How an early earthquake warning works
In the next few years, an alert advising of a slight chance of earthquake might fly across your social media accounts in the same week an Amber Alert-like blast hits your cellphone, warning of an imminent temblor.
The first one might lead you to avoid bridges for a few days; the second should prompt you to duck and cover.
They’re two of the communication tools the California Office of Emergency Services is refining as it builds out the state’s early earthquake warning system, a project that gained a $10 million boost from a bill Gov. Jerry Brown signed in September.
It aims to give Californians a few seconds or minutes to prepare for a shake. That sounds short, but could buy enough time to stop a full-speed BART train or give a construction crew a moment to find cover.
“You might have time to think about it and prepare yourself,” said Tom Jordan, director of the Southern California Earthquake Center. “I went in for back surgery a couple years ago and I remember thinking, ‘Gee, I wish we had an earthquake early warning system’ ” in case a temblor struck at a critical moment in his operation.
He’s among the geologists and emergency management leaders who are urging ever-more communication about earthquake risks in California.
They worry that people become complacent as time passes without a major earthquake. They hope alerts – either a fairly long-term forecast or instant bulletins from the early earthquake warning system – may jolt Californians into better preparing themselves for a disaster.
“In my view, they should be put out on a regular basis, weekly seismic weather reports,” Jordan said. “They’re always there.”
The new surge in funding for the early earthquake warning system is intended to strengthen a network that is already in use by a handful of public agencies. It will give the state more earthquake sensors to place near major faults, which should help it issue more precise warnings.
They will mostly be placed in the Bay Area and Southern California, which face greater earthquake risks than inland counties, though Yolo County last week experienced a swarm of low-magnitude shakers. If a big one hits, Sacramento residents would most want to be prepared to help evacuees from the coast, said Steve Cantelme, chief of the county’s Office of Emergency Services.
Eventually, the state Office of Emergency Services wants the system to quickly assess an earthquake’s direction and warn the public through cellphone blasts that would resemble alerts for child abductions or flash floods. It’s similar to a system in Japan that instantly warns residents of coming earthquakes.
“We need to get that same reach with this warning,” said Tina Curry, the deputy director at the department.
Since 2012, BART has tested a preliminary version of the warning system that automatically slows trains when sensors detect shaking.
It appears to work, although it has not yet had a real-world test. The network caught a 2014 Napa County earthquake that hurt more than 120 people, but the damage occurred in the middle of the night when BART trains were not running.
Adding more sensors and expanding the warning system should “make things better by virtue of having more sensors out there, and by having a better ability for that signal to go out faster,” said BART Commissioner John McPartland.
Had it been in place in 1989, people in downtown San Francisco might have had a quarter of a minute to prepare themselves for the devastating Loma Prieta earthquake. A model of the warning system based on that event shows it took 16 seconds for the shaking to travel from its epicenter in Santa Cruz County to San Francisco City Hall.
McPartland noted that would have been enough time to slow a top-speed BART train from 70 mph to about 25 mph.
Today, California’s earthquake monitoring network has about 500 sensors. Curry said it would need about 1,000 to build out the full early warning system. Each one costs about $40,000.
False alarms could occur. In early August, Japan’s system terrified Tokyo with a warning predicting an imminent magnitude-9 earthquake. People on social media reported their relief that the earthquake didn’t happen, but acknowledged that it had confused them.
Before the early warning system began taking shape, California’s best effort at predicting earthquake risk came from a council of scientists that convenes a few times a year at the request of state emergency management officials.
Usually, the California Earthquake Prediction Evaluation Council convenes after clusters of small temblors, which sometimes are indicators of more earthquakes.
It has issued advisories warning of increased earthquake risk from time to time, but gained new attention in September when one of its alerts startled Southern Californians and rocketed around social media.
It advised that a series of small earthquakes near the Salton Sea raised the likelihood of a major earthquake on the San Andreas Fault by 0.03 percent to 1 percent. It was a small chance, but the council concluded the warning was worthwhile. San Bernardino temporarily closed its City Hall in response to the advisory.
The earthquake didn’t come.
But Jordan and Curry were glad the bulletin seemed to connect with people.
“It got quite a lot of people talking about it, which is good,” Curry said.