RUPTURE PROCESSES OF STRONG EARTHQUAKES ON X1ANSHUIHE FAULT BELT AND SEISMIC ACTIVITY

Xian Shuihe fault belt is the seismic ally strongest and most active of belts in Southwest China. In this paper the relationship between the fracture processes of strong earthquakes and the seismic activity was investigated toy studying the source mechanism, the distribution of afterslloks and the migration of strong earthquakes occurring on this belt and combining with the configuration of macroisoseismic lines and the distribution of ground fissures. The results show that:1) The foundimantal way of rupture of Xian Shuihe fuult belt is left-laterjal strike slip. There is a dominant direction with good coincidence with the principal compres-sive axes, that is in the ENE-WSWdirection, and nearly horizontal.2) The results of study by using Pwave spectra and directivity function of surface waves show that, except for some earthquakes in the NWand SEsegments, the rupture surfaces of the strong earthquakes of M≥7.0 and most of those of M=6—7 are in the NWdirection, which is foundmantally coincident with the general striek of Xian Shuihe belt.3) The distribution of rupture planes of the strong earthquakes in Xian Shuihe fault belt since 1890 and the distribution of the epicenters (M≥3.0) since 1955 show that the gap segment of the rupture surface (about 10 km in length) between Daofu and Qianning is distinctly shorter thau the segment of earthquake gap of M≥3.0 since 1955 (about 40 km in length) ; this indicated that, the rupture surface of the Qianning earthquake in1893 recently healed to some extent. The length of the segment without earthquakes is nearlyequal to a rupture length for an earthquake of about M=7.4) Those 4 earthquakes of M≥7.0 occurred in the belt since 1890 had a common feature of migration from one end of the belt to the other. And considering the fact that the last earthquake of M7.0 was the Luhuo earthquake of 1973, we can venture to estimate that maybe the Iqcation of the next earthquake will be in the SEsegment. It is most probable that it will occur in the segment of earthqiuake gap near Daofu—Qianning.