| The Tibetan Plateau,roof of the world,is formed by the collision of the Indian plate and the Eurasian plate.Its formation and evolution is one of the greatest geological events in the history of the Earth.The northern and eastern Tibetan Plateau are the front parts of the inland expansion of the Tibetan Plateau with active structural deformation,and they converge here with the Alashan block,Beishan block,Tarim basin,Ordos block,South China block and Sichuan basin,and mainly develop large-scale faults such as the Qilian-Haiyuan fault,Altun fault,East Kunlun fault,Longmenshan fault and Xianshuihe fault.This area has complex and changeable topography,remarkable structural deformation and active seismic activity.In this paper,the northern and eastern Tibetan Plateau are taken as the research areas,and the earthquake stress triggering on the 2022 M_S6.9 Menyuan-Halahu earthquake swarm and the 2022 M_S6.1 Lushan-Maerkang earthquake swarm are taken as the research contents.Based on that,the Coulomb stress changes of the surrounding main faults are studied,and the future earthquake occurrence trend of the fault zone is evaluated.The main work and conclusions of this paper are as follows:(1)The Haiyuan M 8?earthquake in 1920,the Gulang M 8.0 earthquake in1927 and the Shandan M 7? earthquake in 1954 have the most significant loading effects on the M_S6.9 Menyuan earthquake in 2022,which are equivalent to advancing the Menyuan earthquake by 7.6 years,5.3 years and 5.22 years respectively.From the comparison of the coseismic and post-earthquake effects of these three earthquakes,it can be seen that the viscoelastic relaxation of the lower crust and upper mantle plays an important role in the long-term earthquake preparation and stress evolution.In1986,the Menyuan earthquake with M_S6.4 played the most significant role in unloading the Menyuan earthquake,which delayed it by about 14.4 years.For the high stress accumulation area of Qilian Mountain,the earthquake with unloading function may also cause stress disturbance to the Menyuan earthquake.For example,the positive and negative dividing line of shear stress of the 2021 Maduo earthquake passes through the source area of the 2022 Menyuan earthquake,and there is the possibility of direct triggering.Finally,the Menyuan earthquake in 2022 triggered the later M 5.8 Hala Lake earthquake,and affected the subsequent Hala Lake earthquake swarm.(2)By analyzing the evolution characteristics of Coulomb stress of historical strong earthquakes caused by Menyuan M_S6.9 earthquake and four subsequent moderate earthquakes in the western part of Qilian Mountain,and the viscoelastic Coulomb stress of historical earthquakes,it is considered that the stress accumulation in this area is at a high level,and the internal faults in Qilian Mountain are prone to instability and sliding when disturbed by stress.Among them,the fault sections near the Menyuan earthquake zone,the west part of the Halahu in Qilian Mountain,the west part of the Laohushan fault,the middle part of northern Qilian Mountain fault,the middle part of Changma-Obo fault,the northern part of Altun fault,the western part of Tolaishan fault,the Elashan fault and the eastern part of Dachaidan-Zongwu Longshan fault are all in areas with high Coulomb stress,which should be paid attention to.(3)The Kangding M 7.6 earthquake in 1955 and the Wenchuan M_W7.9 earthquake in 2008 were the most significant loading events for the Lushan M_S6.1 earthquake in 2022,while the Lushan M_W6.6 earthquake in 2013 was the most significant unloading event,which led to the occurrence of the Lushan earthquake in 2022 nine years after the Lushan earthquake in 2013.The Maerkang earthquake swarm in 2022 may be triggered by two Lushan earthquakes in 2013 and 2022.The 2021 Maduo earthquake has a loading effect on the 2022 Lushan earthquake,and the Lushan earthquake in 2022 may trigger the Maerkang earthquake swarm.(4)The tectonic stress of Songpan Ganzi terrane has accumulated to a high level,and the focal points of the Lushan-Maerkang earthquake sequence in 2022 all occurred near the boundary between positive and negative stress.This phenomenon may indicate the location of future earthquakes.In addition,there are positive and negative stress dividing lines in the middle section of Yuke fault,the southern section of Xianshuihe fault(verified by the M_W6.8 Luding earthquake on September 5,2022),the eastern section of Dari fault,Bayankalazhufeng fault and Wudaoliang-Changsha Gongma fault are close to the positive and negative boundary of Coulomb stress and are positive,which should be paid attention to. |
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