Abstract. Recent development of ambient noise tomography, in combination with increasing number of permanent seismic stations and dense networks of temporary stations operated during passive seismic experiments, provides a unique opportunity to build the first high-resolution 3-D shear wave velocity (v_S) model of the crust of the Bohemian Massif (BM). The velocity model with a cell size of 22 km is built by conventional two-step inversion approach from Rayleigh wave group velocity dispersion curves measured at more than 400 stations. The shear velocities within the upper crust of the BM are ~0.2 km s⁻¹ higher than those in its surroundings. The highest crustal velocities appear in its southern part, the Moldanubian unit. The model provides compelling evidence for a regional-scale of velocity distribution. The Cadomian part of the region has a thinner crust, while the crust assembled, or tectonically transformed in the Variscan period, is thicker. The sharp Moho discontinuity preserves traces of its dynamic development expressed in remnants of Variscan subductions imprinted in bands of crustal thickenings. A significant feature of the presented model is the velocity drop interface (VDI) modelled in the lower part of the crust. We explain this feature by anisotropic fabric of the lower crust, which is characterized as vertical transverse isotropy with the low velocity being the symmetry axis. The VDI is often interrupted around the boundaries of the crustal units, usually above locally increased velocities in the lowermost crust. Due to the NW SE shortening of the crust and the late Variscan strike slip movements along the NE SW oriented sutures preserved in the BM lithosphere, the anisotropic fabric of the lower crust was partly or fully erased along the boundaries of original microplates. These weakened zones accompanied by a velocity increase above the Moho, which indicate an extrusion of mantle rocks into the lower crust, can represent channels through which portions of subducted and later molten rocks have percolated upwards providing magma to subsequently form granitoid plutons.

中文翻译：

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波西米亚断层块的环境噪声层析成像法拍摄的瓦里斯坎中欧横向各向同性下地壳

摘要。环境噪声层析成像技术的最新发展，与越来越多的永久地震台站和被动地震实验期间运行的临时台站密集网络相结合，为建立第一个高分辨率3-D剪切波速度（v _S）模型提供了独特的机会波希米亚地块（BM）的地壳。通过常规的两步反演方法，根据在400多个站点测得的瑞利波群速度色散曲线，建立了具有22 km像元大小的速度模型。BM上地壳内的剪切速度为〜0.2 km s ^-1高于周围的环境。最高的地壳速度出现在其南部，即摩尔达努比亚单位。该模型为区域速度分布提供了令人信服的证据。该地区的Cadomian部分地壳较薄，而在Variscan时期组装或构造转换的地壳则较厚。强烈的莫霍面不连续性保留了其动态发展的痕迹，表现在地壳增厚带上印有的瓦里斯卡俯冲的残余。该模型的一个重要特征是在地壳下部建模的速度下降界面（VDI）。我们用下地壳的各向异性织物解释这一特征，其特征是垂直横向各向同性，低速是对称轴。VDI通常在地壳单元边界附近被打断，通常高于最低地壳中局部增加的速度。由于地壳的NW SE缩短以及沿BM岩石圈中保留的NE SW定向缝线的晚期Variscan走向滑动运动，下部地壳的各向异性结构沿原始微板的边界被部分或全部消除。这些减弱的区域伴随着莫霍面之上速度的增加，这表明地幔岩石被挤出到下地壳中，可以代表通道，部分俯冲的和后来的熔融岩石通过这些通道向上渗透，从而提供岩浆，随后形成花岗岩类云母。由于地壳的NW SE缩短以及沿BM岩石圈中保留的NE SW定向缝线的晚期Variscan走向滑动运动，下部地壳的各向异性结构沿原始微板的边界被部分或全部消除。这些减弱的区域伴随着莫霍面之上速度的增加，这表明地幔岩石被挤出到下地壳中，可以代表通道，部分俯冲的和后来的熔融岩石通过这些通道向上渗透，从而提供岩浆，随后形成花岗岩类云母。由于地壳的NW SE缩短以及沿BM岩石圈中保留的NE SW定向缝线的晚期Variscan走向滑动运动，下部地壳的各向异性结构沿原始微板的边界被部分或全部消除。这些减弱的区域伴随着莫霍面之上速度的增加，这表明地幔岩石被挤出到下地壳中，可以代表通道，部分俯冲的和后来的熔融岩石通过这些通道向上渗透，从而提供岩浆，随后形成花岗岩类云母。