EFFECT OF ACQUISITION PARAMETERS ON THE RESOLUTION OF DISPERSION IMAGE IN MULTI-CHANNEL ANALYSIS OF SURFACE WAVES METHOD

Multi-channel Analysis of Surface Waves (MASW) is a method for determining the shear wave velocity profile in depth. Shear wave velocity is an important ‌arameter for geotechnical, earthquake, and geophysical engineers. Configuration of data acquisition by the MASW method is variable based on the purpose of the work (depth of identification, data resolution, etc.). For instance, the resolution of dispersion image will be different according to the recorded data by different configurations of the MASW method. Hence, in this paper, the effects of data-acquisition parameters on the resolution of dispersion spectrum were evaluated in the frequency-velocity domain. These parameters consisted of the receiver spacing, length of the receiver array, offset, and the element size. Different receiver spacings with 8, 4, 2, and 1 meters were evaluated in two layered soil models with the shallow thickness of 2 and 4 meters. The distance between the source and the first receiver (offset) and the length of the receiver array were selected based on the desired depth and the maximum wavelength. In this regard, different lengths of the receiver array with dimensions of 96, 48, 24, and 12 meters were considered. Also, different sizes of elements (1, 0.5, 0.25, and 0.125 m) were selected based on the shortest wavelength. The results showed that the receiver spacing should be proportional to half of the shortest wavelength and minimum thickness of the shallow layer. The resolution range of the dispersion spectrum increased approximately twice by increasing the length of the receiver arrays from 12 m to 24, 24 to 48, and 48 to 96 m. Also, the results of the element resizing showed that considering 8 or more elements (10) in one wavelength would be necessary to obtain the optimal accuracy of the simulations. Generally, with regard to the condition of the site and the expected goal, it could be possible to obtain suitable results with desirable accuracy in field-data acquisition analysis and software simulations by utilizing the effect of the mentioned parameters in different ranges. Moreover, the presented result in this paper can be used as guidelines for field parameters related to data acquisition in the MASW method.