Man-Made Quake Triggered Larger Temblor

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A human-caused earthquake may have triggered the strongest quake in Oklahoma history, reports a new study published in the Journal of Geophysical Research.

United States Geological Survey scientists recently presented evidence that a magnitude 5.0 quake that shook Prague, Okla., resulted from fossil-fuel extraction operations. That may have triggered a second quake, which struck on Nov. 5, 2011, p.m., less than a day after the initial quake centered near Prague.

The record-setting quake destroyed 14 homes. Thousands of aftershocks followed.

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During the past two decades, the number of earthquakes rattling the central and eastern United States increased dramatically, and industrial activities may be responsible. A 5.7 quake would rank as the strongest ever associated with waste-water storage operations.

Oil and natural gas facilities use empty underground wells as reservoirs for polluted waste water near Prague and many other cities in Arkansas, Texas, Ohio and Colorado. Rising use of that practice coincided with a rapid increase in quakes in the central United States. Three hundred quakes shook the region between 2010 and 2012, compared to only 21 events per year from 1967 to 2000, according to the USGC.

“The observation that a human-induced earthquake can trigger a cascade of earthquakes, including a larger one, has important implications for reducing the seismic risk from waste-water injection,” said USGS seismologist and coauthor of the study Elizabeth Cochran in a press release.

In the case of the Oklahoma quake, the geologic fault jumped and caused the initial 5.0 quake. Pumping waste water into an empty well may have over-pressurized the fault, known as the Wilzetta. That released other geologic pressures which had previously pinned the fault into place. The fault then slipped and shook the Earth.

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The epicenter of the 5.0 quake occurred within 200 meters (700 feet) of a waste-water injection site, according to a study in Geology.

Geologists have also suggested that underground wastewater disposal triggered a magnitude 5.3 quake in Raton Basin, Colo. Seismologists in Arkansas, Colorado, Ohio, Oklahoma and Texas currently keep tabs on  triggered tremors, known as induced earthquakes.

Photo: An oil pump in Glenpool, Oklahoma, located 66 miles east of Prague where USGS scientists suggest that earthquakes coincided with pumping waste water into empty oil wells. Credit: Roy Luck,Wikimedia Commons

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