Estimation of the high-resolution Moho discontinuity beneath the Korean peninsula by receiver function analysis

Receiver functions derived from teleseismic events are sensitive to subsurface structural effects beneath a seismic station and are therefore useful for estimating crustal thickness. More than 300 seismometers have been installed on the Korean Peninsula since the 2016 Gyeongju earthquake (ML 5.8), the largest instrumentally recorded earthquake in the region. This monitoring environment is suitable for obtaining high-resolution estimates of Moho depth and Vp/Vs ratios, considering the spatial resolution of receiver function analysis. Receiver functions were computed from 2,361 teleseismic events (Mw 5.5–7.0; epicentral distances of 30°–90°) recorded between January 2003 and January 2024. Azimuthal corrections were applied to the receiver functions by searching for the direction that minimizes energy on the transverse component. For specific stations, temporal variations in the azimuth angle were observed. Consequently, a moving-average technique was applied, and only periods with stable azimuth angles were used for the analysis. Subsequently, the Moho depth and Vp/Vs ratio were determined at the location of the maximum stacking amplitude in the H–κ domain. For stations exhibiting double peaks in the H–κ domain, normalized receiver functions were clustered based on the sum of Euclidean distances, and the H–κ analysis was repeated. The derived Moho depths indicate that crustal thickness is thinnest (~30 km) beneath the Gyeonggi Massif and thickest (~34 km) beneath the Yeongnam Massif. In the eastern Korean Peninsula, the observed crustal thickness is inconsistent with isostatic equilibrium, suggesting the influence of dynamic-topography-related downwelling. A Moho depth exceeding 34 km is also observed in the southwestern Okcheon Belt. The Gyeonggi Massif shows the lowest Vp/Vs ratio (1.72), whereas higher values (>1.78) occur in the eastern Gyeongsang Basin and the northeastern Gyeonggi Massif. High Vp/Vs ratios are interpreted to be related to the emplacement of Cretaceous Bulguksa granites.