3-D modelling of the crustal S-wave velocity structure from active source data: application to the Eastern Alps and the Bohemian Massif
3-D modelling of the crustal S-wave velocity structure from active source data: application to the Eastern Alps and the Bohemian Massif
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DOI：
10.1111/j.1365-246x.2009.04259.x
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发表时间：
2009-10
影响因子：
2.8
通讯作者：
M. Behm
中科院分区：
文献类型：
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作者：
M. Behm
摘要在这里，我提出的结果从3-D建模的地壳S波速度在东部和南部阿尔卑斯山和南部的波希米亚地块的东部。数据是在2000年至2003年期间在三个大型三维广角反射和折射实验中获得的。这些调查的目的是地壳和上地幔的P波速度结构，因此只使用了垂直分量检波器。然而，许多炮集显示出强S波，特别是来自地壳的折射（Sg波）和来自莫霍面的反射（SmS波）。与P波到相比较，S波的走时只能以相对较大的不确定性拾取。此外，大约80%的数据代表交叉线记录，在这些记录上更难为到达者分配某些阶段。由于这些原因，我应用信号检测和叠加例程来尽可能地使用3D数据集。关于地壳，一个平滑的3-D速度模型是基于从地壳内的折射（Sg），而壳幔边界模拟反射（SmS）从莫霍面不连续。考虑到这些项目是为P波研究而设计的，所提出的方法提供了令人惊讶的详细图像。横波速度和泊松比与构造单元相关，在上地壳表现出显著的特征。在波希米亚地块的摩拉维亚部分、南阿尔卑斯山和北方石灰质阿尔卑斯山及其东阿尔卑斯山内的基底观察到高泊松比。中地壳和下地壳仅覆盖在波希米亚地块的摩尔达努比亚部分，那里的泊松比很低。这将有利于长英质成分。SmS波的评价是根据先前提出的P波速度模型，这表明在东阿尔卑斯山的中心成三个地壳块的碎片。
SUMMARY Here, I present results from 3-D modelling of crustal S-wave velocities in the eastern part of the Eastern and Southern Alps and the southern part of the Bohemian Massif. Data were acquired between 2000 and 2003 during three large 3-D wide-angle reflection and refraction experiments. The surveys aimed at the P-wave velocity structure of the crust and uppermost mantle, and therefore only vertical-component geophones were used. Nevertheless, many shot gathers show strongS waves, in particular refractions from the crust (Sg waves) and reflections from the Moho discontinuity (SmS waves). Compared to P-wave arrivals, the traveltimes of S waves can only be picked with a relatively large uncertainty. Furthermore, approximately 80 per cent of the data represent crossline recordings on which it is more difficult to assign certain phases to the arrivals. For these reasons, I apply signal detection and stacking routines to put the 3-D data set to best possible use. Concerning the crust, a smooth 3-D velocity model is based on refractions from within the crust (Sg), whereas the crust–mantle boundary is modelled by reflections (SmS) from the Moho discontinuity. Considering that the projects were designed for P-wave studies, the proposed methodology provides surprisingly detailed images. S-wave velocities and Poisson’s ratio correlate with tectonic units and show significant features in the upper crust. A high Poisson’s ratio is observed in the Moravian part of the Bohemian Massif, in the Southern Alps and in the Northern Calcareous Alps and their basement within the Eastern Alps. The middle and lower crust are only covered in the Moldanubian part of the Bohemian Massif, where Poisson’s ratio is low. This would favour a felsic composition. The evaluation of SmS waves is in accordance with previously proposed P-wave velocity models, which indicate a fragmentation into three crustal blocks in the centre of the Eastern Alps.