MOHO DEPTH AND CRUSTAL VP/VS VARIATION IN SOUTHERN KOREA FROM TELESEISMIC RECEIVER FUNCTIONS: IMPLICATION FOR TECTONIC AFFINITY BETWEEN THE KOREAN PENINSULA AND CHINA

Abstract

We estimated Moho depths and VP/VS ratios of the crust under 21 broadband stations in southern Korea by using a grid search in the crustal thickness-VP/VS ratio (H-κ) domain. The Moho depth varies from 25.9 km to 32.5 km, and the VP/VS ratio ranges from 1.71 to 1.82 inland. Moho depths in the southernmost area of the Korean Peninsula were estimated shallower than those of the previous results obtained assuming a Poisson solid in the joint analysis of receiver functions and surface-wave dispersion. This southernmost area is roughly in accord with the Yeongnam massif, where relatively high VP/VS ratios of 1.78-1.82 are estimated. On the contrary, comparatively low VP/VS ratio measurements (1.71-1.76) are generally distributed in the Gyeonggi massif, which is located in the central area of the Korean Peninsula. The major factor for the high VP/VS ratios in the Yeongnam massif is thought to be the plagioclase-rich mafic composition of the lower crust rather than partial melting or crustal fluids, because high crustal S-wave velocities are reported in the Yeongnam massif. The mafic composition might have been supplied by the magmatic underplating. From the clearly divided feature of VP/VS ratios in southern Korea and the VP/VS ratio similarities between southern Korea and China, it seems that the Yeongnam massif might be related to the Sino-Korea craton, whereas the Gyeonggi massif is related to the Yangtze craton.