Effects of Physical and Acquisition Parameters on Fundamental Dispersion Curve in MASW Method

In this study, the effect of physical and acquisition parameters on the continuity and resolution of fundamental dispersion curve (frequency-phase velocity) has been examined by modeling the synthetic seismograms in Multichannel Analysis of Surface Waves (MASW). The influences of decreasing S-wave velocity or increase in the thickness of the layer on the dispersion curve are observed rapidly as drop in lower frequency zone, while the effect of the increase in the velocity or decreasing of the thickness caused fundamental dispersion curve to shift to higher modes. For the effects of acquisition parameters (offset-XO, geophone interval-dx, number of geophones-N, spread length-L=(N-1)*dx), the fundamental dispersion curve was re-picked from seismograms synthetically modeled by using the simple harmonic summing technique. The tests show that the largest spreading length and offset must be used to obtain the dispersion curve in a widest frequency range and high quality. However, geophone interval for larger spreading should be selected by without wavenumber aliasing. Therefore, synthetic tests showed that if one wants to obtain continuity and resolution of fundamental dispersion curve when analyzing of field data, acquisition parameters may be selected as 1m≤dx≤2m, X0≥Zmax or X0=L for N<24 and 0.5m≤dx≤2m, X0≥L/5 or at least X0 4*dx.