L.A.'s ShakeAlert earthquake warning app worked exactly as planned. That’s the problemLos Angeles Times
Latimes.com - Wed 17 Jul 00:18 GMT

After complaints that the ShakeAlert app failed to warn users of the Ridgecrest quakes, officials will lower the notification threshold. But there are risks.

  More than 500,000 people have downloaded Los Angeles County’s new ShakeAlertLA app to warn them of impending earthquakes.

  By the end of July, the app will send alerts for local quakes with a magnitude of at least 4.5 and for any quake that results in "weak" shaking locally despite officials' concern that too many warnings could lead to complacency.

  But the USGS had instructed the app's developers to deliver the message to L.A. County users only if the shaking there would be strong enough to cause significant damage: shelves toppling, people being thrown around, “your favorite decorative plate from Reno flying off the wall,” De Groot said.

  Japan's Meteorological Agency established its Early Earthquake Warning system after the 1995 Kobe temblor that killed more than 6,000 people.

  In 2011, the Early Earthquake Warning system automatically signaled high-speed trains to slow down during the 9.1 Tohoku quake that struck off Japan's east coast, helping prevent deadly derailments.

  After public awareness campaigns explained the workings of the early warning system, more than three-quarters of the Japanese public understood that false alarms were a possibility, according to a study in Earthquake Spectra, a journal published by the Earthquake Engineering Research Institute.

  In L.A. County, seismologists believe one way to address concerns of an oversensitive system is to find creative ways to convey warnings, such as tailoring the messaging on the alert for varying degrees of intensity.