Ground motions simulation of hypothetical earthquake sources in the upper North Island, NZ (2020)
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The upper North Island of New Zealand has low rates of seismicity compared to the rest of the country. However, large concentrations of population and infrastructure mean this region is exposed to moderate magnitude earthquakes on the Kerepehi Fault within the Hauraki Rift, and the Wairoa North Fault in the Hūnua Ranges. Using a physics-based simulator, we modelled ground motions for Mw 7.3 and Mw 6.6 characteristic earthquakes on these structures. Low-velocity sediments in basins beneath the Hauraki Rift and the city of Hamilton were explicitly represented. For the Hauraki Rift earthquake, there was a 2 to 3 times amplification of shaking in Hamilton and towns near the Firth of Thames for periods longer than 1 s. Severe to violent MMI 8-9 shaking with cumulative absolute velocity exceeding 2 g.s is modelled close to the source, which would be a potential liquefaction hazard to stop banks and farmland in the Hauraki depression. Auckland, Hamilton and Tauranga would experience moderate to very strong MMI 5-7 shaking. Simulated impacts in Auckland are larger for the Wairoa North Fault earthquake, which would generate spectral accelerations in excess of 1.0 g at reservoir dams in the Hūnua Ranges, 0.4 g at the international airport, and 0.3 g at the CBD and port. Road, rail and electricity networks are particularly vulnerable to disruption where they converge at Takanini (South Auckland) just 10 km from the fault.
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