Seismic activity triggered by human actions

Context: 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.

Findings of the latest study:

• While it is well known that injection of fluid into subsurface of the earth (one kilometer deep) can cause events like earthquakes, it was until now believed that such disturbances are limited to an area near the site of injection.
• The new study has, however, 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.
• 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.

Significance:

Understanding this 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.

Sources: down to earth.