Combined Effect of A-Priori Information and Varying Source Offset in Minimizing Propagation of Near-Field Effects in MASW Testing and Subsequent Site Response Analysis

Seismic site characterization has witnessed a recent surge in the adoption of surface wave methods, with multi-channel analysis of surface waves (MASW) taking the forefront. MASW relies on the generation of Rayleigh waves through an energy source applied to the soil. Yet, alongside these Rayleigh waves, body waves emerge, introducing intricacies termed 'near-field effects.' This phenomenon leads to uncertainties in the estimated V_s profile, a pivotal parameter in geotechnical assessments. The near-field effects depend on the source-to-first geophone distance (source offset). This study systematically explores how source offset and the strategic incorporation of a-priori information collaboratively minimize the propagation of uncertainties in the V_s profile obtained from MASW testing and subsequent site response analysis (SRA). To rigorously assess this, numerical simulations of MASW test were carried out, varying source offset and considering scenarios with and without a-priori information during V_s profile generation. Additionally, the assessment was extended to SRA to unravel the implications of these factors. To validate these results practically and anchor them in the real world, an investigation was carried out in the field. The culmination of these investigations substantiates a prominent trend: An augmented source offset, coupled with judicious a-priori information utilization, significantly mitigates the propagation of uncertainties in MASW testing and subsequent SRA. Roughly, a source offset of 10–20 m emerges as an effective strategy to counter near-field effects when combined with the strategic integration of a-priori information. However, the value of the optimal source offset remains site-specific, ideally derived through tailored MASW tests at varying source offsets.