Different software may adopt slightly different algorithms in dispersion and inversion analyses.
For dispersion analysis, the phase-shift method by Park et al. (1998) is most commonly used after investigations by many researchers (e.g., Moro et al., 2003) because of its proven high-resolution capability in comparison to other conventional methods such as f-k and tau-pi transformation methods (e.g., McMechan and Yedlin, 1981). The high-resolution dispersion-imaging scheme is the most critical component of MASW analysis because of its ability to discriminate different modes of plane waves that may include both body and surface waves travelling horizontally along the surface.
For inversion analysis, the fundamental-mode (M0) generation algorithm (e.g., Schwab and Knopoff, 1972) is most commonly used. Although there has been a great deal of research and development in multi-mode utilization, software that takes full advantage of multi-mode while efficiently handling all the associated complications (e.g., mode misidentification and mode mix) has not yet been developed. This is because of the fact that modal identities of higher modes in reality cannot be uniquely determined. In consequence, the higher-mode inversion methods generate results often less reliable than those from the traditional fundamental-mode (M0) inversion method. This is further illustrated in this video (from 3:40 time line). Yet, the traditional approach of the fundamental-mode (M0), or an apparent mode (AM0), inversion provides an excellent outcome under most common near- surface (overburden and bedrock) settings, and can provide a 1st-degree approximation of other more complex settings.
Practical (Yet Critical) Algorithms
In addition to such obvious aspects of algorithms that are extensively described through major publications, there are also practical aspects of software that are not publicly well addressed, yet can influence significantly on the final result of velocity (Vs) profiles. They may include, but not limited to, the way the following issues are addressed:
how the process to update model velocity (Vs) is optimized in inversion,
how computational artifacts are suppressed during the dispersion-image generation,
the way incoherent ambient noise is handled during the dispersion-image generation and subsequent curve (M0) extraction,
how the maximum depth of velocity (Vs) profile is determined,
the way the initial velocity (Vs and Vp), density, and thickness models are created,
how the apparent mode (AM0) is handled during inversion,
how the overburden/bedrock interface is detected during inversion, and
how non-uniqueness of inversion process is handled.
These practical aspects should be properly calibrated in the software throughout extensive research and development based on both theoretical and empirical experiments using diverse data sets.
A new version of ParkSEIS (v. 3.0) AUTO is now available. The most significant feature is the "AUTO" now watch this on YouTubenow generate shear-wave velocity (Vs) profiles (1D or 2D) with advanced one click after importing seismic data. . The options for research and QA/QC purposes. More details about the AUTO feature are explained
here. All other additions, updates, modifications, and bug fixes incorporated in this version of ParkSEIS are explained here.
ParkSEIS provides the most up-to-date comprehensive tools in the history of MASW development. The technical algorithms have evolved through the last two decades of author's career as developer and practitioner of MASW, making it the most robust and reliable MASW analysis tool available today. A brief introduction of the software features is presented here. More technical details of the software can be found online. Overall features of ParkSEIS are introduced in this video.