Kinematics of the southwestern U.S. deformation zone inferred from GPS motion data

Abstract

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. Copyright 2005 by the American Geophysical Union.