WASHINGTON – Man-made earthquakes, a side effect of some high-tech energy drilling, cause less shaking and in general are about 16 times weaker than natural earthquakes with the same magnitude, a new federal study found.
People feeling the ground move from induced quakes – those that are not natural, but triggered by injections of wastewater deep underground – report significantly less shaking than those who experience more normal earthquakes of the same magnitude, according to a study by U.S. Geological Survey geophysicist Susan Hough.
Distance matters in this shaking gap, however. For people within 6 miles of the fault, artificial and natural quakes feel pretty much the same, she said.
Hough studied similar-sized man-made and natural quakes in the central and eastern United States from 2011 to 2013, comparing the reported magnitude to what people said they felt in the USGS electronic “Did You Feel It” survey.
She found that while two different types of temblors may have had the same magnitude as measured by seismographs, they had distinct differences in what people said they felt.
The way artificial quakes felt was equivalent on average to a natural quake that had a magnitude 0.8 smaller. So a 4.8 induced quake felt like a 4.0 quake, Hough said.
The magnitude scale used by USGS and others is mathematically complex, but a drop in 0.8 magnitude translates to about 16 times less strength or energy released.
Sometimes the difference is even bigger. Hough said a 5.3 August 2011 man-made quake in Trinidad, Colorado, actually felt like a 4.0 quake, which is about 90 times weaker, based on the thousands of responses in the “Did You Feel It” survey system.
The study, published Monday in the Bulletin of the Seismological Society of America, looked at quakes in Oklahoma, Colorado, Arkansas, Texas and Ohio.
It included a 5.7 quake in Prague, Oklahoma, in November 2011 that injured two people and damaged 14 houses, which Hough said felt like 5.1 magnitude natural quake.