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利用位于青藏高原东南缘云南地区的中国地震科学探测台站(ChinArray)一期300多个宽频带流动台站记录到的XKS波形(包括SKS,SKKS,PKS)进行了S波分裂分析。XKS分裂结果最主要的特征是快波偏振方向(φ)在26~27°N附近,从北部的近N—S向突变为南部的近E—W向。研究区西部喜马拉雅东构造结附近的结果较好地反映了岩石层左旋剪切变形下发育的各向异性。26°N以南地区,快波分裂方向以E—W向为主,与中上地壳最大张应力的方向一致,表明云南地区整个岩石层都可能处于纯剪切变形环境。但是该区岩石层厚度不足80km,产生的XKS分裂快慢波时差(<0.7s)仅能解释部分观测值(0.9~1.5s)。因此,软流层中的各向异性对于该地区的S波分裂结果(快波偏振方向为NW—SE和近E—W向)可能产生了重要的作用。一方面,NW—SE向快波偏振方向可能反映了缅甸块体的俯冲及其随后撤退引起的上地幔流动造成的各向异性。另一方面,伴随着高原构造演化发生的从青藏高原向中国东部的软流层物质流动,以及由于绝对板块运动造成的软流层顶部的剪切作用,将产生快波方向为近E—W向的各向异性。本研究结果为研究青藏高原东南缘不同深度的变形特征及其差异提供了重要的信息,尤其在研究青藏高原的构造抬升及其向东南缘的扩展方面产生了新的认识。
S-wave splitting analysis was carried out using XKS waveforms (including SKS, SKKS and PKS) recorded by more than 300 broadband mobile stations in the first phase of China Earthquake Scientific Exploration Station (ChinArray) in the Yunnan area of the southeastern margin of the Qinghai-Tibet Plateau. The most prominent feature of the XKS splitting results is the fast wave polarization (φ) near 26-27 ° N, from near N-S in the north to near E-W in the south. The results near the east Himalayan tectonic knot in the western part of the study area well reflect the anisotropy of development under the left-lateral shear deformation of the lithosphere. In the area south of 26 ° N, the fast-wave splitting direction is dominated by E-W direction, consistent with the direction of the maximum tensile stress of the middle-upper crust, indicating that the entire lithosphere in Yunnan may be in a pure shear deformation environment. However, the thickness of lithosphere in this area is less than 80km. The time-frequency difference between fast and slow XKS splitting waves (<0.7s) can only explain part of the observed values (0.9 ~ 1.5s). Therefore, the anisotropy in the asthenosphere may play an important role in the S-wave splitting results in this region (NW-SE and near-E-W directions). On the one hand, the NW-SE fast wave polarization direction may reflect anisotropy due to the subduction of the Myanmar block and the subsequent mantle flow caused by its subsequent retreat. On the other hand, along with the material flow in the asthenosphere from the Tibetan Plateau to the eastern part of China due to the plateau tectonic evolution and the shearing action at the top of the asthenosphere due to the absolute plate motion, a fast wave direction is generated near E-W To the anisotropy. The results of this study provide important information for studying the deformation characteristics and their differences at different depths in the southeastern margin of the Qinghai-Tibet Plateau, especially in the study of tectonic uplift of the Tibetan Plateau and its expansion to the southeastern margin.