Moratalla, J.M.; Ristau, J.; Fry, B.; Goded, T.; Gusman, A.R.; Clark, K.J. 2021 Understanding cascading hazard impacts of a large subduction earthquake on the Hikurangi subduction margin, New Zealand, using a simulation of the MW 9.1 Tohoku-Oki earthquake. Lower Hutt, N.Z.: GNS Science. GNS Science report 2021/59. 30 p.; doi: 10.21420/88HQ-9792
Abstract:
One of the largest, most complex earthquakes that New Zealand could potentially face is a large subduction earthquake on the Hikurangi subduction zone. The purpose of this report is to document the processes and analysis behind the development of a Hikurangi subduction earthquake simulation for the purposes of a National Geohazards Monitoring Centre response exercise. A workshop was held in 2019 to select an earthquake scenario for development into a response exercise. It was decided to use the 2011 MW 9.1 Tohoku-Oki earthquake transposed onto the Hikurangi subduction zone for the exercise. The main advantage of using the Tohoku-Oki scenario over a completely synthetic event is that real-world seismic data from the Japanese networks could be mapped to the New Zealand network, making a more realistic exercise. The earthquake rupture geometry of the Tohoku-Oki earthquake was transferred to the Hikurangi subduction zone, and New Zealand strong-motion stations were mapped to the nearest Japanese stations. ShakeMap was used to develop peak ground acceleration and modified Mercalli intensity maps for a MW 9.1 subduction event with the same length and width characteristics as the Tohoku-Oki earthquake. The inputs for the ShakeMap modelling included the mean peak strong-motion recordings mapped to the New Zealand strong-motion station sites, as well as the fault rupture area and the epicentre location mapped to the Hikurangi subduction zone. We also mapped 21 Japanese broadband sites to the New Zealand broadband sites that had a similar distance and azimuth from the epicentre. Distances range from ~105 to 725 km and covered the North Island and the northern half of the South Island. All of the mapped broadband records clipped, which limited their usefulness for earthquake magnitude estimation; however, the waveforms are instructive from an exercise perspective, as it is the type of signal expected if a MW 9.1 Hikurangi earthquake was to occur. Tsunami modelling was undertaken to derive a simulated tsunami threat-level map and tsunami time histories for the New Zealand DART stations, both for the DART stations that are currently sending data in real time as well as for those that are planned to be deployed. All products of this project have been provided to GeoNet for use in developing a response exercise for the first three hours after the simulated earthquake.(auth)
