Doctor of Philosophy (PhD)
Geology and Geophysics
The substantial research and the uncertain timeline to achieve deterministic earthquake prediction make the ground-shaking estimation of realistic earthquake scenarios a helpful approach in seismic hazard assessment. The accuracy of these computations depends on having structural subsurface models with good representations of sedimentary basins, fault zones, and crustal heterogeneity. We develop higher resolution seismic models for the Coachella Valley in Southern California and Indo-Burma. These areas have rising populations, expanding infrastructure, and highly anticipated disruptive earthquakes. We utilize data from recent seismic deployments and newly developed seismic imaging algorithms and the techniques of travel time tomography, wave propagation simulation, and receiver function to update the models. We test the waveform prediction ability of the newly developed models using earthquakes unassociated with them and a multiscale merging procedure.
The Coachella Valley sedimentary basin has a maximum thickness of ~4 km at the northern end of the Salton Sea, gradually decreasing to a thickness of ~2 km at the north end of the valley. The basin shape is asymmetric, with more sediments around the San Andreas fault on the eastern side. Combined interpretation of seismicity, lateral velocity changes, and geologic offset reveal a potential fault zone in the Lost Horse Valley. Some results show that hybrid models developed when we smoothly merge the Coachella Valley model and another similarly constructed model in Imperial Valley with existing community models can significantly improve ground motion estimates. Exploring the effects of several model representations on wavefield simulations shows that the addition of shallow geotechnical information or topography may not enhance low-frequency waveform fit. In Indo-Burma, ~14-17 km of sediments exist in the Bengal Basin. A crust that varies from continental to transitional is underneath the thick deposits, revealed by thinning from ~30 km to ~16 km in the subduction direction. The ~30-40 km thick Myanmar crust is downwarped by the weight of the ~10 km thick Central Myanmar Basin, and the subducted Indian crust is of oceanic origin. Future research endeavors, particularly the extension to higher frequencies of interest to structural engineers, will benefit from the current work.
Ajala, Rasheed, "Seismic Inversion and Modeling for Improving Earthquake Hazard Assessment" (2022). LSU Doctoral Dissertations. 5803.
Available for download on Friday, April 04, 2025