Geophysical investigation of the Quaternary paleo-earthquake evidence using ERT and MASW surveys: A case study along the Yangsan Fault, SE Korea

This study evaluates the effectiveness of integrating electrical resistivity tomography (ERT) and multi-channel analysis of surface waves (MASW) for detecting Quaternary paleo-earthquake ruptures, with direct applications to engineering geology. We conduct non-invasive geophysical surveys at five sites along the Yangsan Fault system in Southeast Korea where surface ruptures were previously identified through trenching. The integrated approach images electrical resistivity (ρ) and shear wave velocity ( V S ) anomalies, with widths ranging from 9 to 66 m and extending to depths of 20–25 m, significantly exceeding typical trenching capabilities. We classify anomalies into Type 1 (rupture-related) and Type 2 (other geological factors). Type 1 anomalies demonstrate good agreement between the two surveys and are consistently identified adjacent to inferred surface rupture locations. The complementary nature of these methods proves important: ERT effectively detects fluid-filled fractures in sedimentary environments, while MASW identifies mechanically damaged zones even in crystalline rocks where hydraulic barriers limited fluid circulation. We provide baseline geophysical signatures for paleo-earthquake damage zones (ρ: 10–500 Ωm; V S : 150–800 m/s) applicable to similar geological settings globally. This methodology provides a reproducible, cost-effective protocol for fault characterization beneath urban infrastructure where traditional invasive methods are limited, contributing quantitative reference values essential for seismic hazard assessment and foundation design in tectonically active regions. • Integrated ERT–MASW approach establishes baseline geophysical signatures for paleo-earthquake damage zones. • ERT and MASW image subsurface anomalies at depths beyond trenching limits. • Site-specific evidence shows anti-correlation between ρ and Vs in fractured crystalline rocks. • Findings highlight engineering geology applications for urban fault characterization.