EGL Ref: 9215 23 June 2022 Page 12 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. Deterministic estimates were calculated for the Kerepehi Fault worst-case scenario (Mw7.3 discussed previously) and the most likely scenario, which is considered to involve a rupture length of 65 km, with a magnitude of Mw7.2, resulting in normal (dip-slip) fault displacement of 2.9 m. There was insignificant difference between the two scenarios in terms of estimated shaking intensity at the Development Site. The 150-year return period spectrum is commonly adopted as the Operating Basis Earthquake (OBE) for dam design as defined by the NZDSG. For a High PIC dam, the NZDSG recommend that the Safety Evaluation Earthquake (SEE) be taken as the 84th percentile level ground motion associated with the CME if developed by a deterministic approach. Furthermore, this need not exceed the 10,000-year return period ground motion developed by a probabilistic approach. The 84th percentile level shaking from a CME on the Kerepehi Fault and 1 in 10,000-year return period ground motion has been adopted for the SEE design, along with an aftershock one magnitude less. The uniform hazard spectral accelerations from the probabilistic and deterministic estimates of seismic hazard are shown in Figure 9. The spectra are for a 5% damped oscillator, for the larger horizontal component ordinate for rock conditions. Horizontal Peak Ground Acceleration (PGA) values and corresponding average magnitudes at the base of the embankment at the rock surface are as follows: 150-year return period (OBE): PGA = 0.10g, Mw = 6.3 84th percentile level for CME (SEE): PGA = 0.23g Mw = 7.3 2,500-year return period: PGA = 0.27g Mw = 6.6 10,000-year return period: PGA = 0.39g, Mw = 6.9 PGA and spectral acceleration values are provided as values of gravitational force (g) i.e., 0.1g is 10% of the force of gravity. Amplification of ground accelerations do occur through soil profile as well as the embankment. This amplification is allowed for in specific design calculations as it varies with each application.
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