16 December 2009

Earthquakes in the Lone Star State

Posted by Michael McFadden

The old saw is that everything in Texas is big: trucks, hats, even garlic bread (a.k.a. Texas toast). But one thing that has never been big in the Lone Star State is seismic activity.

So when I went to the S31E. Observation and Analysis of Natural and Induced Microearthquakes II presentation, I was really surprised to hear that the Dallas Ft. Worth Metroplex has been experiencing earthquakes recently, likely caused by natural gas extraction.

Pipeline locations, from the U.S. Energy Information Administration I was also concerned on a personal level: my parents live in Ft. Worth, and draw royalties for a gas pipeline that snakes under their property. Indeed, Texas is crisscrossed with natural gas pipelines, as seen in the US Energy Information Administration map on the right.

Luckily, the quakes weren’t exactly Earth-shattering affairs. None of 150 tremors topped a magnitude 3.3, according to a team led by C. A. Frohlich from the University of Texas at Austin.

The shaking seems to be originating around the DFW airport. When the team dug deeper, they found the tremors were very near a gas well in the area.

It turns out the whole region is pockmarked with wells, because the Barnett Shale that underlies the area is rich in natural gas.

But it’s difficult to extract. To squeeze the natural gas out of the earth, producers dig deep (around 5 km), then use hydraulic fracturing to create fissures in the rock. Extracting the gas creates brine, which is then re-injected into the hole.

The team thinks that process of salt water injection from one particular well could be triggering the tremblors.

The extraction from this well has stopped, so there probably won’t be much shaking going on after this. Even if it was, Texas isn’t likely to experience "the big one" anytime soon, because the state has no real history of quakes.

Still, maybe I should tell my parents to brush up on their earthquake drills, just in case.

–Tia Ghose, UC Santa Cruz Science Communication Graduate Student