The Mechanics of Active Faulting and Mountain Building

The aims of this thesis are to place new constraints on the rheological properties of active faults, and to investigate the influence of fault rheology on mountain building. The first chapter studies the postseismic deformation following the 2003 Bam earthquake in south-eastern Iran, with the intention of probing the material properties of the fault zone. Measurements of ground deformation following the earthquake made using InSAR suggest there was an unusually small amount of postseismic afterslip at Bam compared to similar earthquakes. I use numerical calculations of stress-driven afterslip to show that, in order to account for the limited postseismic afterslip at Bam, most of the fault zone must remain frictionally locked. I also find that, to explain the postseismic InSAR measurements and the long-term growth of topography at Bam, there must be either an E-W deviatoric stress of 2-10 MPa acting across the fault zone, or some component of fabric on the fault zone controlling the rake of fault slip. The second chapter expands in scope, investigating the orogen-scale deformation of the high Andes in south Peru. First I present a source model for a Mw 6.1 normal-faulting earthquake that occurred in the shallow crust of the south Peruvian Altiplano, which indicates that the Andes are extending parallel to the direction of shortening in the adjacent sub-Andean forelands. I then discuss a compilation of earthquake source models from across the Andes, using the earthquake depth distribution and slip vectors to infer that buoyancy forces are important in controlling the pattern of deformation. Calculations of the buoyancy forces indicate that faults cutting through the foreland support forces ~4-8 TN/m and have effective coefficients of static friction