Rare earthquake warning issued for Oklahoma

Credit: US Geological Survey

Tuesday, August 19, 2014, 9:53 AM - Due to a worrisome increase in the number of earthquakes throughout central and north-central Oklahoma, federal and state seismologists have issued a rare earthquake warning for the region.

(EDITOR'S NOTE: THIS ARTICLE ORIGINALLY RAN ON MAY 7, 2014)

Although this warning does not represent an actual forecast of an impending major earthquake, simply because earthquake forecasting is extremely unreliable, the record number of small earthquakes recorded in Oklahoma since the beginning of the year is raising concerns about the possibility of a much larger earthquake in the near future.

"Because earthquake sequences are statistically abnormal behaviour, when you get a large increase in the number of small earthquakes, the potential for a larger earthquake also goes up," Bill Leith, the USGS Senior Science Advisor for Earthquakes and Geologic Hazards told StateImpact.

According to a USGS press release, there were around 110 earthquakes recorded in Oklahoma in all of 2013. From January 1 to May 2, 2014, the state has experienced over 140. The above map, courtesy of the USGS Latest Earthquake site, shows the cluster of earthquakes recorded there just over the last 30 days, which was around 120, ranging between magnitude 2.5 and 3.5. The map below shows the expected earthquake risk throughout the United States.

While there has been a history of earthquakes in Oklahoma, the risk there is fairly low, since most of the quakes felt there are light. The largest risk in the region is to the east, from southern Illinois through northeastern Arkansas. However, since 2009, the frequency and strength of quakes in the state of Oklahoma has been on the rise, with over 20 registering as magnitude 4.0 or higher, including one of magnitude 5.6 that shook the city of Prague, OK, on Nov. 5, 2011. To date, that was the strongest earthquake ever recorded there.

"While it’s been known for decades that Oklahoma is 'earthquake country', we hope that this new advisory of increased hazard will become a crucial consideration in earthquake preparedness for residents, schools and businesses in the area," Leith said in a statement. "Building owners and government officials should have a special concern for older, unreinforced brick structures, which are vulnerable to serious damage during sufficient shaking."

What's the reason for this increase in earthquakes over the past few years? Although there are certainly natural tremors that occur in the region, scientists are seeing a contribution due to wastewater injection by the oil and gas industry. A recent study has linked the 2011 Prague earthquake to this practice, and other research indicates that more earthquakes in the region have been caused by this as well.