SCEC Award Number 22152 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Impact of Contact and Interface Modeling on Precarious Rock Fragilities – Phase 4: Probabilistic Assumptions
Investigator(s)
Name Organization
Christine Wittich University of Nebraska, Lincoln
Other Participants 1 Graduate Research Assistant (TBD)
SCEC Priorities 5b, 5c, 4d SCEC Groups Geology, Seismology, SAFS
Report Due Date 03/15/2023 Date Report Submitted 03/09/2023
Project Abstract
 The long-term research goal is to reduce epistemic uncertainty in the probabilistic overturning predictions for precariously balanced rocks (PBRs). Recent studies highlight the significant impact that interface geometry and interface modeling parameters can have on the probabilistic overturning response. In addition, SCEC Awards #20106 and #21058 conducted experimental shake table testing on representative PBRs to gage the uncertainty associated with the interface geometry and materials. This previous research has highlighted the large inherent uncertainty associated with overturning, particularly when cast in the traditional probabilistic framework. This 1-year project had two primary objectives: 1) identify an appropriate set of computable intensity measures that efficiently predict overturning responses of PBRs; and 2) quantify and assess the impact of the choice of probabilistic model and its parameters for PBR overturning fragilities. This study recommends the use of logistic regression for PBR fragility and the use of a pair of intensity measures: cumulative absolute velocity and peak ground acceleration.
Intellectual Merit The analysis of precariously balanced rocks and other fragile geologic features has been identified as a particular strategy to evaluate ground motion hazard and inform seismic hazard methodologies. While precarious rocks are recognized as a means to evaluate hazard, it is also understood that existing analysis techniques carry potentially significant uncertainty and the development of analysis techniques is a noted research priority of SCEC. The proposed project directly addresses this research priority through the analysis and quantification of epistemic uncertainty associated with the probabilistic assumptions and choice of ground motion intensity measures, and the impact that this may have on subsequent fragility analyses.
Broader Impacts This project supported 2 Ph.D. students and 1 undergraduate research assistant. The Ph.D. students acted as advisors to the undergraduate research assistant. This structure provided professional development via mentoring for the Ph.D. students, who also gained additional research experience, as well as provided new research experience for an undergraduate student.
Exemplary Figure Figure 2. (a) Sample logistic regression fragilities for freestanding structures, and (b) a sample AUC curve of the ROC analysis. Generated by: C. Wittich.