利用瑞雷面波的H/V比与纯路径相速度频散曲线联合反演获取浅地表横波速度

S-wave velocities of near-surface materials are fundamental parameters in environmental and engineering studies. How to achieve a high-resolution (including both horizontal and vertical) S-wave velocity profile is one of the most difficult problems in high-frequency Rayleigh-wave method. The multichannel analysis of surface wave (MASW) method is widely utilized to estimate S-wave velocities in shallow layers due to strong anti-interference ability and simple data acquisition. The inverted 1D S-wave velocity profile, however, is an averaged geophysical model under the receiver spread length, so the MASW method has low horizontal resolution. In addition, because higher mode Rayleigh waves are not obvious at some cases, inversion of only fundamental-mode Rayleigh-wave phase velocities may cause low vertical resolution of S-wave velocities. A measurement of Rayleigh-wave horizontal-to-vertical (H/V) ratios is proposed as an important tool for depicting a 1D S-wave velocity profile. Since depth sensitivity kernels of H/V ratios are different from those of dispersion data, H/V ratios provide good complementary information for dispersion-based inversion methods. This application develops the surface-wave phase-velocity tomography in combination with the MASW method to obtain pure-path phase-velocity dispersion curves. And then a joint inversion method is proposed using Rayleigh-wave H/V ratios and pure-path phase-velocity dispersion curves based on the Bayesian Monte-Carlo approach for acquiring a high-resolution pseudo-2D S-wave velocity section. Synthetic and real-world examples will be used to demonstrate the effectiveness of this proposed method. The results of this study will provide a powerful method for near-surface engineering exploration.

横波速度是环境与工程研究中的基本参数，如何获得高（水平和垂向）分辨率的横波速度是瑞雷面波方法研究的难点。面波多道分析（MASW）方法因其抗干扰能力强，采集方式简单，被广泛应用于估计浅地表横波速度，然而该方法确定的横波速度是整个检波器排列的平均结果，因此水平分辨率较低。另外，由于某些地区的高阶模式面波不发育，仅利用基阶模式瑞雷面波相速度频散曲线的反演可能导致横波速度的垂向分辨率较低。基于径向和垂向分量观测的瑞雷面波的H/V比是确定浅地表横波速度的又一重要手段，且具有和相速度频散曲线不同的深度敏感核，二者可相互补充。本课题拟结合MASW方法和面波相速度层析成像技术计算纯路径相速度频散曲线，利用贝叶斯—蒙特卡洛算法联合反演瑞雷面波的H/V比和纯路径相速度频散曲线，以获得高分辨率的拟二维横波速度结构。通过理论模型和实际资料验证联合反演方法的有效性，期望为浅地表工程勘探的应用提供新的可靠的方法。

高频（≥2 Hz）瑞雷波频散特征已被广泛应用于确定浅地表横波速度。然而，仅反演高频瑞雷波相速度频散难以约束浅地表横波速度异常（譬如，城市地区坚硬的马路），不准确的浅地表横波速度亦会造成更深部反演结果的偏差。相较于高频瑞雷波相速度，相同频率的瑞雷波径向分量和垂向分量的振幅比（H/V比）对横波速度的敏感深度明显更浅。因此，基于主动源激发的高频地震记录，本文提出了一套联合反演瑞雷波纯路径相速度频散曲线和H/V比确定浅地表横波速度的技术流程。首先，利用高分辨率线性拉东变换技术（HRLRT）从原始地震记录中分离得到基阶模式瑞雷波。然后，对分离后的基阶模式瑞雷波基于两道间反褶积和频率-时间分析技术（FTAN）测量任意两道之间瑞雷波相旅行时和每一道的H/V比。接着，根据提取的相旅行时，利用射线理论的层析成像技术计算纯路径相速度频散曲线。最后，通过联合反演瑞雷波纯路径相速度频散曲线和H/V比获得拟二维横波速度结构。理论测试和实际数据都表明通过引入H/V比进行联合反演可显著提高横波速度反演结果的准确度。联合反演瑞雷波纯路径相速度频散和H/V比是一种在复杂浅地表情况下（譬如，城市环境）探测横波速度的有效方法。