Man-made earthquakes triggered by fracking and dams are not
May 04th 2019 (India Science Wire): Seismic activity triggered
by human actions like construction of large reservoirs or injection of
wastewater into the ground for oil and gas production can have far greater
implications than previously thought, a new study has revealed.
Dinesh C Sharma
While it is
well known that injection of fluid into subsurface of the earth (one kilometer
deep) can cause events like earthquakes, it was believed till now that such
disturbances are limited to an area near the site of injection. The new study
has found that subsurface disturbances due to fluid injection can result in
earthquakes spread over larger regions, going far beyond the area invaded by
the injected fluids. This means, earthquake-triggering stresses can travel far.
the most famous fluid-induced earthquake had occurred in 1967 at Koyna in
Maharashtra and was attributed to seismic activity generated due to the
impoundment of the Koyna dam there. Earthquakes occurring in tectonically quiet
region of Oklahoma have also been linked to oil and gas exploration activity
there. It is believed that such regions of
man-made earthquake activity surpass the level of seismic activity in hotspots
like southern California.
In the new
study published in the journal Science, researchers from India and
America used data from earlier experiments and a hydro-mechanical model developed by them to explain the
full dimensions of fluid-induced earthquakes. The field data came from
experiments done in France by the University of Aix-Marseille and the
University of Nice Sophia-Antipolis.
shows that fluid-injection has the potential to cause significant, rapidly
spreading earthquake activity beyond the fluid diffusion zone,” explained
Pathikrit Bhattacharya of the Indian Institute of Technology, Bhubaneswar, lead
author of the study, while speaking to India Science Wire.
Oil and gas
extraction using fluid injection, as well as wastewater disposal, is known to
increase seismicity rate in surrounding regions. Tremblors attributed to these
activities have been thought to occur as higher fluid pressures in surrounding
rocks trigger instabilities in pre-existing networks of faults. However,
injection may also cause aseismic slip—deformation caused along a fault line
without any accompanying seismic waves—that may in turn trigger earthquakes.
“The field experiments by the French scientists had demonstrated that when fluid injection occurs near existing faults, their primary response could be slow, quiet, aseismic slip rather than violent earthquakes. We used this data to show that aseismic slip could rapidly outpace the region of fluid-diffusion and transmit potentially earthquake-inducing stress perturbations to regions remote from the location of injection,” said Robert C. Viesca of Tufts University’s School of Engineering, co-author of the study.
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Understanding the science behind fluid-induced earthquakes could help in unraveling reservoir-induced earthquakes in Koyna. The ‘Deep Drilling at Koyna’ initiative led by Noida-based National Centre for Seismology and CSIR-National Geophysical Research Institute in Hyderabad is studying detailed behaviour of fluid-induced earthquakes in the region. “These efforts are expected to yield data about fault behaviour at greater depths in the earth’s crust. Our study is a proof-of-concept of how such data can be used in practice to produce more reliable models of earthquake hazard,” added Bhattacharya.