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首页> 外文期刊>Pure and Applied Geophysics >Rayleigh-Wave, Group-Velocity Tomography of the Borborema Province, NE Brazil, from Ambient Seismic Noise
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Rayleigh-Wave, Group-Velocity Tomography of the Borborema Province, NE Brazil, from Ambient Seismic Noise

机译：Rayleigh-Wave，来自巴西东北部Borborema省的群速度层析成像，来自环境地震噪声

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Ambient seismic noise has traditionally been regarded as an unwanted perturbation that "contaminates" earthquake data. Over the last decade, however, it has been shown that consistent information about subsurface structure can be extracted from ambient seismic noise. By cross-correlation of noise simultaneously recorded at two seismic stations, the empirical Green's function for the propagating medium between them can be reconstructed. Moreover, for periods less than 30 s the seismic spectrum of ambient noise is dominated by microseismic energy and, because microseismic energy travels mostly as surface-waves, the reconstruction of the empirical Green's function is usually proportional to the surface-wave portion of the seismic wavefield. In this paper, we present 333 empirical Green's functions obtained from stacked cross-correlations of one month of vertical component ambient seismic noise for different pairs of seismic stations in the Borborema Province of NE Brazil. The empirical Green's functions show that the signal obtained is dominated by Rayleigh waves and that dispersion velocities can be measured reliably for periods between 5 and 20 s. The study includes permanent stations from a monitoring seismic network and temporary stations from past passive experiments in the region, resulting in a combined network of 34 stations separated by distances between approximately 40 and 1,287 km. Fundamental-mode group velocities were obtained for all station pairs and then tomographically inverted to produce maps of group velocity variation. For short periods (5-10 s) the tomographic maps correlate well with surface geology, with slow velocities delineating the main rift basins (Potiguar, Tucano, and Recncavo) and fast velocities delineating the location of the Precambrian So Francisco craton and the Rio Grande do Norte domain. For longer periods (15-20 s) most of the velocity anomalies fade away, and only those associated with the deep Tucano basin and the So Francisco craton remain. The fading of the Rio Grande do Norte domain fast-velocity anomaly suggests this is a supracrustal structure rather than a lithospheric terrain, and places new constraints on the Precambrian evolution of the Borborema Province.
机译：传统上，环境地震噪声被认为是“污染”地震数据的有害干扰。然而，在过去的十年中，已经表明可以从环境地震噪声中提取有关地下结构的一致信息。通过同时记录在两个地震台站处的噪声的互相关，可以重建它们之间传播介质的经验格林函数。此外，在小于30 s的时间段内，环境噪声的地震频谱主要由微地震能量主导，并且由于微地震能量主要以表面波传播，因此经验格林函数的重建通常与地震的表面波部分成比例。波场。在本文中，我们介绍了巴西东北部Borborema省不同对地震台对一个月垂直分量环境地震噪声的堆叠互相关获得的333个格林经验函数。格林经验函数表明，所获得的信号主要由瑞利波控制，并且色散速度可以在5到20 s的时间内可靠地测量。该研究包括来自该地区监测地震网的永久台站和该地区过去被动实验的临时台站，从而形成了一个由34个台站组成的联合网络，相隔约40至1,287 km。获得所有测站对的基本模式群速度，然后进行断层扫描以生成群速度变化图。在短时间内（5-10 s），层析成像图与地表地质有着很好的相关性，慢速描绘了主要裂谷盆地（波提瓜尔，图卡诺和雷肯卡沃），而快速描绘了前寒武纪苏弗朗西斯科克拉通和里奥格兰德的位置做北域。在较长的时间内（15-20 s），大多数速度异常消失了，只有与深部的Tucano盆地和So Francisco克拉通相关的速度异常消失了。北里奥格兰德地区快速速度异常的衰落表明，这是一种超壳结构，而不是岩石圈地形，这给博尔博雷马省的前寒武纪演化带来了新的限制。

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