三维散射系数结构揭示的龙滩库区水的渗透特征

使用2006年10月1日至2010年5月14日9个固定台站和2009年4月4日至2010年5月14日15个临时台站记录的地震波形资料,采用尾波包络线反演方法,得到了龙滩库区地壳的三维散射系数结构,结果表明:(1)龙滩水库下方地壳中存在明显的非均匀结构.由大坝附近布柳河与红水河交汇处至三江(红水河、油拉河和牛河)交汇处的河段下方是研究区最明显的高散射系数区,高散射系数延伸深度达10 km,但在8 km以下高散射系数范围明显减小,除此之外,八茂断裂东西两端和八腊断裂周围也存在小范围的高散射系数区.(2)龙滩库区高散射系数主要分布在碳酸盐地层及与之接壤的透水性较好的砂页岩中,并且主要位于主干河流附近,河流和断层交汇处附近及与河流相交的断层附近,高散射系数分布与水的渗透密切相关.库区的水向河流两岸的渗透宽度约为10 km左右,深度不超过10 km.(3)龙滩库区地震主要集中在7~10 km深度的高散射系数区内,在水库地震中震源明显偏深,可能与库区水渗透引起的古岩溶水活化有关.

Water infiltration of Longtan reservoir area revealed by three-dimensional distribution of scattering coefficient

Using the seismic wave data from October 1, 2006 to May 14, 2010 recorded by 9 permanent stations and the seismic wave data from April 4, 2009 to May 14, 2010 recorded by 15 temporary stations, we obtained the three-dimensional spatial distribution of scattering coefficient in the crust of Longtan reservoir area through seismic coda envelope inversion analysis. The results show that: (1) The structure is inhomogeneous in the crust of Longtan reservoir area. The crust under rivers from the convergence of Buliu river and Hongshui river near the dam to the junction of Hongshui river, Youla river and Niu river is the largest scattering coefficient zone in this area. The large scattering coefficient zone extends to 10 km in depth, and its range significantly diminishes till the depth of 8 km. Moreover, there are large scattering coefficient zones at the eastern and western ends of Bamao fault and the surrounding area of Bala fault on a relatively small scale. (2) Large scattering coefficient zones are mainly distributed in carbonate formations and its adjacent sandy shale of large water penetration coefficient, which are mainly located near the main rivers, the convergence of rivers, and near the faults intersection with rivers.The distribution of large scattering coefficient is closely related with the water penetration. The range of water infiltration can extend to as wide as 10 km from two banks of rivers, and the depth of water infiltration is less than 10 km. (3) Clusters of earthquakes in Longtan reservoir area mainly concentrate on the large scattering coefficient zones at depths from 7 to 10 km. The focal depths of these earthquakes are deeper than reservoir earthquakes. It might be related to the activation of paleokarstic groundwater induced by water penetration.