26 Seismic and Landslide Hazards in the Inland Northwest (Posters)

Thursday, 19 May 2016
8:00 AM - 5:00 PM
Clearwater Room

STRAIN ACCOMMODATION WITHIN EMERGING SHEAR ZONES: INSIGHTS FROM THE CENTENNIAL SHEAR ZONE, MONTANA AND IDAHO

Paper number: 26-2
Program: Theme Sessions
Time: 8:00 AM – 5:00 PM

Authors

Abstract

Dextral shear has been proposed as a mode of strain accommodation between the Centennial tectonic belt and the eastern Snake River Plain, yet no throughgoing strike-slip fault has been identified. A thick conglomerate of Neogene age constrains the Centennial shear zone hypothesis. Strain is distributed across numerous high angle conjugate strike-slip faults sub parallel to the orientation of maximum principle stress (σ1). Shear experiments suggest that inherited fractures suppress formation of a throughgoing strike-slip fault. Subcritical offset and inherited structures have suppressed throughgoing strike-slip fault formation within the 2 Ma Centennial shear zone. Strain is distributed among a wide yet discrete primary deformation zone (PDZ). Results of this study illustrate fundamentally unique kinematics of emerging shear zones. Strain is distributed among many high angle, possibly conjugate, strike-slip faults that sub-parallel σ1 and the PDZ. Deformation features are unorganized until total offset collapses strain upon a single linked fault. For these reasons, emerging and immature shear zones lack characteristic offset topography and centralized fault geometries of developed systems, bearing little resemblance to classical models of shear.

Geological Society of America Abstracts with Programs. Vol. 48, No. 6

doi: 10.1130/abs/2016RM-275865

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