3D Photogrammetric Analysis of a Fault Tip Damage Zone

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Authors:

Abstract:

A damage zone, the volume of fractured rock that surrounds a fault plane, is generated by fault tip propagation, fault core dynamics, flexure of rock adjacent to the fault plane, or dissipation of energy in earthquakes. Damage zones increase permeability, which enhances groundwater flow rates, hydrocarbon migration, ore mineralization, and geothermal energy production potential. We focus on the development of a damage zone near the tip of a low-displacement normal fault. Our outcrop analysis provides important insight, because damage zone fracturing in the subsurface cannot be detected by geophysical methods.

In this study, we investigated a damage zone associated with a segment of the Sevier fault zone in southern Utah. The exposure is located near Orderville, Utah, and is composed of 100-200m high inaccessible cliff walls. We used imagery from an unmanned aerial vehicle (UAV) to document the fracture network and used a tripod-mounted laser range-finder to georeference the outcrop for later model construction.

We built and georeferenced the VOM using Agisoft Metashape Professional following a well-tested workflow. Once the overview VOM was built, several orthomosaics, in both cross-sectional and map view, were created for scanline and network topologic analysis. Scanline analysis was performed in Agisoft Metashape Professional and initial qualitative topologic analysis was performed on the orthomosaic. Our analysis reveals an asymmetric, four-zone fault architecture, including a ~40-m wide footwall damage zone, a narrow fault core, and a ~70-m hanging wall damage zone that transitions over about 40 m to a transfer zone. It appears that the fault-related damage zone overprints the broader strain transfer zone between this fault zone and a nearby, higher displacement fault segment.

Scanline and qualitative network topologic analysis show that the hanging wall and transition zones display the highest fracture intensities, geometric complexities, and greatest network connectivity, while footwall and transfer zone fracturing is planar, vertically continuous, less connected, and less intense. Average fracture intensity increases up section across all zones. 

These initial results suggest that fracture-related permeability would permit higher fluid flow values in the hanging wall damage zone relative to other zones. Additionally, our results show that wide, asymmetric damage zones may develop very early in a fault’s displacement history. Our next step will be to perform quantitative topologic analysis of the fracture network with Network GT.