| 蒙古中南部地区地壳各向异性及其动力学意义 |
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| 引用本文： | 强正阳,吴庆举,李永华,何静,高孟潭,M. Ulziibat,S. Demberel.蒙古中南部地区地壳各向异性及其动力学意义[J].地球物理学报,2016,59(5):1616-1628. |
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| 作者姓名： | 强正阳 吴庆举 李永华 何静 高孟潭 M. Ulziibat S. Demberel |
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| 作者单位： | 1. 中国地震局地球物理研究所, 北京 100081;2. 蒙古科学院天文与地球物理研究中心, 乌兰巴托 210351 |
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| 基金项目： | 科技部国际科技合作专项《远东地区地磁场、重力场及深部构造与模型研究》(2011DFB20210)资助. |
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| 摘 要： | 利用蒙古中南部地区布设的69套宽频带数字地震仪2011年8月—2013年7月记录的远震事件,使用时间域反褶积方法提取接收函数,并挑选高质量Pms震相,通过改进的剪切波分裂方法对研究区地壳各向异性参数进行了研究,最终获取了1473对各向异性参数.经过统计分析,有48个台站可以归纳出两个方向的各向异性,11台站得到单个方向的各向异性,而剩余10个台站各向异性方向比较发散.结果显示,各向异性在蒙古中南部地壳中呈不均匀分布,有54个台站得到了NE-SW向各向异性,快波偏振方向平均值为N58°E±16°,与最大水平主应力σHmax方向和区域内主要断层走向一致,说明这部分地壳各向异性的主要成因存在于上地壳,可能与流体填充的微裂隙有关.而NW-SE向各向异性在53个台站被观测到,各向异性方向变化范围平均N132°E±16°,与研究区大部分SKS分裂快波方向具有较好的一致性,说明下地壳成岩矿物晶体定向排列是各向异性的主要成因.研究区地壳各向异性的分层特征总体上支持岩石圈受到NE-SW向挤压的动力学模型.
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| 关 键 词： | Pms转换波 剪切波分裂 地壳各向异性 蒙古中南部地区 |
| 收稿时间： | 2015-09-11 |
Crustal anisotropy beneath central-south Mongolia and its dynamic implications |
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| QIANG Zheng-Yang,WU Qing-Ju,LI Yong-Hua,HE Jing,GAO Meng-Tan,M. Ulziibat,S. Demberel.Crustal anisotropy beneath central-south Mongolia and its dynamic implications[J].Chinese Journal of Geophysics,2016,59(5):1616-1628. |
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| Authors: | QIANG Zheng-Yang WU Qing-Ju LI Yong-Hua HE Jing GAO Meng-Tan M Ulziibat S Demberel |
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| Institution: | 1. Institute of Geophysics, Chinese Earthquake Administration, Beijing 100081, China;2. Research Center of Astronomy & Geophysics of Mongolian Academy of Science, Ulaanbaatar 210351, Mongolia |
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| Abstract: | Mongolia is located in the core part of the Central Asian Orogenic Belt, one of the largest Paleozoic orogens which has suffered strongest tectonic movement and crust-mantle interaction and always been regarded as the hot issues of Earth science. Being a transition zone with NE-SW shortening from the west and E-W extension in the east, central-south Mongolia is a key area to understand the deformation of crust and the whole lithosphere beneath the Mongolia. Seismic anisotropy determined by the splitting of Pms shear waves is one of the most direct and effective ways to image the structure and deformation of crust. Whenever the shear wave travel through an anisotropic layer, it will split into two orthogonal waves propagating at different speeds. Then the anisotropy is described by the fast polarization direction (φ) and the splitting time between the fast and slow waves (δt), respectively.#br#Two years' high-quality broadband seismic data from 69 temporary stations deployed in central-south Mongolia provide a good opportunity to study the crustal anisotropy-forming mechanism of this area. In this study we calculate P-wave receiver functions by time-domain iterative deconvolution method, from which the Moho P-to-S phases are isolated and calculated by the improved shear-wave splitting method after we discern the anisotropy of horizontal layered medium from the receiver functions. Pms phase is converted from a near-vertically incident P wave at the crust-mantle boundary, and the propagation velocity of its radial and tangential components depends on their anisotropic polarity and propagation direction. According to the different behaviors of the radial and tangential components, the whole crustal anisotropy could be measured by Pms splitting analysis. Finally, 1473 pairs of anisotropy parameters are acquired and described by the fast polarization direction and the time delay.#br#Eighty six percent of the delay times are between 0.20~0.34 s and correspond to a 23~43 km thick layer if 4% anisotropy is assumed, which suggests that the distribution of the crustal anisotropy in central-south Mongolia is uneven, compared to the thickness of the crust (38~46 km). NE-SW trending anisotropy is measured beneath 54 stations, ranging from N8°E to N88°E with an average value close to N58°E±16°, which is subparallel to the stress direction. We suppose that the anisotropy is located in the upper crust and may be associated with fluid-filled microcracks. At the same time, the NE-SW trending anisotropic directions are parallel to the most of strikes of surface fractures which may possibly cause the anisotropy. On the other hand, NW-SE trending polarization directions are measured at 53 stations, varying between N97°E—N165°E, with an average value of N132°E±16°. These fast directions are well consistent with most SKS splitting fast wave directions, indicating a vertically coherent deformation between the lower crust and upper mantle, and the deformation-induced lattice preferred orientations of the crystallographic axis of mineral in lower crust is probably the main cause of the anisotropy. Most of the crust anisotropy in the study area support a dynamic model that the lithosphere is subject to a strike-slip extrusion trending NE-SW. |
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| Keywords: | Pms converted phases Shear wave splitting Seismic anisotropy Central-south Mongolia |
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