Oklahoma earthquakes linked to oil and gas drilling

http://www.eurekalert.org/pub_releases/2015-06/ssoe-oel_1061215.php

Public Release: 18-Jun-2015
Stanford's School of Earth, Energy & Environmental Sciences

Stanford geophysicists have identified the triggering mechanism responsible for the recent spike of earthquakes in parts of Oklahoma-a crucial first step in eventually stopping them.

In a new study published in the June 19 issue of the journal Science Advances, Professor Mark Zoback and PhD student Rall Walsh show that the state's rising number of earthquakes coincided with dramatic increases in the disposal of salty wastewater into the Arbuckle formation, a 7,000-foot-deep, sedimentary formation under Oklahoma.

In addition, the pair showed that the primary source of the quake-triggering wastewater is not so-called "flow back water" generated after hydraulic fracturing operations. Rather, the culprit is "produced water"-brackish water that naturally coexists with oil and gas within the Earth. Companies separate produced water from extracted oil and gas and typically reinject it into deeper disposal wells.

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