Surface Wave Constraints on the Oceanic Lithosphere-Asthenosphere Boundar

The lithosphere-asthenosphere boundary (LAB) is a fundamental concept of plate tectonics theory but its origin remains elusive. The lithospheric plate thickness and its relation to crustal age can help better understand the nature of the rheology contrast between the plate and the underlying asthenosphere. This dissertation discusses resolving oceanic lithosphere-asthenosphere boundary (LAB) using surface waves. It first talks about an important step in surface wave tomography - crustal corrections. By studying the effects of using different a priori crust models on the final mantle structure, we find out that differences between resulting mantle models is small compared to model uncertainty itself obtained using a model space search method. Secondly, we focus on analyzing different seismological proxies for LAB detection, using three different datasets and a model space search approach. The resulting statistical distributions of possible models allows us to infer the reliability of the velocity and anisotropy models of the Pacific upper mantle and determine whether the differences between the proxies are significant. We found that the LAB depth constrained by surface wave phase velocities is associated with large uncertainties for all proxies. Including surface wave group velocity data affected the radial anisotropy models, but did not satisfactorily reduce the uncertainties on the LAB depth proxies. We finally compared our LAB depth results with theoretical predictions from lithosphere cooling models under different conditions. It is shown that a half space cooling model with dehydration effects at the ridge best explains our models, though there remains significant uncertainties and dependence on the dataset that need to be investigated in future work.