People in parts of Oklahoma and Kansas now face the same threat of destructive earthquakes as Californians, with human-induced tremors from oil and gas production helping spread earthquake vulnerability across much of the US.
For the first time, the US Geological Survey mapped out areas of the country vulnerable to earthquakes caused by human activity as well as natural events and found that around seven million people in the central and eastern US are at risk from ground-shaking episodes.
The risk of a major tremor over the next year is greatest in northern Oklahoma and southern Kansas, the USGS study found, with the largest number of at-risk people found in Oklahoma and Texas. Colorado, New Mexico and Arkansas also have a significant number of people potentially disturbed by earthquakes caused by human activity.
Oil and gas production has ramped up significantly in these states over the past decade, with the USGS pointing to wastewater disposal from these operations as being the “primary cause for recent events” in central and eastern parts of the country.
In such cases, salty water that is a byproduct from fossil fuel production is injected deep underground, below drinking water aquifers. This process can increase fluid pressure in fault zones, causing earthquakes in certain circumstances.
Water is also injected underground in a separate, controversial practice known as hydraulic fracturing, or fracking. This process, aimed at liberating pockets of gas found in rock formations, can result in small “micro earthquakes”. However, the USGS said that fracking is rarely the cause of earthquakes felt by people on the surface.
“By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the US,” said Mark Petersen, chief of the USGS national seismic hazard mapping project. “This research also shows that much more of the nation faces a significant chance of having damaging earthquakes over the next year, whether natural or human-induced.”
The USGS has documented what it calls a “dramatic increase in seismicity” in the central US over the past decade. From 1973 to 2008, there was an average of 24 earthquakes of magnitude three or larger per year. By 2014, this figure had ballooned to 688 earthquakes.
Earthquakes can be induced at distances of 10 miles or more away from where water is injected underground, leading to concerns that property is at increasing risk as drilling operations expand.
Oklahoma, which is predominantly affected by wastewater-induced earthquakes, now ranks behind only Alaska and California for earthquake frequency. The largest human-caused tremor experienced to date was a 5.6-magnitude quake near Prague, Oklahoma.
