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Evaluating the New Zealand National Seismic Hazard Model 2022 with Fragile Geologic Features

Description: 

In the past year effort has gone into understanding and evaluating the biggest increases in estimated hazard in the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022) relative to NZ NSHM 2010. The southeastern North Island shows greater than a factor of two increase in peak ground acceleration for the 500 year return period. In this area, the new Hikurangi subduction zone ground motion modeling has driven this increase, along with an additional increase attributed to crustal sources. Our work has involved reconnaissance of the coastal eastern North Island (above the Hikurangi subduction interface) for fragile geologic features (FGFs) such as sea stacks, balanced rocks, and unstable delaminated rock slabs. FGFs at two sites, White Rock and Cape Palliser, were subsequently studied. A greywacke FGF at Palliser is balanced on a sloping pedestal, and its fragility has been quantified according to assumptions of toppling and sliding. Fragilities of delaminated carbonate rock slabs on a large sea stack at White Rock have been quantified according to assumptions of rocking. ¹⁰Be and ³⁶Cl cosmogenic exposure dating is currently being carried out on the greywacke and carbonate FGFs. Our preliminary interpretation from field observations is that they are older than the last Hikurangi subduction interface megaquake that occurred less than 1 kyr ago and will therefore provide useful constraints on the associated ground motions.

Session: Earthquake Shaking and the Geologic Record: Triggered Phenomena and Preserved Fragile Geologic Features - I

Type: Oral

Date: 4/17/2025

Presentation Time: 02:00 PM (local time)

Presenting Author: Mark

Student Presenter: No

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