A Study Of Earthquake Recurrence Model Along The Eastern Altyn Tagh Fault

The Altyn Tagh fault is an intracontinental sinistral strike fault that forms a major boundary fault between Tibetan Plateau and Tarim Basin on the northern margin of the Tibetan Plateau.As the key parts of structural transformation between the Altyn Tagh Fault and a series of strike and thrust faults belong to the western Qilian faults,the eastern Altyn Tagh Fault has been widely concerned by seismic geologists.Although the linear fault traces are clear,the historical record of earthquakes in this area is incomplete before 1900,and there has been a lack of surface-rupturing earthquakes?M>6.5?on the ATF since 1609.Besides,the eastern Altyn Tagh Fault crosses“the Silk Road on Land”proposed by our country,and the study of the recurrence behavior of large earthquakes is essential to ensure the seismic safety of the“The Belt and Road Initiative”.In this paper,we take the eastern Altyn Tagh Fault as our research object.Based on Li DAR and other high-precision topographic data,we reconstruct detailed characteristics of the cumulative offset distribution.Synthesis of the offsets distribution and previous paleo-earthquake studies,we establish the completed paleo-earthquake parameters?include time,magnitude and coseismic slip distribution?of the latest large earthquakes on the eastern Altyn Tagh Fault,finally combining with the numerical simulations,we build an earthquake recurrence model of the eastern Altyn Tagh Fault.The result of this research can not only provide quantitative parameters and theoretical basis for regional earthquake risk assessment,but also provide a demonstration for carrying out refined quantitative research about strike-slip active faults.Based on the above studies,we draw the following conclusions.1)By systematically measuring the horizontal offset data of?150 kilometers along the eastern Altyn Tagh Fault?95.4°E-97.2°E?and calculating the Cumulative Offset Probability Distribution?COPD?,the results show that the peaks of cumulative offsets present an integer multiple of?6 meters,and the Coefficient of Variation?CV?is less than 0.25.2)The distribution of offsets and paleoseismological data together reveal that the eastern Altyn Tagh Fault exhibits characteristic slip behavior,with the characteristic slip of?6 m and a recurrence period ranging from 1170 to 3790 years.Assuming a 10km rupture depth and a 30 GPa shear modulus,we estimated a characteristic slip event Mw of?7.6.3)The Coefficient of Variation?CV?and the Late Quaternary activity studies of the eastern Altyn Tagh Fault together show that the Shulehe triple junction is the kinematics demarcation point of the eastern Altyn Tagh Fault,and the parts between the Subei triple junction to the Shulehe triple junction is dominated by left strike-slip,while to parts of the Shule River triple point is dominated by vertical thrusting.Combining with the previous studies of slip-rate along the eastern Altyn Tagh fault,we believe that the kinematic model in the northeastern margin of the Qinghai-Tibet Plateau is more in line with the“lateral slip extrusion”model4)To simulate the observed displacement measurement results and paleo-earthquake time series of the eastern Altyn Tagh Fault,we use the statistical model of Zielke?2018?to design three groups of simulation experiments,each of which corresponds to an earthquake recurrence model,respectively Characteristic Earthquake model?CE?,bimodal model?Bimod?and GR relationship model?GR?.Based on the analysis and discussion of the simulation results,we believe that the lower CV_slip and CV_time on the eastern Altyn Tagh Fault conform to the Characteristic Earthquake model?CE?.Although the results show that the Characteristic Earthquake?CE?model is more in line with the observation results,for various reasons,the current research on the seismic recurrence model is still controversial.More accurate earthquake recurrence models rely on more complete paleo-earthquake time series results or the development of new technologies to directly date gullies.