Side Scattering Analysis (SSA)

Surface waves are known to be sensitive to the presence of near-surface anomalies such as near-vertical fractures and voids. A significant amount of surface wave energy impinging against them is transformed into scattered surface waves due to anomalies acting as new sources of surface waves (Fig. 1). Therefore, MASW data collected for normal 2-D Vs mapping can be used to detect possible subsurface anomalies existing off the survey line by using a processing scheme similar to conventional reflection processing (Fig. 2). This process is called a side-scattering analysis (SSA) of surface waves (Fig. 3). With this approach focal depths can be controlled by changing the frequency (wavelength) range used for the processing (Fig. 4). A brief explanation of the processing scheme can be found here.

Fig. 1. A schematic illustrating principle of the side scattering analysis (SSA).
Fig. 2. A SSA modeling result showing the location of the modeled voids.
Fig. 3. SSA map obtained from an actual field data set.
Fig. 4. SSA maps of different focal depths processed from another field data set.