Project Abstract
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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.
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