Mineral, Va., quake?: 'Yeah, we felt it.'

The once-a-century earthquake that shook the East Coast on Aug. 23 marked a milestone for the U.S. Geological Survey's decade-old Did You Feel It? earthquake report crowdsourcing page.

Within hours of the quake that originated in Mineral, Va., the page had recorded more than 140,000 responses from as far north as Maine, as far south as Atlanta, and as far west as Indianapolis. That nearly doubles the site's previous record of about 72,000 responses for a single quake, said David Wald, a USGS seismologist who developed the crowdsourcing page.

At their height reports on the Virginia quake were coming into the page at about 13 per second, he said.

USGS launched DYFI? in California in 1999 and nationwide in 2001. Since 2005 the site has collected reports on quakes worldwide, wherever people have Internet access and the site is not blocked by unfriendly governments.

DYFI? now gets enough responses to most quakes that researchers can estimate the intensity, reach and origin point of a quake in a matter of minutes through online responses alone, Wald said, long before seismological data can give more definitive answers. When USGS geologists compare "shake maps" created by seismological equipment with maps created by DYFI? reports, the resemblance is almost spot on, he said.

Citizen reports on the intensity of quakes also can be extrapolated into crucial early damage assessments that take days or weeks to confirm through on-the-ground engineers' observations, he said.

In some cases, DYFI? reports can fill in information gaps when quakes hit regions that are not prone to seismological activity and where there is less high-caliber and high-cost detection equipment, Wald said.

Wald was speaking at a discussion arranged by the nonprofit Woodrow Wilson Center's Science and Technology Innovation Program.

The DYFI? site requests users' ZIP codes and addresses on the first page, then drills down into intensity questions on the second page, asking whether they were inside, outside, or in a moving vehicle when the quake hit, and whether there was damage or disarray in their building.

The site has been largely free of pranksters, Wald said, so geologists have to do very little sifting out of false reports. More often, people will post a second time to correct an error in their first report, such as accidentally listing the wrong ZIP code in the spot for the time they felt the quake, he said.

"People tend to be pretty sober after an earthquake," he said.

In some cases, the DYFI? page has helped advance the geological community's understanding of earthquakes, Wald said. Before the page's launch, for instance, seismologists generally believed people couldn't feel earthquakes with a magnitude lower than 2.0. When such quakes hit, though, the DYFI? page will now frequently get a dozen or so reports from very near the epicenter.

Scientists had long known that earthquakes of equal intensity will be felt over a greater distance on the East Coast than on the West Coast, Wald said, a result of differences in the regions' Mohorovicic discontinuity or "Moho," an area between the earth's crust and its upper mantle where seismic waves change their velocities. DYFI? reports didn't alter that belief, but confirmed it "like gangbusters," he said.

The 5.8 magnitude quake that hit Mineral, Va., for example, was felt more than 1,000 kilometers away. A similar quake on the West Coast would only have been felt about 300 kilometers away, Wald said.

When it comes to crowdsourcing quake information, DYFI? isn't the only game in town. Stanford University researchers have launched the Quake Catcher program in cooperation with USGS to embed small, cheap seismic sensors in hundreds of volunteers' laptop and desktop computers.

A USGS researcher also is mining Twitter data and has been able to pinpoint the epicenter of an earthquake within seconds based on the origin of a spike in Tweets using the word "earthquake," Wald said.

The volume of DYFI? responses has been about the same for East and West coast earthquakes if the quake's intensity and the number of people in the affected area are accounted for, Wald said. Responses from abroad are significantly lower, largely because of language barriers, he said. The response to the Virginia quake was likely elevated by the quake's high intensity over a huge landmass that included major cities such as Washington, Baltimore and New York, he said, rather than the novelty of East Coast quakes as some speculated.