Thousands of people in California were alerted to an earthquake before it hit: how?

Updated on: 28 October 2022

Gintaras Radauskas
Senior journalist

People usually learn about an earthquake post-factum – and often when it’s already too late. But last Tuesday in California, thousands of local people, specifically Android users, were alerted to the seismic activity before the ground even started moving.

The alert was sent to smartphone users owning a novel MyShake app. It was developed by the Berkeley Seismology Lab and sent a warning to millions of devices – to some, up to 18 seconds before the 5.1 magnitude earthquake hit.

The message advised users to “drop, cover, and hold on,” said officials from the California Office of Emergency Management and the United States Geological Survey (USGS).

It might be just a few seconds, but alerts like this can take some of the unpredictability of earthquakes out of the equation – and save millions of lives. For comparison, one can imagine seeing lightning before hearing thunder.

The earthquake in the Bay area was quite moderate, though, reaching a magnitude of 5.1. No injuries were reported.

To be clear, MyShake is no magic weapon and does not predict earthquakes – no one can do it. But the app does detect seismic waves earlier than people usually feel them, and experts hope that someday alerts can be sent even quicker.

MyShake works on both Android and iPhone, but Google announced in 2020 it would implement Berkeley’s technology directly into Android, thus supporting far more people. It is also part of the ShakeAlert operations team, a project under the USGS.

Here’s how it works: while not everyone in the earthquake’s area will feel softer seismic waves, known as P waves, 1,300 USGS sensors will. And when four sensors are simultaneously triggered, an alert is sent to a data processing center.

If the ShakeAlert system determines that stronger S waves, able to cause damage and hurt people, could be coming, alerts will be sent – either by apps like MyShake or federal government’s programs - to residents’ smartphones.

Google has turned these into miniature earthquake sensors – all smartphones have accelerometers that can pick up signals of an earthquake and also send messages to relevant data centers.

Since Tuesday’s earthquake and the news of the timely alert, tweeted about by several influential people at Google, signups for the MyShake app have surged. It has already been downloaded by over two million users.

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So far, My Shake, though available for download anywhere, is only fully operational in three US West Coast states of California, Oregon, and Washington.

USGS has calculated that the probability of a powerful and damaging earthquake measuring magnitude seven hitting California’s Bay Area within the next 30 years is a solid 51%.

For each numerical increase in magnitude, the seismic energy released increases by about 32 times. That means a magnitude seven earthquake produces 32 times more energy – or is 32 times stronger – than a magnitude six. That also means a magnitude eight releases 1,000 times more energy than a magnitude six.