The investigation by the U.S. Geological Survey did not suggest that fracking was causing the increase in quakes, though noted: “USGS scientists have found, however, that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells.”
While most induced temblors are not strong enough to be felt on the surface, a 5.7-magnitude earthquake linked to a disposal well in November 2011 in Oklahoma knocked down 14 homes and injured two people. Sichuan is almost eight times more densely populated than Oklahoma.
A 2008 earthquake in Wenchuan, Sichuan, the most powerful in China in more than a decade, killed 69,227 people, including 5,335 schoolchildren, after thousands of classrooms crumbled. China is home to three of the 10 deadliest earthquakes of all time, according to the U.S. Geological Survey.
Shale drilling is under way in California, also a seismically active region. Since the beginning of 2008, the state had 19 quakes with a magnitude of 5 or greater, according to the USGS. Sichuan had 59, according to the China Earthquake Networks Center.
“Anytime you’re going into an area that’s more heavily faulted, the risk is higher that you could cause induced earthquakes,” said Briana Mordick, a staff scientist at the Natural Resource Defense Council and former geologist at Anadarko Petroleum Corp. “Sichuan is definitely a concern.”
Mordick said calculating seismic risk from tectonic stress is not simple.
Southwest China, which includes Sichuan, and the Upper Yangzi area account for 40 percent of the country’s shale gas reserves, according to the Ministry of Land and Resources. China aims to produce 6.5 billion cubic meters of shale gas by 2015 and as much as 100 billion cubic meters by 2020, from zero output this year. Current regulations don’t require earthquake surveys as part of the standard environmental impact assessment.
The Ministry, which regulates the oil and gas industry, didn’t respond to calls and faxes seeking clarity on rules governing seismic studies before drilling.
“We do detailed structural analysis as routine part of our pre-drill evaluation,” Shi Jiangtao, a Shell spokesman in Beijing, said in an e-mail. “This means that we evaluate the geology by using seismic, surface geology, nearby well data, etc.”
Shell, which plans to invest $1 billion a year in China’s shale gas industry, declined to comment directly on earthquake hazards in Sichuan. China National Petroleum, Shell’s partner, didn’t respond to an e-mailed list of questions. China Petrochemical Corp., which is also drilling in the area, didn’t respond to calls and e-mails seeking comment.