The earth is big, and so are the tectonic plates—it doesn’t seem possible that anything humans could do to the earth would have an effect on those immense plates. But evidence is mounting that we cause earthquakes.
I listened in fascination to a presentation from earthquake scientist Christian Klose at the 2006 American Geophysical Union fall meeting in which he showed how coal mining was responsible for earthquakes, including the most-damaging ever in Australia. (The 5.6-magnitude Newcastle earthquake of 1989, though relatively small by international comparison, killed 13 people.) The removal of coal, rock and, especially, water from underground can cause enough stress to trigger an earthquake, Klose said. Other potential earthquake triggers he mentioned were oil and gas extraction, creation of reservoirs behind dams and, he conjectured, sequestering carbon dioxide underground.
Now Science reports that Klose is one of several scientists who are pondering the possibility that last May’s 7.9-magnitude earthquake in China’s Sichuan Province, which left 80,000 dead, could also have had a man-made trigger, this time in the form of the Zipingpu Dam.
Then the magnitude-7.9 Wenchuan earthquake struck, many scientists wondered if a reservoir was to blame. Ruling out the much-maligned Three Gorges Dam as too distant, experts considered the Zipingpu Dam, just 500 meters from the fault that failed and 5.5 kilometers from the quake's epicenter. The timing was right. The Zipingpu reservoir began filling in December 2004, and within 2 years the water level had rapidly risen by 120 meters, says Fan Xiao, a chief engineer of the Sichuan Geology and Mineral Bureau in Chengdu.
The several hundred million tons of water blocked by the dam wouldn’t have been enough to cause an earthquake that big on its own, but it could have weakened the fault and changed the stresses on it. Fan further explained:
Judging by the history of known reservoir-triggered quakes, the rapid filling of Zipingpu as well as its considerable depth would have favored triggering, he says. The delay between filling and the great quake would have given time for reservoir water to penetrate deep into the crust, where it can weaken a fault. And the greatest danger of triggering comes not at the time of maximum filling, he argues, but when the water level is falling. "As we now know, a week before the May 12 earthquake, the water level fell more rapidly than ever before," says Fan.
The scientists aren’t convinced that the dam and the earthquake are linked, but shouldn’t this be on the list of concerns when building dams? In Turkey, for example, they are building the Ilisu Dam on the Tigris River in an area of the country crisscrossed by faults. (In our March issue, we write about the ancient city of Hasankeyf, which would be wiped out by the dam.) Might that dam lead to an earthquake there?
(Hat tip to the Knight Science Journalism Tracker.)