The 6.4 earthquake along the far reaches of the Northern California coast didn’t rattle windows or knock items off the shelf in the Bay Area, but it did wake up hundreds — as far south as San Diego — who’d registered for the fledgling earthquake warning system that sends alerts to cell phones.
“This definitely needs some fine tuning if it is going to wake people up in the middle of the night,” one San Diego recipient replied Tuesday to the U.S. Geological Survey’s ShakeAlert system query on Twitter.
In Burlingame, Rohit Vashisht also woke to his phone buzzing with an alert early Tuesday morning. But he and his wife didn’t mind.
“It was very helpful in a sense,” Vashisht said later. “We were ready, just in case. We slept very comfortably after that.”
After a decade of development, an earthquake early-warning system has come online for some 50 million people on the West Coast. It got trial runs with a magnitude 4.4 earthquake near Santa Rosa in September and a magnitude 5.1 east of San Jose in October. But Tuesday’s powerful 6.4 was its biggest test yet, and state officials were thrilled.
Mark Ghilarducci, director of the California Office of Emergency Services, said the Shake Alert system developed by the U.S. Geological Survey “was able to actually push out alerts 10 seconds in advance of the earthquake shaking to some 3 million people in Northern California.”
Those alerts covered a range of areas from southern Oregon south to Sacramento and the Bay Area and signaled where the reported epicenter was and its magnitude.
“I was really happy to have given individuals an opportunity to drop, cover and hold, or get to a place of safety within that 10-second time frame,” Ghilarducci said at a Tuesday news conference. “The system did operate as we had hoped.”
Several countries, including Japan, Mexico, China and Turkey, have long had such earthquake warning systems in place. The U.S. system is more than 80% complete. It is planned to have 1,115 California sensors and quicker transmission times, with additional sensors in Oregon and Washington and a goal of giving residents critical seconds of warning before an earthquake strikes.
The ShakeAlert system detects an earthquake’s initial waves of ground motion, which travel quickly and are weaker than the more damaging second set of waves. Processing centers in Seattle, Menlo Park and Pasadena analyze the data to identify the epicenter and strength of the earthquake and publish a ShakeAlert message, which then goes to various government and private partners to be sent as alerts.
The alert thresholds vary — wireless emergency cell phone alerts to the general public are triggered at magnitude 5 or greater, and a Modified Mercalli Intensity scale of at least IV for light shaking. The scale goes from I, not felt, to X, extreme shaking. People also can download private apps that issue alerts at magnitude 4.5 and intensity level III for weak shaking.
Among apps are MyShake, developed by UC Berkeley, and QuakeAlertUSA, by Early Warning Labs.
Joshua Bashioum, founder and chief executive of Early Warning Labs, maker of QuakeAlertUSA, said their app calculates shaking intensity at the user’s location to provide more meaningful warnings.
“We really only alerted users we knew for a fact would be feeling the shaking,” Bashioum said. “It worked out pretty well.”
Other systems have features that base alerts on the user’s home or work locations.
The San Diego recipient had the ShakeReady SD alert, San Diego County’s early warning Shake Alert app. The organization didn’t answer questions about why alerts there went out Tuesday for an earthquake at the other end of the state.
But Robert de Groot, the national coordinator of outreach and education for ShakeAlert at the USGS’ Pasadena Field Office, said the focus has been meaningful warning to those who can use it. He said some of those at risk from the quake got as much as 20 seconds of warning, though others didn’t get any warning time because they were too close to the epicenter. But false alarms so far have been a lesser concern.
“Shake Alert didn’t make any errors in its calculations,” de Groot said. “We provide that data to delivery partners, their mechanisms do exactly what the data ask them to do. What we’re maximizing through this is human safety. And you could say, ‘How are you fostering human safety if people get alert after alert after alert?’ But we’re not at a level now where we’ve reached exhaustion with people. By having it the way it’s set up now, it gives people who are really and truly potentially in danger an opportunity to be safer.”
Like many who got alerts but felt no shaking, Debi Smith, of Ashland, Oregon, 225 miles from the earthquake, wasn’t too put off but hopes they can fine tune the system to avoid causing unnecessary alarm.
“When the alert came through, there wasn’t anything happening,” Smith said. “It was a little confusing, so I didn’t sleep for a couple hours while I looked it all up. My daughter called from nearby, and we had a good laugh for a few hours, wondering how many people were crouched in their doorways.”
Source: www.mercurynews.com