SCEC Award Number 20068 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Rock towers as ground motion constraints: A case study of the Trona Pinnacles fragile geologic features in the wake of the 2019 Ridgecrest sequence
Name Organization
Domniki Asimaki California Institute of Technology Devin McPhillips United States Geological Survey
Other Participants Joaquin Garcia Suarez, Post doctoral researcher at Caltech
SCEC Priorities 4a, 4c, 4b SCEC Groups GM, Seismology, EEII
Report Due Date 03/15/2021 Date Report Submitted 03/14/2021
Project Abstract
Fragile geologic features, such as precariously balanced rocks (PBRs), have been used to constrain the intensity of past earthquake shaking. We analyzed the seismic response of another category of fragile geologic features, rock towers (RTs), using high-resolution, finite-element simulations. RTs differ from PBRs because RTs are materially connected to bedrock at their bases. We conducted the simulations using cm-resolution photogrammetric shape models and compared the results to paired broad-band seismic recordings from RTs and far-field bedrock as well as other field observations at the Trona Pinnacles, a group of RTs in southern California. The results of our simulations capture the first vibrational mode and the magnitude of amplification. However, simulations predict an important second vibrational mode, which was not observed. We interpret the differences to result from variations in material properties such as density and stiffness. Simulations also indicate that peak stresses occur near the base of the RT during earthquake shaking. Ongoing work aims to constrain the probability of intensity measure exceedance through dynamic modeling of a RT toppling, given shaking intensity, geometric parameters, and bulk tensile strength.
Intellectual Merit Fragile geological features (FGFs) allow us to pose a contradiction test over seismic hazard models and their predicted ground motions: dating experiments of these features can be used to contradict PSH models that predict high probability of events which, should they have taken place, unequivocally would have led to the failure of these features. While precariously-balanced rocks have been used in the recent past to constraint PSHAs, the seismic capacity and evolution of rock towers (RTs) studied here has received much less attention. This research addresses the need of a better understanding of tower's response and evolution using numerical and analytical tools, which we use to analyze instrumented features and to put forward hypotheses to be tested in future work.
Broader Impacts Results from this work can lead to the development of revised empirical models that can generate ground motion intensity measure constraints from the spatiotemporal distribution of Rock Towers in the vicinity of active faults.
Exemplary Figure Figure 2