|Fig. 1: Earthquakes per year in California.  (Source: F. Voris)|
Since earthquake tracking began, it has always been clear that seismic events occur most commonly at the boundaries of tectonic plates. At these faults, plates moving in opposite directions push, pull, or slide against one another until the Earths crust can no longer resist these forces. Once this occurs, the effects are felt on the surface in the event of an earthquake. 
These boundaries where tectonic plates meet and earthquakes regularly occur are known as faults. It stands to reason that states which lie on fault lines would experience the highest propensity of earthquakes. California and Alaska, home to the world renowned San Andreas fault and Denali fault, respectively, have historically proven this axiom. In years past, they have often been at the top of earthquake frequency charts, joined by Hawaii, an island on top of a perpetually active volcano. For reference, we can see that in the last three reported years California has experienced between 100-200 earthquakes per year with a relatively uniform distribution.  (See Fig. 1.) In this sense, nature has been predictable and works as expected. Earthquakes happen in places of high geothermal and tectonic activity.
This held true until 2011, when occurrences of earthquakes in Oklahoma made an exponential leap compared to previous years.  (See Fig. 2.) What could possibly justify Oklahoma, a state that meets neither of the tectonic or geothermal criteria, being the undisputed leader in earthquakes per square mile within The United States?
Geologists attribute the environmental impact to human causes. In the years that correlate to Oklahomas earthquake boom, Hydraulic Fracturing in the area has seen the same meteoric rise.  Hydraulic Fracturing is a process that requires pumping high pressured liquid thousands of feet underground. The high pressure fluids then crack the shale rocks that contain natural gas making the resource far easier and more efficient to extract. The method of extraction has increased in popularity in The United States, putting thousands to work and providing relatively easy access to clean burning natural gas. Many have seen this boom as having a positive impact, and indeed natural gas produces fewer emissions than the burning of coal or oil.  Information regarding Oklahomas earthquake epidemic paints a much darker and less environmentally friendly picture of Hydraulic Fracturing.
|Fig. 2: Earthquakes per year in Oklahoma.  (Source: F. Voris)|
The detriment to the environment is thought to come not from the fracking process itself, but from the methods used to dispose of waste from the extraction.  After pumping the high pressure liquid into the Earth it becomes contaminated with metals, the oil/gas itself, and the hydraulic fluid used to reach ground-breaking pressures. Once this water is retrieved it is not safe for drinking, or any other industrial purpose. In order to dispose of this waste, as of 2014, over 10,000 wastewater sites have been constructed in Oklahoma alone. These sites pump the wastewater below the water table to be disposed of forever. In doing so, they increase the subterranean pressure and disrupt the delicate equilibrium of inactive faults well below Oklahomas surface inducing seismic events.  Earthquake maps support this theory, as the location of seismic events are concentrated in locations where dormant faults meet wastewater disposal sites. 
These events have been noticed by the United States Geological Service, and they predict that serious harm might come from mans alteration of the Earths crust. While many small tremors might not get the attention of the population or its lawmakers, the continued escalation of the threat will surely be noticed. The stakes became clear on September 3rd, 2016 when a 5.8 magnitude Earthquake struck Pawnee, Oklahoma. This was the strongest earthquake in Oklahoma history and the USGS predicts a 40% chance that another major earthquake will strike Oklahoma in 2017.
© Frank Voris. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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