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利用中国地震年报、四川和云南区域地震台网观测报告的23298个Pn波到时资料,反演得到川滇地区及周边的Pn波速度细结构及各向异性。结果表明:该区Pn波速度在7.7～8.3km/s范围内变化,横向变化较为明显,在滇西南部、腾冲火山区、攀西构造带,Pn波速度都明显较低,这些地区地震和构造活动十分活跃,且在地表观测到较高的大地热流值;另一方面较为稳定的地区,如:扬子地合中部,Pn波速度相对较高;研究区内最明显的Pn高速区位于成都东南部的四川盆地;上述结果说明该区Pn波速度与现代构造活动及地热活动存在较明显的关联。Pn各向异性的变化呈现出区域内岩石形变的复杂图像,从藏东块体经川滇菱形块体到滇西南部,Pn快波方向里左旋运动,这可能与印-欧板块碰撞挤压,致使青藏高原物质向东南方向逃逸有关。由此表明区域内壳幔间存在较强的耦合关系,由事件和台站的静延迟分布可以看出从青藏高原到中国东部地区地壳由厚减薄,这与人工地震测深所得到的地壳厚度变化具有较好的一致性。
Based on the 23298 Pn arrival data from the annual reports of China Earthquake and the observation reports of Sichuan and Yunnan Seismic Networks, the fine structure and anisotropy of Pn wave velocities are obtained by inversion. The results show that the Pn wave velocity changes in the range of 7.7 ~ 8.3km / s and the horizontal variation is obvious. The velocity of Pn wave in the southwestern Yunnan, Tengchong volcano and Panxi tectonic belt is obviously lower. The seismicity and Tectonic activity is very active, and the value of the geothermal heat flow is high on the surface; on the other hand, the relatively stable Pn wave velocity is relatively high in the central part of the Yangtze, such as the middle part of the Yangtze; the most obvious Pn high-speed area in the study area is located in Chengdu Southeast of the Sichuan Basin; the above results show that Pn wave velocity in this area and modern tectonic activities and geothermal activities there is a clear correlation. The Pn anisotropy shows a complex image of rock deformation in the region. From the block of eastern Tibet to the southwestern Yunnan, , Causing the Tibetan Plateau material to escape in the southeast direction. This shows that there is a strong coupling between the crust and the mantle in the region. From the events and station static delay distribution, it can be seen that the crust is thinned from the Qinghai-Tibetan Plateau to the eastern part of China. This is consistent with the crust obtained by artificial seismic sounding Thickness variation has good consistency.