Man-made earthquakes, a side effect of some 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 — 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, however. For people within 6 miles of the fault, artificial and natural quakes feel pretty much the same, she said.
Hough studied 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 even when the two types 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. A drop in magnitude of 0.8 translates to about 16 times less energy released, according to her study, published in the Bulletin of the Seismological Society of America.
— The Associated Press