Date of Award

5-2019

Document Type

Thesis open access

Department

Geology

First Advisor

Benjamin Surpless

Abstract

Deformation associated with normal fault propagation and displacement places controls on the distribution and flow of sub-surface fluids. With a better understanding of how sedimentary units deform in response to a propagating fault, I can better predict how fluids might flow through the system at initial stages of displacement. To elucidate the role of sedimentary layering on fault tip propagation, I use ABAQUS/Standard to conduct a finite element analysis of a propagating normal fault to identify patterns of stress distribution and accumulation. While holding material properties constant (e.g., Young’s Modulus, Poisson’s Ratio, dilation angle, and the internal angle of friction), I simulate the initial stages of plastic failure in front of a normal fault tip propagating at 60° through bedded sandstone at low levels ( < 0.09 m displacement). I test the effects of incrementally increasing the number of mechanical layers from a single 20-m thick layer to five 4-m thick layers. I find that the presence of layering allows for simultaneous, but discontinuous, plastic failure in multiple locations ahead of a propagating fault tip. Additionally, although inter-layer stress accumulation is hindered by an increased number of layers, elevated regions of maximum stress occur further ahead of the propagating fault tip with an increased number of layers. Additionally, I show that the coefficient of friction between beds controls the angle at which off-fault-plane stress develops. My results show that mechanical layering systematically re-distributes stress ahead of a propagating fault tip so that a section of sandstone with multiple layers will fracture differently than a single massive bed. This predictable mechanical behavior is likely to influence the development of fluid conduits associated with fracturing during the early stages of normal fault propagation, a finding that has implications for the evolution of permeability structure of real-world fault zones in the subsurface.

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