By C. CLAIBORNE RAY
Q. Can human actions cause earthquakes?
A. “Yes, human engineering has been triggering earthquakes for more than half a century,” said Leonardo Seeber, Lamont research professor at the Lamont-Doherty Earth Observatory, and manmade quakes may be more common than is acknowledged.
Some such quakes have been disastrous, like the one in 1967 associated with the Koyna Dam in India, Dr. Seeber said. “This and many other earthquakes are obviously human-triggered, but distinguishing natural from triggered earthquakes is generally difficult,” he said. “Agents triggering the earthquakes often refuse to admit responsibility and make it difficult to obtain the data that could prove it.”
Even a small stress increase can cause a fault to fail, Dr. Seeber said; humans tend to do it in two ways. One is by changing the load on the crust, typically with artificial lakes, which increase the load, and with quarries and oil fields, which decrease the load.
A less obvious way is “to weaken the rock by increasing the pressure of the interstitial fluid,” Dr. Seeber said. The question often comes up with regard to hydrofracking, a process that uses high volumes of water, sand and chemicals to release natural gas from dense rock.
Dr. Seeber said that the process was not likely to set off earthquakes, but that it required disposing of fluid in deep wells, which was “much more likely to trigger earthquakes than fracking itself.”
(Source: www.nytimes.com )