Why do earthquakes often occur in Lu Xian County?

Luding belongs to the Xianshuihe seismic belt. From Ganzi County, through Luhuo, Daofu, Kangding and other counties, to the south of Luding County, the whole belt is in Ganzi Tibetan Autonomous Prefecture, extending from northwest to southeast, which is the strongest seismic belt in Sichuan Province. There have been eight major earthquakes with magnitude above 7 in this seismic zone, and the largest one was173/4 earthquake between Kangding and Luding in 786.