| Tianshan area is the most active area of intraplate tectonic movement and seismicity in the world.Many seismologists have been paying close attention to this area.Recently,there have been many earthquakes with magnitude 5 or more in the western section of North Tianshan.In this paper,two strong earthquakes occurred in Jinghe area in North Tianshan Mountains,Xinjiang.Structures and stresses in Jinghe area can be obtained by precise location of earthquakes,aftershocks and focal mechanism of main earthquakes.Based on the above results,the research was carried out.07:27:52 Am on August 9,2017,an earthquake with M_S6.6 occurred in the Jinghe.In order to determine the seismogenic structure of this earthquake,this paper uses the double differential location method to precisely locate the aftershocks occurring in the focal area from the time of the earthquake to October 2017.At the same time,the focal mechanism solution of the main shock is obtained by using Cap waveform inversion method,and the focal mechanism solution of some aftershocks is obtained by using Gpat inversion method.Based on the two methods,the seismogenic structure of this earthquake is analyzed.The results show that:(1)the main shock is located at(44.27°N,82.85°E)and the focal depth is 17 km.(2)The best double-couple solution of the main shock has one nodal plane with strike 260°,dip51°,rake 84°,and the other nodal plane with strike 89.5°,dip 39.4°,rake97.4°(3)The aftershock sequence is located in the eastern part of the main shock with focal depth of 3—18 km and an extending length of nearly 30 km towards east.The predominant direction of the sequence is EW direction,and the sub dominant direction is SW direction.The result suggests that(1)the Jinghe earthquake is of thrusting type,and the focal mechanisms of a large number of small earthquakes obtained by inversion are consistent with the focal mechanism of the main shock.(2)Combined with the distribution of aftershock epicenters,focal mechanism solutions for the main shock and the aftershocks,as well as geological structure of the source region,it is inferred that the thrusted Kusongmuxieke piedmont fault extending in near EW direction is the seismogenic structure for the Jinghe main shock..(3)In addition,the source mechanism,P-axis direction and T-axis direction of a large number of small earthquakes are obtained by inversion.By averaging the obtained P-axis direction,it is concluded that the direction of tectonic stress field in the focal area is North-South.Fourteen months after the and 2017 earthquakes,another M5.4 earthquake occurred in the Jinghe area.The aftershock sequence was precisely located by double-difference location,and the focal mechanism of the main earthquake was inverted by Cap.After positioning,the main shock locates at 82.51°E,44.15°N,and the depth is 18.96 km.The aftershocks are distributed in the range of 16 km to 20km.The moment center depth of the main shock is 14 km,the moment magnitude is5.15,the nodal plane I:strike 269.3°,dip 48.2°,rake 82.5°.Section II:strike 100.9°,dip 42.6°,rake 82°.The focal mechanism of the two earthquakes is basically the same,and the seismogenic fault is a reverse fault striking near EW.The main faults in the vicinity of the focal area are East-West strike.Although there are no obvious faults near the source,combined with the focal mechanism and the distribution of aftershocks sequence,it is inferred that the seismogenic structure of the 2018 Jinghe earthquake is an east-west strike reverse fault. |
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