What caused the "Great Irving Earthquake of Halloween '08"?

That's my own personal name for the earthquake that kicked of a string of minor earthquakes in the area, although I guess technically that was Grand Prairie. I, however, am in Irving so whatever. There were 11 earthquakes in that string. Although people around here were plenty shook up (ha ha) most geologists asked said essentially "Eh, these things happen." However, with another minor string just in May, it appears that people are finally starting to realize something may be wrong.

Researching a 100-mile radius around Fort Worth, the U.S. Geological Survey recorded 11 minor earthquakes from 1973 to 2006, the period the government database spans.

But, in the last seven months, 15 more minor quakes have happened, including the four most recently in Cleburne. Still, most occurred along the Dallas and Tarrant County line.

More earthquakes have happened in North Texas since last October than in the previous three decades combined, according to the USGA data.

Hm, what could it be? Not drilling, surely! (From the first article):

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.

Wait a sec. Really? It hasn't happened?

So, the hunt is on for what is causing so many earthquakes – a common occurrence in many parts of the world. Some have noted the increase is seismic activity has come at a time of increased drilling in the Barnett Shale. Energy exploration has triggered earthquakes before in Colorado.

More on that here (via Dallas Observer).

And from the same WFAA article:

"In Texas, there have been earthquakes associated with oil and gas production at a number of fields,” according to the State of Texas Hazards Analysis Manual from the Department of Public Safety. " Usually petroleum production does not cause earthquakes; in Texas there are more than two thousand oil and gas fields but only about five seem to have generated earthquakes."

The state listed six counties it says drilling has induced earthquakes.

“These include the Wortham field in Freestone County, the East Texas and Longview fields in Upshur and Gregg Counties, the Cogdell field in Scurry and Kent Counties, and the Fashing and Jourdanton fields in Atascosa County,” according to the web page.

So...what was that about no connection between drilling and quakes again? Look, nobody is panicking and suggesting that this is going to bring on an earthquake big enough to sink Dallas or something, but if my glass is going to get broken and my bookshelves fall over, I want some compensation!