Coseismic Deformation,Surface Rupture Characteristics And Fault Slip Model Using Multi-source Satellite Images

In recent decades,image geodesy is one of the most effective technologies to determine the surface deformation caused by earthquakes,landslides and glacier migration.In SAR can measure all or most of the coseismic ground deformation,but In SAR can not provide the near-field displacement of the ruptured fault due to the interference phase decoherence caused by large displacement or strong ground vibration.In fact,the near-field displacement contains a lot of important information,including the geometry of the fault,the deformation model controlling the surface rupture and the shallow rupture model.Optical image correlation technology can obtain coseismic horizontal displacement field,and the reconstructed horizontal displacement field includes both near-field displacement(within a few hundred meters from the fault)and far-field displacement(1km away from the fault).Therefore,multi-source satellite image measurement can enable us to obtain more precise coseismic displacement to make up for the lack of single image measurement.On the other hand,the constraints on the geometric parameters of seismogenic faults are more important to the ground motion analysis of coseismic deformation field,the fault information given by geological data and the search for optimal fault parameters by nonlinear inversion.However,for large earthquakes with large coseismic surface deformation,complex fault slip and multiple fault rupture,these methods introduce great uncertainty to the constraint of fault geometric parameters.The surface rupture model based on multi-source remote sensing images can well constrain the geometric structure of faults,thus solving the problem of uncertainty of fault slip model caused by the difficulty in determining the geometric parameters of faults.Based on optical image correlation matching technology and DIn SAR technology,this study uses Multi-source Satellite images(Sentinel-1A/B SAR image and Sentinel-2 optical image)to carry out coseismic deformation observation,surface rupture characteristics and fault slip model inversion,taking the 2018 Palu earthquake and the 2019 Ridgecrest earthquake sequence as the research objects,in order to realize the recognition of coseismic surface rupture characteristics,the construction of surface rupture model and inversion of fault slip model constrained by surface rupture model are studied.The main achievements are as follows:(1)We obtained high-resolution(10 m)horizontal displacement fields from pre-and post-seismic Sentinel-2 optical images of the 2018 Mw7.5 Palu earthquake using subpixel image correlation.From these,we calculated the curl,divergence,and shear strain fields from the north-south(NS)and east-west(EW)displacement fields.Our results show that the surface rupture produced by the event was distributed within the Sulawesi neck(0.0974–0.6632°S)and Palu basin(0.8835–1.4206°S),and had a variable strike of 313.0–355.2° and strike slip of2.00–6.62 m.The NS and EW displacement fields within the Palu basin included fine-scale displacements in both the near-and far-fault,the deformation patterns included a small restraining bend(localized shortening),a distributed rupture zone,and a major releasing bend(net extension)from the curl,divergence,and shear strain.Surface rupture was dominated by left-lateral strike-slip from initiation to termination,with a localized normal slip component peaking at ?3.75 m.The characteristics and geometric variation of the ruptured fault controlled both the formation of these surface deformation patterns and sustained supershear rupture.(2)The 2019 Ridgecrest,California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults.To characterize the surface rupture kinematics and fault slip distribution,we used optical images and Interferometric Synthetic Aperture Radar(In SAR)observations to reconstruct the displacement caused by the earthquake sequence.We further calculated curl and divergence from the north-south and east-west components,to effectively identify the surface rupture traces.The results show that the major seismogenic fault had a length of ?55 km and strike of 320° and consisted of five secondary faults.On the basis of the determined multiple-fault geometries,we inverted the coseismic slip distributions by In SAR measurements,which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip(maximum strike-slip of ?5.8 m at the depth of ?7.5 km),with a small dip-slip component(peaking at ?1.8 m)on an east-dipping fault.The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault.These earthquakes triggered obvious aseismic creep along the Garlock fault(117.3° W–117.5° W).These results are consistent with the rupture process of the earthquake sequence,which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults.(3)The displacement field of 2018 Mw7.5 Palu earthquake published by previous scholars indicates that there are two obvious settlement areas on the east side of the main fracture.Compared with the profile of divergence value at fault location extracted in this study,it is found that the settlement area on the vertical deformation field is consistent with the positive dispersion value,and the divergence is highly sensitive to the tensile or extrusion fracture caused by vertical movement,It is a convenient way to qualitatively identify the rupture related to the vertical motion of earthquake.The special surface deformation modes(such as cracks,local uplift and settlement,fracture zones,etc.)produced by earthquakes are too small or the characteristics are not obvious,so they can not be directly observed or interpreted visually from the displacement fields of NS and EW of the same earthquake.However,the rotation field,divergence field and shear strain field obtained from ns and EW displacement fields of the same earthquake can highlight the surface fracture characteristics in detail,which enables us to recognize the surface fracture characteristics in a simpler and more automatic way.