Anomalous seismic and rheological behavior of the asthenosphere beneath oceanic and continental plates

The discovery of plate tectonics brought with it many questions regarding the very nature of a plate, how and why a rigid outer planetary shell is broken up, and what physical properties of the underlying mantle allow mobility of these rigid bodies. In addition early fluid dynamic models of mantle convection in the Earth's interior had to be reconciled with the idea of tectonics at the Earth's surface. In this doctoral thesis, I explore the seismic properties of the lithosphere and asthenosphere in continental and oceanic settings using inversion methods for Rayleigh waves and SKS phases. I improve previous inversion methods by considering the frequency-dependence of the incoming wavefield, testing for lateral resolution of velocity through checkerboard tests, measuring attenuation of Rayleigh waves, and considering the contribution from smaller 4theta terms in theoretical approximations for azimuthal anisotropy. I compare shear wave splitting in region S and teleseismic SKS phases for the first time in a continental setting in the western Himalayan syntaxis indicating strong sublithospheric mantle flow beneath the intensely compressional India-Asia collision zone. I also present fluid dynamic experiments of Saffman-Taylor instabilities and propose a new geodynamic model for asthenospheric flow in the oceanic mantle relating mantle converting plumes to surface plate tectonics. All of the studies presented here emphasize the importance of asthenospheric flow but is often only established after careful resolution of the lithospheric mantle. These studies show that there is significant and often complex interaction between whole mantle convection and surface plate tectonics warranting continued investigation into both continental and oceanic mantle dynamics.