利用地震勘探面波反演巨厚戈壁区的表层结构

INVERSE SURFACE STRUCTURE BY SEISMIC URFACE WAVE FOR ULTRA THICK GOBI AREA

塔里木盆地山前构造带地表主要被巨厚砾石层覆盖,低降速层厚度大,表层结构建立难度大。巨厚戈壁区地震采集单炮中的面波发育能量强,频散特征突出,蕴含着丰富的近地表结构参数信息。根据地震勘探面波属性与近地表结构参数之间的关系,建立利用地震面波反演巨厚戈壁区表层结构的技术流程。通过小波变换与F-K法相结合,精细分离单炮的面波信号,对面波进行频散分析计算,将不同频率的面波分量分离开来,拾取面波的频散曲线。采用权重自适应迭代阻尼最小二乘法与遗传算法相结合的方法,反演频散曲线的地层厚度和横波速度参数,利用横波与纵波的转换关系,计算出地层的纵波速度,进而建立表层结构,解决了巨厚戈壁区表层结构反演难题。

The piedmont tectonic zone of Tarim Basin is covered with ultra thick gravel layers. So, it's hard to establish its surface structure due to the very thick low-deceleration zone.Featured by strong energy and prominent dispersion, the surface wave from single shot of seismic data acquisition in ultra thick Gobi area contains a great deal of parameter information of near-surface structure. According to the relation between the property of seismic surface wave and the parameter of near-surface structure, a technical process inversing surface structure of ultra thick Gobi area using seismic wave is established. Based on the combination of wavelet transform with F-K method, and fine separation of the surface wave signal of single shot, the dispersion of surface wave is analyzed and calculated, surface wave components of different frequencies are isolated,and dispersion curve of surface wave is obtained. A method that integrates the self-adaptive weighted iteration damped least square method and genetic algorithm is used to inverse the formation thickness and S-wave velocity parameter of the dispersion curve. By using the conversion relation between S- and P-wave, P-wave velocity can be calculated, and then the surface structure can be established. It solves the problem of surface structure inversion of ultra thick Gobi area.