Was last year's devastating China earthquake, which killed 80,000 people and left more than 5 million homeless, really just a tragic natural event? Speculation is growing that the magnitude-7.9 quake may have actually been triggered by the tremendous water weight behind a nearby dam.

Scientists in China and the U.S. say that water behind the Zipingpu Dam, just 3.4 miles (5.5 kilometers) from the epicenter of the May 12 quake in Sichuan in southern China, may have weakened the fault that ruptured, the British Telegraph reports today. 

It's "very likely" that the construction and filling of the reservoir in 2004 led to the quake, Fan Xiao, chief engineer of the Sichuan Geology and Mineral Bureau in Chengdu, told the newspaper.

Two dam-related factors may have sparked the earthquake: Water from the dam that lubricated — and weakened — the Beichuan fault line, and a dramatic decline in water levels between December 2007 and last May, according to a paper published in December in a Chinese journal, Geology and Seismology. Science reported on that research last month, and also noted a talk by Christian Klose, a Columbia University geophysical hazards researcher, who told the annual American Geophysical Union meeting in December that several hundred million tons of water would have put "25 times" the stress of natural tectonic movements on the fault line.

Klose did not answer his phone at Columbia and did not immediately respond to an email this afternoon. In October, Klose wrote on his blog that "a major question is whether this earthquake might have been triggered by these mass changes" in water accumulation near the epicenter. "But, scientific evidence for such a statement is needed! Some questions need to be answered: How much water was impounded, where and when? Did resulting stress changes alter stresses deep in the Earth's crust? Were stress alterations significantly large enough? Where was the highest seismic energy release — close to the reservoir?"

There is precedent for dam-related quakes, Science notes. A magnitude-6.3 quake in India in 1967 that killed 200 people was caused by impoundment behind the country's Koyna Dam. The Chinese government, however, has insisted that its construction projects have nothing to do with the quake, the Telegraph reports.

Daughters of a man who was trapped in a collapsed building beg for him to be rescued following Sichuan quake/Miniwiki via Wikimedia Commons