Seismic Sequence Characteristics of the March 21,2008,M_S 7. 4 Yutian,Xinjiang Earthquake and Seismological Anomalies before the Earthquake

摘要

The parameters,stress field background,geological tectonics and seismic sequence of the March 21,2008,M_S 7. 4 Yutian,Xinjiang earthquake are discussed in this paper. The characteristics of seismic activity in the epicenter and its adjacent region before the earthquake are analyzed; and a comparison is made between the M_S 7. 4 Yutian earthquake sequence,the Wenchuan M_S 8. 0 earthquake sequence and the Wuqia M_S 6. 9 earthquake sequence. The results show the M_S 7. 4 Yutian earthquake occurred in the junction between the Altyn Tagh fault and the western Kunlun fault,resulting perhaps from the tensile fracture of the branch fault located southwest of the Ashikule basin due to left-1ateral dislocation of the Altyn Tagh fau the seismic sequence is of main shock-aftershock type, the strongest aftershock being M_S 5. 8. The aftershocks attenuated quickly,and occurred in groups; the focal mechanism solutions and epicenter distribution have revealed a unilateral rupture source of this earthquake. Seismic activity shows that there was medium and medium-short term abnormity before the earthquake,but there was not short-imminent abnormity. Seismic activity of this earthquake sequence enhanced before the M_S 8. 0 Wenchuan and the M_S 6. 9 Wuqia earthquakes,showing the window effect to some extent.