摘要
根据本文提出的更为严格的地震数据筛选方法——横向分区地震均值筛选法,选取了四川、云南、重庆和贵州地震台网的224个固定台站和49个流动台站在2008年1月1日—2017年12月31日期间记录的48,177个地震、372,483条初至P波绝对到时数据以及2,413,407条精度较高的相对到时数据,利用区域双差地震层析成像方法联合反演了青藏高原东南缘川滇地区三维P波速度结构和地震震源参数.研究结果表明:(1)川滇地区上地壳结构横向不均匀性明显,四川盆地上地壳10 km深度范围内表现为低速异常,而松潘—甘孜地块、滇中地块则表现为明显的高速异常;(2)川滇地区地震主要沿着边界断裂分布,大多数地震为浅源地震,震源深度主要集中在5~15 km深度范围内,震源主要位于高速异常与低速异常交界区域且偏向高速异常体一侧;(3)震源分布研究推测龙门山断裂带前山断裂东南侧可能存在一条倾向北西、倾角约为40°的北东向走向的隐伏断裂,且为芦山地震的主要发震断裂;(4)川滇地区中下地壳低速异常体可能反映了中下地壳弱物质流的存在,中下地壳物质流不是广泛分布在川滇地区,而是沿着川滇块体东部有限的通道向南流动.中下地壳流可能是沿着鲜水河断裂带向东南方向流出,在雅安一带遇到坚硬稳定的四川盆地的阻挡,一部分物质向北东方向流动,而另一部分物质转向南沿着安宁河断裂带和则木河断裂带分布,并继续向南沿着小江断裂带流动.
Based on the improved method, we selected 372,483 P-wave absolute arrival data and 2,413,407 high-precision relative arrival data from 48,177 earthquakes recorded by 224 permanent stations and 49 temporary stations of Sichuan, Yunnan, Chongqing and Guizhou Seismic Network. A high-resolution three-dimensional P-wave velocity structure and hypocentral parameters of 39,985 events are obtained with regional double-difference seismic tomography(tomoFDD) in the Sichuan-Yunnan area. The tomographic inversion shows that obvious lateral heterogeneity in the upper crust structure beneath Sichuan-Yunnan area, the low-velocity anomalies in the upper crust of Sichuan Basin and high-velocity anomalies in Songpan-Garzê block and the central Yunnan block above 10 km depth. The relocated hypocenters show an even clear configuration along the major faults. Moreover, some of them are concentrated along the major faults in a shape of alignment. The majority of the hypocenters are located in the conjunctional area of the low and high P-wave velocity anomalies. And they are slightly closer to the high-velocity anomaly areas. Our results show that Lushan mainshock locates at 30.29°N, 102.98°E with focal depth 16.7 km. A NW-strike and dip angle of about 40° blind fault in the southeastern segment of Qianshan fault is inferred from hypocenter distribution analysis, which is also the seismogenic fault of the Lushan mainshock. An obvious low-velocity anomaly is visible in the middle and lower crust beneath Sichuan-Yunnan area, which may reflect the weak material flow in the middle and lower crust in the southeastern margin of Tibetan Plateau. The distribution of low velocity anomalies may represent the same feature of the crust flow, which expands towards southeast along Xianshuihe fault and is blocked by the Sichuan Basin(high-velocity anomalies) at Ya’an so that part of crust flow moves northeastward, while the other turns southward along Anninghe fault and Zemuhe fault and Xiaojiang fault. Furthermore, the crust flow only exists b
作者
邓山泉
章文波
于湘伟
宋倩
DENG ShanQuan;ZHANG WenBo;YU XiangWei;SONG Qian(College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《地球物理学进展》
CSCD
北大核心
2021年第3期863-876,共14页
Progress in Geophysics
基金
国家自然科学基金项目(42074062,41374105)资助。
关键词
青藏高原东南缘
川滇地区
三维P波速度结构
中下地壳流
Southeast margin of Tibet Plateau
Sichuan-Yunnan area
3D P-wave velocity structure
Middle-lower crustal flow
