Eastward expansion of the Tibetan plateau: Insights from stress drops of the 2021 Ms 6.4 Yangbi, Yunnan and Ms 7.4 Maduo, Qinghai earthquake sequences in China
Eastward expansion of the Tibetan plateau: Insights from stress drops of the 2021 Ms 6.4 Yangbi, Yunnan and Ms 7.4 Maduo, Qinghai earthquake sequences in China
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DOI：
10.3389/feart.2023.1081605
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
Xi He;Lian‐Feng Zhao;Xiaoyan Xie;Lei Zhang;Z. Yao
中科院分区：
文献类型：
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作者：
Xi He;Lian‐Feng Zhao;Xiaoyan Xie;Lei Zhang;Z. Yao
青藏高原的东扩导致青藏高原东部广泛的地震活动，并伴随着该地区各种类型的断裂过程。然而，与这些现象相关的地壳应力状态仍不清楚。2021年5月21日，在青藏高原南部和北部的川甸和巴彦哈尔地块相继发生了震源机制不同的羊壁6.4级和玛多7.4级地震，为直接对比侧向扩张高原两侧的应力提供了独特的机会。在这项研究中，我们从Lg波谱估计了所有M≥3.0地震的羊壁和马多地震序列的应力降。基于建立的宽带LG波衰减模型，适当地消除了路径衰减和场地效应。然后，通过高精度的地震定位，细化应力降的分布。在两次主震后，都观察到应力下降的快速衰减。羊壁序列具有较高的中值应力降，部分前震的应力降明显偏高，可能是主震成核的级联触发机制。相比之下，玛多序列具有主震应力降较大、余震应力降波动大的特点。马多余震从主震向东西两个方向延伸，东部应力降相对较低，表明主震期间超剪破裂花费了大量的能量。我们还发现，应力降与羊壁序列的断层连接有关，与玛多序列的强度沿断层的变化有关，这很可能与青藏高原东部的地壳运动和变形模式有关。
The eastward expansion of the Tibetan Plateau has resulted in extensive seismic activities in the eastern Tibetan Plateau, along with various types of faulting processes across this region. However, the crustal stress status related to these phenomena remains unclear. On 21 May 2021, the Ms 6.4 Yangbi and Ms 7.4 Maduo earthquakes with diverse focal mechanisms occurred consecutively in the Chuandian and Bayan Har blocks in the southern and northern parts of the eastern Tibetan Plateau, providing a distinct opportunity to directly compare the stresses in both flanks of the laterally expanding plateau. In this study, we estimate the stress drops of the Yangbi and Maduo earthquake sequences for all M ≥ 3.0 events from the Lg-wave spectra. Both the path attenuation and site effect are properly removed based on an established broadband Lg-wave attenuation model. Then, the distribution of the stress drops is refined through high-precision earthquake relocation. Quick decays in stress drops were observed after both mainshocks. The Yangbi sequence has a relatively high median stress drop value, with significantly high stress drops for some foreshocks that possibly indicate a cascade triggering mechanism for the nucleation of the mainshock. In comparison, the Maduo sequence is characterized by a higher stress drop for the mainshock and sustained large fluctuation in stress drops for aftershocks. The Maduo aftershocks extend both the eastern and western directions from the mainshock, with relatively low stress drops in the east, suggesting a large amount of energy has been spent to drive the supershear rupture during the mainshock. We also find that the stress drops are associated with fault junctions for the Yangbi sequence, and are associated with variations in strength along the fault for the Maduo sequence, which are very likely linked with patterns of crustal motion and deformation in the eastern Tibetan Plateau.