November 8, 2011 – OKLAHOMA – A 4.7 magnitude earthquake struck 9 km (5 miles) from Prague, 10 km from Sparks and about 71 km (44 miles) from Oklahoma City. It is the strongest tremor to strike the state since the 5.6 magnitude earthquake struck over the weekend. Geologists still have no explanation for why such intense earthquakes are rattling the state. The number of earthquakes recorded in Oklahoma has soared from its historical average of about 50 a year to 1,047 last year and that record is likely to be broken this year, said Austin Holland, a seismologist at the Oklahoma Geological Survey. Until last year, the highest number of earthquakes Oklahoma state had recorded was 150, in the mid-1990s.
Mystery intensifies: Scientists are puzzled by the recent seismic activity. It appeared the latest quake occurred on the Wilzetta fault, but researchers may never know for sure. Earthquakes that hit east of the Rocky Mountains are harder to pinpoint because the fault systems are not as well studied as major faults like the San Andreas in California. There are 181 injection wells in the Oklahoma county where most of the weekend earthquakes happened, said Matt Skinner, spokesman for the Oklahoma Corporation Commission, which oversees oil and gas production in the state and intrastate transportation pipelines. But natural gas companies claim there is no proof of a connection between injection wells and earthquakes, and a study released earlier this year by an Oklahoma Geological Survey seismologist seems to back that up. It found most of the state’s seismic activity didn’t appear to be tied to the wells, although more investigation was needed. “It’s a real mystery,” seismologist Austin Holland of the Oklahoma Geological Survey said of the recent shaking.”At this point, there’s no reason to think that the earthquakes would be caused by anything other than natural” shifts in the Earth’s crust, Holland said. –NY Daily News