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

June 12, 2020

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 We note that while in use for various applications, several of the models incorporated in the hybrid map are unpublished and have thus not necessarily had peer review, nor do all report uncertainties (see Table 1).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.

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