Investigating the impact of restraining bend dip on fault evolution using scaled experiments

Michelle M. Nishimoto, & Michele L. Cooke

Submitted August 30, 2026, SCEC Contribution #15491, 2026 SCEC Annual Meeting Poster #054

Scaled experiments provide direct observations of and detailed insights into evolving fault networks. Active strike-slip fault systems host many restraining bends, which can serve as points of earthquake initiation or termination. Because the geometry of the restraining bends evolve, their seismic hazard can change over time. Previous experiments explored the impact of restraining bend geometry using vertical restraining bends. However, many restraining bends segments, such as the San Andreas through the San Gorgonio Pass are not vertical. Here, we varied the dip of a gentle (15˚) restraining bend using wet kaolin as an analog for the upper crust material. Five cameras capture images from which we can extract displacement and uplift data.

All experiments follow similar fault evolution with the near simultaneous growth of two new faults from the kinks at both ends of the restraining bend segment; one each in the hanging wall and footwall. These faults propagate and curve to link with the precut fault so that dip slip along the two secondary faults form a spindle-shaped region of uplift. The secondary faults in the footwall of the restraining bend have greater slip rate than faults in the hanging wall. Trenches ~1 cm deep at the end of the experiments reveal consistent ~30˚ dip of the new thrust faults regardless of restraining bend dip. The kinematic efficiency (KE), which is the ratio of fault slip in the loading direction to applied velocity, increases as the fault systems mature and become more efficient. The steady state KE of the mature fault systems does not vary significantly with restraining bend dip suggesting that the fault systems have similar capacity to accommodate strike slip.

Results suggest that restraining bend dip impacts how strain is distributed as slip along faults and uplift. Restraining bends with shallower dip tend to have a smaller total area and volume of uplift and lower maximum elevation. At the same time, the most compact uplift on the hanging wall occurs for the bend with vertical dip.

As geologic and geophysical constraints on subsurface fault dip are often limited, slip partitioning and uplift patterns from laboratory experiments with a range of fault dips can provide guidelines for interpreting subsurface crustal fault geometry and help improve seismic hazard assessments.

Key Words
Restraining bend, slip rate, experiments

Citation
Nishimoto, M. M., & Cooke, M. L. (2026, 08). Investigating the impact of restraining bend dip on fault evolution using scaled experiments. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)