Many felt the earthquakes, which originated over 100 miles away in Ridgecrest, but received no alert through their ShakeAlertLA phone apps. But the app didn’t err — it was designed to alert users when shaking was expected to reach the Modified Mercalli Intensity of 4, a level at which shaking is thought to be strong enough to cause some damage, such as a dish or book falling off a shelf.
Angelenos made enough of a buzz that they soon got their way. Officials announced the next day that the threshold for setting off the alert had been lowered to MMI 3, a level at which shaking is widely felt but rarely damaging, which is about the same as that caused by a large truck driving nearby. Then, in October, Governor Gavin Newsom announced the launch of a statewide earthquake alert system. Now, residents across the state can get alerts through the MyShake app, as well as through wireless emergency alerts much like Amber Alerts or flash flood warnings.
