ACTIVITY OF SMALL EARTHQUAKE SWARMS AND INTERMEDIATE MAGNITUDE EARTHQUAKES IN THE SICHUAN-YUNNAN REGION
Lei Suhua(Seismologica! Bureau of Yunnan Province, Kunming)
This paper has studied 239 small earthquake swarms recorded since the local network of stations has been set up for 21 years. It is found that most of strong earthquakes occurred when the annual frequency of small earthquake swarms was increaing. And the characteristic value, the normalized entropy value K, has been applied to weigh the homogeneity of energy distrbution in the earth-pueka swarm sequences. The correlativity between the various k-value swarms and the intermediate magnitude earthquakes has been analysed. It is found that the correlative coefficient between the swarms (K≥0.8) ami the earthquakes (M≥5.5) is 59.3%, the rate of false forecasts 40%, that of missing forecasts 14.0%. About 56% of the earthquake swarms satisfy aseismic conditions.The above results show that the method that precursory earthquake swarms and general ones were discriminated by using the normalized entropy value K (K≥0.8), is not as clear as that of North China region. In the Sichuan-Yunnan region", if the strong earhquakes (M = 6.5) were dealt with, the results would be better.