according to the U.S. Geological Survey.
While Friday’s was the largest in the sequence, officials have also recorded a recent 4.5, a 4.9 on July 23 and a 4.7 last year. Earthquakes were first introduced to the area via water flooding, a process in which water is injected into the ground to increase production from oil reservoirs. Oklahoma experienced a dramatic spike in the number of earthquakes in the early 2010s that researchers linked to wastewater from oil and gas extraction that was being injected deep into the ground, activating ancient faults deep within the earth’s crust. The wastewater is left over from oil and natural gas production and includes saltwater, drilling fluids and other mineralized water.