The most widely accepted explanation of how dams cause earthquakes is related to the extra water pressure created in the micro-cracks and fissures in the ground under and near a reservoir. When the pressure of the water in the rocks increases, it acts to lubricate faults that are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces. In deep and large reservoirs, the extra load of the water over an existing fault line can also lead to movement along a fault. Thus the rapid filling of a large reservoir may trigger an earthquake that would have otherwise naturally occurred several if not hundreds of years later.It is well established (although little known to the general public) that large dams can trigger earthquakes.
Experts in China and the US have for years researched the possible link between the Wenchuan quake and the filing of the Zipingpu Reservoir – just 5.5 kilometers away from the epicenter. While the results are not conclusive, the phenomenon known as RIS has been studied for decades, with global estimates identifying over 100 cases of earthquakes that scientists believe were triggered by reservoirs.