Segmental nature of the Red River fault revealed by seismic anisotropy and geological structures

IF 6 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Ying Li, Yuan Gao
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Abstract

As the western boundary of the Sichuan-Yunnan block (SYB), the Red River fault (RRF) is a major fault that controls deep crustal movement and deformation in the southeast margin of the Tibetan Plateau and regulates middle-lower crustal flow. Geophysical data suggest that the RRF is segmented and exhibits distinct variations in seismicity, velocity structure and crustal deformation from north to south. Seismic anisotropy reveals a complex pattern of lateral spatial and vertical stratified distributions. (1) From the perspective of crustal stratification, in the upper crust, the fast wave polarization in the north segment of the RRF is complex and possibly influenced by the Sanjiang lateral collision zone and adjacent faults with varying strikes. The fast wave polarization in the middle segment is in the NW-SE direction, indicating a localized area of closed down or locked up with consistent deformation. And in the south segment, it presents a disordered pattern, signifying complex deep tectonics and stress conditions at the wedged intersection zone. In the middle-lower crust in the north and south segments of the RRF, the azimuthal anisotropy is strong and consistent with the spatial strike of the weak zone characterized by low-velocity and high-conductivity. This suggests a connection between the anisotropy and the material migration. (2) In the whole crustal scale, the fast wave directions in two sides of the RRF are consistent with the NW-SE tectonic strike. It indicates that the RRF, as a large fault potentially cutting through the whole crust, strongly controls the surrounding media. (3) In the lithospheric scale, the fast wave polarizations are oriented nearly E-W and independent of the fault strike, consistent with the low P- and S-wave velocity structures and positive radial anisotropy in the upper mantle. The fast wave directions could be related to lithospheric olivine deformation and asthenospheric flow. This paper suggests a decoupling of deformation between the crust and the lithospheric mantle in the south of approximately 26°20′N near the RRF, which can potentially be attributed to the subduction and rollback of the Indian plate. Based on various geophysical observations and inversions, we can determine the detailed anisotropic structure in the crust and the upper mantle around the RRF. Denser geophysical arrays and more accurate records can be used to explore the intricate anisotropy in segmentation and stratification around the RRF, enhancing the understanding of its tectonic significance.

地震各向异性和地质结构揭示的红河断层分段性质
作为四川-云南断块(SYB)的西部边界,红河断层(RRF)是控制青藏高原东南缘深部地壳运动和变形、调节中下地壳流动的主要断层。地球物理数据表明,红河断层是分段的,从北到南在地震活动性、速度结构和地壳变形方面表现出明显的差异。地震各向异性揭示了横向空间和纵向分层分布的复杂模式。(1)从地壳分层的角度看,在上地壳中, RRF 北段快波极化复杂,可能受到三江侧向碰撞带和相邻不同走向断层的影响。中段的快波极化方向为NW-SE向,表明局部地区有持续变形的闭锁或锁闭。而在南段,快波极化呈现无序形态,表明楔形交汇带的深部构造和应力条件复杂。在RRF北段和南段的中下地壳,方位各向异性很强,与以低速高导为特征的弱区空间走向一致。这表明各向异性与物质迁移之间存在联系。(2)在整个地壳尺度上,RRF两侧的快波方向与NW-SE构造走向一致。这表明,RRF 作为一个可能切割整个地壳的大型断层,对周围介质具有强烈的控制作用。(3) 在岩石圈尺度上,快波极化方向接近于 E-W,且与断层走向无关,这与上地幔的低 P 波和 S 波速度结构以及正径向各向异性相一致。快波方向可能与岩石圈橄榄岩变形和星体层流动有关。本文认为,在 RRF 附近约 26°20′N 的南部,地壳与岩石圈地幔之间的变形脱钩,这可能是印度板块俯冲和回滚造成的。根据各种地球物理观测和反演,我们可以确定 RRF 周围地壳和上地幔的详细各向异性结构。可以利用更密集的地球物理阵列和更精确的记录来探索 RRF 周围分段和分层中错综复杂的各向异性,从而加深对其构造意义的理解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Science China Earth Sciences
Science China Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
9.60
自引率
5.30%
发文量
135
审稿时长
3-8 weeks
期刊介绍: Science China Earth Sciences, an academic journal cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China, and published by Science China Press, is committed to publishing high-quality, original results in both basic and applied research.
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