| In this paper,the Longmenshan fault zone and its neighboring areas were selected as research areas.The four earthquakes in Wenchuan,Yushu,Lushan and Kangding occurred in this region as the research object,and the aftershocks occurred in the Sichuan area and its adjacent areas from 2000 to 2018 were used.The results of fine localization were studied through the Coulomb failure stress criterion and seismic stress triggering theory(including static stress triggering and viscoelastic stress triggering).First,determine the variable sliding source models to be used for the four major earthquakes.Based on the static stress triggering,discuss the spatial distribution of the Coulomb failure stress changes after the four earthquakes,the influence of the distribution of stress changes on the distribution of aftershock events and the effect of seismogenic faults on other fractures in the study area.The main conclusions:1?The Coulomb failure stress range generated by the Wenchuan Earthquake has an extremely wide range of influences.Two extremely strong stress increase regions are formed at the north and south ends of the Longmenshan fault zone,and two stress-reducing zones are formed on the east and west sides of the fault.The distribution of aftershocks reflects a good correlation;from the perspective of the impact of various faults,the East Kunlun fault and the Zhouqu fault zone have been subjected to extremely strong stress loading,which is conducive to the acceleration of subsequent earthquake events and occur.2? The spatial distribution of the positive and negative changes of the stress produced by the Yushu earthquake is generally center-symmetric,and most of the aftershocks are distributed in the stress increase area.From the fracture point of view,the Yushu earthquake has a significant impact on the western region,including the eastern section of the East Kunlun fault zone and Deqin fault zone,appears as a stress unloading effect.3?Although the Wenchuan earthquake is co-located with the Longmenshan fault zone,the Lushan earthquake is an independent earthquake event,and the Coulombfailure stress distribution after the earthquake also has its own characteristics.The concrete manifestation is the positive and negative phase distribution;the main impact is the south of Longmenshan fault and its surrounding fault zone.4?The main characteristic of the Kangding earthquake is a double-shock event.The two successive earthquakes are different from the stress distribution results.However,from the trigger effect of the aftershocks,the dominant one is the Ms6.3occurrence.Due to the magnitude and geographical location of the earthquake,the affected fractures are mainly in the southern section of the Xianshuihe fault zone and nearby areas.5?Combined with the viscoelastic relaxation conditions,it can be concluded that in the past 10 years,the stress state in the eastern part of the study area was mainly controlled by the Wenchuan earthquake.The evolution of the stress field generated by the Yushu earthquake that occurred in the western part of the study area is not sufficient to influence the eastern stress state;The Lushan earthquake and the Wenchuan earthquake occurred about five years apart.The Lushan earthquake is also just in the stress increase area in the eastern part of the study area.This shows that the Wenchuan earthquake under the conditions of viscoelastic relaxation has triggered the Lushan earthquake.The subsequent stress evolution of the Lushan earthquake and the occurrence of the Kangding earthquake have further changed the stress conditions in the southern region.The Xianshuihe fault zone is the most affected,and the possibility of subsequent major earthquakes in this area cannot be ruled out.6?For the seismicity of the overall study area,the results of ETAS analysis show that the fitting of earthquake sequences in each region is relatively satisfactory,indicating that the seismic activity in the study area is affected by several major earthquakes. |
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