First-Time Use of Precariously-Balanced Rocks to Constrain Seismic Hazard Estimates for a Major Engineered Structure: Clyde Dam, New Zealand

Session: Earthquake Ground Motion and Impacts [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

We develop a probabilistic seismic hazard (PSH) assessment for the Clyde Dam, the largest concrete hydroelectric dam in New Zealand, and responsible for roughly 6% of the nation’s annual electricity supply. Our initial estimates of the Safety Evaluation Earthquake (SEE; 10,000 year return period) showed a PGA of 0.96g, a very large increase from the original design estimate of 0.54g. The increase was largely attributed to a revised location of the local Dunstan fault and consideration of hanging wall effects in the PSH model. Considerable additional work was then undertaken to refine the PSH results with updated ground motion prediction equations, additional epistemic uncertainty and assessment of the age and fragility of seven ancient precariously-balanced rocks (PBRs) near the dam site. The final SEE for the dam was then constrained using an adaptation of the methods developed during the Yucca Mountain Extreme Ground Motion project to evaluate the PSH model with the PBRs. The final SEE has a PGA of 0.55g, a considerable reduction from our initial 0.96g estimate. The study represents the first-ever use of PBRs to constrain the PSH estimates for a major engineered structure in New Zealand.

Presenting Author: Mark Stirling

Authors