We provide an overview of the treatment of site effects in the New Zealand National Seismic Hazard Model (NZ NSHM), including a case study of basin effects in central Wellington. The NZ NSHM 2022 includes a change in site parameter from subsoil class (NZS class) to VS30⁠. Poor NZ VS30 characterization is a major source of uncertainty in the NSHM; however, advanced site characterization in Wellington allows for in‐depth study. First, we construct a regional 3D shear‐wave velocity model and maps of site parameters (⁠T0⁠, NZS class, and VS30⁠) for central Wellington. At central city soil sites, we find the ratios of NZ NSHM 2022 hazard spectra with respect to the current equivalent design spectra range from factors of ∼0.8–2.6 (median ∼1.5), depending on local site conditions and spectral period. Strong amplification peaks at 0.5–2 s are observed in central Wellington. Linear site‐specific amplifications from multiple methods are compared at 13 stations and are well‐defined by both site‐to‐site residuals and response spectral ratios relative to station POTS. At many deeper soft sites (⁠VS30<300 m/s⁠), strong amplification peaks occur around T0 that are underpredicted by mean ergodic ground‐motion model (GMM) predictions. This underprediction is slightly enhanced when using basin‐specific Z1.0 as an additional site parameter. Our study highlights outstanding challenges in modeling strong basin response within shallow basins in NSHMs, including the need to consider region‐ or basin‐specific modeling approaches as well as nonlinear effects at high shaking intensities that dominate the hazard. For New Zealand, in general, as illustrated in the Wellington case study, a priority is the further characterization of VS30 (and VS⁠) for the seismic network to better isolate and quantify uncertainties in seismic hazard and allow useful exploration of regional–GMM adjustments and partially nonergodic approaches.

中文翻译：

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2022年新西兰NSHM在新西兰惠灵顿盆地的场地效应及应用概述

我们概述了新西兰国家地震灾害模型 (NZ NSHM) 中场地效应的处理，包括惠灵顿中部盆地效应的案例研究。NZ NSHM 2022 包括场地参数从底土等级（NZS 等级）更改为 VS30⁠。不良的 NZ VS30 表征是 NSHM 不确定性的主要来源；然而，惠灵顿先进的场地特征可以进行深入研究。首先，我们构建了惠灵顿市中心的区域 3D 剪切波速度模型和场地参数地图（T0、NZS 级和 VS30）。在中心城市土壤站点，我们发现 NZ NSHM 2022 危险谱与当前等效设计谱的比率范围为~0.8–2.6（中值~1.5），具体取决于当地场地条件和光谱周期。在惠灵顿市中心观察到 0.5-2 秒的强扩增峰值。在 13 个站点对多种方法的线性位点特异性放大进行了比较，并且通过站点间残差和相对于站点 POTS 的响应谱比明确定义了线性位点特异性放大。在许多较深的软站点（⁠VS30<300 m/s⁠），T0 附近出现强放大峰值，而平均遍历地震动模型 (GMM) 预测低估了这些峰值。当使用特定盆地的 Z1.0 作为附加场地参数时，这种低估会略有增强。我们的研究强调了在 NSHM 浅盆地内强烈盆地响应建模方面面临的突出挑战，包括需要考虑区域或盆地特定的建模方法以及在主导灾害的高震动强度下的非线性效应。一般来说，对于新西兰来说，如惠灵顿案例研究所示，优先事项是进一步表征地震网络的 VS30（和 VS⁠），以更好地隔离和量化地震灾害的不确定性，并允许对区域 GMM 调整进行有用的探索和部分非遍历方法。