Study On Seismic Risk Of Maqin-Maqu Segment Of East Kunlun Fault Based On Time Series InSAR

The East Kunlun Fault is one of the most active left-lateral strike-slip faults in the Qinghai-Tibet Plateau,and it is the northern boundary of the Bayan Har block.Slip rates and their spatial variation along the East Kunlun fault play an important role in understanding the associated tectonic evolution,crustal deformation,and seismicity.The Maqin—Maqu segment on the eastern segment of the East Kunlun fault is an area where the slip rate of the East Kunlun fault decreases significantly from west to east,and it is an earthquake gap where no strong earthquakes above magnitude 5 occurred in the past 400 years.Paleoearthquakes,modern tectonic activities,strain accumulation,seismicity and other data show that the Maqin—Maqu segment of the East Kunlun Fault is at the risk of strong earthquakes;the study of its deformation characteristics and the risk of strong earthquakes is not only a hot study of crustal deformation,but also has practical value.Based on PS-InSAR technology,this paper uses the ESA Sentinel-1A/B ascending and descending SAR data to obtain the interseismic slip velocity in the LOS direction of the Maqin—Maqu segment from 2016 to 2021.Combined with the GNSS velocity field from 1991 to 2016,we obtain the InSAR velocity and the three-dimensional velocity field in Eurasian reference frame.Using the TDEFNODE software based on the negative dislocation model and the Markov chain Monte Carlo method,slip rate,locking depth and seismic moment loss is helpful for understanding the motion state and current deformation mechanism of the Maqin—Maqu segment of the East Kunlun fault.The main results and conclusions of the paper are as follows:（1）After processing the Sentinel-1A/B SAR data acquired from 2016 to 2021,we obtained the InSAR LOS deformation referenced to the selected reference point.Combining with the existing GNSS velocity field from 1991 to 2016,we solved the Eurasian referenced InSAR LOS slip velocity field.The InSAR LOS velocity of the ascending and descending tracks,with the north-south velocity constrained by GNSS velocity,are used to solve the three-dimensional velocity components.The results show that the fault’s slip rate variation is mainly appears in the east-west direction,the variation in the south direction is small,and the fault is mainly left-lateral strike-slip.（2）We transform the three-dimensional velocity field to a fault-parallel velocity field,and use the Markov Chain Monte Carlo method to invert for the slip rate and locking depth of the Maqin—Maqu segment and surrounding faults.The research results show that: Maqin—Maqin shows no obvious creep phenomenon in the Maqu segment,and its slip rate gradually decreased from west to east from the Animaqing Mountain（300 km away from the end of the East Kunlun）from 4.7 mm/a to 2.3 mm/a.Most of the Qin-Maqu segment has a locking depth of more than 10 km,and the maximum depth is about 15 km.（3）Based on the negative dislocation model,the inversion results using GNSS and InSAR+GNSS are roughly the same.Higher spatial resolution of InSAR can provide more details,the results show that the slip rate decreases from west（4.5 mm/yr）to east（3.5 mm/yr）.Maqin has a large range of locking areas with a depth of about 16 km,and has two relatively obvious earth asperities.The high locking areas are concentrated at a depth of 7-8 km,with the maximum depth is 16 km,with larger slip velocity deficit and higher seismic moment accumulation rate.（4）Most of the Maqin—Maqu segment has a locking depth of 10 km,and the strain is constantly accumulating,which is close to the recurrence period of paleoearthquakes.Combined with the strain field distribution and previous geological results,the segment is divided into Maqin segments and Maqu by 101°E.The seismic moment accumulation of the Maqin and Maqu segments can reach ～1.00×10²⁰ Nm by MCMC method,which is equivalent to the energy of a Mw 7.3 earthquake;TDEFNODE’s inversion of the seismic moment accumulation of the two segments can reach ～0.80×10²⁰ Nm,which is equivalent to the energy of a Mw 7.2 earthquake.The seismic moment accumulation calculated by the two methods is consistent.If the two segments rupture at the same time,the released seismic moment energy is equivalent to a Mw 7.5 earthquake.The major earthquakes around the East Kunlun Fault in the past century has a certain stress load on the Maqin—Maqu section,so earthquake hazards of the Maqin—Maqu segment deserve attention.