How Wide Are Faults?
Description:
Fault zones are often represented as an hourglass shape, wider at the surface, narrow through the seismogenic zone, and wider ductile shear zones at depth. This conceptual model predates decades of observations of the width of deformation zones in continental strike slip faults. We compiled the width of seismic and aseismic strain zones from 0-30 km depth using rupture maps from single earthquakes, creeping zone widths from repeat monument surveys and InSAR, aftershock locations, low velocity and high anisotropy zones, as well as widths of pseudotachylyte, ultramylonite, and mylonite zones in exhumed faults. We assert that ultramylonites are the down-dip equivalent of fast creeping zones measured at the surface. We equate the width of pseudotachylyte-bearing zones to the width of primary coeseismic surface rupture traces over geologic time. To date, we have not observed systematic width-depth trends in the seismogenic width, creeping zone width, or total fault zone width, suggesting no clear “hourglass” narrowing across faults through the seismogenic zone. The fast-creeping zones are somewhat thinner than the maximum width of single earthquake ruptures at the surface and in the exhumed faults. The width of rupture zones measured at surface from individual earthquakes is similar to the width of fast creeping zones at the surface and at depth. The width of damage zones measured in the upper 10 km is similar to the width of lower strain mylonite zones at 20-30 km depth. These dimensions may be important for parameterizing faults zones within probabilistic fault displacement hazard analyses and for earthquake cycle modeling that considers post-seismic recovery and viscous relaxation. The compiled fault zone widths in this study may help constrain appropriate rheologies and deforming zone widths for interseismic and off-fault deformation.
Session: Exploring the Complexity of Fault Discontinuities - I
Type: Oral
Date: 4/17/2025
Presentation Time: 02:00 PM (local time)
Presenting Author: Christie
Student Presenter: No
Invited Presentation:
Poster Number:
Authors
Christie Rowe Presenting Author Corresponding Author rowec@unr.edu University of Nevada, Reno |
Alexandra Hatem ahatem@usgs.gov U.S. Geological Survey |
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How Wide Are Faults?
Session
Exploring the Complexity of Fault Discontinuities