A 4.8 magnitude Karnes County earthquake rattled doors Thursday morning. (Atascosa County is now reported as the epicenter) You can view USGS data Here. It isn't the first earthquake in the area, but was larger than previous quakes. It was just 2008, which is before Eagle Ford Shale development began, when a 3.7 magnitude quake struck the area and 1993 when the largest I can remember hit the area (4.3 mag). Yesterday's disturbance is likely the largest on record for the area, but one of a dozen or so since 1990. Tremors were felt as far as San Antonio. Oil & gas drilling activity has not been linked to this event. If drilling directly led to earthquakes, West Texas would have fallen off the map a long time ago. It just so happens that oil & gas are present in areas of high tectonic activity. The Los Angeles basin is one of the most active areas in the world and also boast the most hydrocarbons per cubic ft of rock in the world.
There have been concerns that deep disposal wells where fluids are being injected into the ground could be tied to small earthquakes. It won't be clear for a long time if that might be the case here. Test are ongoing in more established shale plays in North Texas' Barnett Shale and in Arkansas' Fayetteville Shale.
No injuries or major damage was reported, and the light quake wasn't even noticed by some residents living close to the epicenter, near Karnes City. Yet small vibrations felt in San Antonio did cause occupants to briefly evacuate a downtown federal building as a precaution.
The quake struck at 7:24 a.m. The U.S. Geological Survey said it was the largest earthquake on record for the area, surpassing a magnitude-4.3 shock recorded in 1993.
Thursday's earthquake occurred in a zone that has shaken in the past. From 1990 to 2006, at least a dozen small quakes rattled this region.
"It's an area where we've seen events before," said U.S. Geological Survey seismologist Susan Hough in Pasadena, Calif. "So it's not a big surprise."
Read a full news release at nydailynews.com
Here's an interview with a geologist at ksat.com and an article from caller.com that details the total number of earthquakes expected worldwide this year.