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Abstract Rock friction tests have made profound contributions to our understanding of earthquake processes. Most rock friction tests focused on fault strength evolution during velocity steps or at specific slip rates and the characteristics during stick‐slip events such as dynamic rupture propagation and the transition from stable sliding to instability, with little attention paid to the transient acceleration and deceleration periods. Here, we present Westerly Granite fault friction test results using a unique pneumatically powered apparatus with high acceleration of up to 50 g, focusing on the transient stages of fast fault acceleration and deceleration during both high‐speed sliding and stick‐slip events. Our data demonstrates the dominating velocity‐weakening behavior at transient stages of fault acceleration and deceleration, with a 1/V dependence for peak friction and deceleration lobe consistent with the flash‐heating model but with the acceleration lobe consistently deviating from the 1/V dependence. Our analysis of velocity‐dependent friction between dynamic rupture events, stick‐slips, and high‐speed friction tests reveals the significance of high acceleration in influencing transient fault weakening during dynamic weakening. We further demonstrate that the deviation of the friction‐velocity curve from the 1/V trend during fault acceleration is associated with the contribution of the dynamic rupturing process during the initiation of fault slip.
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This content will become publicly available on September 19, 2026
Unsteady Friction in Mixed-Flow Models Based on the Saint-Venant Equations
Transient flow models are expected to represent rapid flow changes, whereby acceleration and deceleration significantly influence energy dissipation. Such effects on energy dissipation can be expressed in terms of unsteady friction (UF) losses, which is a well-established process for closed-pipe flow models, but not in the context of mixed-flow models. Mixed flow refers to flow conditions where pressurized and free-surface flow regimes coexist or transition between each other within the same system. Many water systems experience significant flow acceleration and deceleration while in mixed-flow conditions, but current models have only the ability to account for these effects through steady roughness terms. This work builds from existing modeling approaches to adapt mixed-flow models based on the Saint-Venant equations that incorporate unsteady friction losses. The approach used to incorporate unsteady friction losses is a modification of a well-established formula based on local acceleration and spatial velocity gradient. The proposed numerical model, referred to as SVUF, is compared with three experimental data sets, and the results were improved, particularly for longer-duration flow simulations.
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- Award ID(s):
- 2048607
- PAR ID:
- 10636868
- Publisher / Repository:
- American Society of Civil Engineers
- Date Published:
- Journal Name:
- Journal of hydraulic engineering
- ISSN:
- 0733-9429
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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