Short-term seismicity characteristics before large earthquake obtained from the space-time scanningin Sichuan-Yunnan regions

Through the space-time scanning for the earthquakes occurred in Sichuan and Yunnan regions during the past 30 years,the seismicity factors A-value and the space-concentrating degree C-value are calculated.Their change images results show that in the period of 1-3 months before a large earthquake occurs,the seismicity factors A-value and the space-concentrating degree C-value about the small and moderate earthquakes appear some changes near the epicenter region.The seismicity factors A-value can express the comprehernsive situation of seismicity in Sichuan and Yunnan regions well.