洞察印度地下上地幔地震各向异性的形成机制

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Tectonophysics Pub Date : 2024-08-08 DOI:10.1016/j.tecto.2024.230454
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引用次数: 0

摘要

我们通过对 357 个宽带地震台站记录的波形进行连贯分析,综合确定了 2064 个约束良好的剪切波分裂参数,从而确定了印度地下地震各向异性的可能来源。我们的工作包括汇编以前的成果、重新分析旧数据、分析来自以前网络和新台站的新数据。我们的研究结果表明,整个印度及其各构造省的平均延迟时间为 0.83 秒,表明各向异性的强度适中。虽然快速极化方位角(FPAs)比较分散,但东北方向的趋势占主导地位。由于快速极化方位角与 APM 方向有明显的相关性,而 i)分裂参数与反向方位角和 ii)平均延迟时间与岩石圈厚度之间缺乏相关性,我们得出结论,各向异性的主要原因来自于岩石圈上部的剪切或岩石圈底部到岩石圈上部的过渡层。此外,我们推测印度北部、中部和东南部各向异性较弱的岩石圈是由于过去的构造事件造成的冻结各向异性。印度北部和中部、阿鲁纳恰尔喜马拉雅山脉和缅甸弧南部具有简单的各向异性。空间一致性技术的应用显示,印度北部的震源深度为 290 千米。然而,在印度东南部和缅甸弧北部,一个两层模型(上层分别是冻结和现今各向异性,下层分别是剪切和地幔流动)符合各向异性。在印度南部,FPA 与 APM 的巨大偏差表明了与过去构造事件有关的变形印记。上下层冻结各向异性的双层模型是可信的。印度盾牌中部的 FPAs 变化归因于岩石圈龙骨北部边缘的地幔流偏转。
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Insights into the mechanisms forging seismic anisotropy in the upper mantle beneath India

We identify possible sources of seismic anisotropy beneath India by synthesizing 2064 well-constrained shear-wave splitting parameters determined from a consistent analysis of waveforms recorded at 357 broadband seismic stations. Our effort includes compilation of previous results, reanalysis of old data, analysis of new data from previous networks and new stations. Our results reveal that the average delay time for entire India and its constituent tectonic provinces is 0.83 s suggesting moderate strength of anisotropy. Although the fast polarization azimuths (FPAs) are scattered, a NE trend appears dominant. Due to significant correlation of FPAs with the APM direction and lack of correlation between i) splitting parameters and backazimuths and ii) average delay times and lithospheric thickness, we conclude that the major contribution to anisotropy is from shearing in the upper part of the asthenosphere or a transitional layer from the base of the lithosphere to the upper part of the asthenosphere. Further, we postulate that a weakly anisotropic lithosphere in northern, central and south-eastern India is due to frozen anisotropy from past tectonic events. Northern and central India, Arunachal Himalaya and southern part of Burmese arc have simple anisotropy. Application of the spatial coherency technique reveals a source depth of 290 km for northern India. However, for south-eastern India and northern part of the Burmese arc, a two-layer model, with frozen-in and present-day anisotropy in the upper layer, and shearing and mantle flow in the lower layer, respectively, fits the anisotropy. In southern India, a large deviation of the FPAs from APM suggests imprints of deformation related to past tectonic events. A two-layer model, with frozen-in anisotropy in the upper and lower layers, is plausible. Variation in FPAs in the central part of the Indian shield is attributed to deflection in mantle flow at the northern edge of the lithospheric keel.

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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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