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There's been a surge in earthquakes in the U.S. over the last few years. In Texas, there are ten times the number of earthquakes now than there were just a few years ago. Scientists say this increase is probably linked to all the oil and gas activity there. Mose Buchele reports from member station KUT in Austin.

MOSE BUCHELE, BYLINE: Here's how Pat Jones of Snyder, Texas describes the earthquake that struck her town in 2010.

PAT JONES: It just sounded like some car hit the back of our house. We got up and checked around and we didn't, you know, see or hear anything else.

BUCHELE: In 2012, in Alvarado, Texas Craig Bender called 911 about an earthquake.

CRAIG BENDER: There was an explosion type sound somewhere which does kind of concerned me, so. But I'm not seeing anything burning outside anywhere.

BUCHELE: And just this year, Greg Morrison described a quake shaking in Reno, Texas where he lives. He was speaking to state oil and gas regulators at a public forum.

GREG MORRISON: Feels like a semi-truck hitting your house with a bomb going off. And I am serious.

BUCHELE: Outside Texas, people are hearing those booms as well, often in states where there's been an upsurge in drilling and the use of disposal wells to store drilling waste. Scientists have linked those wells to quakes, and some quakes can get loud.

WILLIAM ELLSWORTH: Yeah, they're actually hearing the wave that traveled through the rock all the way to the earth's surface.

BUCHELE: William Ellsworth is a seismologist with the U.S. Geological Survey. He says it's a pretty common occurrence.

ELLSWORTH: So, when a fault slips underground it radiates two different kinds of seismic waves.

BUCHELE: One is a P-wave. That's an acoustic wave you can actually hear.

ELLSWORTH: The other wave is called the S-wave, or shear wave. It's the wave that carries most of the energy and it's the one that we typically feel.

BUCHELE: That first wave, the P-wave, travels faster than the S-wave. So, before the ground even starts to shake, people may hear something.

ELLSWORTH: It's a little bit like thunder. That you may see the flash in the distance, and then it takes a little longer for the wave, the air wave in this case, to propagate that makes the boom that you associate with lightening.

BUCHELE: The USGS even keeps an online catalog of earthquake noises. They range for a rumbling boom like this.


BUCHELE: To a sound almost like a bass drum.


BUCHELE: Most of the quakes in Texas are weak. But those are the kinds that make the loudest noise. Ellsworth says stronger quakes often register at a frequency too low for people to hear. For NPR News, I'm Mose Buchele in Austin.


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