Research On Co-seismic And Post-seismic Deformation Of The 2015 Pishan Earthquake Based On Sentinel-1A Data

Earthquakes are formed by the vibration caused by the rapid release of crustal energy,which often causes landslides,collapses,destruction of artificial buildings and facilities,and seriously affects human life and property safety.Therefore,seismic prediction and defense research has become one of the hot topics in the world.Seismic crustal deformation is a kind of crustal deformation phenomenon related to the eruption and gestation of earthquakes,which is monitored by various space technologies,and the information of disaster deformation is expected to be interpreted to explore the mysteries of earthquakes.The geodesic In SAR technique has the characteristics of large range,all-day time and high precision,and has become one of the effective methods to monitor seismic crustal deformation.the author selected the 2015 M_W 6.4 earthquake in Pishan,Xinjiang,the northern margin of the Tibetan Plateau which have drastic crustal deformation,frequent seismic disasters in China.The In SAR technology was utilized to observe the co-seismic and post-seismic deformation in the research area and the theory of elastic half-space dislocation was applied to invert the source mechanism parameters,so as to analyze the possible genetic mechanism of co-seismic and post-seismic deformation.It provides a basis for further understanding of the collision activities related to the West Kunlun Mountains and possible earthquake disasters in the future.The main contents and conclusions of this paper were obtained as follows:1.Based on the Sentinel-1A satellite data,the author utilized the D-In SAR technology to acquire the co-seismic deformation fields of the line-of-sight(LOS)in the ascending and descending orbits respectively;the deformation field of ascending orbits has two elliptical deformation centers,presenting a relatively symmetrical butterfly shape,with the maximum LOS displacement of 10.6cm,and the minimum LOS displacement of-6.2cm.The deformation field of descending orbits presents an obvious,asymmetrical elliptical deformation,with the maximum LOS displacement of 10.8cm and the minimum of-5cm.By analyzing the deformation fields characteristics of the two models,it is concluded that the LOS deformation detected by the radar was the upper wall of the fault,which lifted toward the northeast.The LOS deformation on southwest side of the faut was negative,which might be caused by the detached thrust fault.The northeastern region covering the desert was the footwall of fault.The interference images in this area is severely decoherent,and the deformation of the footwall cannot be effectively observed.The deformation profile of the ascending and descending was relatively consistent,indicating that the rupture property of the earthquake was mainly the inverse dip slip.2.The SDM program was used to invert the co-seismic fine-slip distribution of the Pishan earthquake.The results show that the epicenter location obtained by the inversion was(78.05°E,37.56°N).There was a major slip center for fault slip,and the slip is mainly concentrated at the distance of 20?30km along the fault dip;the average slip moment was 0.24m and the average slip angle is 91.6°;the maximum slip was approximately 0.88m at the distance of 25km along the fault dip.The shear modulus of the local crust was 3.0×10¹⁰Pa,the inversed seismic moment M₀=6.02×10¹⁸,which was about moment magnitude of Mw 6.5.3.Based on the 13-scenario Sentinel-1A satellite descending orbits data from 2015/07/18to 2017/05/08,SBAS-In SAR technology was utilized to obtain the LOS annual average deformation rate after the mainshock in the study area and the time-series cumulative deformation starting from 2015/07/18.The results show that the LOS deformation rate of the upper wall of the fault was in a positive interval,ranging from 8?43 mm/a;the maximum LOS deformation rate of 45 mm/a and the minimum LOS deformation rate of-36 mm/a were in the desert area on the northeast side of the footwall.As of May 8,2017,the LOS deformation of the epicenter area was mainly between 10?43mm;the cumulative LOS deformation curve at point A conformed to the deformation characteristics driven by aftershock and the cumulative LOS deformation curve at point B corresponded to the deformation characteristics of afterslip and viscoelastic relaxation.It was speculated that the near-field post-seismic deformation was mainly driven by afterslip,and the far-field post-seismic deformation might be driven by the combined effects of afterslip and viscoelastic relaxation and porelastic rebound.