Case Study Evaluation of the Interface Geometry on Fragility of Precarious Rock Systems

Christine Wittich, & M. Khalid Saifullah

Published August 14, 2019, SCEC Contribution #9554, 2019 SCEC Annual Meeting Poster #119

Reliable estimates of seismic hazard are essential for the development of resilient communities; however, estimates of rare, yet high-intensity earthquakes are highly uncertain due to a lack of observations and recordings. In the absence of significant earthquake observations, the existence of certain precariously balanced rocks and other fragile geologic features provide a means to deduce the maximum possible ground motion at a site over the lifetime of the rock – i.e., that which precludes overturning or toppling. Current state-of-the-art methods for predicting overturning of a precarious rock include detailed surveying of the rock’s geometry followed by numerical simulations and ultimately fragility analysis, in which the probability of overturning is related to a measure of earthquake intensity. Recent field surveys of precarious rocks have highlighted the potential for complex interface conditions that are not readily captured by traditional surveying techniques. For example, a precarious rock may appear that is in uniform contact with a rock pedestal. However, the base of the rock may have eroded into a configuration where it is in contact at only a few discrete points on the pedestal. As a result, the overall objective of this study is to quantify and assess the impact of interface geometric variations on the probabilistic overturning predictions of precarious rocks. To this end, overturning predictions will be generated for a sub-set of precariously balanced rocks in southern California assuming varying levels of detail for the interface geometry. The resulting overturning probabilities are then compared and statistically analyzed to understand and quantify the impact of interface geometry uncertainty.

Key Words
Fragile geologic features (FGF), precariously balanced rocks (PBR), distinct element modeling (DEM)

Citation
Wittich, C., & Saifullah, M. (2019, 08). Case Study Evaluation of the Interface Geometry on Fragility of Precarious Rock Systems. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology