六分量地震观测在工程勘查中的应用试验

利用面波频散曲线反演地下介质的S波速度结构, 是浅层工程地震领域一种重要的方法技术.传统的面波法包括主被动源的面波多道分析方法(MASW)和被动源的空间自相关(SPAC)方法, 均需要多台地震仪同时记录地面振动; 而记录平动和旋转运动的单台站六分量地震数据理论上也可以获得面波频散曲线.本文以河北唐山城区煤矿采空区浅层工程勘探实际六分量地震数据为例, 对比了利用单台站六分量地震数据与主、被动源法多台站提取的Rayleigh波频散曲线.试验结果表明利用纵波扫描可控震源时, 30 Hz以下频段利用单台站六分量地震数据提取的基阶Rayleigh波频散曲线与主、被动源MASW方法提取的频散曲线结果一致, 说明在浅层工程地震勘查中, 利用单物理点的六分量地震观测反演浅层横波速度是可行的.

A case study: application of six-component seismic observations in urban engineering investigation

Using the surface wave dispersion curves to invert the S-wave velocity of subsurface media is an important method in shallow engineering seismic exploration. Traditional surface wave analysis methods include Multichannel Analysis of Surface Waves (MASW) and Spatial Auto-correlation (SPAC), which require the use of z-component or 3-component leveling seismometer arrays to simultaneously record ground motion. However, the surface wave dispersion curves can be theoretically obtained by recording only the six-component seismic data from a single station with translational and rotational motions. A case study of shallow engineering exploration in Tangshan City is introduced in this paper. Through comparing the Rayleigh wave dispersion curves extracted with different observations, the experiment shows that, when the P-wave vibroseis is used as the seismic vibration source, the fundamental Rayleigh wave dispersion curve below 30 Hz extracted from the six-component seismic data with only single-station observation is consistent with the dispersion curves extracted with array of geophones. The study suggests that in the shallow engineering seismic exploration, it is feasible and convenient to invert the S-wave velocity of subsurface media by using six-component seismic data instead of dense translational observations.