<p>Passive margins offer valuable insights into the interplay between tectonic processes and surface elevation, as topographic signals are often preserved under long-term tectonic quiescence. Gangwon Province, located in the mid-eastern Korean Peninsula, exemplifies such a setting, shaped by back-arc opening of the East Sea (Sea of Japan). Here, we present Vp/Vs ratios, residual topography, and high-resolution S-wave crustal velocity models from joint inversion of teleseismic receiver functions and Rayleigh-wave dispersion curves. Our results reveal low S-wave velocities and high Vp/Vs ratios throughout the crust beneath the coastal region, suggesting shallow-reaching thermal effects from mantle upwelling. In contrast, west of the Taebaek Mountain Range, low velocities are confined to the lower crust, and Vp/Vs ratios are relatively low, consistent with thick, felsic crust inhibiting upward thermal propagation. These findings demonstrate how crustal properties modulate the surface and thermal expressions of mantle upwelling, likely caused by edge-driven convection in passive margin settings.</p>