Integrated Mapping and Physics-Engine-Based Fragility Modeling of Precariously Balanced Rocks

Zhiang Chen, Ramon Arrowsmith, Christopher M. Madugo, & Albert R. Kottke

Submitted August 30, 2026, SCEC Contribution #15543, 2026 SCEC Annual Meeting Poster #TBD

Precariously balanced rocks (PBRs) can constrain the upper bounds of earthquake ground motions over long timescales, but their use in seismic hazard assessment is limited by two major challenges: (i) scalable extraction of rock and contact geometry from field data and (ii) computationally efficient modeling of overturning fragility. We address these challenges through complementary workflows for three-dimensional rock characterization and physics-based dynamic simulation. First, UAV Structure-from-Motion, UAV lidar, and handheld lidar datasets collected at Granite Dells, Arizona, and the southern Sierra Nevada, California, are used to detect freestanding rocks, associate 2D rock detections with 3D point clouds, and segment individual rocks using interface-constrained region growing. Sparse user-defined rock-support constraints prevent segmentation from leaking across contact boundaries. Benchmarking against classical, unsupervised, and foundation-model baselines shows that the proposed method achieves the highest accuracy and F1 score while more effectively preserving rock-support interfaces. Field applications demonstrate population-scale PBR mapping and estimation of minimum contact angles and overturning accelerations with constraints that make sense based on regional hazard. Second, we develop a simulated shake-table platform using a physics engine and calibrate its contact parameters against large-scale experiments on a natural PBR subjected to 582 recorded earthquake displacement histories. The platform reproduces overturning with predictive reliability comparable to a state-of-the-art discrete element method while reducing wall-clock cost by approximately (10^2) to (10^5). This efficiency enables large ensemble simulations and systematic evaluation of contact-parameter uncertainty. Lateral friction has the strongest influence on predicted fragility, whereas restitution and spinning friction have comparatively minor effects. Together, these methods provide a practical pathway from remote-sensing observations and rock-support geometry to quantitative fragility estimates and long-term constraints on earthquake ground motions.

Key Words
PBR, PSHA, Fragile geological features, physics simulation

Citation
Chen, Z., Arrowsmith, R., Madugo, C. M., & Kottke, A. R. (2026, 08). Integrated Mapping and Physics-Engine-Based Fragility Modeling of Precariously Balanced Rocks. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology