The USGS point out that areas across the central and eastern United States (CEUS) have been experiencing a rapid increase in the number of “induced” earthquakes over the past seven years – with Oklahoma experiencing around ten times more than what would normally be expected. The key to their origin is in their use of the word “induced.”
Numerous studies have linked these quakes to wastewater injection through deep wells in various locations. Along with other potential mechanisms, including oil recovery and fracking processes, humans are destroying the underlying geology to such a degree that faults that were previously stuck suddenly have space to jut forwards. As they do, they release energy in the form of earthquakes.
The USGS are keen to stress that, although more research is needed to confirm this link, the circumstantial evidence is certainly fairly compelling.
Kansas serves as a good case study in this regard. Both Kansas and Oklahoma saw a jump in the number of quakes greater than 3.0M since 2010, but only the former began to limit its wastewater disposal. Kansas saw a 60 percent drop in quakes, but Oklahoma’s continued to rise.
In terms of other intraplate quake-prone regions, the nearby New Madrid Seismic Zone (NMSZ) is one that seismologists are fairly concerned about. Three unexpected ruptures occurred in the NMSZ between 1811 and 1812, with one registering at 7.7M. If this happened today, it would cost $300 billion in damages and kill many people.
Map showing earthquakes taking place in Oklahoma above M3.0 from January 2013 to April 2016. USGS