Progress validating physics-engine simulations of precariously balanced rocks for hazards applications

Devin McPhillips, Zhiang Chen, & Kari Klaboe

Submitted September 7, 2025, SCEC Contribution #14624, 2025 SCEC Annual Meeting Poster #TBD

Precariously balanced rocks may be used to constrain maximum shaking intensity over timescales at which damaging earthquakes recur. Developing such valuable data requires estimating a precariously balanced rock’s fragility, which we define as the probability of toppling as a function of one or more intensity measures. At present, fragilities are typically calculated using empirical equations derived from a combination of shake table data and numerical modeling results. These equations are limited to a few geometric parameters, rather than a realistic representation of a real rock, but simplified geometric representations have been necessary because of the complexity and computational costs of discrete element simulations. Recently, Chen et al. (2024) developed the Virtual Shake Robot (VSR), a physics-engine approach for simulating both toppling and large-displacement dynamics of precariously balanced rocks, which promises accuracy and efficiency. Like other models, the VSR requires careful selection of macro-physical parameters. The VSR was designed as the digital twin of a real-world shake table, and the VSR has been tested against a small number of shake table experiments. Here, we begin to extend the validation of the VSR with a larger ensemble of shake table data. Klaboe et al. (2018) conducted 312 shake table experiments, where 5 concrete blocks were excited by variously scaled earthquake records from 6 earthquakes. For each experiment, displacement was recorded with video and optical image tracking. We propose to replicate these experiments virtually, using the VSR, and compare both the outcome (i.e., toppled or not) and the displacement histories. A thorough validation of the VSR could provide the tools to efficiently develop customized fragility functions for specific precariously balanced rock, thereby improving their accuracy as ground motion constraints.

Z. Chen, R. Arrowsmith, J. Das, C. Wittich, C. Madugo, A. Kottke, 2024. Virtual Shake Robot: Simulating dynamics of precariously balanced rocks. Seismica. doi:10.26443/seismica.v3i1.692

K. Klaboe, S. Pujol, L. Laughery, 2018. Seismic response of rocking blocks. Earthquake Spectra, 34(3), pp. 1051-1061.

Key Words
ground motion, precariously balanced rocks, models

Citation
McPhillips, D., Chen, Z., & Klaboe, K. (2025, 09). Progress validating physics-engine simulations of precariously balanced rocks for hazards applications. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology