Using a method suggested by Yanovskaya, we obtained Rayleigh wave group velocities with a resolution of 1.0o ×1.0o in a period range between 10 and 80 s in and around the Korean peninsula. Both regional and distant earthquake data sets were used together in analysis of group velocities. The resolution of the group velocity maps has been remarkably enhanced by the method, especially in the sparse/non-station region in the northern Korean peninsula. Some qualitative geophysical information was inferred from the group velocity maps. In the East Sea, the slow group velocities at periods longer than 40 s suggest the existence of an oceanic lithosphere at depths of 50-70 km, assuming 4 km/s of S wave velocity at a period of 40 s. On the other hand, a thick lithosphere can be inferred in the continental area from the fast group velocities at periods longer than 50 s. For most periods, the group velocities change rapidly over a short distance of about 200 km across the eastern coast of Korean peninsula, which may suggest a rapid change in the thickness of lithosphere in this area.

Introduction
 Geology and Tectonic Setting
 Data and Method
 Determination of Group Velocity
 Results and Discussion
 Conclusions
 References

• Heeok Jung(Department of Ocean Engineering, Kunsan National University, 1170 Daehangno Kunsan, Korea 54150) Corresponding author
• Yong-Seok Jang(Department of Ocean Engineering, Kunsan National University, 1170 Daehangno Kunsan, Korea 54150)