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CyberShake: A Physics-Based Seismic Hazard Model for Southern California

机译：Cyber​​Shake：南加州基于物理的地震危险模型

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摘要

CyberShake, as part of the Southern California Earthquake Center’s (SCEC) Community Modeling Environment, is developing a methodology that explicitly incorporates deterministic source and wave propagation effects within seismic hazard calculations through the use of physics-based 3D ground motion simulations. To calculate a waveform-based seismic hazard estimate for a site of interest, we begin with Uniform California Earthquake Rupture Forecast, Version 2.0 (UCERF2.0) and identify all ruptures within 200 km of the site of interest. We convert the UCERF2.0 rupture definition into multiple rupture variations with differing hypocenter locations and slip distributions, resulting in about 415,000 rupture variations per site. Strain Green Tensors are calculated for the site of interest using the SCEC Community Velocity Model, Version 4 (CVM4), and then, using reciprocity, we calculate synthetic seismograms for each rupture variation. Peak intensity measures are then extracted from these synthetics and combined with the original rupture probabilities to produce probabilistic seismic hazard curves for the site. Being explicitly site-based, CyberShake directly samples the ground motion variability at that site over many earthquake cycles (i.e., rupture scenarios) and alleviates the need for the ergodic assumption that is implicitly included in traditional empirically based calculations. Thus far, we have simulated ruptures at over 200 sites in the Los Angeles region for ground shaking periods of 2 s and longer, providing the basis for the first generation CyberShake hazard maps. Our results indicate that the combination of rupture directivity and basin response effects can lead to an increase in the hazard level for some sites, relative to that given by a conventional Ground Motion Prediction Equation (GMPE). Additionally, and perhaps more importantly, we find that the physics-based hazard results are much more sensitive to the assumed magnitude-area relations and magnitude uncertainty estimates used in the definition of the ruptures than is found in the traditional GMPE approach. This reinforces the need for continued development of a better understanding of earthquake source characterization and the constitutive relations that govern the earthquake rupture process.
机译：Cyber​​Shake，作为南加州地震中心（SCEC）社区建模环境的一部分，正在开发一种方法，该方法通过使用基于物理的3D地面运动模拟，将确定性源和波传播效应明确纳入地震危险性计算中。为了计算感兴趣站点的基于波形的地震危险估计，我们从统一加利福尼亚地震破裂预测2.0版（UCERF2.0）开始，并确定感兴趣站点200公里以内的所有破裂。我们将UCERF2.0破裂定义转换为震源位置和滑移分布不同的多个破裂变化，每个位置产生约415,000个破裂变化。使用SCEC社区速度模型版本4（CVM4）计算感兴趣位置的应变绿色张量，然后使用互易性，针对每个破裂变化计算合成地震图。然后从这些合成物中提取峰值强度测量值，并与原始破裂概率结合，以生成该地点的概率地震危险曲线。 Cyber​​Shake是基于现场的，因此可以直接在许多地震周期（即破裂场景）中对该站点的地面运动变化进行采样，从而减轻了对基于遍历假设的需求，该假设被隐含在传统的基于经验的计算中。到目前为止，我们已经模拟了洛杉矶地区200多个站点的破裂，震荡周期为2 s或更长时间，为第一代Cyber​​Shake危险图谱提供了基础。我们的结果表明，相对于传统的地面运动预测方程式（GMPE）而言，破裂方向性和盆地响应效应的结合可能导致某些地点的危险等级增加。此外，也许更重要的是，我们发现，基于物理的危害结果比传统的GMPE方法对破裂定义中使用的假定的震级关系和震级不确定性估计要敏感得多。这就需要继续发展，以更好地了解地震震源特征和支配地震破裂过程的本构关系。

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