Faux Quake, Less Shake - Study: Frack Tremblors Not as Powerful
19 August 2014
WASHINGTON- Man-made earthquakes, a side effect of some high-tech
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 - those that
are not natural, but 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
Distance matters in this shaking gap, however. For people within 6
miles of the fault, artificial and natural quakes feel pretty much
the same, she said.
Hough studied similar-sized 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 while two
different types of temblors may have 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. The magnitude scale used
by USGS and others is mathematically complex, but a drop in 0.8
magnitude translates to about 16 times less strength or energy
Sometimes the difference is even bigger. Hough said a 5.3 August
2011 man-made quake in Trinidad, Colorado, actually felt like a
4.0 quake, which is about 90 times weaker, based on the thousands
of responses in the "Did You Feel It" survey system. The study,
published Monday in the Bulletin of the Seismological Society of
America, looked at quakes in Oklahoma, Colorado, Arkansas, Texas
and Ohio. It included a 5.7 quake in Prague, Oklahoma, in November
2011 that injured two people and damaged 14 houses, which Hough
said felt like 5.1 magnitude natural quake.
"The hazard of these earthquakes is lower than what you'd expect,"
Hough said. "It's not that there's no hazard, it's just that it's
a little better than you might think."