One Dimensional versus Three-Dimensional Crustal Velocity Models for the Korean Peninsula

The current study is intended to determine the crustal velocity structure of the Korean peninsula to help obtain precise earthquake locations. To achieve these goals, travel-time analysis of Korean Meteorological Administration (KMA) waveform data was performed for data from 2001 through 5/2008. Waveform data from 270 local and regional earthquakes published by KMA were used in the current study. The earthquakes were recorded by 119 stations (velocity and accelerometers) located throughout the southern Korean peninsula. The lack of seismicity is typical for the metamorphic crust of the Korean peninsula which produces and average of 30-35 events per year. Nevertheless, ray coverage was sufficient to perform 3-D joint inversion for velocity structure and hypocenter locations. All phase data were hand-picked and preliminary hypocenter locations were estimated using a 1-D velocity model (IASPEI 91). Additionally, regional 1-D velocity models for crust and upper mantle were derived for P- and S-wave velocities and their uncertainties determined. The standard deviations were of magnitude 0.01 or less indicating a good fit of a 1-D model for the Korean peninsula. Static corrections for each seismic station were subsequently calculated to remove any bias introduced by near-surface inhomogeneities in the vicinity of the stations. Although the three-dimensional velocity inversion reduced the variance between observed and modeled travel-times by more than 70 %, the resulting velocity structure reveals a homogeneous distribution which appears, to a large degree, uncorrelated to the tectonics of the peninsula. Crustal velocities of 6.2 km/s and 3.6 km/s for P- and S-waves, respectively, were obtained for the upper crust, while these values increase beneath 25 km to 7 km/s for P- and 4.3 km/s for S-waves. Mantle velocities are encountered below 32 km depth reaching 8.5 km/s and 4.8 km/s for P- and S-waves, respectively. Comparison of hypocenter locations based on 1-D and 3-D inversions indicate shifts to slightly deeper locations for the latter method. Despite these slight differences, the overall result corroborates an acceptable fit of a 1-D velocity model to the crustal structure of the Korean peninsula.