In the well-developed parts of the world prone to temblors, including the West Coast of the United States, Mexico, parts of Europe, China and Japan, governments have invested in sensitive earthquake detection systems. But according to Sarah Minson, a U.S. Geological Survey geophysicist, high-risk regions without seismic monitoring could benefit by using satellite-tracking technology inside a smartphone, a crowdsourced key to early earthquake warnings.
In 2011, when a minor (but relatively powerful) quake rattled most of the United States eastern seaboard, there wasn’t (and still isn’t) a dedicated early warning system as part of the regional seismograph network. It’s the same throughout much of South America, the South Pacific and east and central Asia, but those places lack warning systems for sheer economic reasons—standard earthquake detection equipment is expensive.
In a crowdsourced earthquake early warning system, GPS sensors in smartphones near an earthquake's epicenter could sense the resulting ground displacement, and send warnings to more distant smartphones before the shaking reaches them. (Emiliano Rodriguez Nuesch and Martin Zeta of Pacifico)
Smartphones could fill that gap, according to Sarah Minson. She is the lead author of a new study in Science Advances that examines the potential for using cell phones’ GPS data as an early warning network.
Cheap yet loaded with sophisticated technology, cell phones are everywhere: there are an estimated 7 billion mobile devices in use across the globe.
“People are recognizing that cell phones can be incredible tools for science,” Minson says. “The advantage of crowdsourcing is that there are a ton of sensors, but also that there are a ton of little handheld computers that are processing power,” able to crunch data quickly.
But mobile GPS data hasn’t been seriously looked at for seismic use, primarily because cell phones can’t tell your exact location with great precision, and because people fiddle around with lots of apps unrelated to earthquake listening. What phones are good at, however, is talking with triangulated satellites to detect your very incremental movements from one spot to another—as little as half an inch from a previous position.
That motion tracking is the key to earthquake detection, where measurements of displacement, or how much a fault has moved, are as important as how much shaking a person experiences. If enough people have devices recording and reporting that movement, an app designed to transmit a warning based on that aggregated data would make for a fairly accurate early warning tool.
Most quaking you feel during an earthquake is caused by secondary waves, or s waves, which travel through Earth at a rate of two miles per second. But data travels much faster, quickly outpacing poky s waves in regions miles away from the epicenter. Even a few seconds’ warning time can be valuable—time enough, say, for a surgeon to put down a scalpel, or to allow a teacher to get students under tables. There’s also some calming virtue in being forewarned of a sudden shaking.
So in the case of the Mineral, Virginia earthquake, cities like Washington, D.C., 84 miles away, would have had around 40 seconds of advance notice. Depending on the parameters in a potential mobile phone app, Minson thinks with enough users near the epicenter contributing data to rule out a false alarm, a warning could be triggered and sent out in seconds.
Relatively few devices would need to be engaged. As part of her research, Minson matched up actual GPS data from 462 monitoring stations in Japan captured during the 2011 magnitude-9.0 Tohoku quake with hypothetical data that mirrors what a cell phone would generate in such a situation. The curves that measured the permanent shift of the Earth’s crust at the stations aligned very closely. Minson estimates that just .0004 percent of Japan’s population of 127 million would need to be carrying cell phones to collect the same data as those monitoring stations.
There are a few catches, though. First of all, the technique really only works for fairly strong earthquakes, above a 7 magnitude on the Richter scale. Secondly, there aren’t many cell phones hanging out on the seafloor, where many quakes originate. And lastly, phone companies haven’t shown much inclination so far to allow access to the raw location data their devices collect.
“None of this can happen unless there comes a way to get access to the data on the phones,” Minson says.
The geophysicist is already working on launching a USAID-funded pilot program over the next year to deploy hundreds of cell phones and secondary external GPS sensors. Spread out in a network across Chile, a region with high seismic activity yet without a functional early warning system, researchers will be able to gather real-time data from the external sensors as earthquakes happen.
John Vidale, a seismologist with the University of Washington who has long been involved in work on early warning systems, praises Minson’s idea of mining cell phones for GPS data as sensible and innovative. However, he points out that phones can never replace sensitive scientific equipment.
“Cell phone earthquake early warning systems may be a great solution in some situations, particularly in the Third World and where earthquakes are infrequent,” says Vidale. “But phones will never have the emplacement deep underground that gives dedicated seismometers their tremendous sensitivity. I expect places such as Japan, Taiwan and the West Coast will ante up for more sophisticated and dedicated systems.”
Minson notes that one great advantage of cell phones is that they are frequently updated.
“If we’re borrowing data from crowdsourced cell phones, the users are helpfully replacing their old phones with the best technology every two years,” she says. “We’d be getting everyone’s fanciest and best data.”