Interseismic and coseismic surface deformation deduced from space geodetic observations : with inferences on seismic hazard, tectonic processes, earthquake complexity, and slip distribution

Abstract

In this thesis I am concerned with modeling the kinematics of surface deformation using space geodetic observations in order to advance insight in both interseismic and coseismic surface response. To model the surface deformation field I adopt the method of Spakman and Nyst (2002) which resolves the velocity (displacement) field and the motion (slip) on the fault simultaneously. The methods allows the determination of the localization of deformation near slipping faults and provides a complete description of surface deformation. The implementation of fault motion is particularly important for the purely kinematic estimation of a coseismic surface deformation field. In chapter 2 the surface deformation field of the southwestern US deformation zone is estimated by inversion of 497 geodetic velocities. The surface deformation field shows distributed deformation in a zone around the faults exhibiting shear strains and relative rotations. Significant localization of deformation is observed east of the San Andreas fault between the Transverse Ranges and San Francisco Bay. This is attributed to a relative rigidity contrast across the fault of ~ 1:8. A seismic hazard analysis based on the surface deformation model shows an increased risk of a Mw = 6:1 - 6:3 earthquake in the San Francisco Bay on the Hayward and southern Calaveras faults. In chapter 3 I am concerned with the determination of the present-day tectonic setting of Taiwan by a combination of the surface deformation field, seismicity and seismic tomography. In southern Taiwan the derived strain, rotation and fault slip rates are indicative of lateral extrusion towards the south. In northern Taiwan the onset of gravitational collapse is inferred which is induced by the on land extension of the Okinawa Trough. In the eastern Central Range the observed inverted NW-SE extension is the result of southward propagating exhumation of crustal material. Offshore east Taiwan strong evidence of a southward propagating crustal tear fault is deduced. The tear is the crustal response to incipient northwestward subduction of the Phillipine Sea Plate. Thus, the Ryukyu Trench is bending southward becoming almost perpendicular to the convergence direction. In chapter 4 the kinematic surface deformation of the August 17 1999, Izmit (Turkey) earthquake is inferred in a joint analysis of GPS and InSAR data. The fault slip contribution shows two distinct peaks: one of ~ 4m of slip at Gölcük, and a second of ~ 2.9m slip near Sapanca Lake. The strain field portrays four distinct quadrants reflecting the earthquake focal mechanism. I have deduced that the surface deformation field shows distinct evidence of a two-stage source rupture process caused by step-over features in the fault geometry, as well as two consecutive sources at the Akyazi Gap and Hersek. Chapter 5 describes a quantitative analysis of the resolution of slip distribution models based on surface displacement data. Assuming the theory of elastic dislocations in a half-space and adopting a parameterization for which model predictions are capable of fitting the spatial variations of the data, the inverse problem proves to be intrinsically ill-conditioned.