The cellphone in your pocket could soon save you from an earthquake. Researchers have shown that it is possible to use GPS data from smart phones to detect tremors, potentially providing an early warning system to those who have not yet been hit.
"What’s really nice about this work is they are using sensors that people carry around anyway," says geophysicist Kristine Larson of the University of Colorado, Boulder. "It could be very, very useful."
In the moments before an earthquake, a few extra seconds can mean the difference between life and death. With a little bit of warning, people can take shelter, nuclear power plants can take last-minute precautions, and natural gas utilities can shut down pipelines. Japan has an early warning system that relies on more than 1000 seismometers throughout the country, which saved lives during the magnitude-9 Tohoku earthquake that hit in 2011. A similar system exists in Mexico, and another is under study in California. But such systems are expensive and time-consuming to install and maintain, making cellphones an attractive alternative, especially for earthquake-prone countries in the developing world.
Previous studies of crowdsourcing earthquake early warning systems have relied on phones' accelerometers, which estimate the phone's movement, rather than GPS tracking, which locates the absolute position of the phone using satellites. Scientific GPS stations have already been used to detect earthquakes, but the new study found that even consumer devices with GPS could be useful for crowdsourcing warnings. And as more and more of our devices integrate GPS navigation, including vehicles, increasing amounts of data could boost the sensitivity of such efforts.
To understand whether smart phones and other consumer devices could detect quakes with GPS at all, researchers tested the sensitivity of such devices. Cell phones typically use a coarser method of positioning than do the most sensitive scientific instruments, which take advantage of more information encoded in the GPS signal. The scientists studied the accuracy of cellphone GPS by shaking a phone and comparing its recorded displacements with a more accurate scientific device. And by monitoring the phone for movement while holding it stationary, they measured the chance for false alarms. The researchers determined that consumer GPS devices could detect earthquakes of magnitude 7 and above, allowing possible warnings for people located away from the epicenter of the most destructive quakes, they report today in Science Advances.
Next, the researchers tested the concept using a computer simulation of a magnitude-7 earthquake near Oakland, California, on the Hayward fault, a likely spot for future tremors that runs through the San Francisco Bay Area. By simulating the typical response of cellphones to shaking, they estimated the signals in cellphones near the epicenter. In the researchers' system, a quake "triggers" a phone if it and four neighboring devices all record simultaneous movements greater than 5 centimeters. To weed out coincidences, the system only issues an alert if more than 100 devices see such triggers. Assuming data from 0.2% of the population—less than 5000 people—the system was able to detect the simulated earthquake within 5 seconds, a speed that would have allowed a few seconds of warning before the strongest shaking began in San Francisco and 10 seconds before it began in San Jose, providing time for children to get under their desks and for trains to put on the breaks.
The researchers then tested their system with real data from the Tohoku quake. The team used an array of 462 GPS stations spread across Japan to approximate the data that would come from cellphones. Although these scientific instruments are more precise than cellphones, they record lower quality data as well, which is similar to data from consumer devices. In this scenario, the researchers set the bar for detection so that the chances of a false alarm would be about one in 2 million. The system would have detected the earthquake 77 seconds after it began, which would have allowed a warning of about 10 seconds before the earthquake reached Tokyo. What’s more, it would have allowed several minutes' warning before the accompanying tsunami. Although scientific detection systems might provide even faster warnings, these systems might be useful in places without warning systems.
As technology advances and more devices integrate GPS tracking, the system will become more useful, says study author Benjamin Brooks, an earthquake scientist at the U.S. Geological Survey in Menlo Park, California. "It’s not really just about smart phones, it’s about all sorts of Internet-connected devices that have positioning associated with them. … We think the numbers are going to be so large that you could be very liberal with your criteria for using a specific device." Detection with cellphones is difficult because users are constantly moving them around, but with enough data, the system could rely on devices that weren't in motion before the quake, improving warning capabilities.
However, computational earthquake seismologist Jesse Lawrence of Stanford University in Palo Alto, California, points out a few challenges to the approach. Using GPS drains phone batteries, so data collection might need to be restricted to times when phones are recharging, meaning that few phones will be operating during the day. And the software has to deal with phones behaving unpredictably during an earthquake, such as falling from a table onto the floor. Because of that, Lawrence says, "the way that they’ve done the simulations, I would argue, doesn’t really match real world." But he is optimistic about the possibilities for this technology in the future. "It’s great research, and this is the first step."