2016-09-03. Seismic Hazard in the Midwest.

posted Sep 7, 2016, 10:22 PM by Alan Gould
Berkeley Seismological Laboratory. For GSS Energy Use chapter 3. Excerpt: The earthquake that rattled at least seven mid-western states on Saturday morning was a stark reminder that a new type of seismic hazard exists, which is associated with human activity. The temblor with a magnitude of 5.6 was located near the town of Pawnee, about 75 miles north-northeast of Oklahoma City. Although the quake caused only minor damage, it shook an area of the United States which - until a few years ago - was considered basically free of any significant seismic activity. But ever since an earthquake of the same magnitude struck a region immediately east of Oklahoma City in November 2011, it has become clear that a sizable seismic hazard, widely ignored until then, lurks under the oil producing states in the Midwest. ...When seismologists started to study the enormous increase in earthquake activity in Oklahoma, it very quickly became clear that it was not caused by natural phenomena. Instead, the cause was human activity. The first suspect was fracking. ...The real culprit, it turned out, also had something to do with oil and gas production. Virtually every hydrocarbon field in the world contains a significant amount of water, which is pumped to the surface together with the oil. In the United States alone, about 21 billion barrels of this so called "produced water" are generated each year from about 900,000 wells. This is equivalent to a volume of 2.4 billion gallons per day. Because this produced water contains salts, remnants of the oil and many other organic and inorganic chemicals, it cannot be flushed into regular wastewater treatment plants or even released untreated into rivers or creeks. It is simply too hazardous. To dispose of this water, it is pumped back into the ground, usually in injection wells deep below the groundwater aquifers and the oil producing formations. There are more than half a million such injection wells in the US, most of them in Texas, California, Oklahoma and Kansas....  http://seismo.berkeley.edu/blog/seismoblog.php/2016/09/03/seismic-hazard-in-the-mid. See also Geologist Sees Clues, and Further Dangers, in Puzzle of Oklahoma’s Earthquakes  by Michael Wines, The New York Times.