Quake alerts

A single modern smartphone is a powerful tool: It can sense, compute, and communicate. But a large network of smartphones is so powerful that scientists say it might be able to substitute for seismographic sensor arrays, providing critical early warning in the event of an earthquake.

In a study published in April in the online journal Science Advances, a team led by researchers from the U.S. Geological Survey showed how a large network of cell phones, with their built-in GPS position location sensors, accelerometers, and data connections, might work almost as well as the detection systems in earthquake-prone countries such as Japan and Mexico.

“The GPS on a smartphone is shockingly good,” study leader Sarah Minson, a geophysicist at the U.S. Geological Survey in Pasadena told the Los Angeles Times. “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.”

Minson and her team studied the early warning data from the 2011 Tohoku earthquake in Japan that a network of 462 GPS-based sensors collected. To simulate the type of data that 462 phones would have collected, the researchers removed data until the sensors’ readings were what would be expected from a smartphone’s GPS and accelerometer. The much noisier data set was still sufficient to detect an earthquake just 77 seconds after the first tremors.

But a crowdsourced cell-phone-based detection system can’t rely on dedicated sensors in specific places. So the researchers did another simulation in which they assumed a magnitude 7 earthquake near San Francisco. They then used population maps to estimate how many phones would be in range in the event of a quake and then compared that to how much data they would need to detect it. If only 0.2 percent—or about 4,700 phones—were actively reporting data, the earthquake could be detected within about five seconds.

Of course, our cell phones are constantly being jostled around, so how do you differentiate seismic shaking from typical phone movements? The scientists addressed this problem by developing what they called “triggers” to detect false alarms by correlating the movement of a phone and its closest neighbors to see if they all recorded the same event at the same time.

Minson told the Times that the main benefit of crowdsourcing earthquake detection is that it’s inexpensive, because users have already bought the phones. 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 research team plans a real-world pilot test of the concept next year in Chile.

A shoe that grows

Many children living in poor countries have only one pair of shoes that they quickly outgrow. But their families can’t afford new shoes every year. Poverty charity Because International founder Kenton Lee recognized this problem and developed an inexpensive shoe that grows as children’s feet grow. The shoe comes in two sizes, from kindergarten to fourth grade, and fifth to ninth grade. Each size can be adjusted another five sizes. A crowdfunding campaign is underway to help produce and deliver the light, rubber-soled shoes, which sell for $10 a pair. —M.C.