基于频率-贝塞尔变换法的浅地表三维S波速度成像

Three-dimensional S-wave velocity imaging of shallow surface based on frequency-Bessel transform method

100 m以内浅地表的高精度勘探对城市发展具有重要意义,近年来利用环境噪声研究浅地表横波速度结构的被动源面波勘探方法得到快速发展.为探讨频率-贝塞尔变换法在浅地表勘探中的应用效果,本文将频率-贝塞尔变换法应用到杭州东部某地区布设的小尺度密集台网的环境噪声数据中,有效地从环境噪声中提取了基阶和高阶面波频散曲线.利用提取的各阶频散曲线联合反演了该地区浅地表的横波速度结构,并将反演结果与Chen的Maps法、层析成像结果和测井数据进行对比.结果表明:频率-贝塞尔变换法较于Maps法具有更高的水平和垂直分辨率;在反演横波速度结构时,加入高阶面波频散曲线能够加强深部的约束效果,使深部的反演结果更接近测井值;其在小尺度的浅地表勘探中也具有较好的应用效果.研究为浅地表高精度被动源面波勘探方法的选择和频率-贝塞尔变换法在小尺度地区的应用提供了指导.

High-precision exploration of shallow surface within 100 m is of great importance for urban development,and the passive-source surface wave exploration method using environmental noise to study the transverse velocity structure of shallow surface has been rapidly developed in recent years.To explore the effect of frequency-Bessel transform method in shallow surface exploration,this paper applies the frequency-Bessel transform method to the environmental noise data collected from a small-scale dense station network in the eastern part of Hangzhou,and effectively extracts the fundamental-order and high-order surface wave dispersion curves from the environmental noise.The extracted dispersion curves were used to jointly invert the transverse velocity structure of the shallow surface in this area,and the inversion results were compared with Chen's Mapes method,laminar imaging results and logging data.The results show that the inversion results are similar to the logs,and the frequency-Bessel transform method has higher horizontal and vertical resolution than the Maps method;the inclusion of higher-order surface wave dispersion curves in the inversion of the transverse velocity structure can strengthen the constraint effect at depth and make the inversion results at depth closer to the logs;the frequency-Bessel transform method also has better application in small-scale shallow surface exploration.The study provides guidance for the selection of high-precision passive source surface wave exploration methods and the application of frequency-Bessel transform method in small-scale areas.