According to two studies which were published this week the earthquake rate in the US has increased six times since 2009. One of the studies was conducted by researchers from the Stanford University and the other by researchers from the University of Colorado. According to the studies what has caused this increase are the wastewater injections used for gas and oil development.
The average-size injections are not the main cause, but the supercharged wastewater injections. According to the study conducted at the University of Colorado wells that injected more than 12 million gallons of saltwater into the ground every month were more likely to shake the ground than those who used smaller amounts. The lead author of the study, Matthew Weingarten who is a doctoral student at the University of Colorado, said that compared to the 1970s when there was a handful of earthquakes per year in 2014 there were 650 earthquakes.
Weingarten said that this is the first research which links wastewater injections with earthquakes. He remarked:
“We saw an enormous increase in earthquakes associated with these high-rate injection wells, especially since 2009, and we think the evidence is convincing that the earthquakes we are seeing near injection sites are induced by oil and gas activity.”
Some of the most damaging earthquakes were reported in 2011 and 2012 and they had magnitudes ranging from 4.7to 5.6. They took place in Arkansas Colorado, Oklahoma, Texas and Timpson.
Researchers at the University of Colorado analyzed 18,757 wells which were connected with earthquakes that took place within 9 miles of them. 170.000 wells were not linked with earthquakes. Although only 10% of the wells were connected with earthquakes more than 60% of them were connected with nearby earthquakes. It seems that the wells associated with earthquakes were mainly discovered in Oklahoma and Texas.
Rall Walsh, the lead author of the study conducted at Stanford University, focused on Oklahoma. He said that 8% of Oklahoma’s land contained 27 percent of the water disposal and 71 percent of the earthquakes. He also mentioned that there might be a series of other factors which can make an area more vulnerable to earthquakes. Such factors include for example the regional state of stress and also the orientation to the stress field.
Walsh drew attention to the fact that geology is different across the US and it can vary depending on the position of the well. Not just the rate in one well is important, but also the fact that there are many wells in a small area.
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