Determining a detailed 3-D velocity model with high resolution for the sedimentary layer in the Sichuan Basin is potentially beneficial both to the industrial oil/gas exploration and earthquake hazards’ mitigation. In this study, we apply the ambient noise tomography method to construct a 3-D S-wave velocity model. This model focuses on the sedimentary layer of the Sichuan Basin, with a 0.3° × 0.3° grid precision. Dispersion curves of both group and phase velocities of Rayleigh wave at 4 to 40 s periods are utilized, which are extracted from 87 broad-band stations in the Sichuan Basin and the surrounding areas. The 3-D model reveals a thick sedimentary layer of the Sichuan Basin with S-wave velocity ranging from ∼2.0 to 3.4 km s⁻¹. The sediment thickness in the margins of the Sichuan Basin is generally greater than the typical values of 6–10 km in the central areas due to surrounding orogenic activities, with a maximum depth of ∼13 km in the northwestern margin. Moreover, a prominent low S-wave velocity anomaly in the margins may be caused by the sediment accumulations from large-scale landslides and pronounced denudation of the surrounding orogenic belts. Major geologic units in the sedimentary layer are delineated in this study. The S-wave velocity values within each geologic unit and their bottom interfaces are obtained. Based on our model, we calculate synthetic ground motions for the 2013 Lushan earthquake and obtain the distribution of the peak ground acceleration from the earthquake epicentre to the western Sichuan Basin. The result clearly illustrates the basin amplification effect on the seismic waves.

中文翻译：

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基于地震环境噪声层析成像的四川盆地沉积结构

为四川盆地的沉积层确定高分辨率的详细3-D速度模型，可能对工业油气勘探和减轻地震危害都有好处。在这项研究中，我们应用环境噪声层析成像方法来构建3-D S波速度模型。该模型关注于四川盆地的沉积层，网格精度为0.3°×0.3°。利用瑞利波在4到40 s周期内的色散和相速度色散曲线，这些曲线是从四川盆地及周边地区的87个宽带站提取的。3-D模型揭示了四川盆地的厚沉积层，其S波速度范围为〜2.0至3.4 km s ^-1。由于周围的造山活动，四川盆地边缘的沉积物厚度通常大于中部地区6-10 km的典型值，西北边缘的最大深度约为13 km。此外，边缘大型低S波速度异常可能是由于大规模滑坡的沉积物堆积和周围造山带的明显剥蚀所致。本研究描述了沉积层中的主要地质单位。在小号获得每个地质单元内及其底部界面的波速值。根据我们的模型，我们计算了2013年庐山地震的合成地震动，并获得了从地震震中到四川盆地西部的峰值地面加速度分布。结果清楚地说明了盆地放大对地震波的影响。