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Uncertainty in Ground-motion Forecast: A Perspective From New Zealand National Seismic Hazard Model Revision

Description: 

Recent revision of New Zealand National Seismic Hazard Model (NZ NSHM 2022) represents a major change in hazard results as well as in the methodology and processes to capture the plausible range of uncertainty in ground-shaking forecast. The change in ground-motion characterization modelling (GMCM) scheme also represents as a major change in comparison to the approach adopted in the penultimate version of NZ NSHM. In the GMCM scheme, four typically used NGAWest2 GMMs along with three NZ specific GMMs were used for crustal earthquake sources. For subduction sources, recently developed three NGA-Sub GMMs along with a NZ-specific GMM were used. The changes in GMCM for NZ NSHM 2022 dominate changes in hazard across majority of the regions in the country. Particularly in high hazard regions such as along the eastern coast of the North Island proximal to Hikurangi subduction zone. The change in hazard due to the change in GMCM is 1.5-2 times than that from the previous nation-wide hazard model.

Clearly, the GMMs and the GMCM scheme adopted in the NZ NSHM 2022 represent state-of-the art nevertheless, the changes caused by the change in GMCM alone are significantly large. This requires further scrutiny for better understanding and future planning. One major challenge in the context of NZ is that dominant contribution in hazard comes from the potential earthquake magnitudes and distances that are beyond (or at the limit of) the calibration range of the typically used GMMs resulting in weak empirical constraints on both median and sigma models. Thus, it results in significant uncertainty in the ground-shaking forecast which ultimately affects hazard. Additionally, the efficacy of nonlinear soil response models used in the GMMs is also considered a major source of uncertainty. The non-ergodic GMMs are expected to provide reduction in sigma estimate however, challenges persist in constraining such GMMs for data-scarce regions. In this presentation, we discuss our perspective and plans to address some of these challenges in the context of NZ.

Session: Challenges and Opportunities in Constraining Ground-motion Models from Physics-based Ground-motion Simulations - III

Type: Oral

Date: 4/17/2025

Presentation Time: 03:00 PM (local time)

Presenting Author: Sanjay Singh

Student Presenter: No

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