'Human-induced' earthquakes indistinguishable from natural ones?

Washington, Aug 3 (IANS) Naturally occurring earthquakes and human-induced ones are actually "indistinguishable", a new study has revealed. The study, published on Wednesday in the US journal Science Advances, contradicted previous observations suggesting that induced earthquakes exhibit weaker tremors than the natural ones, reports Xinhua news agency. Earthquakes in the central US have increased in the past 10 years due to the expansion of unconventional oil and gas operations that discard wastewater by injecting it into the ground. About three million people in Oklahoma and southern Kansas live with an increased risk of experiencing induced earthquakes. A key question is whether these induced earthquakes excite ground motions that are substantially different than those of naturally occurring earthquakes. To answer this question, the new study used available instrumental recordings to estimate the stress drop -- the difference between the stress across a fault before and after an earthquake -- of 39 moderate-magnitude induced and natural earthquakes in the central US and in eastern North America. Once the faulting mechanism and the depth of the quakes are accounted for, the stress drops of induced and natural earthquakes in the central US share the same characteristics, results showed. "Our study shows that induced earthquakes and natural earthquakes in the central U.S. are inherently similar, and we can predict the damaging effects of induced earthquakes using the same framework as natural earthquakes," said first author Yihe Huang, an assistant professor at the University of Michigan. The scientists said that the types of rocks being exploited by unconventional oil and gas recovery in the US and Canada can be found all over the world, making the results of this study widely applicable.

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