Seismic source characteristics of nine strong earthquakes from 1988 to 1990 and earthquake activity since 1970 in the Sichuan-Qinghai-Xizang (Tibet) zone of China

The Chinese provinces of sichuan, Qinghai and Xizang (Tibet) are situated i n a very active seismic zone. From 1988 to 1990, nine strong earthquakes (M > 5.9) occurred in these provinces. A method of analyzing seismic waveform s using apparent source time functions (aSTF) and apparent time differences (aTD) is adopted to derive rupture characteristics for the strong earthqua kes. Combining the source characteristics with aftershock data, regional te ctonics and geology, this paper examines the migration of strong earthquake s. The Qinghai earthquakes in this study were found to have strong reverse- slip faulting, which is different from the strike-slip focal mechanisms of past earthquakes in the region. The steepness of compressional axes of Sich uan earthquakes is related to the local complicated tectonics. Finally, the single-link cluster (SLC) method is used to analyze the spatial-temporal b ehavior of the all strong earthquakes that occurred in the region since 197 0. The SLC analysis suggests that the patterns of earthquake activity can b e identified well and that continental earthquakes occur seemingly with bas ic regularity.