Crustal velocity structure along the Ganghwa-Yeongdeok seismic refraction survey line in South Korea

Along a 300 km survey line of NW-SE direction in the central and northern parts of South Korea crossing four different tectonic structures, the crustal wide-angle reflection and refraction survey was carried out in November 2008. In this survey, portable seismometers were deployed at stations with approximately 500 m of interval and 8 shots were exploded with charge of shots from 250 to 1500 kg. Travel-times of P wave phases (Pg, PmP, Pn, PiP) and S wave phases (Sg, SmS) based on interpretation of 8 record data obtained from this experiment were identified. The result of layered crustal velocity model using forward modeling of 2D ray tracing with P wave phases show that the thickness varies from 30 to 34 km. The crust is thickest in the central part of survey line (34 km) and it becomes shallower at the northwestern (30 km) and southeastern (31km) tips of the survey line. The P wave velocity of the upper crust in southeastern part of survey line was larger than northeaster part in survey line. The mid-crustal velocity discontinuity was identified at depth 20 ± 1 km along the survey line and at depths 10 ± 2 and 15 ± 1 km in limited areas. The P velocity under Moho ranges from 7.8 to 8.0km/s depending on place.