There’s so much you can do with a smartphone today – much more than just browsing the web or social media. When you can combine them in a network, however, the possibilities might be endless. For instance, researchers at Caltech and the United States Geological Survey (USGS) are working on an earthquake early warning system based on the collective data fed in by thousands of smartphones. Only a couple of countries in the world give vulnerable cities an early warning – often just enough time to hit cover and save your life – but smartphones are virtually ubiquitous all over the world, even in poor countries which lack basic infrastructure like roads or flushing toilets.
Hundreds of millions of people live in earthquake prone areas, like those along fault lines. Yet, there are only a couple of countries and states that use an early warning system for earthquake, since the monitoring equipment and staff can be prohibitively expensive. Some might actually be surprised to hear that California, a notoriously vulnerable region of the United States, is well behind countries like Mexico, Japan and even Turkey in terms of early warning capabilities. These can send up to a minute heads start to schools, fire stations and even individuals who signup for an early warning, where this is available. These exploit a simple principle: shaking from an earthquake travels slower than the speed of today’s telecommunications system. For example, it would take more than a minute for a 7.8 earthquake near the Salton Sea to shake up Los Angeles, 150 miles away. But within a few seconds since the shaking starts, seismic sensors would pick up the signal and send it through the network in a heartbeat.
Sarah Minson, a USGS geophysicist and lead author of the study which appears in the April 10 issue of the new journal Science Advances, realized that smartphones could very well be used as seismic sensors, albeit not as sensitive. Harnessing the collective power of many smartphones can thus help build a crowd-sourced alert network. Their findings suggest that GPS receivers in smartphones are sufficient to detect the permanent ground movement, or displacement, caused by fault motion in earthquakes that are approximately magnitude 7 and larger. The signal is passed through the network and an algorithm analyzes it to determine where the earthquake took place and how long it will take until reaches an individual user, which becomes alerted.
“Thirty years ago it took months to assemble a crude picture of the deformations from an earthquake. This new technology promises to provide a near-instantaneous picture with much greater resolution,” says Thomas Heaton, professor of engineering seismology and a coauthor of the new study.
The crowd-sourced earthquake early warning (EEW) system was tested on data that simulated a magnitude 7 earthquake, and with real data from the 2011 magnitude 9 Tohoku-oki which devastated Japan. The results show that EEW works fairly good with as little as 5,000 smartphones connected in a large metropolitan area – these are enough to send an early warning to a city farther away.
According to the paper, earthquakes with a magnitude smaller than 7 can’t be detected by GPS, which isn’t sensitive enough. However, all smartphones are equipped with accelerometers (the kind that help you tell where north is or let you play really cool video games just by moving your phone around). A new system based on these microelectromechanical systems might detect earthquakes as low as magnitude 5. Caltech’s Community Seismic Network Project is currently developing an EEW system based on accelerometers. Seismologists from the National Institute of Geophysics and Volcanology in Italy have already built one – they report promising results for earthquakes larger than magnitude 5.
“The U.S. earthquake early warning system is being built on our high-quality scientific earthquake networks, but crowd-sourced approaches can augment our system and have real potential to make warnings possible in places that don’t have high-quality networks,” says Douglas Given, USGS coordinator of the ShakeAlert Earthquake Early Warning System.
“Crowd-sourced data are less precise, but for larger earthquakes that cause large shifts in the ground surface, they contain enough information to detect that an earthquake has occurred, information necessary for early warning,” says study coauthor Susan Owen of JPL.