The Koyna-Warna area in Maharashtra is one of the best worldwide examples of reservoir-induced seismicity.
It had generated the largest known induced earthquake of a magnitude of 6.3 (M6.3) on the Richter Scale on December 10, 1967.
Induced quakes
It has been followed by persistent tremors of moderate magnitude (greater than M5) over the past 50 years or more.
The right-lateral faults extend beyond the immediate Koyna-Warna, possibly suggesting a more extensive zone of seismic hazards for Central India, say experts.
Since the early 20th century, it has become clear that filling of large water reservoirs can induce potentially dangerous earthquakes.
The following decades have seen earthquakes happen with a rise and fall in the annual reservoir-level cycles. Quakes of M5 or more have punctuated the nearby landscape every four years.
Global trend
Last year, the Nederlandse Aardolie Maatschappij BV commissioned a comprehensive global review of all human-induced earthquakes.
The catalogue it has come out with found that, to date, some 170 reservoirs the world over have reportedly induced quake activity.
These are now available in a database at www.inducedearthquakes.org prepared by Gillian Foulger, Jon Gluyas and Miles Wilson.
In 2008, an M8 earthquake struck Ngawa Prefecture, China, killing about 90,000 people, destroying 100 towns and collapsing houses, roads, and bridges.
Not proven
Attention quickly turned to the Zipingpu Dam whose reservoir had been filled just a few months previously, although the link between the two event and the reservoir is yet to be proven.
The minimum amount of stress load which scientists think is needed to induce earthquakes, is creeping steadily downward, the review says.
The Three Gorges Dam in China, which now impounds 10 cubic miles of water, has already been associated with earthquakes as large as M4.6 and is under careful surveillance.
Because small earthquakes can trigger larger ones, industrial activity has the potential, on rare occasions, to induce extremely large, damaging events.
But according to s per findings, mining and geology has been found to be the most frequent cause for human induced seismicity.
Mining threat
The total amount of rock removed by mining worldwide now amounts to several tens of billions of tonnes per year. That’s double what it was 15 years ago – and it’s set to double again over the next 15.
Much of the coal that fuels the world’s industry has already been exhausted from shallow layers, and mines must become bigger and deeper to satisfy demand.
Hundreds of deaths have occurred in coal and mineral mines over the last few decades as a result of induced earthquakes of up to M6.1.
Other activities that might induce earthquakes include the erection of heavy superstructures.
The 700-megaton Taipei 101 building raised in Taiwan in the 1990s has been blamed for the increasing frequency and size of earthquakes in the vicinity.