Earthquake App Test at 3:19 A.M. Startles Users on the West Coast

Some West Coast residents were jolted awake on Thursday when they received an earthquake alert test that was sent to their cellphones at 3:19 a.m. because of a time zone mix-up, the United States Geological Survey said.

The noisy alerts were sent to people who use MyShake, an early-warning app for earthquakes, said Robert-Michael de Groot, a spokesman for ShakeAlert, the U.S. Geological Survey system that powers the app.

Mr. de Groot did not know how many users had received the alert, but he said that the app had been downloaded 1.4 million times and that the alarm could have reached more than a million people. The app is intended for people in California, Oregon and Washington, but alerts can also be sent to other users, he said.

MyShake had planned to send a test alert Thursday to its users in California, Oregon and Washington for a fictitious earthquake in San Francisco at 10:19 a.m. Pacific time, according to its website. Instead, app users received the warning at 3:19 a.m. Pacific time, which is the same as 10:19 a.m. Coordinated Universal Time. The warning text said the alert had been sent at 10:19 a.m. U.T.C.

Some people who received the alert were awakened by a recorded voice saying, “This is a test,” according to posts on social media.

MyShake was developed by the University of California, Berkeley, which did not immediately respond to a request for comment on Thursday.

The app is powered by ShakeAlert, a system managed by the U.S. Geological Survey that detects earthquakes and estimates which areas could experience strong shaking to alert the public in an effort to minimize harm.

ShakeAlert is used in California, Oregon and Washington, the states with some of the highest number of people that could experience very strong ground shaking from earthquakes. Governments can send the ShakeAlert information to televisions, telephones and radios. Some privately owned apps, such as MyShake, partner with ShakeAlert to broadcast warnings.

These alerts are meant to give users a few seconds’ warning to take cover and to give organizations extra time to take steps to protect people and critical equipment, by slowing down trains or issuing public announcements, for example.

ShakeAlert warnings were first sent to cellphones in California in 2019 and in Oregon and Washington in 2021.

Mr. de Groot said that ShakeAlert was in a “constant state of improvement” and that each event taught the U.S. Geological Survey something new about how to improve the early-warning system.

“Certainly, I think the lesson that needed to be learned was learned for people who run this at 3:20 a.m.,” Mr. de Groot said.

About 143 million people in the United States live in places that have some potential for shaking from an earthquake that can cause damage, according to the U.S. Geological Survey.

To prepare for possible earthquakes, a national earthquake drill, The Great ShakeOut, is held each year, this year on Thursday. Families, schools, businesses and other organizations were encouraged to practice what to do during an earthquake.

In Northern California, there was a real-life opportunity for earthquake preparations Wednesday morning, when the ShakeAlert system was activated after an earthquake struck in Sacramento County, triggering an alert. The U.S. Geological Survey had initially registered the earthquake above a magnitude 5, prompting the alert, but it was later downgraded to a magnitude 4.2.

As emergency management officials across the country have tested new technologies to better warn people about potential disasters, there have been occasional mistakes.

In April, the Florida Division of Emergency Management apologized after it sent a screeching alarm to cellphones across the state at 4:45 a.m. after a test of the emergency alert system.

In January 2018, people in Hawaii received a false alert warning of an incoming ballistic missile, and it took about 38 minutes for the state to send another alert that said the first one was an error. The false alert was sent by a worker with a long history of poor performance who had thought that the state faced an actual threat, Federal Communications Commission and Hawaii officials said.