Shallow-depth shear wave velocity structure of the Southern Korean Peninsula obtained from two crustal-scale refraction profiles

Abstract

Short-period Rayleigh waves from the two crustal-scale seismic refraction profiles, KCRT2002 and KCRT2004, were analyzed to determine the shear wave velocity and attenuation structure of the uppermost crust in different tectonic regions of the Korean peninsula and to examine if this can be related to the surface geology and tectonics of the study area. The refraction profiles were obtained using large explosive sources along a 294-km WNW–ESE line in 2002 and a 335-km NNW–SSE line in 2004. The two refraction profiles, recorded on 2-Hz portable seismometers, contained Rayleigh waves in the period range of 0.2 to 1.2 s, and the distance range up to 30–60 km from the sources. The profiles, which traverse four tectonic regions (Gyeonggi massif, Okcheon Fold belt, Yeongnam massif and Gyeongsang basin), were divided into twelve subsections based on the tectonic boundary and lithology. We obtained shear wave velocity models in the upper 1.5 km of the crust. The average shear wave velocity of the twelve subsections increases from ~ 2.4 km/s at the surface to ~ 3.2 km/s at 1.5 km depth. Overall, the shear wave velocities for the Okcheon fold belt and Gyeongsang basin are lower than those for the Gyeonggi and Yeongnam massifs by ~ 0.3 km/s. Shear wave velocity differences also exist among the subsections within the same tectonic region when there are distinct differences in lithology. We obtained the values of Q β − 1 in the upper 0.6 km. Q β − 1 for the Okcheon fold belt (~ 0.025) is approximately twice larger than Q β − 1 for the massif areas (~ 0.012). The low shear wave velocity and high attenuation for the Okcheon fold belt seem to be related to the rock types of the area, which are mostly conglomerates and phyllites.