Estimation of non-linear seismic site effects for deep deposits of the Mississippi embayment

This dissertation describes the development of a new one-dimensional nonlinear site response model and application of the model in probabilistic hazard analysis of the Mississippi embayment (ME) for estimation of depth dependent site coefficients.; The first part of the thesis describes the development of a new one-dimensional nonlinear site response model, DEEPSOIL, to simulate seismic wave propagation through deep deposits. DEEPSOIL incorporates several enhancements over currently available non-linear models. A confining pressure dependent non-linear constitutive soil model is developed. Full and extended Rayleigh viscous damping formulations have been incorporated in the site response analysis code to increase the accuracy of the solution. Current formulations of non-linear site response analysis contain a frequency dependent viscous damping term that often artificially filters out high frequency components of ground motion. The proposed formulations preserve most of these components.; The second part of the thesis describes the probabilistic seismic hazard analysis with non-linear site effect performed in the ME to develop site coefficients. Current site coefficients, proposed in National Earthquake Hazard Reduction Program (NEHRP), are used with USGS hazard maps to develop site specific recommended response spectrum. The coefficients are developed for 30 m thick soil profile and do not account for the depth of the soil column. A suite of ground motion time histories are developed that in sum result in the same hazard level as USGS hazard maps. The generated motions are propagated through the generic profiles of the ME using DEEPSOIL. The results of the analyses are presented in the form of site coefficient as functions of (a) depth of the soil profile and (b) level of shaking (spectral accelerations at 0.2 and 1.0 sec, both at B/C boundary). The site coefficients are comparable to NEHRP coefficients for 30 m thick profiles, but they show significant depth dependence for thicker soil profiles. A wide range of depth dependent site coefficients is developed for the ME.