| Plate boundaries are the sites where deformation induced by the relative motion of lithospheric blocks occurs. Observation of surface deformation, relative velocity of regions of the crust, and seismicity, all provide information on this process. In this thesis, I study lithospheric deformation at several complex plate boundaries. Lithospheric rheology and the earthquake cycle can have large effects on the observed surface velocity field. The Eastern California Shear Zone, an area likely characterized by a contrast in viscosity in the lower crust/upper mantle, provides a plate boundary segment to analyze those effects. I find that the contrast in the rheology of the lower layers (lower crust/upper mantle) can induce an asymmetric strain accumulation. This opens up the possibility of asymmetric coseismic displacement during an earthquake. Strike-slip creeping faults and their interaction with the surrounding lithosphere affect the patterns of strain accumulation and earthquake potential. In particular, I analyze the effect of fault geometry and of locked patches of the fault on the surface creep rate, and the possibility to apply observed patterns of micro-seismicity as a further constraint to map the distribution of fault creep. This allows me to further assess the seismic risk on the Hayward Fault. I find that the transition creates regions of higher stress that may generate the micro-seismicity. Comparing the results of my model with the micro-seismicity, the non-recurrent earthquakes mainly cluster in the transition zones while the repeating earthquakes occur principally in the fully creeping areas. Another aspect of plate boundary deformation analyzed in this thesis is the accommodation of the transpressional regime in the region of Fiordland, South Island, New Zealand. I find that the bending of the Australian plate, which is subducting beneath Fiordland, can provide that needed support. Furthermore, I find that in order to provide the correct dynamic support it is necessary to mechanically decouple the subducting sliver of Australian plate from the main plate. This suggest the presence of a tear or a weak zone within the Australian plate. |
