Crustal Velocity Structure and Unresolved Isostatic Uplift in Gangwon Province, South Korea, from Joint inversion analysis of Receiver Functions

The northeastern part of South Korea, Gangwon Province, is closely connected to major tectonic activities of the Korean Peninsula, such as the formation of the Taebaek Mountain ranges and the opening of the East Sea (Sea of Japan). Therefore, analyzing the velocity structure of Gangwon Province can provide insights into the tectonic history of the Korean Peninsula. We calculated receiver functions for 96 broadband and accelerometer seismic stations using 369 teleseismic event data (Mw ≥ 5.8, with epicentral distances from 30° to 90°), recorded between March 18, 2019, and May 31, 2024. We estimated Moho depth and Vp/Vs ratio in Gangwon Province using H-k stacking method, and we obtained 1-D S-wave crustal velocity models for each stations using joint inversion of receiver functions and surface-wave dispersion. Moho depth and Vp/Vs ratios derived from H-k stacking method ranged from 23.0 to 35.6 km and 1.68 to 1.85, respectively. Most stations located along the eastern coast exhibited relatively shallow Moho depth and high Vp/Vs ratios. From the 1-D S-wave crustal velocity models obtained using the joint inversion, we identified velocity inversion layer and mid-crustal discontinuities beneath several stations. The Moho depth was determined as the layer with an S-wave velocity exceeding 4.0 km/s and the largest velocity gradient, resulting in depths ranging from 23.9 to 35.7 km, which are consistent with the Moho depths obtained from H-k stacking. The trend of Moho depth distribution in Gangwon Province is shallow along the coast and deepens through the Taebaek mountain ranges, but it does not align with Airy isostasy. Accordingly, We calculated residual topography, and the result suggests the possibility of additional isostatic uplift along the Taebaek Mountain ranges and the eastern coast.