Crust and upper mantle structures of the region between Korea and Taiwan by surface wave dispersion study

Abstract

We have investigated the crust and upper-mantle shear velocity structures of the region between Korea and Taiwan by analyzing the path-averaged group-velocity dispersion characteristic curves derived from surface waves. The depth of the East China Sea between Korea and Taiwan is mostly less than 100 m. We selected data from earthquakes of magnitude greater than 6.0 that occurred in Taiwan from 1999 to 2007. We used data from 219 seismograms recorded at three-component broadband seismic stations in South Korea. We also used data from 19 events from South Taiwan for our study of crust and upper-mantle shear-wave velocity structures. By examining the wave period between 5 s and 100 s, the group velocities of Rayleigh waves and Love waves were inverted jointly. These waves were computed using the multiple filter technique (MFT) and using the single-station method. The inversion results from the dispersion curves provide a detailed one-dimensional velocity profile of the East China Sea. The main features of the derived velocity profile are: 1) the unconsolidated sediments surface layer shows a fairly low shear-wave velocity value; 2) the crustal shear-wave velocity increases from 2.92 km/s to 3.90 km/s, as the depth increases to 30 km; 3) shear-wave velocities in the uppermost mantle exhibit a clear low-velocity zone between 50 km and 90 km, with the velocity varying between 4.33 km/s and 3.99 km/s; 4) the variation in shear-wave velocities in the upper mantle increases with increasing depth. We can infer that the crustal structure of the study area is continental crust. The average Moho depth is 30 km beneath the East China Sea.