Small earthquakes shake the ground across California daily, popping up every half hour or so on thousands of earthquake monitors statewide. To give residents up to 10-20 seconds of warning of larger earthquakes, those over 4.5 on the Richter scale, the state rolled out a cell-phone app this month. Called MyShake, the app simply tells the recipient an earthquake has happened nearby and to drop, cover, and hold on — the current recipe for riding out a quake safely.

Dr. Richard Allen, the seismologist whose lab at UC Berkeley helped develop the app, explained the brief message: “It’s based on our work to understand what is the right message to send to users,” he said. “Any more information just causes confusion.” Allen also emphasized that depending on their proximity to an epicenter, recipients will get the message after, during, or before a quake. “It’s vital to know,” he said, “for every earthquake, there will be a region near the epicenter where the alert will not arrive in time.” It takes time to detect the quake, and then calculate the magnitude and level of shaking before the affected part of California gets the alert, Allen explained.

Early warning has been proposed since the 1906 San Francisco quake, Allen said, with radios used in 1989 to warn rescuers of aftershocks as they dug people out from under the bridges collapsed by the Loma Prieta earthquake. Allen stood with state officials before the Bay Bridge during the announcement of the app in mid-October. After Senate Bill 135 added funding in 2014, the early-ground-motion sensors have been planted, software written, and tests conducted with Allen’s seismology lab, the U.S. Geological Survey, Cal Tech, the state Geologic Survey, and also the states of Washington and Oregon, said Mark Ghilarducci, California’s emergency director. The app is only written in English, and new versions are already in development.

In an intense earthquake, the ground jerks violently sideways and every unsecured object nearby can fall or go flying, the Earthquake Country Alliance warns. The “drop, cover, hold on” direction advises people to drop to their hands and knees to avoid falling, and then cover their head — either with their arms or a sturdy table, for instance — to protect them. Although the alert’s time frame is only seconds, it may be just enough to get fire station doors open, notify hospital operating rooms, and signal mass transit operations.

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