2010 was an active year for earthquakes in Oklahoma. The Oklahoma Geological Survey has recorded more than 200 earthquakes which occurred in Oklahoma. There have been nearly 60 earthquakes which were felt. This is a much greater number than in years past. The seismicity at this point appears consistent with normal background seismicity. Presently, the number of Earthquakes recorded in Oklahoma for 2010, appear more numerous than in years past but the fact remains that earthquake monitoring in our state was only initiated 50 years ago. This is a very short period of the Earth’s history, and this activity may not be as unusual as it appears to us today.
On October 13, 2010, there was a magnitude 4.7 earthquake near Noble, Oklahoma in Cleveland County. This earthquake had a maximum reported intensity of VI (capable of producing small amounts of damage) and was the second largest recorded earthquake in Oklahoma history. The largest recorded earthquake in Oklahoma history was a M5.5 on April 9, 1952 in El Reno, Oklahoma in Canadian County.
There was also a swarm of felt earthquakes in Canadian County with eleven felt earthquakes in just a few days time. The last such swarm occurred in 2004. The additional seismic stations associated with the Earthscope US Array provided much better data for this swarm than what was obtained during the 2004 swarm. The additional seismic stations in the state would be expected to increase the number of located earthquakes due to the greater coverage of the state. This does not, however, explain the increase in the number of felt earthquakes.
The greatest number of earthquakes have occurred in eastern Oklahoma County near Jones, OK. The analysis of these earthquakes has been greatly improved from the Earthscope US Array as well. In addition the OGS and the US Geological Survey have partnered to deploy another 10 strong-motion accelerograph stations in eastern Oklahoma County. This data is being used for both routine analysis, including locations, and more advanced research as well. The “Jones seismicity” does not appear to have the characteristics of seismicity that would be triggered by oil production activities, which are minimal in the area. Poorly located earthquakes tend to have shallow focal depths. Part of our research at the OGS is to dramatically improve our estimation of how deep these earthquakes are occurring. Well located events tend to concentrate between 3 and 6 km depth (~2-4 miles). The largest earthquakes occurring in eastern Oklahoma County are two which occurred 9 minutes apart on January 15, with adjusted magnitudes of 3.8 and 3.7 respectively. The additional instrumentation and dense seismic station distribution has made it possible to determine the sense of slip on faults associated with some of the earthquakes. These motions appear generally consistent with the regional stress field. This means that the seismicity is not inconsistent with what would be considered normal background seismicity. Before 2009 there had only been 7 earthquakes located in Oklahoma County. In 2009 there were 27 felt events in Oklahoma County.
The following links provide local and statewide earthquake hazard information: