College

Buchtel College of Arts and Sciences

Date of Last Revision

2022-12-16 12:29:17

Major

Geology

Honors Course

3370 497;002

Number of Credits

6

Degree Name

Bachelor of Science

Date of Expected Graduation

Fall 2022

Abstract

The effect of fault orientation relative to the applied stress on reactivation of pre-existing brittle faults instead of forming new faults is well-explained by Mohr-Coulomb theory. However, Mohr-Coulomb theory does not explain the effect of orientation on reactivation of faults with a ductile rheology and no work has been performed to assess the effect of orientation of a pre-existing ductile fault on fault strength. In order to determine how rock strength and localization of strain into a ductile fault is affected when the orientation of the pre-existing fault (artificial fault) is changed, experiments were performed on pre-faulted cores of a fine grained (d = 150 μm) granitic gneiss at a pressure of 1500 MPa, temperature of 750°C, and axial strain rate of 6.8x10-7 s-1. The foliation of the gneiss was oriented 45° to the vertical compression direction and the artificial faults were cross cutting the foliation at 45° or 60° to the compression direction. Strain localized into the pre-fault oriented at 45° to the foliation. However, strain was accommodated by the host rock and a new shear zone along the foliation plane that crosscuts the artificial fault oriented at 60° to the compression direction. These results indicate that, like in brittle faults, the range of possible orientations for ductile fault reactivation is limited, and that reactivation of preexisting faults may not always occur in orogenies with multiple deformation events.

Research Sponsor

Caleb W Holyoke

First Reader

John A Peck

Second Reader

Molly Witter

Honors Faculty Advisor

John A Peck

Proprietary and/or Confidential Information

No

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