Explosions are traditionally discriminated from earthquakes, using the relative amplitude of compressional and shear waves at regional and teleseismic distances known as the P/S discriminant. Pyle and Walter (2019) showed this technique to be less robust at shorter distances, in detecting small‐magnitude earthquakes and low‐yield explosions. The disparity is largely due to ground motion from small, shallow sources being significantly impacted by near‐surface structural complexities. To understand the implications of wave propagation effects in generation of shear motion and P/S ratio during underground chemical explosions, we performed simulations of the Source Physics Experiment (SPE) chemical explosions using 1D and 3D velocity models of the Yucca Flat basin. All simulations used isotropic point sources in the frequency range 0–5 Hz. We isolate the effect of large‐scale geological structure and small‐scale variability at shallow depth (⁠<5 km⁠), using a regional 3D geologic framework model (GFM) and the GFM‐R model derived from the GFM, by adding correlated stochastic velocity perturbations. A parametric study of effects of small‐scale velocity variations on wave propagation, computed using a reference 1D velocity model with stochastic perturbations, shows that the correlation length and depth of stochastic perturbations significantly impact wave scattering, near‐surface wave conversions, and shear‐wave generation. Comparisons of recorded and simulated waveforms for the SPE‐5 explosion, using 3D velocity models, demonstrate that the shallow structure of the Yucca Flat basin contributes to generation of observed shear motion. The inclusion of 3D wave scattering, simulated by small‐scale velocity perturbations in the 3D model, improves the fit between the simulated and recorded waveforms. In addition, a relatively low intrinsic attenuation, combined with small‐scale velocity variations in our models, can confirm the observed wave trapping and its effect on duration of coda waves and the spatial variation of P/S ratio at basin sites.

中文翻译：

---

源物理实验对随机3D相关速度摄动对地震动数值模拟的影响

传统上，爆炸是通过使用在区域和远程地震距离上称为P / S判别式的压缩波和切变波的相对振幅来区别地震的。Pyle和Walter（2019）表明，该技术在检测小震级地震和低产爆炸时，在较短距离下的鲁棒性较差。差异主要是由于小型浅层来源的地震动受到近地表结构复杂性的显着影响。为了了解地下化学爆炸过程中波传播效应对剪切运动和P / S比的产生的影响，我们使用丝兰平原盆地的1D和3D速度模型进行了源物理实验（SPE）化学爆炸的模拟。所有模拟都使用0-5 Hz频率范围内的各向同性点源。我们使用区域3D地质框架模型（GFM）和源自GFM的GFM-R模型，并通过添加相关系数，来分离浅层深度（⁠<5km⁠）的大规模地质结构和小规模变异的影响随机速度扰动。使用带有随机扰动的参考一维速度模型计算出的小尺度速度变化对波传播的影响的参数研究表明，随机扰动的相关长度和深度会显着影响波散射，近地表波转换和剪切力。波的产生。使用3D速度模型对SPE-5爆炸的记录波形和模拟波形进行比较，表明丝兰平原盆地的浅层结构有助于产生观测到的剪切运动。包含3D波散射 通过在3D模型中进行小规模速度摄动模拟，可以提高模拟波形和记录波形之间的拟合度。此外，相对较低的固有衰减，再加上我们模型中的小尺度速度变化，可以确认观测到的波捕获及其对尾波持续时间和盆地部位P / S比的空间变化的影响。