1-D and 2-D Shear-Velocity (Vs) Profiling

Various types of surveys can be taken depending on the thoroughness of the site characterization being sought. If only the overall vertical (depth) variation of stiffness information is needed, then a 1-D Vs profiling is sufficient (Fig. 1). If the lateral variation information is also important, a 2-D profiling can be conducted along a certain direction (Fig. 2). Considering that the minimum field operational cost for the 1-D profiling is usually more than half the cost for a 2-D profiling, a 2-D profiling is usually the recommended minimum approach. An anomaly—defined as a localized area significantly different in elastic property (strength and density) than ambient material—can be delineated through either 1-D or 2-D profiling if its size (dimension) is significant (for example, greater than 20% of its depth) (Fig. 3). Average and interval shear velocities are also provided as by-products for each 1-D or 2-D profiling survey (Fig. 4)

Fig. 1. Typical 1-D MASW survey and its 1-D shear-wave velocity (Vs) profile.
Fig. 2. Typical 2-D MASW survey and its 2-D shear-wave velocity (Vs) map.
Fig. 3. Anomaly detection by 1-D (illustration) and 2-D (field data) surveys.
Fig. 4. Display of average and interval shear-wave velocities at a site