Regional seismic characteristics before a medium strong earthquake ( M≥6 + 3/4) in Sichuan and Yunnan province

The regional seismic activity changes about 22 earthquakes before a medium strong earthquake( M ≥634)in Sichuan and Yunnan provinces.The objectivity and universality about some precursory earthquakes were also tested.We conclude that:(1) the regional seismic activity before a medium strong earthquake is high;(2) Several earthquakes( M 5～6) may occur near an earthquake source;(3) An active relatively area or belt of earthquake forms around the future earthquake source area;(4) A quiet seismic area appears near the earthquake epicenter.Tracing the seismic changes for a medium strong earthquake is useful for the prediction of strong earthquake.