Crowd-sourced Network Gets the Shakes

Earthquake-prone Southern California would benefit greatly from having highly accurate ground maps of shaking activity during and after earthquakes—all that’s required is the installation of professional-grade seismometers covering every block. Unfortunately, the units cost several thousand dollars each, so the plan is unlikely at best.

The Community Seismic Network stations small, inexpensive seismic sensors like this one in homes throughout Pasadena. The sensors send information about seismic events to the CSN researchers.
The Community Seismic Network stations small, inexpensive seismic sensors like this one in homes throughout Pasadena. Photo by Lance Hayashida

That’s why, in 2011, Professor of Geophysics Rob Clayton decided to get the crowd involved, creating the Community Seismic Network (CSN). The network asked residents of the greater Pasadena area to volunteer to host small, inexpensive seismic sensors in their homes. After being plugged into the volunteer’s home computer, the sensor—which is only about the size of a loaf of bread—begins sending information about seismic events to the CSN researchers.

The CSN is a more passive form of crowdsourcing. Ordinarily, the sensors just sit in the corner of someone’s house recording data and waiting for a seismic event to happen, but when an event occurs, the sensor’s little on-board detectors will detect movement and send a notice—or “pick”—to researchers via the attached computer. “When there is an event, we get hit with a bunch of picks coming in that contain the amplitude of the event, and from that we can make a map of ground acceleration over the entire region covered by the network,” he says.

Maps like these are important guides for first responders like medical staff and firefighters; since the region with the most severe shaking is often the region with the most damage, the ground acceleration map could help responders decide which area is in the greatest need of immediate help. And the more volunteers that offer to host a sensor, the more accurate the map can be.

“We want to have a high density of sensors in the area because we believe that the kind of acceleration from an earthquake varies on a scale of one kilometer—so if we’re a kilometer apart, you’re going to experience a different acceleration than I am,” Clayton says. “Oftentimes people try to attribute irregular patterns of damage to poor building materials, and although that’s a factor, I also think it’s because the ground shakes differently in different places.”

So far, the CSN has distributed more than 500 sensors in the greater Pasadena area—and Clayton and his colleagues are working on new projects that will expand the sensors’ reach even further. For example, sensors are now housed in 100 schools in the L.A. Unified School District with the goal of expanding to all of the more than 1,000 schools in the district.

In order to get a broader reach, Matt Faulkner, one of Clayton’s former graduate students, has been working on an app to exploit the accelerometers that are already installed on most cell phones for purposes including fitness tracking and gaming. “The initial problem with these accelerometers is that if I drop the phone to the floor, that is larger than an earthquake is going to put it through. So simple motions you can do to a phone cause it to have a signal that is larger than the thing you’re trying to measure,” Clayton says. But Faulkner found a clever way to develop algorithms that can separate anthropogenic motions—like running or riding a bike—from earthquake motions.

The app hasn’t yet been fully deployed, but if Clayton and his colleagues could get seismic information from every cell phone in Los Angeles, they project it would give the some of most detailed information about earthquakes ever made available.

“Sometimes the general idea of trusting crowdsourcing during a natural disaster can make problems,” Clayton says. “Often, people talk about only the worst damage and only the things that are most out of the ordinary, and the same thing is true of earthquakes. If you rely on eyewitness speculation, they can say, ‘Well, I wasn’t personally affected, but I saw lots of damage up there.’ That doesn’t work, but having actual sensors in the crowd is part of the solution.”

—Jessica Stoller-Conrad