, US quake count hovers around 750-850.

Well, no, as some people who felt the ground shake late Thursday and Friday can attest. At least six small quakes centered between Dallas and Fort Worth alarmed some residents, but no damage or injuries were reported.

Irving resident Christine Laughland said she was sleeping when a quake woke her. She's from California and knew what was happening. But she couldn't say the same thing for her dogs.

"They were barking hysterically because it was their first one," she said.

The first small shake came about 11:30 p.m. Thursday, rattling the ground in Irving, Grand Prairie and nearby communities. Several more quakes followed over the next 3 _ hours, according to the Center for Earthquake Research and Information at the University of Memphis. At least two more were reported about 4 p.m. Friday in the same general area.

More small aftershocks are possible, experts said.

Irving police spokesman David Tull said his agency received about 25 calls about midnight from people asking about the vibrations, which set off car and building alarms.

"The whole building just vibrated, just, bam! It's really scary," one woman told a dispatcher, according to a recording released Friday.

The U.S. Geological Survey also got reports of shaking from Dallas, Euless, Hurst and Fort Worth. The strongest two quakes measured at magnitude 3.0. In the scales seismologists commonly use to measure earthquakes, each whole number represents 10 times the power of the one before. So, the magnitude 9.1 killer quake off the coast of Indonesia's Sumatra on Christmas Day 2004 was more than a million times stronger than what North Texas experienced.

This area gets small quakes about every 10 years, said John Ferguson, a geosciences professor at the University of Texas at Dallas. Sixteen years ago, there was a similar event near Commerce. And in 1985, there was one near Valley View.

Areas of high seismic activity, such as parts of California, sit next to the edge of huge sliding plates on the earth's crust. North Texas is a long way from an edge. But like much of the world, this area rests above cracks, called faults, that sometimes shift and cause shaking on the surface.

But quakes in North Texas are puny. In fact, there is no geological evidence that this area has seen a strong quake in thousands of years, Dr. Ferguson said. And this week's quakes are not necessarily evidence of more to come. If the area receives more quakes, people may not even feel them, he said.

Nobody knows exactly what causes a particular quake, Dr. Ferguson said. But it's possible that the recent increased drilling and extraction of natural gas from the Barnett Shale had an effect. The extraction process affects the fluid pressure deep inside the earth, which is the sort of thing that could nudge a nearby fault, he said. It's happened elsewhere.

"There is no way to rule that out," Dr. Ferguson said.

But there is also no way to rule it in, said Chip Minty, spokesman for Devon Energy Corp., the largest and one of the earliest producers of the Barnett Shale.

Mr. Minty said it's unlikely the drilling and extractions caused the tiny quakes. Even if it did, he said, there has never been a connection between the drilling process and any significant earthquake.

"To draw a correlation between earthquakes and oil and gas production, that just hasn't happened," he said.

If these had been just a little weaker, most people wouldn't have known they happened.

The first few quakes were probably more noticeable because they happened late at night, said Bryan Stump, a geology professor at Southern Methodist University.

"At midnight, that's when I'm quiet and maybe reading my book, and it's the time I'm most likely to notice a quiet event," he said.

Dr. Stump's students got a chance to read data from the school's earthquake detectors Friday morning. And their professor got to drop some local news into his class, an introduction to geology focusing on earthquakes and volcanoes.

"We started right out with it," he said.

Staff writer Arlinda Arriaga contributed to this report.

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