We have estimated the surface deformation field of the southwestern U.S. deformation zone in terms of the velocity gradient field and surface creep simultaneously by inversion of 497 geodetic velocities. The model shows aseismic fault motion consistent with aseismic creep measurements and a sense of motion consistent with geological observations. We deduce that our surface deformation field shows distributed deformation in a zone around the faults containing shear strains and rotations. The eastern California shear zone acts as a distinct fault zone bounded by more rigid blocks. The faults within the zone partition the shear motion, while right-lateral shear strain rates and clockwise rotations are concentrated between the bounding faults. In the same way, the San Jacinto and southern San Andreas faults act as bounding faults of a fault zone. The Mojave Desert is dominated by right-lateral shear, whereas the western Transverse Ranges (WTR) is subjected to contraction. We find significant localization of deformation east of the San Andreas fault between the Transverse Ranges and the San Francisco Bay. We attribute this to a relative rigidity contrast across the fault of ∼1.8. Finally, a moment deficit analysis shows an accumulation of moment deficit between 1973 and 2000 corresponding to a Mw = 6.1–6.3 earthquake along the San Andreas fault just north of the Big Bend, around the Imperial and southern San Andreas faults, and in the San Francisco Bay area along the Hayward and southern Calaveras faults.

The spatial slip distribution of the August 17, 1999, Izmit (Turkey) earthquake has previously been determined from both geodetic and seismological data. Though the models derived agree on a broad scale, they are significantly different in detail. These differences could be due to the inversion techniques applied and/or additional constraints implemented and/or be due to poor resolution. It is also conceivable that the relative agreement at larger scales results in part from a resolution artifact common to all models. To investigate this we perform a resolution analysis of fault slip models based on the inversion of 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.

We have determined the present-day surface deformation of Taiwan by computing the velocity gradient field and fault slip from 143 GPS velocity vectors. In southern Taiwan the derived strain and rotation rates and fault slips are indicative of lateral extrusion toward the south. In northern Taiwan we infer the onset of gravitational collapse which is induced by the on-land extension of the Okinawa Trough. In the eastern Central Range the observed inverted NW-SE extension is consistent with geological observations and high heat flow measurements. This could be the result of exhumation of crustal material. The model further shows a significant decrease in slip rate northward along the Longitudinal Valley fault at 23.7°N. The northern Coastal Range shows high strain rates and two oppositely rotating blocks. By combining the surface deformation model with seismicity data and seismic tomography we are able to propose a coherent model for the present-day tectonic activity. Both seismicity and tomography show further evidence for active, southward propagating exhumation of a crustal slice in the eastern Central Range. Offshore east Taiwan we deduce strong evidence of a southward propagating crustal tear fault, accommodating most of the Philippine Sea Plate-Eurasian Plate convergence. The tear is the crustal response to incipient northwestward subduction of the Philippine Sea Plate. Thus the Ryukyu Trench is bending southward becoming almost perpendicular to the convergence direction, while subduction of the Philippine Sea Plate continues. In this setting a sudden rapid southward propagation of the afore mentioned tear is conceivable.