Potential short-term aftershock sequences of an Alpine Fault earthquake and their ground motion fields

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Van Houtte, C.; Gerstenberger, M.C. 2019 Potential short-term aftershock sequences of an Alpine Fault earthquake and their ground motion fields. Lower Hutt, N.Z.: GNS Science. GNS Science report 2019/13. 23 p.; doi: 10.21420/33J4-TW37

Abstract:

An Mw8.2 Alpine Fault earthquake (AF8) is expected to result in surface fault rupture, high intensity ground shaking and landslides, which will cause severe damage to a large area in the South Island. In particular, landslides are likely to block transport networks and disrupt response and recovery efforts. Many aftershocks can also be expected following the main earthquake, some of which could also trigger co-seismic landslides. This report models potential ground motion from simulations of three possible Alpine Fault aftershock scenarios. These hypothetical aftershock scenarios are presented as low-productivity, average-productivity and high-productivity aftershock sequences, and are intended to span the months to years following an AF8 event. Ground motions are calculated for all events in these hypothetical aftershock sequences, then we calculate the number of times an assumed landslide triggering threshold is exceeded. The results indicate that Alpine Fault aftershocks may only trigger isolated landslides near the fault itself, or there could be widespread landslides throughout the Southern Alps, with some landslides reactivating multiple times. These scenarios can be used by relevant authorities in their response and recovery preparation. (auth)