Continental Deformation at Varying Spatial and Temporal Scales

This thesis investigates continental deformation at many different spatial and temporal scales and at several plate-tectonic settings. Our main purpose is to understand how the continental crust behaves under applied forces, both over geologic times and over shorter time scales such as the seismic cycle. The thesis consists of separate investigations of long-term and short-term plate boundary deformation and also a two-part study investigating the interactions between deformation at these two time scales. In the first part of the thesis we investigate the long-term flexural elastic response of the lithosphere to vertical loads due to normal faulting and extension. Our study suggests that high topography in the Stara Planina range in Central Bulgaria is probably related to flexural footwall uplift in response to Pliocene to Quaternary normal faulting in this region. In the second part we focus on small scale deformation on an individual brittle fault in the upper crust and study how frictional properties and constitutive behavior of the fault, described by laboratory-derived rateand state-variable friction laws, govern the nucleation of earthquakes. The last part of the thesis investigates how the average rheologic properties of the crust govern deformation at a strike-slip plate boundary. In particular, we study the growth and evolution of fault networks within the upper crust over geologic times and how this process interacts with deformation at deeper crustal levels. Short time scale deformation such as sudden brittle failure on upper crustal faults is combined with longterm elastic and viscoelastic responses in the upper crust. Our results indicate that the rheology of the lower crust places strong controls on the nature and growth of fault networks at a strike-slip plate boundary. Thesis Supervisor: Leigh Royden Title: Professor of Geology and Geophysics