Abstract: A new technique of simultaneous inversion for 3-D seismic velocity structure using Pg, Sg, PmP, SmS, Pn and Sn arrival times of 32 events with 404 seismic rays are inverted for locations and crustal structure. These methods are applied to the Central and Southern parts of the Korean Peninsula. 3-D seismic velocity tomography including 8-sections from earth surface to the Moho, 13 profiles along latitude and longitude, and depth distribution was determined. The velocities fluctuate strongly in the upper crust. There are big an-isotrophy bodies near north of Seoul in the upper crust, implying that they may be related to the Chugaryong Rift Zone. They found that there were low velocity bodies beneath the Kyongiu area at the depth 10-15 km, the Youngwol area at the depth 10 km, and the Hongsung area at the depth 5-10 km, indicating that they must be due to the earthquake sources of Kyongju (6/25/1997), Youngwol (12/13/1996), and Hongsung (10/07/1978), respectively. These results are also well consistent with Bouguer gravity anomalies showing very complex and low velocity bodies beneath the Chugaryung Rift Valley and/or deep fault systems and the earthquake hrpocenters, respectively.