Mechanical models of interseismic deformation in California and Taiwan.

摘要

Geodesists typically model measurements of interseismic surface velocities with dislocations in an elastic half-space or in an elastic layer overlying a viscoelastic half-space. In these kinematic models, the slip distribution and slip rate are prescribed. The analytical form of these models allows for efficient inversion of the data for model parameters, such as fault geometry and slip rates. The disadvantage is that inversions with kinematic models can lead to physically implausible slip distributions. In this thesis, two-dimensional mechanical models of interseismic deformation are developed in which slip on the faults is not prescribed, but is solved for by placing stress boundary conditions on the faults. The models are developed using a boundary element method. An earthquake cycle is modeled with deep interseismic creep on vertical strike-slip faults or dipping reverse faults in an elastic lithosphere coupled to a Maxwell viscoelastic asthenosphere.; GPS data across the Carrizo Plain and northern San Francisco Bay segments of the San Andreas fault and triangulation measurements of postseismic strain following the 1906 San Francisco earthquake are inverted to obtain an elastic thickness in the range 44--100 km (95% confidence level), fault zone viscosity of 0.5--8.2 x 1017 Pa s/m, and asthenosphere viscosity of 0.1--2.9 x 1020 Pa s. Slip rates on the northern San Francisco Bay San Andreas fault are in the range 21--27 mm/yr with recurrence times in the range 188--315 years. For the Carrizo Plain section of the San Andreas fault, slip rates are in the range 32--42 mm/yr with recurrence times of 247--536 years.; GPS measurements of interseismic velocities in central Taiwan are inverted to estimate slip rates and geometry of active faults. The inversions indicate a 28--38 km thick elastic lithosphere overlying a viscoelastic asthenosphere with viscosity of 1.5--4.7 x 1019 Pa s. The estimated combined slip rate on the frontal thrusts in western Taiwan is 30--50 mm/yr and the Longitudinal Valley fault slips 60--80 mm/yr. A decollement dips ∼10° under western Taiwan and increases in dip by as much as 8° under the Central Ranges.