Selection of representative ground motion input for Wellington

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Abbott ER, Van Houtte C. 2020. Selection of representative ground motion input for Wellington. Lower Hutt (NZ): GNS Science. 90 p. (GNS Science report; 2019/43). doi:10.21420/Z6DQ-MM22.

The goal of the Stability of Land In Dynamic Environments (SLIDE) project is to better understand the behaviour of slopes in order to develop strategies for more robust remediation approaches and improve resilience of New Zealand’s buildings and infrastructure. Numerical simulations of slope stability are used to better understand how anthropogenically modified slopes may perform in future strong earthquakes. The aim of this report is to provide a range of realistic earthquake ground motions, selected using the method outlined in the New Zealand Standard (NZS) 1170.5, that can be used as input into slope stability simulations for slopes in the Wellington city region. To select the records, the peak ground acceleration (PGA) hazard for a range of annual exceedance probabilities was disaggregated, resulting in three magnitude-distance sets that were used to inform the earthquake characteristics that should be considered during selection of strong motion records (accelerograms). Potential accelerograms were evaluated using the NZS1170.5 criteria, with the exception of application of near-fault factors. Near-fault factors were not evaluated or applied as the hazard spectra are not intended for use in seismic design and the periods of interest, as they relate to the landslide analyses, are below those which would be affected by near-fault factors. A total of twelve records were selected for use. Forward directivity in approximately 1/3 of selected records is usually required for accelerograms chosen for engineering design but was not considered as a requirement in records selected for this study based on the end use of the records. (auth)