Are offset channels accurate representations of strike-slip fault displacement? Implications from landscape evolution modeling

Nadine Reitman, Karl J. Mueller, Gregory E. Tucker, & Katherine R. Barnhart

Published August 15, 2018, SCEC Contribution #8735, 2018 SCEC Annual Meeting Poster #227

Strike-slip fault slip rates are commonly determined by correlating offset channels and dating the incised deposits. This approach is complicated by large uncertainties in pre-faulted channel morphology and temporal variation of stream incision, stream capture, and channel abandonment. In this study, we use landscape evolution modeling to investigate how slip frequency, fault zone width, and oblique slip influence fault zone geomorphology and the apparent channel offset distance. We model evolution of a theoretical channelized landscape in response to progressive lateral shear in a variety of strike-slip tectonic settings. Models are run for 100 ka, accumulating 300 m of lateral displacement. The explored parameter space includes slip frequency (continuous small displacement events vs. infrequent large displacement events), fault zone width (0–1000 m), and oblique slip (uplift by 0-50% of lateral slip). We evaluate the differences between final topography by comparing channel pixel aspects (fault-parallel vs. fault-perpendicular) and ridge connectivity across the fault zone and model domain. Preliminary results suggest that fault zone width plays a larger role in determining fault zone geomorphology than slip frequency. Diagnostic patterns of fault zone width are readily preserved in the landscape, whereas indicators of slip frequency are subtler. Modeled offset channels were then measured and compared to the prescribed slip amount as a test on our ability to accurately correlate and measure offset channels from digital elevation data. We find that offset channels are rarely reconstructed to within error of the total or per-event slip amounts, especially for fault zone widths > 100 m. This study provides insight into how slip frequency and fault zone width are recorded in the landscape within 1-2 km of a strike-slip fault, and highlights how these complexities can affect our ability to accurately measure channel offsets. In the future, these models can be modified by varying soil transport and channel incision parameters to investigate the roles that lithology and climate play in modulating channel preservation and fault zone morphology.

Citation
Reitman, N., Mueller, K. J., Tucker, G. E., & Barnhart, K. R. (2018, 08). Are offset channels accurate representations of strike-slip fault displacement? Implications from landscape evolution modeling. Poster Presentation at 2018 SCEC Annual Meeting.

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Earthquake Geology