Study On The Rupture Model Of Blind Fault Earthquake From Joint Inversion Of Multi-source Geodetic Data

Study on the coseismic slip model of earthquake based on the dislocation theory,geodetic data and inversion method is one of the important contents of the seismological study.Coseismic slip distribution model is the important basis for studying afterslip and viscoelastic relaxation,and also essential not only to reveal the mechanism of the development,occurring of earthquake,but also to judge the regional seismic hazard.This thesis estimates the coseismic displacements using traditional and space geodetic data and inverts for the fault slip distribution associated with three blind earthquakes?2013 Ms7.0 Lushan earthquake,2017 Ms7.0 Jiuzhaigou earthquake,2017Ms6.9 Mainling earthquake?around the Tibetan plateau to reveal the stress accumulation,release,geometric and kinematic characteristics of the seismogenic fault of the blind earthquakes.Firstly,I introduced the present research status at home and abroad of fault slip model inversion,and expounded systematically the homogeneous elastic half-space dislocation theory,layered elastic half-space dislocation theory and inversion method.Secondly,the coseismic deformation fields of the 20 April 2013 Ms7.0 Lushan earthquake were obtained from GPS,In SAR,leveling,and strong motion measurements.We modeled both the GPS and leveling coseismic displacements to investigate the fault geometry parameters using nonlinear least squares algorithm.The result shows that the Lushan earthquake occurred on a blind thrust fault in the southern segment of the Longmen Shan fault zone with strike N208.5°E and dip 42.1°to the NW and did not rupture the back reverse fault.The 68%and 95%confidence intervals of the fault geometric parameters were estimated using bootstrap method.The scatter plots indicates there is a significant trade?off between the fault length and dip slip,another significant trade?off exists between the fault width,the depth of the fault bottom edge,and the center position of the fault bottom edge.The optimal fault model and bounded variable least?squares algorithm were applied to invert for the coseismic slip model of Lushan earthquake.The result shows that the Lushan earthquake is dominated by reverse faulting with a slight left?lateral strike?slip motion.The coseismic slip is distributed at depth of 4-16 km,with the maximum slip of 1.2 m at depth 13.4 km.There is no slip occurred near the surface,which indicates the earthquake didn't rupture the surface.The total seismic moment released in the Lushan earthquake is 7.63×10¹⁸ Nm,corresponding to an Mw 6.53 event.The coseismic rupture of the Lushan earthquake terminates on the southwestern side of the seismic gap between Wenchuan and Lushan earthquake.Topographic stress may be related to the coseismic rupture termination.Thirdly,I used GPS,In SAR and strong motion data to compute the coseismic deformation fields of the 8 August 2017 Ms7.0 Jiuzhaigou earthquake.Then I used nonlinear and linear least squares algorithm to invert for the fault geometry and slip distribution of the Jiuzhaigou earthquake based on elastic half-space dislocation model constrained by coseismic displacement data.The result shows that the strike and dip of seismogenic fault of Jiuzhaigou earthquake are154 and 80,respectively.The Jiuzhaigou earthquake is dominated by left?lateral strike?slip motion with a slight normal faulting.The coseismic slip is distributed at depth of 2-12 km,with the maximum slip of 1.6 m at depth 6 km.There is no slip occurred near the surface,which indicates the earthquake didn't rupture the surface.The total seismic moment released in the Jiuzhaigou earthquake is 5.59×10¹⁸ Nm,corresponding to an Mw 6.44 event.Lastly,the coseismic displacement fields of the 18 November 2017 Ms6.9 Mainling earthquake were derived from GPS and In SAR observations.Then the coseismic displacement fields were adopted to invert for the fault geometry and slip distribution of the Mainling earthquake.The result shows that the strike and dip of seismogenic fault of Mainling earthquake are 125 and 15,respectively.The Mainling earthquake is dominated by reverse faulting with a slight left?lateral strike?slip motion.The coseismic slip is distributed at depth of 0.5-7.2 km,with the maximum slip of 0.72 m at depth 3.6 km.There is no slip occurred near the surface,which indicates the earthquake didn't rupture the surface.The total seismic moment released in the Mainling earthquake is 7.81×10¹⁸ Nm,corresponding to an Mw 6.54 event.