Offset channels may not accurately record strike-slip fault displacement: Evidence from landscape evolution models

Journal of Geophysical Research Solid Earth
By: , and 

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Abstract

Slip distribution, slip rate, and slip per event for strike‐slip faults are commonly determined by correlating offset stream channels—under the assumption that they record seismic slip—but offset channels are formed by the interplay of tectonic and geomorphic processes. To constrain offset channel development under known tectonic and geomorphic conditions, we use numerical landscape evolution simulations along a theoretical strike‐slip fault with uniform and steady uplift, erosion, and diffusion. We investigate the influence of four tectonic parameters (fault zone width, earthquake recurrence interval, variance of the recurrence interval, and total slip relative to channel spacing) on offset channel development through multiple earthquake cycles. Analysis of >3,000 automatically measured offsets from >135 simulations suggests ~30% variability in individual measurements, but modeled displacement is recovered by averaging multiple measurements. However, the average of multiple offset measurements systematically underestimates modeled slip except when the fault zone is less than ~5 m wide, total slip is less than channel spacing, and offsets are measured shortly after an earthquake. In these simulations, postearthquake landscape evolution widens the geomorphic expression of the fault zone and modifies apparent channel offsets. We distinguish this “geomorphic fault zone” from the tectonic fault zone (zone of coseismic distributed deformation). This study highlights the capability of landscape evolution models to explore a range of conditions not easily defined in natural examples and the importance of averaging multiple measurements. Our results verify that paleoseismic studies must consider how geomorphic change has modified offset markers and use caution interpreting slip histories with multiple earthquakes.

Publication type Article
Publication Subtype Journal Article
Title Offset channels may not accurately record strike-slip fault displacement: Evidence from landscape evolution models
Series title Journal of Geophysical Research Solid Earth
DOI 10.1029/2019JB018596
Volume 124
Issue 12
Year Published 2019
Language English
Publisher American Geophysical Union
Contributing office(s) Geologic Hazards Science Center
Description 25 p.
First page 13427
Last page 13451
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