Dynamic Evolution Characteristics of Seismicity Factor A-value Abnormity before Strong Earthquakes in Yunnan

We studied the temporal and spatial dynamic evolution of seismicity factor A-value before strong earthquakes,especially before the first shock in the active period of strong earthquakes in Yunnan.The results show as follows:(1) A-value would appear evident high value near future epicenters during 1 ～ 2 years before strong earthquakes,abnormal value is A≥0.6.(2) The high value anomalous areas of A≥0.6 mainly distributed in the surrounding areas or the boundary areas of Yunnan Province,but rarely distributed in the inner of Yunnan Province during 3 ～ 4 years before strong earthquakes.With the approach of the strong earthquakes occurred,the areas in which A-value was abnormal expanded gradually and moved toward the future epicenters or the inner of Yunnan Province.During one year or 1 ～ 2 years before strong earthquakes,the unit area in which A-value was abnormal in Yunnan and the ratio of the unit area in which A-value was abnormal between inside and outside of Yunnan significantly turned and picked up.