| 摘 要： | In this paper,the focal mechanisms of the fore-main-after shocks of the 1989 Datong-Yanggao earthquake are determined by fitting Pnl and SH waveforms,and the earthquake processes and seismotectonics are inferred.The results show that the fore-main-after shocks occurred on a composite fault plane,The fault motion at the shallow part is right-lateral strike-slip with mechanisms:strike 201,dip 75,rake 191; at the deeper part,the fault movement is strike 201,dip 58,rake 222.The epicentral area is subject to a ENE-WSW horizontal compression and a NNW-SSE extension which is consistent with the tectonic stress orientation of North China.The P-axis at greater depth has an azimuth of 54.5 and a plunge of 51.The relatively large P-axis plunge in depth corresponds with the great depressive deformation in this area.In addition,the similarities and differences between the Datong-Yanggao earthquakes and general graben-associated earthquakes are discusses.
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