The populace of Los Angeles, California, was startled by shaking from the M 7.1 earthquake that struck the city of Ridgecrest located 200 km to the north on 6 July 2019. Although the earthquake did not cause damage in Los Angeles, the experience in high‐rise buildings was frightening in contrast to the shaking felt in short buildings. Observations from 560 ground‐level accelerometers reveal large variations in shaking in the Los Angeles basin that occurred for more than 2 min. The observations come from the spatially dense Community Seismic Network (CSN), combined with the sparser Southern California Seismic Network and California Strong Motion Instrumentation Program networks. Site amplification factors for periods of 1, 3, 6, and 8 s are computed as the ratio of each station’s response spectral values combined for the two horizontal directions, relative to the average of three bedrock sites. Spatially coherent behavior in site amplification emerges for periods ≥3 s⁠, and the maximum calculated site amplifications are the largest, by factors of 7, 10, and 8, respectively, for 3, 6, and 8 s periods. The dense CSN observations show that the long‐period amplification is clearly, but only partially, correlated with the depth to basement. Sites with the largest amplifications for the long periods (⁠≥3 s⁠) are not close to the deepest portion of the basin. At 6 and 8 s periods, the maximum amplifications occur in the western part of the Los Angeles basin and in the south‐central San Fernando Valley sedimentary basin. The observations suggest that the excitation of a hypothetical high‐rise located in an area characterized by the largest site amplifications could be four times larger than in a downtown Los Angeles location.

中文翻译：

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2019 Ridgecrest地震揭示洛杉矶地区，加剧了高层震动

加利福尼亚州洛杉矶的居民因2019年7月6日袭击北部200公里的里奇克莱斯特市的7.1级M地震而感到震惊。尽管地震并未在洛杉矶造成破坏，但高地震的经历与短建筑物的震动相比，高层建筑令人恐惧。从560个地面加速度计进行的观测显示，洛杉矶盆地发生了超过2分钟的振动变化很大。这些观测结果来自空间密集的社区地震台网（CSN），结合了稀疏的南加州地震台网和加州强震仪器计划网。计算1、3、6和8 s周期的站点放大因子，作为两个水平方向上每个站点的响应频谱值之比，相对于三个基岩站点的平均值。在≥3 s周期内出现站点放大中的空间连贯行为，并且在3 s，6 s和8 s周期内，计算出的最大站点放大率最大，分别是7、10和8倍。密集的CSN观测表明，长周期的放大率与基底的深度明显相关，但仅部分相关。长期（≥3s⁠）放大倍数最大的站点不靠近盆地的最深部分。在6和8 s周期，最大的放大率出现在洛杉矶盆地的西部和中南部的圣费尔南多谷沉积盆地。