Wastewater wells occur when oil and gas companies inject wastewater deep underground. Scientists believe that the wastewater acts as a lubricant in existing fault lines, causing more movement. Hydraulic fracturing, commonly known as fracking, has also been linked to earthquakes, though the majority of Oklahoma's tremors were caused by wastewater wells.
Comment: The principal seismic hazard from injection-induced earthquakes comes from the disposal of wastewater into deep strata, i.e: basement formations. When the balance of applied shear stress is less than the strength of contact, the fault remains locked. Injection wells can promote a slip by increasing pore pressure, compounded by a change of load above a fault (such as the removal of oil). As faults slip, earthquakes release stored energy. The intensity of the earthquake is proportional to the stored energy and the triggers for release.
The USGS and Oklahoma officials are adding monitor stations to best determine which wastewater wells are causing the earthquake issue. There are currently 15 permanent stations and 17 temporary stations.
Thus far, none of the earthquakes in Oklahoma have caused major damage. However, USGS geophysicist Rob Williams believes it is only a matter of time, "Given the rate of earthquakes over the last six months, it's concerning enough to be worried about a larger, damaging earthquake happening, let alone what might happen in the future."
Comment: Proponents of fracking believe that a few small tremors are nothing more than the price of our modern technological civilization and environmentalists are merely creating another brouhaha. What they fail to consider is that large earthquakes around the globe have been found to specifically remote-trigger earthquakes near well sites via surface waves. A U.S. Geologic Service survey studied sites that had a long history of regional subsurface injection. Each triggered site had potential to host a moderate magnitude earthquake, suggesting critically stressed faults. And, each site had a relatively low level of seismicity rate before the first triggering episode. Industrial activity has a strong correlation to the increase in tremors. At least half of the 4.5 magnitude or larger earthquakes to strike the interior of the U.S. in the past decade have occurred in regions of injection-induced seismicity, with the seismic onset following injection by merely days or weeks.