Optimum MASW Survey—Revisit after a Decade of Use

As an attempt to study systematically on the optimum source offset— the distance between source and the closest receiver— and total receiver spread length with the MASW method, we present our observations with modeling and field data sets indicating that the most accurate analysis of phase velocities can be accomplished only for wavelengths up to one spread length, and subsequent analysis for the longer wavelengths inevitably involves a certain degee of fluctuating inaccuracy that seems to originate from the Gibbs—phenomenon of Fourier transformation. The inaccuracy, however, seems to be within five percentfor those wavelengths shorter than twice the spread length. Also, results from the field data study suggest that importance of the source offset has been previously underestimated and the maximum wavelength can be extended simply by extending the source offset. In addition, they showedthat phase velocities tend to be underestimated if the source offset is smaller than one spread length. The degree of underestimation, however, appears highly site dependent and sometimes becomes negligible even if the source offsetis as short as only one receiver spacing.