People who live in seismically active areas are so good about posting earthquake tweets that you may even be warned of a quake via Twitter before the shaking actually starts at your house. Now two USGS employees have found that Twitter is also an accurate reporting tool when it comes to earthquake detection.

The USGS has long used something called Shake Maps to crowdsource the human-perceived ground motion from an earthquake. After the quake, you’re supposed to go to the website, pinpoint your location and rate the amount of shaking you felt. The result are beautiful color-coded maps that help them verify and evaluate the event.

But USGS seismologist Paul Earle and developer Michelle Guy had a hunch that people posting their geotagged reactions to Twitter might build a dataset that was at least as accurate as those self-reported maps. They pulled Twitter’s API to search for tweets related to earthquakes and discovered something fascinating:

They found that people Tweeting about actual earthquakes kept their Tweets really short, even just to ask, “earthquake?” Concluding that people who are experiencing earthquakes aren’t very chatty, they started filtering out Tweets with more than seven words. They also recognized that people sharing links or the size of the earthquake were significantly less likely to be offering firsthand reports, so they filtered out any Tweets sharing a link or a number. Ultimately, this filtered stream proved to be very significant at determining when earthquakes occurred globally.

Of course this only works if the data can be corroborated with the USGS’s own sensors, about 2,000 of which are sprinkled around earthquake-prone regions. But it does offer a free, nearly universal reporting tool that can work with the sensors, which are expensive to install and maintain.

The great thing about this news is that data is gathered very accurately and automatically without people having to get to a computer afterwards. I admit—and I’ve written about this before—my first instinct when I feel the shaking start is to grab my phone to report on what I’m experiencing. (After I, like, get to safety and stuff.) I just hope they’ve adjusted their search for my kind of updates:

As I’ve also written about before, tweets travel faster than seismic waves so there is the potential for Twitter to help—at least a little—with the early warning system that will soon be deployed in the US. Drop, cover, and hold on is still your first priority when it’s really shaking. But in the meantime, keep those earthquake tweets coming.

[Twitter blog]