The quake happened because a part of the earth's surface, called the "Indian plate", is slowly moving north. It is moving about every year. It crashes into the "Eurasian plate". This has pushed up the ground and made the Himalaya mountains. Some of the earth's crust gets pushed into Sichuan and southern China. This pushing has caused many earthquakes in China. The epicentre was in the mountains on the eastern edge of the Qing-Tibet Plateau. This is on the north west edge of the Sichuan Basin. The earthquake was caused by movement on a north east fault. This is the Longmen Shan fault, that runs along the edge of the basin.