VP/VS ratios in the upper crust of the southern Korean Peninsula and their correlations with seismic and geophysical properties

Abstract

The P and S velocity ratio, VP/VS, is a seismic property that is convertible to Poisson’s ratio, a widely-analyzed physical property of elastic materials. The lateral variation in the VP/VS ratios of the upper crust of the southern Korean Peninsula is investigated based on the travel times of P and S waves of local events with epicentral distances of 50km or less and focal depths of 25km or less. The dense seismic networks in the Korean Peninsula allow us to investigate the regional variation of VP/VS ratios. These VP/VS ratios are estimated to be 1.60–1.91 with an average of 1.69. The VP/VS ratios are as high as 1.73–1.91 in the Gyeongsang basin, Jeju island and offshore region of the eastern Okcheon belt, but have relatively low values of 1.64–1.72 in Precambrian massif regions. The stability of the VP/VS ratios is tested with randomly-resampled travel-time data, the results of which suggest nearly constant VP/VS ratios with increasing depth in the upper crust. The influences of plausible errors on origin times and arrival times are quantified to verify the VP/VS estimates. The VP/VS ratios are correlated with geological and tectonic structures. Comparisons with known seismic and geophysical properties suggest that structural features observed on the surface may extend at least to the mantle lid.