Ciel Elizalde

Graduation Semester and Year

2015

Language

English

Document Type

Thesis

Degree Name

Master of Science in Earth and Environmental Science

Department

Earth and Environmental Sciences

First Advisor

William Griffith

Abstract

Oil shales often form the roof and floor rocks of many coal mines in the Appalachian basin. These mines offer outstanding 3D exposures of fresh rocks, otherwise only accessible via boreholes or heavily weathered surface outcrops, and present an excellent opportunity to directly observe pristine in situ natural fractures in shale. In Carroll County, Ohio, small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal-shale contacts are steepest, causing roof rock instability. We hypothesize that sloping bedding contact surfaces serve as natural displacement discontinuities which augment the local stress state, resulting in localized secondary thrust fault development. Using borehole and in-mine survey data, we digitally constrain bedding surface geometry to model slip along this interface and calculate related stress perturbations. Our modeling results suggest inherited non-planarity in bedding contact discontinuities influences the nucleation of secondary thrust faults. Simulation results as constrained by the integrated field and modeling approach taken in this study will help better understand the relationship between subsurface stress perturbations caused by natural discontinuities and the formation of secondary fractures. For mining purposes, recognizing subsurface stress heterogeneities due to bedding geometry can improve our predictive capabilities of underground structural hazards.

Disciplines

Earth Sciences | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

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