Multi Channel Surface Wave In Engineering Geophysical Prospecting

Surface wave, or ground roll wave, is usually used as a strong amplitude noise that interferes with the reflected signal and needs to be attenuated or eliminated. But the basic idea of this task is to use the dispersion characteristics of surface wave to analyze the surface wave, so as to deduce the formation velocity.

The near surface investigation is usually used to explore the depth from tens of meters to hundreds of meters. This task usually uses wavelets greater than 50 Hz as signals. MASW, that is, multi-channel surface wave analysis, usually deals with low-frequency (such as 1-30Hz) surface waves. Generally, the detection ranges from several meters to tens of meters, which is shallower than the above one.

S wave = shear wave = secondary wave = shear wave

P wave = pressed wave = primary wave = longitudinal wave

The S-wave velocity has a great relationship with the hardness of the material, so we need to invert the S-wave velocity.

Compared with other methods, the inversion of surface wave, i.e. ground roll, is relatively economic. And the velocity of the transverse wave is determined by the velocity of the transverse wave in the medium.

The basic process of MASW is divided into three steps

(1) acquiring multichannel field records (or shot gathers);

(2) extracting dispersion curves (one from each record);

(3) inverting these dispersion curves to obtain 1D (depth) VS profiles (one profile from one curve)