Twitter, inexpensive seismic equipment transform citizens into scientists

By Sid Perkins

Web edition: December 16, 2009
Print edition: January 16, 2010; Vol.177 #2 (p. 15)

SAN FRANCISCO — Via two innovative programs at the U.S. Geological Survey, people interested in helping the agency collect earthquake data can become citizen seismologists.

One of the agency’s new seismology efforts is the Twitter Earthquake Detection Program, in which software scours the torrent of tweets flowing through the popular social network. After a quake, the number of such messages containing quake-related words spikes, says Paul Earle, a scientist with the USGS in Denver. The most common message — a simple “Earthquake! OMG!” or some variation thereof — is little more than a sign that the tweeter felt a quake, Earle noted in a press conference December 14 during the annual meeting of the American Geophysical Union.

But more detailed messages, especially those that include information about where the tweeter is located, provide excellent clues about how widely felt an earthquake was, and how strongly it shook various areas. The USGS already collects similar data via its website, where people can submit information at a quake-related Web link titled, “Did You Feel It?”

One benefit of the new monitoring program is its speed, says Earle. The info gleaned from the Twitter posts is available almost instantly, whereas even the preliminary analyses the agency’s scientists use to pinpoint a quake’s origin and size often take 15 minutes or more.

The other program, which the agency has dubbed NetQuakes, will use inexpensive seismometers in urban zones of quake-prone areas to fill gaps in its equipment network, says Jim Luetgert, a USGS seismologist in Menlo Park, Calif.

Most of the agency’s seismometers are extremely sensitive instruments. To discern slight ground motions, the equipment typically must be installed in areas far from sources of seismic noise such as highways and industrial activity. Besides rendering these instruments difficult to install and maintain, this requirement also creates gaps in the network in urban areas, says Luetgert. Adding to the expense of operating these remote seismometers, data transfer to office-bound scientists usually takes place over a satellite link.

But now the agency is deploying a new type of seismometer, a so-called NetQuakes instrument, that will address many of these issues, says Luetgert. Because this equipment will be installed in seismically noisy urban areas, it doesn’t need to be incredibly sensitive — which means the seismometers can be much less expensive. In fact, the seismometers are designed so they can be installed in the basement of a home or an unused space in an office building in no more than a couple of hours. If a component in the equipment fails, USGS can mail a replacement part, or an entire replacement unit, which the citizen seismologist can easily swap out.

Data gathered by the seismometers, including accelerations associated with back-and-forth ground motions, are stored on a flash drive. When accelerations exceed 0.25 percent g, the instrument considers that as a sign an earthquake has occurred, says Luetgert. Then, software in the seismometer assembles a data package — a record of all ground motions and accelerations stretching from 40 seconds before the quake began until 50 seconds after it ended — and transmits it to scientists via the citizen seismologist’s broadband Internet connection.

If a quake cuts power to the unit, batteries allow the seismometer to collect data for 10 days or so. Each unit costs about $4,000, says Luetgert. “This program is a good way to collect research-quality data without spending a lot,” he notes.

Since March, 68 NetQuakes seismometers have been installed in homes and businesses in the San Francisco area, and the agency seeks to deploy another 90 next year. Bay Area residents who would like to host one of these seismometers can get more information here.