SUMMARY

Surface wave analysis provides important information on crustal structure, but it is challenging to obtain accurate/robust models in aseismic regions because of the lack of local earthquake records. In this paper, interstation empirical Green's functions retrieved by ambient seismic noise in 75 broad-band stations from 2016 January to 2018 September were used to study crustal structure in west-central Brazil. Fast marching method was applied to calculate the 2-D surface wave tomographic maps, and local dispersion curves were estimated in the period range of 4–80 s for each geographic cell. 1-D damped least squares inversion method was then conducted to obtained shear wave velocity model. Finally, the average ($\tilde{\rm V}$_S) of the calculated VSV and VSH quasi 3-D models were used to characterize the crustal structure. Besides the checkerboard test resolution, a stochastic test with the effect of errors in the dispersion curves and choice of inversion parameters were carried out to better evaluate model uncertainties. Our results show a clear relation between the sedimentary thickness and geological units with the shorter period tomographic maps. Agreement has also been observed in longer periods such as the clear N–S anomaly along the Asuncion and Rio Grande Arches representing the boundary between the Chaco-Paraná and the Paraná basins. A 3-D composite velocity model shows a crustal structure consisting of three main layers. Some differences in lower crustal properties were found between the Paraná and Chaco-Paraná basins, consistent with a recently postulated, gravity-derived Western Paraná suture zone. However, no high velocities along the SW–NE axis of the Paraná basin were found to confirm proposed underplating. At the eastern edge of the Pantanal basin, the thin crust seems to be associated with a very thin (or lack of) lower crustal layer, consistent with a recently proposed crustal delamination hypothesis for the formation of the Pantanal basin.

中文翻译：

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巴西中西部和南部的环境地震层析层析成像，表征了查科-帕拉纳，潘塔纳尔和帕拉纳盆地的地壳结构

概要

表面波分析提供了有关地壳结构的重要信息，但是由于缺乏本地地震记录，因此在抗震地区获得准确/稳健的模型具有挑战性。本文利用2016年1月至2018年9月在75个宽带站的环境地震噪声获取的站间经验格林函数对巴西中西部的地壳结构进行了研究。应用快速行进法计算二维表面波层析成像图，并估计每个地理单元在4–80 s的周期范围内的局部弥散曲线。然后采用一维阻尼最小二乘反演方法获得剪切波速度模型。最后，平均（$ \ tilde {\ rm V} $ _S）计算的VSV和VSH准3-D模型用于表征地壳结构。除了棋盘格测试分辨率外，还进行了具有色散曲线误差和反演参数选择影响的随机测试，以更好地评估模型的不确定性。我们的结果表明，在较短的层析X射线摄影图中，沉积厚度与地质单位之间存在明确的关系。在更长的时期内也观察到了一致，例如沿着亚松森和里奥格兰德拱门的清晰的南北异常，代表了查科-巴拉那和巴拉那盆地之间的边界。3-D复合速度模型显示了由三个主要层组成的地壳结构。在Paraná和Chaco-Paraná盆地之间发现了下地壳特性的一些差异，这与最近的推测一致：重力衍生的WesternParaná缝合带。但是，没有发现沿巴拉那盆地SW-NE轴的高速度能证实建议的下伏。在潘塔纳尔盆地的东缘，薄壳似乎与非常薄（或缺乏）的下地壳层有关，这与最近提出的潘塔纳尔盆地形成的地壳分层假设相一致。