Crowd-sourc­ing quake alerts

The si­mul­ta­ne­ous shift­ing of many cell­phone GPS sen­sors may prove to be a re­li­able pre­dic­tor.

Los Angeles Times - - CALIFORNIA - DEB­O­RAH NETBURN deb­o­rah.netburn @la­ Twit­ter: @Deb­o­rahNet­burn

Your smart­phone is a cam­era, a cal­cu­la­tor, a flash­light and a pe­dome­ter. Sci­en­tists be­lieve it could be part of an earth­quake ear­ly­warn­ing sys­tem too.

It turns out that the GPS sen­sors built into most smartphones are sen­si­tive enough to de­tect the ear­li­est signs of quakes that are mag­ni­tude 7 and stronger, new re­search shows. The data they col­lect could be used to give nearby com­mu­ni­ties a few sec­onds’ no­tice that seis­mic waves are headed their way.

“The GPS on a smart­phone is shock­ingly good,” said study leader Sarah Min­son, a geo­physi­cist at the U.S. Ge­o­log­i­cal Sur­vey in Pasadena. “If you take your phone and move it six inches to the right, it knows with sur­pris­ing ac­cu­racy that it moved six inches to the right — and that is ex­actly what we want to know when study­ing earth­quakes.”

In the past, sci­en­tists have ex­am­ined whether the ac­celerom­e­ters that come stan­dard in smartphones are able to de­tect early signs of earth­quakes. (One of the jobs of th­ese ac­celerom­e­ters is to let the phone know whether the user is hold­ing it ver­ti­cally or hor­i­zon­tally so that the ori­en­ta­tion of the screen is cor­rect.)

In this study, the re­searchers were in­ter­ested in whether the GPS data our phones col­lect could be use­ful in earth­quake de­tec­tion as well.

Min­son and her coau­thors cre­ated a hy­po­thet­i­cal data set of cell­phone read­ings that would have been cap­tured dur­ing a mag­ni­tude 7 earth­quake on the Hay­ward fault in North­ern Cal­i­for­nia.

They also looked at data recorded by state-of-the-art GPS-based earth­quake sen­sors in Ja­pan dur­ing the mag­ni­tude 9 To­hoku quake in 2011. This in­for­ma­tion was much more de­tailed than what a typ­i­cal smart­phone could get, so the re­searchers used only what a phone would record and disregarded the rest.

With both sets of data in hand, the re­searchers tested whether the phones would be able to de­tect an earth­quake if it oc­curred, pin down its lo­ca­tion and de­ter­mine its mag­ni­tude.

The ob­vi­ous chal­lenge to us­ing cell­phones to reg­is­ter an earth­quake is that they are of­ten in mo­tion, bump­ing around when we drive over a pot­hole, trip on a curb or bound up the stairs.

Dou­glas Given, co­or­di­na­tor of the ShakeAlert earth­quake early-warn­ing sys­tem at the USGS, de­scribed the co­nun­drum: “You have a lot of cell­phones bounc­ing around all over the place, and you are try­ing to mea­sure what the ground is do­ing. So how do you tell the dif­fer­ence?”

To solve this prob­lem, the re­searchers came up with some­thing called a trig­ger — a set of cri­te­ria that would dis­tin­guish be­tween an earth­quake and a bunch of cell­phones on a bus get­ting jos­tled as it went over a big bump.

With the hy­po­thet­i­cal Hay­ward fault earth­quake, the trig­ger they de­cided on was whether a phone and its four clos­est neigh­bors recorded the same amount of dis­place­ment at the same time and the same could be said for 100 phones in the same area. Then, and only then, the re­searchers’ ear­ly­warn­ing sys­tem would reg­is­ter that a quake had oc­curred and send an alert to other com­mu­ni­ties.

The re­searchers used the To­hoku quake data to see whether it would be pos­si­ble to keep the rate of false alarms be­low 1 in ev­ery 2 mil­lion ap­par­ent de­tec­tions. It was — as long as 103 phones met the trig­ger cri­te­ria.

The re­sults were pub­lished Fri­day in the jour­nal Science Ad­vances.

Ye­huda Bock, a UC San Diego geode­sist who stud­ies ways of us­ing GPS to de­tect quakes and other nat­u­ral haz­ards, says that although the pa­per is tech­ni­cally sound, he is not sure that the cell­phone net­work would be very prac­ti­cal.

“I’m a lit­tle skep­ti­cal it will work in a real-world sit­u­a­tion,” said Bock, who was not in­volved in the re­search. “I think a sys­tem like that would false-alarm more than they claim in the pa­per.”

Min­son ac­knowl­edges that the sys­tem may not be quite as ac­cu­rate in the real world as it ap­pears to be on pa­per. Real-world tests will help her find out. Those will come next year, when she and her col­leagues will test their early-warn­ing sys­tem in Chile with a few hun­dred smartphones.

“Hope­fully,” she said, “this is go­ing to be a good learn­ing ex­pe­ri­ence for us.”

Min­son said the main ben­e­fit of crowd-sourc­ing earth­quake de­tec­tion is that it’s in­ex­pen­sive, be­cause the phones have al­ready been paid for. All the ex­perts would have to do is write an app to connect them and then find a cen­tral com­puter some­where to col­lect the data.

“The cost is es­sen­tially zero, es­pe­cially since peo­ple buy new phones ev­ery two years or so to have the lat­est-and-great­est model,” she said.

But don’t ex­pect to join your cell­phone to an earth­quake early-warn­ing sys­tem any time soon.

“The point of this pa­per is that the type of mea­sure­ments that are be­ing made by smartphones have the po­ten­tial to be use­ful in earth­quakes,” said Thomas Heaton, a pro­fes­sor of geophysics at Caltech and a coau­thor of the study. “That’s quite a big step from ac­tu­ally mak­ing it use­ful in earth­quakes.”

In Cal­i­for­nia, there is lit­tle in­cen­tive to deploy a sys­tem of earth­quake­sens­ing smartphones. Sci­en­tists are al­ready build­ing an earth­quake early-warn­ing sys­tem that could go public within two years if enough fund­ing comes through. That sys­tem re­lies on hun­dreds of science-grade sen­sors, some of which are so sen­si­tive that they can de­tect the grav­i­ta­tional pull of the moon.

A pro­to­type sys­tem gave San Fran­cisco eight sec­onds of warn­ing that shak­ing from the 2014 Napa earth­quake was on its way. That may not sound like a lot of time, but when it comes to quakes, even a few sec­onds can mat­ter.

“If you are a driver you can pull over, if you are at work you can get un­der your desk, and if you are a sur­geon you can re­tract your scalpel,” Min­son said.

A smart­phone net­work here could aug­ment the of­fi­cial one, the re­searchers said. And in places where there is no al­ter­na­tive, the crowd-sourced so­lu­tion might make more sense.

“If we could make it work well,” Heaton said, “then the next thing to think about is ex­port­ing that tech­nol­ogy to other parts of the world.”

Pho­to­graphs by Luis Sinco Los An­ge­les Times

VOL­UN­TEERS CLEAN UP in Napa af­ter the mag­ni­tude 6.0 earth­quake in Au­gust. A net­work of quake­sens­ing smartphones might be able to aug­ment the of­fi­cial early-warn­ing sys­tem Cal­i­for­nia has in the works.

EVEN A WARN­ING of sev­eral sec­onds could help, for ex­am­ple by giv­ing driv­ers an op­por­tu­nity to pull over and those in­side a chance to take cover.

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