Millions of Southern Californians learned about the 5.2 magnitude earthquake that hit San Diego County on Monday. Not that the windows rattle or the picture frames rattle, but from a loud alert on my phone seconds before the shaking started.
The urgent message – to advise people to “drop, cover, hold. protect yourself” – was created with a US Geological Survey tool known as Shakealert. The system detects earthquakes as soon as it begins to occur, and collects information quickly to determine which areas may experience strong shaking. Shakealert works on the concept that every second is a valuable time that people can use to react and avoid injuries before shaking from an earthquake.
Here's how the system works:
Imagine a small car 6 feet underground.
Shakealert's early warning system, each with the help of tens of thousands of earthquakes, monitors monitors for earthquakes across the West Coast, each of which is compact car sized, buried approximately 6 feet underground. The station is equipped with sensors that detect the full range of seismic waves. It has vibrations that travel through the earth towards the surface after an earthquake.
The waves travel at different speeds, and the success of the system is built on this. A fast-moving primary, or P-wave, travels at about 4 miles per second. They are gentle and unlikely to cause destruction. A stronger secondary, or S-wave, travels much more slowly, at about 2.5 miles per second. They are more likely to cause damage in an earthquake.
The goal of ShakeAlert is to capture P-wave data, process it on USGS' high-speed computers, making it available to government agencies and private companies, such as apps that send alerts before S-Waves comes to the surface.
“It's all automated and everything's happening very quickly,” said Robert de Groot, physical scientist at the agency and Shakealert coordinator.
The closer you get, the less you get.
California has undergone many earthquakes, many of which cause little or no damage. Alerts will disappear only at the strongest. If the earthquake strength is estimated to be magnitude 4.5 or higher. Separately, shaking generated from an earthquake is measured on a scale of 1 to 10, and an alert is sent if the shaking in the area is estimated to be above level 3.
The closer you get to the epicenter, the less likely you are to receive a warning before the strongest shaking arrives. Because people who live near Quake will feel seismic waves as soon as the system begins to process data.
On Monday, people in downtown San Diego were alerted about a second or two before shaking, De Groot said. People in Los Angeles received their messages up to 10 seconds earlier.
“Distance is important,” De Groot said. “For those far from the earthquake, they spent a lot of time before the earthquake.”
Here's how to sign up for an alert:
You can sign up for alerts online and may receive them automatically if you are in the area.
The country's only early warning system was launched in California in 2019 and expanded to Oregon and Washington in 2021, serving around 50 million residents and visitors. (De Groot said the program could be expanded to Alaska if funding is permitted.)
The MyShake app, which can be downloaded to your phone, uses ShakeAlert data to send early earthquake warnings. Wireless emergency alerts that most people receive thanks to their phone default settings (the same technology used to send amber alerts) also provide early earthquake warning messages. Google has its own system integrated into Android phones.
(These alert systems should not be confused with USGS Earthquake Notification Services, which sends emails and texts after an earthquake occurs.)
“I thought it was an Amber Alert.”
Monday's trembling hit at 10:08am Pacific time about two and a half miles south of Julian, a small mountain town about 60 miles northeast of downtown San Diego, feeling as far away as Los Angeles.
Liberal political podcaster Alison Gill was at his San Diego home Monday morning working on a script that saw his phone start to vibrate and make loud noises.
“I thought it was an amber alert,” Gill said.
By the time she realized it was a warning for the earthquake, she felt what she described as “a considerable shock and then a mellow roll.”
Talk show host Jimmy Kimmel shared his own experiences on Monday night's show. He said he and his wife were in their computer bedroom and they both got an alert saying they should drop and cover them. When he finished reading the message, he said the earthquake was there.
“We're trying to understand if this is a good or a bad thing,” Kimmel joked.
