Controls on Fault Geometry During Early Stages of Extension in the Larkspur Hills, Northwest Basin and Range
Document Type
Oral Presentation
Start Date
15-5-2014
End Date
15-5-2014
Keywords
Fault initiation, Pre-existing structures, extension
Abstract
Detailed analyses of normal faults in domains of the Larkspur Hills, northwest Basin and Range, offer insight into factors controlling fault initiation, growth, and distribution in extensional regimes. N-trending faults in the southernmost domain share trends of major range-bounding structures and Pliocene linear volcanic vents; in contrast, NNW- and NNE- trending faults dominate further north and into south-central Oregon. Stress analyses and comparison with experimental and field data suggest that preexisting structures control fault geometries in the northern domains, while faults form perpendicular to σ3 in the southern domain. NNW-trending structures were favorably oriented to slip under E-W extension, so reactivated and continued as the dominant fault orientation in northern domains. NNE structures have the most offset, however, possibly due to pre-existing NE-oriented structures that reactivated as links between newer segments, forming structures with zig-zag traces and an average orientation optimal to slip. The change in fault orientations is abrupt, occurring across a major NNE structure. A regional transition is thus captured within the Larkspur Hills, suggesting they overlie a structural boundary at depth that separates isotropic crust from crust with a pre-existing NW-trending fabric.
For her work on this project, Diana Strickley was nominated for the SOURCE 2014 Scholar of the Year Award.
Recommended Citation
Strickley, Diana and Egger, Anne, "Controls on Fault Geometry During Early Stages of Extension in the Larkspur Hills, Northwest Basin and Range" (2014). Symposium Of University Research and Creative Expression (SOURCE). 95.
https://digitalcommons.cwu.edu/source/2014/oralpresentations/95
Additional Mentoring Department
Geological Sciences
Controls on Fault Geometry During Early Stages of Extension in the Larkspur Hills, Northwest Basin and Range
Detailed analyses of normal faults in domains of the Larkspur Hills, northwest Basin and Range, offer insight into factors controlling fault initiation, growth, and distribution in extensional regimes. N-trending faults in the southernmost domain share trends of major range-bounding structures and Pliocene linear volcanic vents; in contrast, NNW- and NNE- trending faults dominate further north and into south-central Oregon. Stress analyses and comparison with experimental and field data suggest that preexisting structures control fault geometries in the northern domains, while faults form perpendicular to σ3 in the southern domain. NNW-trending structures were favorably oriented to slip under E-W extension, so reactivated and continued as the dominant fault orientation in northern domains. NNE structures have the most offset, however, possibly due to pre-existing NE-oriented structures that reactivated as links between newer segments, forming structures with zig-zag traces and an average orientation optimal to slip. The change in fault orientations is abrupt, occurring across a major NNE structure. A regional transition is thus captured within the Larkspur Hills, suggesting they overlie a structural boundary at depth that separates isotropic crust from crust with a pre-existing NW-trending fabric.
For her work on this project, Diana Strickley was nominated for the SOURCE 2014 Scholar of the Year Award.
Faculty Mentor(s)
Egger, Anne