SCEC Award Number 16039 View PDF
Proposal Category Travel Only Proposal (SCEC Annual Meeting)
Proposal Title Fragile Geologic Features and Semi-Ergodic PSHA
Name Organization
Mark Stirling GNS Science (New Zealand) Chris Van Houtte GNS Science (New Zealand) Glenn Biasi University of Nevada, Reno
Other Participants
SCEC Priorities 6e, 4b, 4d SCEC Groups EFP, GMP, Geology
Report Due Date 10/14/2016 Date Report Submitted 11/09/2016
Project Abstract
In the period January-August 2016 we have developed ground motion simulations for the major Dunstan reverse fault in central Otago, New Zealand, and used the well-studied Cairnmuir Flat precariously-balanced rocks (PBR) to validate the simulations. This represents a geologically-based validation of simulations, rather than the standard approach of using instrumental strong motion records for validation. PBRs are abundant within a few km of the southwestern end of the fault, and are therefore conveniently located for validating simulated ground motions from M>7 near-field Dunstan Fault earthquakes. The fragility (the peak ground acceleration or PGA required to topple the PBR, based on a simple field-based estimates) and fragility age (age since the PBR reached the present unstable morphology) were compared to the recurrence interval and simulated ground motions of Dunstan Fault earthquakes. Earlier studies showed cosmogenic Be10 exposure date for two of the PBRs to be in the range of 40,400 to 55,300 years B.P., and the Dunstan Fault to show a recurrence interval of about 8000 years. Therefore, the PBRs have experienced repeated large earthquakes in which ground-motions did not exceed their fragilities (i.e. PGAs no greater than 0.7-0.8 g). The fragilities generally fall within the range of permissible PGAs according to the PBRs, except for less than 20% of simulations which exceeded the PBR fragilities. Our research in the remainder of the SCEC year will determine the simulation parameters responsible for the higher-then-permissible PGAs. The research represents the first effort at using PBRs to validate ground-motion simulations in New Zealand.
Intellectual Merit The study represents application of the first-ever comprehensive PBR dataset to the validation of strong ground motion simulations. The Cairnmuir Flats PBR dataset is unprecedented in its quality and quantity, and as such is a totally appropriate dataset for use in this area of seismic hazard modeling.
Broader Impacts The study will further the science of seismic hazard validation, and result in improved understanding of the randomness of ground motion at a site. This will move us on from the traditional application of the ergodic assumption in seismic hazard modeling, which often results in the industry having to face expensive engineering solutions. The study provides a substantial precedent for the use of PBRs in the industry, rather than PBRS remaining in the category of scientific research. However, the demise of funding support for foreigners in SCEC5 will severely limit these contributions to SCEC in the future. I am quite sad that foreign contributions to SCEC are always the first item to be compromised by cuts to SCEC funding. I strongly believe that Southern California needs to look outside Southern California in order to fully understand Southern California.
Exemplary Figure Figure 1 from the project report.