The recent development of ambient noise tomography, in combination with the 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 entire crust of the Bohemian Massif (BM). This paper provides a regional-scale model of velocity distribution in the BM crust. The velocity model with a cell size of 22 km is built using a 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 Cadomian part of the region has a thinner crust, whereas 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 thickening. 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 the anisotropic fabric of the lower crust, which is characterised 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 north-west–south-east shortening of the crust and the late-Variscan strike-slip movements along the north-east–south-west 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 emplacement 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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波西米亚断层的环境噪声层析成像法对中部瓦里斯坎的横向各向同性下地壳成像

环境噪声层析成像技术的最新发展，再加上被动地震实验期间不断增加的永久地震台站和密集的临时台站网络，为建立第一个高分辨率3-D剪切波速度（v _S）的整个波西米亚断层块（BM）的模型。本文提供了地壳速度分布的区域尺度模型。使用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 约为0.2  km s ^-1高于周围的环境。最高的地壳速度出现在它的南部，摩尔达努比亚单元。该地区的Cadomian部分地壳较薄，而在瓦里斯卡纳时期组装或构造转变的地壳则较厚。尖锐的莫霍面不连续性保留了其动态发展的痕迹，表现在地壳增厚带中印有的瓦里斯坎俯冲的残余中。该模型的一个重要特征是在地壳下部建模的速度降界面（VDI）。我们用下地壳的各向异性结构解释这一特征，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，通常高于最低地壳的局部速度。由于地壳由西北向南向东缩短，并且沿BM岩石圈保存的沿东北向西南方向的缝线沿后期的瓦里斯纳走滑运动，下地壳的各向异性结构部分或沿原始微孔板的边界完全擦除。这些减弱的区域伴随着莫霍面之上速度的增加（这表示地幔岩石已进入下地壳），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，形成岩浆，随后形成花岗岩类云母。下地壳的各向异性结构沿原始微孔板的边界被部分或全部擦除。这些减弱的区域伴随着莫霍面之上速度的增加（这表示地幔岩石已进入下地壳），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，形成岩浆，随后形成花岗岩类云母。下地壳的各向异性结构沿原始微孔板的边界被部分或全部擦除。这些减弱的区域伴随着莫霍面之上速度的增加（这表示地幔岩石已进入下地壳），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，形成岩浆，随后形成花岗岩类云母。