Time distribution characteristics of regional macroseismic activity in the Sichuan-Yunnan region and its significance to mid-long term prediction

The earthquakes with M _S≥6.0 are often gathered into belts or clusters and are roughly consistent with tectonic structure trends in the Sichuan-Yunnan (Chuan-Dian) region. The middle south part (98°–106°E, 21°–34°N) of South-North Seismic Zone can be zoned into seven small areas. There all were strong quakes with M _S≥7.0 historically in each small area. Ten earthquakes with M _S≥7.0 have occurred in this region since 1970 and they appeared in five small areas respectively. The relationships between occurrence-time and cumulative frequencies of strong quakes in these five areas are shown to be an exponential distribution or power function. By examining the inner coincidence it is indicated that these relationships are of definite significance to mid-long term macroseismic prediction of each area. Foundation item: Key Project 95-04-07-03-01 from China Seismological Bureau Contribution No. 00FE2018, Institute of Geophysics, China Seismological Bureau.