Roadside passive multichannel analysis of surface waves (MASW)

A 2-D receiver array, such as a cross or circular type, should be used in a passive surface wave survey to provide the most accurate results. It is often not possible to secure such a spacious area, however, especially if the survey has to take place in an urban area. A passive version of the multichannel analysis of surface waves (MASW) method is described that can be implemented with the conventional linear receiver array deployed alongside a road. Offline, instead of infine, nature of source points on the road is accounted for during dispersion analysis by scanning recorded wavefields through 180-deg azimuth range to separate wavefields from different azimuths and propagated with different phase velocities. Next, these wave fields are summed together along the azimuth axis to yield the azimuth-resolved phase velocity information for a given frequency. In addition, it is attempted to account for the cylindrical, instead of planar, nature of surface wave propagation that often occurs due to the proximity of source points, by considering the distance between a receiver and a possible source point. Performance of the processing schemes is compared to performance of the scheme that accounts for inline propagation only. Comparisons made with field data sets showed that the latter scheme resulted in overestimation of phase velocities up to 30 percent, whereas the overestimation could be reduced to less than 10 percent if these natures are accounted for according to the proposed schemes.