Advances in Seismic First-arrival Tomography

Seismic first-arrival tomography is a technique currently experiencing a renaissance in popularity due to the simplicity of implementation and promising results for delineating a variety of subsurface targets. The purpose of this study is to investigate seismic first-arrival tomography in a variety of settings and applications, and thus to provide a solid framework for future work. The study largely consists of two separate themes, hydrogeophysics and low-velocity anomaly detection. Hydrogeophysics is an emerging field whereby measured geophysical properties are used as proxies for physical properties of the subsurface. This study represents one of the first high-resolution hydrogeophysical investigations in the upper three meters of the subsurface using seismic first-arrival tomography, and consists of detecting shallow high-velocity zones that are interpreted to be perched water bodies on the basis of geophysical and hydrologic evidence. The delineation and imaging of the perched water bodies is further advanced using trend-analysis techniques. A second theme of this dissertation is the optimization of methods for delineating low-velocity anomalies at depth using seismic first-arrival tomography. In order to locate a low-velocity zone at Oak Ridge, Tennessee, multiple seismic lines were collected and correlated with site-wide geology. The integration of geologic and geophysical data-sets assisted in developing a comprehensive transport conceptual model, and provided a predictive framework for future geophysical investigations at Oak Ridge. As a second component of this theme, a systematic methodology for detecting and delineating shallow low-velocity zones is developed.