A Global Hybrid Vs30 Map with a Topographic-Slope-Based Default and Regional Map Insets

Time-averaged shear wave velocity over the upper 30 meters of the earth's surface (Vs30) is a key parameter for estimating ground motion amplification as both a predictive and diagnostic tool for earthquake hazards. A first-order approximation of Vs30 is commonly obtained via a topographic slope-based or terrain proxy due to the widely available nature of digital elevation models. However, better-constrained Vs30 maps have been developed in many regions. Such maps preferentially employ various combinations of Vs30 measurements, higher-resolution slope, lithologic, geologic, geomorphic, and other proxies, and often utilize refined interpolation schemes. We develop a new hybrid global Vs30 map database that defaults to the global slope-based Vs30 map, but smoothly insets regional Vs30 maps where available. Additionally, we present comparisons of the default slope-based proxy maps against the new hybrid version in terms of Vs30 and amplification ratio maps, and uncertainties in assigned Vs30 values. The inclusion of any regional Vs30 model does not imply an endorsement of the quality or applicability of the model by the authors. Although we are careful to properly represent Vs30 models provided by other sources in our hybrid Vs30 maps, we do not render judgement on their quality or under what conditions their use is appropriate. We note that while in use for various applications, several of the models incorporated in the hybrid map are unpublished and have thus not necessarily had peer review, nor do all report uncertainties (see Table 1). The primary purpose of this platform is to facilitate testing of alternative Vs30 models and help users understand the differences in site amplification that these models produce. Our intension is that this will lead to users making more informed decisions about which models to include for various use cases.

地表浅层30米范围内的时间平均剪切波速（Vs30）是评估地震动放大效应的核心参数，同时也是地震灾害预测与诊断的关键工具。
鉴于数字高程模型（digital elevation models）广泛易得，学界通常基于地形坡度或地表代理变量来获取Vs30的一阶近似值。然而，许多地区已构建了约束性更强的Vs30分布图。这类分布图优先结合使用Vs30实测数据、高分辨率地形坡度、岩性、地质、地貌等代理变量，且通常采用精细化的插值方法。
本研究构建了一套全新的混合式全球Vs30分布图数据库，该数据库默认采用基于地形坡度的全球Vs30分布图，但会在有可用区域Vs30分布图的区域进行平滑嵌入。此外，本研究针对Vs30分布图、地震动放大比分布图以及赋值Vs30值的不确定性三个维度，对比了默认坡度代理分布图与新型混合分布图的差异。
本数据库纳入任何区域Vs30模型，均不代表作者认可该模型的质量与适用性。尽管本研究已审慎处理了其他来源提供的Vs30模型在混合分布图中的呈现方式，但并未对这些模型的质量，或其适用场景作出评判。
需说明的是，尽管混合分布图中纳入的部分模型已被应用于各类场景，但其中不少尚未正式发表，因此未必经过同行评议，且并非所有模型都提供了不确定性评估（详见表1）。
本平台的核心目的在于支持各类备选Vs30模型的测试工作，并帮助用户理解不同模型所带来的场地放大效应差异。本研究期望通过本平台帮助用户针对不同应用场景，更合理地选择适配的Vs30模型。