According to an assessment released by the United States Geological Survey, oil and gas drilling operations have made parts of Oklahoma just as earthquake-prone as the highest risk areas in California. The rising number of earthquakes in Oklahoma coincides with the increased drilling activity for oil and gas, the New York Times reports. The state experienced 907 quakes at magnitude 3 and above, the level at which quakes can be felt, last year. To put this into context, Oklahoma used to have less than 2 such earthquakes each year.
Oklahoma isn’t the only state affected by man-made quakes. Kansas has also seen a substantial rise. There were 54 earthquakes in the state last year at magnitude 3 or above; previously, it experienced even fewer quakes than Oklahoma.
For the first time, the USGS released a map of earthquake risks that considered man-made quakes. “By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the U.S.,” said Mark Petersen, chief of the USGS Natural Seismic Hazard Mapping Project. The map suggests that the increasing number of small human-induced quakes may lead to a large destructive one in the future. According to the USGS, the greatest risk is in a rural area along with Oklahoma-Kansas border.
Oil and gas drilling results in large volumes of toxic wastewater, which is injected deep into the ground for disposal. These wastewater injection wells increase the pressure on faults, and lead to tremors. According to NYT, Oklahoma experienced some of its largest quakes in state history this year, with magnitudes of 4.7, 4.8 and 5.1.
The Oklahoma Corporation Commission placed significant restrictions on underground wastewater disposal in February and March. Since then, the number of quakes seems to have slowed; there were 160 quakes with a magnitude 3 or above this year.