Group B, Poster #084, Earthquake Geology

Impact of Rock Material on Precarious Rock Fragilities

M. Khalid Saifullah, & Christine Wittich
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Poster Presentation

2022 SCEC Annual Meeting, Poster #084, SCEC Contribution #12002 VIEW PDF
Precariously Balanced Rocks (PBRs) are a type of naturally occurring freestanding structures that are important to test and constrain seismic hazard at longer return periods. The exposure ages of these rocks have been established to be between 10,000 to 30,000 years, which is why they are one of the few means to test the seismic hazard estimates for critical infrastructure such as nuclear power plants and nuclear waste repositories. The knowledge of overturning potential/estimates of the precariously balanced rocks is fundamental for the usefulness of these rocks. However, there are significant sources of uncertainties over the overturning estimates/potential of the structures arising from v...arious sources, such as the material of the rock, interface condition/asperities/geometry, numerical modeling, and ground motion parameters. In an effort to quantify the epistemic uncertainties on the overturning predictions, an extensive shake table study has been ongoing at the University of Nebraska’s shake table facility by employing natural rocks specimen as a representative of PBRs. Although the overall study involves the investigation of various numerical and physical parameters, this presentation sheds light on the uncertainty on the probabilistic overturning predictions brought by the material of the rock. Hundreds of shake table tests performed on two rock specimens of different materials, granite, and limestone, under the same set of ground motions selected based on the relevant intensity measures, PGV/PGA and PGA, are utilized to analyze and quantify the uncertainty in the probabilistic domain. The fragility analysis highlights the uncertainty arising from the material of the rock specimen.