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kirkft@umich.edu
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Quantifying near-surface rock strength on a regional scale from hillslope stability models - dataset
- Creator:
- Townsend, Kirk F., Gallen, Sean F., and Clark, Marin K.
- Description:
- These datasets support the findings of Townsend et al. (2020). In this article, we quantify rock strength using two novel applications of hillslope stability models, resulting in estimates of cohesive and frictional strength at the spatial scale of small watersheds. We compare these results against the direct-shear test dataset here for validation of our approach. We find that cohesive strength is dependent on the original burial depth of the sedimentary rocks studied here. The low-temperature thermochronometry data was used to assess the magnitude of burial.
- Keyword:
- Thermochronology, Thermochronometry, Direct-Shear, Landslides, Rock Strength, Landscape Evolution, and Geomorphology
- Citation to related publication:
- Townsend, K.F., Gallen, S.F., & Clark, M.K., in press, Quantifying near-surface rock strength on a regional scale from hillslope stability models: Journal of Geophysical Research Earth Surface. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JF005665
- Discipline:
- Science
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- Creator:
- Townsend, Kirk F., Clark, Marin K., and Niemi, Nathan A.
- Description:
- These datasets support the findings of Townsend et al. (in review) investigating the timing of faulting relative to changes in the orientation of the North American-Pacific plate boundary. Coeval with development of an oblique plate boundary segment (i.e. the “Big Bend” of the San Andreas fault), active shortening is inferred to have initiated at ~5 Ma in the Western Transverse Ranges (WTR). However, new low-temperature thermochronometric transects yield Miocene to Pleistocene apatite (U-Th-Sm)/He cooling ages and partially reset zircon (U-Th)/He ages. Inverse thermal modelling indicate that reverse faulting initiated as early as 10 Ma, several million years prior to our current understanding of the timing of the Big Bend. New and existing thermochronometry data delineate the WTR as the locus of rapid post-Miocene exhumation, and demonstrate that similar exhumation is not present in the broader region surrounding the Big Bend. We posit that reverse faulting is localized in the WTR because of a weak underlying lithosphere and predates the more recent geometric anomaly of the restraining bend in the transform margin.
- Keyword:
- Reverse faults, Fault initiation, Fault propagation, Low-temperature thermochronometry, Western Transverse Ranges, and San Andreas Fault
- Citation to related publication:
- Townsend, K. F., Clark, M. K., & Niemi, N. A., in review, Reverse faulting within a continental plate boundary transform system. Tectonics
- Discipline:
- Science
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Profiles of near-surface rock mass strength across gradients in erosion, burial, and time [Data set]
- Creator:
- Townsend, Kirk F, Clark, Marin K, and Zekkos, Dimitrios
- Description:
- These datasets support the findings of Townsend et al. (2020). In this article, we project profiles of rock mass shear strength into the shallow subsurface (~30 m depth) using the Hoek and Brown criterion with Geological Strength Index (GSI) observations of outcrop structure and surface conditions, and Schmidt hammer rebound values of intact (unfractured) rock hardness. We compare these projected rock mass shear strength profiles to shear-wave velocity profiles collected using shallow geophysical arrays. We evaluate our methods in the Western Transverse Ranges of southern California, which exhibit strong gradients in the depth of latest-Mesozoic through Cenozoic sedimentary rocks exposed at the surface today, and in erosion rates quantified from catchment-average cosmogenic radionuclide concentrations and low-temperature apatite and zircon (U-Th)/He thermochronometry. We find that stratigraphic age and burial depth exerts the strongest apparent control on rock strength and S-wave velocities, likely due to diagenetic changes associated with burial. For rocks of the same age and inferred burial history, we observe that shear strength and S-wave velocities are positively correlated with erosion rate. We suggest that increasing erosion rates cause decreased residence time of rock masses within the critical zone, resulting in less weathered rocks.
- Keyword:
- rock strength, seismic, and erosion rate
- Citation to related publication:
- Townsend, K. F., Clark, M. K., & Zekkos, D. (2021). Profiles of Near-Surface Rock Mass Strength Across Gradients in Burial, Erosion, and Time. Journal of Geophysical Research: Earth Surface, 126(4), e2020JF005694. https://doi.org/10.1029/2020JF005694
- Discipline:
- Science