This study presents the development of two new sedimentary velocity models for the San Francisco Bay Area (SFBA) to improve the near-surface characterization of shear-wave velocity ($V_S$), with the ultimate goal of enhancing the Bay Area community velocity model. A stationary model, based solely on $V_{S30}$, and a spatially varying model incorporating location-specific adjustments were developed using a dataset of 200 measured $V_S$ profiles. Both models were formulated within a hierarchical Bayesian framework, using a parameterization that ensures robust scaling. The spatially varying model includes a slope adjustment term modeled as a Gaussian process to capture site-specific effects based on location. Residual analysis shows that both models are unbiased up to $V_S$ values of 1000 m/sec. Along-depth variability models were also developed using within-profile residuals. Applying the proposed models in the SFBA results in an increase in $V_S$ in the San Jose area and east of the Hayward Fault, supporting simulations that suggest over-amplification in these regions compared to observations. Goodness-of-fit (GOF) comparisons using linear site-response analyses demonstrate that the proposed models outperform the USGS model in capturing near-surface amplification across a broad frequency range. Incorporating along-depth variability further improves GOF scores by reducing over-amplification at high frequencies. These results underscore the importance of integrating community velocity models with detailed sedimentary velocity models to enhance regional seismic hazard assessments.

翻译：本研究为旧金山湾区（SFBA）开发了两种新的沉积层速度模型，旨在改进近地表剪切波速度（$V_S$）的表征，最终目标是完善湾区社区速度模型。利用包含200个实测$V_S$剖面的数据集，我们构建了一个仅基于$V_{S30}$的静态模型和一个结合了位置特异性调整的空间变化模型。两种模型均在分层贝叶斯框架内构建，采用了确保稳健标度化的参数化方法。空间变化模型包含一个建模为高斯过程的坡度调整项，以捕捉基于位置的场地特异性效应。残差分析表明，两种模型在$V_S$值高达1000米/秒的范围内均无偏。此外，利用剖面内残差开发了沿深度变化性模型。在SFBA应用所提模型的结果显示，圣何塞地区及海沃德断层以东区域的$V_S$值有所增加，这支持了模拟结果，表明这些区域相较于观测值存在过度放大现象。使用线性场地响应分析进行的拟合优度（GOF）比较表明，所提模型在捕捉宽频带范围内的近地表放大效应方面优于USGS模型。纳入沿深度变化性进一步提高了GOF评分，减少了高频段的过度放大。这些结果强调了将社区速度模型与详细的沉积层速度模型相结合对于提升区域地震危险性评估的重要性。