利用地脉动信息约束沉积层区域台站下方速度结构反演

Application of microseismic data to constraining inversion for velocity structure beneath stations in sedimentary area

  • 摘要: 利用接收函数和地震面波频散联合反演台站下方速度结构,已成为一种常用技术.联合反演结果能同时匹配两个不同数据集合,使得解的非唯一性在一定程度上得到了有效抑制.然而对于现有地震台站分布,短周期面波由于受多种因素的影响,可以获得的有效频散资料较少, 层析成像的横向分辨率较低,难以反映台站附近局部介质真实的频散特性, 而且这些面波频散与接收函数在不同深度上反映的空间范围也存在一定的差异,在横向构造变化复杂的沉积层地区,二者往往很难同时得到较好的拟合.因此联合反演应尽可能采用反映相同空间上介质信息的约束资料.2009年5月,我们分别在冀北高原和华北平原沉积层区域的两个流动地震台站附近,布设了小孔径台阵进行地脉动观测.采用空间自相关方法获得高频相速度频散曲线,并作为浅部速度结构约束条件运用于沉积层区域接收函数与面波的联合反演.结果表明,高频相速度频散曲线的约束有可能明显提高沉积层地区速度结构反演的稳定性和可靠性.

     

    Abstract: The joint inversion of receiver functions and seismic surface wave dispersion has become a common technique to study the velocity structure beneath stations. The results can simultaneously match the two data sets of different resolution so that the non-uniqueness of solution has been effectively suppressed in a certain extent. However, for the present distribution of seismic stations, due to many factors, there are less effective short-period surface wave dispersion data. The horizontal resolutions of seismic tomography are low, so it is difficult to reflect the real dispersion characteristics of the local media near stations. The spatial extents reflected by these surface wave dispersions and receiver functions at different depths are also different, especially in the sedimentary region with complex lateral variations, where receiver functions and surface wave dispersion can not simultaneously achieve a good fitting result. So the constraint data, which can reflect information of media in the same spatial extent, should be used as far as possible for joint inversion. In May of 2009, we laid a small-aperture seismic array for micro-seismic observation near two mobile seismic stations in a sedimentary region on the plateau of northern Hebei province and in North China Plain, and obtained high-frequency phase velocity dispersion curves by spatial autocorrelation method. The micro-seismic dispersion curves are used as constraint on shallow velocity structure for the joint inversion of receiver functions and surface waves in sedimentary region. The inversion result shows that the constraint of high-frequency phase velocity dispersion curves may obviously improve the stability and reliability of the inversion for velocity structure in sedimentary region.

     

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