An integrated ERT-MASW probabilistic framework for liquefaction susceptibility assessment: A case study in Pohang

초록

This study proposes a probabilistic framework that integrates geophysical surveys with geotechnical investigations to assess site-specific liquefaction risk. Conventional liquefaction assessments based on borehole logs or geophysical data from a single method often fail to capture local heterogeneity and stratigraphic continuity, leading to unrealistic or spatially discontinuous risk interpretations. To overcome these limitations, a two-step probabilistic analysis scheme was implemented. First, electrical resistivity tomography (ERT) data were combined with borehole-derived lithology to estimate the probability of sandy soil (Psand), enabling delineation of sand-clay transition strata and improving representation of subsurface variability. Second, correlations between shear-wave velocity (VS) from multichannel analysis of surface waves (MASW) and standard penetration test (SPT) values were used to estimate the probability of loose sandy soil (PLSS), reflecting relative density variations. These probabilities were then coupled with the liquefaction potential index (LPI) derived from VS to construct a composite index that jointly accounts for subsurface susceptibility and seismic demand. The framework was validated against borehole-based LPIs and stratigraphic logs. Applied to the 2017 moment magnitude (MW) of 5.5 Pohang earthquake site in South Korea, the results successfully identified localized high-risk zones while mitigating the overestimation typical of VS -only approaches. The proposed method offers a applicable across contrasting site conditions for probabilistic liquefaction mapping, demonstrating strong applicability in regions with limited borehole coverage and composite stratigraphic settings. It provides both scientific insight into subsurface heterogeneity and a practical tool for performance-based seismic hazard assessment and geotechnical risk management.

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