Koyna-Warna in Maharashtra is one of the best worldwide examples of reservoir-induced seismicity. It generated the largest known induced earthquake of a magnitude of 6.3 (M6.3) on the Richter Scale on December 10, 1967.

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 area, possibly suggesting a more extensive zone of seismic hazards for Central India, say experts.

Since the early 20th century, it has been clear that filling large water reservoirs can induce potentially dangerous earthquakes.

Throughout the following decades, cyclic earthquake activity has been noticed along with rises and falls in the annual reservoir levels — at an average of an M5 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 has found that, to date, at least 170 reservoirs the world over have reportedly induced earthquake activity.

These are now catalogued in a database at www.inducedearthquakes.org 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.

Attention quickly turned to the nearby Zipingpu Dam, whose reservoir had been filled just a few months previously, although the link between the earthquake and the reservoir has yet to be proven.

The minimum amount of stress-loading the 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 magnitude 4.6 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. Mining and geology has been found to be the most frequent cause for human induced seismicity. The total amount of rock removed by mining worldwide now amounts to several tens of billions of tons 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.

For instance, the 700-megatonne Taipei 101 building, raised in Taiwan in the 1990s, has been blamed for the increasing frequency and size of earthquakes nearby.

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