5:15 PM - 6:30 PM
[SIT11-P03] Crustal structure and opening process on the back-arc basin in the southwestern margin of the Japan Sea
Keywords:Japan Sea, back-arc basin, crustal structure, opening process
This seismic survey using 54 OBSs and a tuned air-gun array (7,800 cu. inch) was conducted from the continental shelf off Echizen-misaki cape, Fukui Prefcture, Oki Trough, Oki Ridge, Yamato Basin to the Kita-Oki Bank, in the southwestern margin of the Japan Sea. This survey line has about 270 km length. In record sections of several OBSs and land stations, not only the first arrived phases but also later phases reflected from interfaces in the crust and uppermost mantle are visible.
The Oki Ridge has about 20 km of the crustal thickness. The upper part of the crust with P-wave velocity of 5.4-6.2 km/s corresponding to the continental upper crust has about 10 km. This shows that the Oki Ridge may have the character of the continental crust. On the other hand, the crust in the Yamato Basin and Oki Trough has 13 and 15 km thick, respectively. These are thinner than that the Oki Ridge. The Yamato Basin and Oki Trough do not have the character of the typical continental crust. The upper part of the crust in the continental shelf area has 10 km with a lateral variation. This crust may have the continental crustal type because the P-wave velocity distribution is similar to that of the continental upper crust in Korean Peninsula (Cho et al., 2006). And, this variation may correspond to the distribution of the deformation. This crustal structure in the southwestern margin of the Japan Sea off Fukui differs from that in the northern part of the eastern margin (No et al., 2006). This might show that the southwestern margin off Fukui is different from the northern one on the back-arc opening process.