We examine the effects that Atlantic Coastal Plain (ACP) strata have on ground motions in the eastern and southeastern United States. The ACP strata consist of widespread, nearly flat‐lying sediments, the upper portions of which are unconsolidated or semiconsolidated. The ACP sediments are deposited primarily on crystalline basement rocks, creating large velocity and density contrasts with the underlying rocks. At 211 sites on ACP strata to thicknesses of 4000 m, we compute spectral ratios relative to the average of four bedrock sites west or northwest of the strata. Sites consist of stations of Earthscope’s USArray Transportable Array (TA), and temporary deployments in the Southeast Suture of the Atlantic Margin Experiment (SESAME), Eastern North American Margin (ENAM) experiment, and the DCShake deployment in Washington, D.C. For the TA and SESAME stations, we use signals from 13 teleseisms and three regional earthquakes as input, combining the north and east components of motion after taking the Fourier transforms. We also include similarly processed site responses from the ENAM and DCShake arrays that were computed in earlier studies. Results show prominent, fundamental resonance peaks at frequencies determined by reverberations in the entire sediment column, and that often define the largest amplifications for each frequency. As frequencies increase, these resonance peaks migrate to thinner ACP strata and increase in amplitude. The peaks are well defined at frequencies below about 1 Hz, but become narrower and less defined regionally at higher frequencies. We develop simple equations to characterize amplification versus ACP thickness, which we approximate by cosine and Gaussian curves with amplifications of 1 on bedrock and rising to the resonance peak, and then decreasing to an average amplification at thicknesses greater than twice the resonance peak. Comparisons with other site corrections for the central and eastern United States based on sediment thickness show similarities on thin ACP strata but divergence on thicker sediments. The results also demonstrate the effectiveness of using teleseismic arrivals to characterize the site responses of sedimentary sequences.

中文翻译：

---

大面积平坦沉积物的地震动放大特征：美国东部大西洋沿岸平原地层的地震响应

我们研究了大西洋沿岸平原 (ACP) 地层对美国东部和东南部地面运动的影响。ACP 地层由分布广泛的、近乎平躺的沉积物组成，其上部是松散的或半固结的。ACP 沉积物主要沉积在结晶基底岩石上，与下伏岩石形成大的速度和密度对比。在 ACP 地层上厚度为 4000 m 的 211 个站点中，我们计算了相对于地层西部或西北部四个基岩站点平均值的光谱比。站点包括 Earthscope 的 USArray 可移动阵列 (TA) 站、大西洋边缘实验东南缝合线 (SESAME)、北美东部边缘 (ENAM) 实验和华盛顿特区 DCShake 部署的临时部署 对于 TA 和 SESAME 台站，我们使用来自 13 个远震和 3 个区域地震的信号作为输入，在进行傅立叶变换后组合了运动的北分量和东分量。我们还包括来自早期研究中计算的 ENAM 和 DCShake 阵列的类似处理的站点响应。结果显示在由整个沉积物柱中的混响确定的频率处出现突出的基本共振峰，并且通常定义每个频率的最大放大。随着频率的增加，这些共振峰迁移到较薄的 ACP 地层并增加振幅。峰值在低于约 1 Hz 的频率下明确定义，但在较高频率下变得更窄且区域性定义更差。我们开发了简单的方程来表征放大与 ACP 厚度的关系，我们通过余弦和高斯曲线近似，在基岩上放大为 1 并上升到共振峰，然后在厚度大于共振峰的两倍时降低到平均放大率。与美国中部和东部基于沉积物厚度的其他站点校正的比较显示，在较薄的 ACP 地层上有相似之处，但在较厚的沉积物上有分歧。结果还证明了使用远震到达来表征沉积序列的现场响应的有效性。与美国中部和东部基于沉积物厚度的其他站点校正的比较显示，在较薄的 ACP 地层上有相似之处，但在较厚的沉积物上有分歧。结果还证明了使用远震到达来表征沉积序列现场响应的有效性。与美国中部和东部基于沉积物厚度的其他站点校正的比较显示，在较薄的 ACP 地层上有相似之处，但在较厚的沉积物上有分歧。结果还证明了使用远震到达来表征沉积序列现场响应的有效性。