An article in Science suggested that the construction and filling of the Zipingpu Dam may have triggered the earthquake. The chief engineer of the Sichuan Geology and Mineral Bureau said that the sudden shift of a huge quantity of water into the region could have relaxed the tension between the two sides of the fault, allowing them to move apart, and could have increased the direct pressure on it, causing a violent rupture. The effect was "25 times more" than a year's worth of natural stress from tectonic movement. The government had disregarded warnings about so many large-scale dam projects in a seismically active area. Researchers have been denied access to seismological and geological data to examine the cause of the quake further.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What have researchers been denied?
access to seismological and geological data