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首页> 外文期刊>Journal of Asian earth sciences >Seismic structure of the Helan-Liupan-Ordos western margin tectonic belt in North-Central China and its geodynamic implications
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Seismic structure of the Helan-Liupan-Ordos western margin tectonic belt in North-Central China and its geodynamic implications

机译：中国中北部贺兰-六盘-鄂尔多斯西缘构造带的地震构造及其地球动力学意义

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摘要

We study high-resolution three-dimensional P-wave velocity (Vp) tomography and anisotropic structure of the crust and uppermost mantle under the Helan-Liupan-Ordos western margin tectonic belt in North-Central China using 13,506 high-quality P-wave arrival times from 2666 local earthquakes recorded by 87 seismic stations during 1980-2008. Our results show that prominent low-velocity (low-V) anomalies exist widely in the lower crust beneath the study region and the low-V zones extend to the uppermost mantle in some local areas, suggesting that the lower crust contains higher-temperature materials and fluids. The major fault zones, especially the large boundary faults of major tectonic units, are located at the edge portion of the low-V anomalies or transition zones between the low-V and high-V anomalies in the upper crust, whereas low-V anomalies are revealed in the lower crust under most of the faults. Most of large historical earthquakes are located in the boundary zones where P-wave velocity changes drastically in a short distance. Beneath the source zones of most of the large historical earthquakes, prominent low-V anomalies are visible in the lower crust. Significant P-wave azimuthal anisotropy is revealed in the study region, and the pattern of anisotropy in the upper crust is consistent with the surface geologic features. In the lower crust and uppermost mantle, the predominant fast velocity direction (FVD) is NNE-SSW under the Yinchuan Graben and NWW-SEE or NW-SE beneath the Corridor transitional zone, Qilian Orogenic Belt and Western Qinling Orogenic Belt, and the FVD is NE-SW under the eastern Qilian Orogenic Belt. The anisotropy in the lower crust may be caused by the lattice-preferred orientation of minerals, which may reflect the lower-crustal ductile flow with varied directions. The present results shed new light on the seismotectonics and geodynamic processes of the Qinghai-Tibetan Plateau and its northeastern margin.
机译：利用13,506个高质量P波到达场，研究了华北中部贺兰—六盘—鄂尔多斯西缘构造带下地壳和最上地幔的高分辨率三维P波速度（Vp）层析成像和各向异性结构。 1980-2008年期间，有87个地震台站记录了2666次当地地震的时间。我们的结果表明，在研究区域下方的下部地壳中广泛存在着明显的低速（低伏）异常，并且低伏区域延伸到了某些局部区域的最高地幔，这表明下部地壳中含有高温物质。和液体。主要断层带，尤其是主要构造单元的大边界断层，位于上地壳低伏异常的边缘部分或低伏异常与高伏异常之间的过渡带，而低伏异常在大多数断层下都被发现在下地壳中。大多数历史大地震都位于边界区域，P波速度在短距离内急剧变化。在大多数历史大地震的震源区之下，下地壳可见明显的低伏异常。研究区域揭示了显着的P波方位各向异性，上地壳的各向异性模式与地表地质特征一致。在下地壳和最高地幔中，主要的快速速度方向（FVD）是银川格拉本下的NNE-SSW，以及走廊过渡带，祁连造山带和西秦岭造山带下的NWW-SEE或NW-SE。是东部祁连造山带下的NE-SW。下地壳的各向异性可能是由于矿物的晶格偏好取向引起的，这可能反映了下地壳韧性流向的变化。本研究结果为青藏高原及其东北缘的地震构造和地球动力学过程提供了新的思路。

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