The metropolitan Los Angeles region represents a zone of high-seismic risk due to its proximity to several fault systems, including the San Andreas fault. Adding to this problem is the fact that Los Angeles and its surrounding cities are built on top of soft sediments that tend to trap and amplify seismic waves generated by earthquakes. In this study, we use three dense petroleum industry surveys deployed in a 16 × 16-km area at Long Beach, California, to produce a high-resolution model of the top kilometer of the crust and investigate the influence of its structural variations on the amplification of seismic waves. Our velocity estimates reveal substantial lateral contrasts and correlate remarkably well with the geological background of the area, illuminating features such as the Newport-Inglewood fault, the Silverado aquifer, and the San Gabriel river. We then use computational modeling to show that the presence of these small-scale structures have a clear impact on the intensity of the expected shaking, and can cause ground-motion motion acceleration to change by several factors over a subkilometer horizontal scale. These results shed light onto the scale of variations that can be expected in this type of tectonic settings and highlight the importance of resolution in modern-day seismic hazard estimates.

中文翻译：

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加利福尼亚长滩的精细结构及其对地面运动加速度的影响

大都会洛杉矶地区代表了一个高地震风险区，因为它靠近多个断层系统，包括圣安德烈亚斯断层。更糟糕的是，洛杉矶及其周边城市建在柔软的沉积物之上，这些沉积物往往会捕获和放大地震产生的地震波。在这项研究中，我们使用部署在加利福尼亚州长滩 16 × 16 公里区域的三个密集石油工业调查来生成地壳顶部公里的高分辨率模型，并研究其结构变化对地壳的影响。地震波的放大。我们的速度估计揭示了显着的横向对比，并且与该地区的地质背景密切相关，显示了 Newport-Inglewood 断层、Silverado 含水层、和圣盖博河。然后我们使用计算模型来表明这些小尺度结构的存在对预期的震动强度有明显的影响，并且可以导致地面运动加速度在亚千米水平尺度上发生几个因素的变化。这些结果揭示了在这种类型的构造环境中可以预期的变化规模，并强调了分辨率在现代地震危险性估计中的重要性。