Earthquakes in Oklahoma

With today’s 4.5 magnitude earthquake, it once again bringing up the question as to why.

It used to be a rare occurrence to feel an earthquake in Oklahoma, not anymore. Between 1975 to 2008 we had around 1 to 3 magnitude 3.0 earthquakes annually. Between 2009 to mid 2013 we have had more than 200 magnitude 3.0 or greater in Oklahoma. This increase is not believed to be due to natural fluctuations in seismic activity.  Since 2000, there have been over 785 quakes over 2.0 in magnitude.

The United States Geological Survey (USGS) released a statement about the earthquake swarms and the believed cause, stating one part of gas and oil drilling could be at fault.

The analysis suggests that a contributing factor to the increase in earthquakes triggers may be from activities such as wastewater disposal–a phenomenon known as injection-induced seismicity.

This is consistent with several recent studies that have linked earthquakes in Oklahoma with wastewater disposal wells. One study even linked Oklahoma’s largest earthquake, back in November of 2011, to disposal wells.

The USGS and Oklahoma Geological Survey (OGS) are making progress in evaluating the swarms. They have also encouraged Oklahomans to be aware of the hazards of these swarms.

Important to people living in the Oklahoma City region is that earthquake hazard has increased as a result of the swarm. USGS calculates that ground motion probabilities, which relate to potential damage and are the basis for the seismic provisions of building codes, have increased in Oklahoma City as a result of this swarm. While it’s been known for decades that Oklahoma is “earthquake country,” the increased hazard has important implications for residents and businesses in the area.

Studies of these swarms will continue but it does appear that wastewater disposal wells have played a role in the swarms.