Shear-wave velocity (Vs) information of subsurface materials is directly related to the stiffness property of the materials, which is the key property dealt in all geotechnical engineering projects. In this sense, the MASW method can be applied to any geotechnical engineering project that requires subsurface mapping of the stiffness in 1-D, 2-D, and 3-D formats.
The most common type of application has been the soil-bedrock mapping that delineates topographic boundary between soil and bedrock by an interface of significant velocity (Vs) increase (e.g., from 300 m/sec to 1000 m/sec). It also shows vertical and horizontal variation of soil stiffness by displaying velocity (Vs) variations within the soil range (e.g., 100 m/sec - 300 m/sec). This boundary often shows a gradual change in velocity over a certain depth range rather than a sharply-defined interface, indicating the possible weathered zone on top of the bedrock. More recently, applications to detect subsurface anomalies are merging. These anomalies may include localized low-velocity zones created by various reasons such as existing utility tunnels, void development due to collapse, severely weathered bedrock, loss of cohesiveness in filled materials, etc. In this case, the detection is often facilitated by non-velocity mapping approaches such as back-scattering analysis and common-offset section generation. Another type of application is the performance evaluation that is executed before and after a specific operation is applied. This includes the compaction evaluation for surface and shallow subsurface materials during road and building construction. It also includes the evaluation of grouting performance.
The seismic site characterization requires an evaluation of an average shear-wave velocity (Vs) for the top 30-m (or 100-ft) depth. This is the most common 1-D (i.e., depth) application of MASW method.
In general, MASW applications can be grouped into following categories: