Title

A Characterization of Critical Zone Architecture and Near-Surface Seismic Anisotropy in Oregon Ridge Park, MD

Date of Award

Fall 12-13-2019

Document Type

Honors Thesis

Department

Earth Sciences

First Advisor

Jorden Hayes

Language

English

Abstract

In this study, we investigate critical zone architecture and seismic anisotropy in Oregon Ridge Park, MD; specifically, the Pond Branch and Baismen Run catchments. Our characterization of critical zone architecture involves analyzing seismic tomography transects taken throughout the catchments, topographic analysis of the Baismen Run catchment, and measurements of seismic anisotropy. Seismic tomography transects reveal thicker sections of regolith beneath ridges than valleys. Topographic analysis of Baismen Run show a correlation between the angle with which the foliation planes of the underlying schist bedrock intersect the surface topography and the local slope steepness. We measured seismic anisotropy with two methodologies; first, radial seismic surveys and secondly, crossline tomography surveys. We implemented both methodologies at two study sites on opposite hillslopes of Baismen Run. The results of our surveys show that the magnitude of anisotropy in subsurface material is not constant with depth. Results from the radial surveys show that at the northern site, measured percent anisotropy increases with offset while at the southern site percent anisotropy initially increases then decreases. In the crossline tomography results for both sites, we see parabolic percent anisotropy versus depth functions with the parabola corresponding to the southern site being tighter and slightly more peaked. We investigate frost cracking as a potential cause of aspect dependent variations in anisotropy. We also produce modelled percent anisotropy versus offset curves by tracing rays through velocity models altered with theoretical percent anisotropy depth functions.

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