10:00 AM - 10:15 AM
[SCG59-05] Crustal structure in the margin of the northern Japan Sea back-arc basin off NW Hokkaido deduced from the seismic survey
Keywords:Crustal structure, Japan Sea, arc-back-arc basin
To obtain the crustal structure, we conducted the active-source seismic survey using ocean bottom seismographs (OBSs) and multi-channel streamer (MCS) in the margin of the northern Japan Sea ranging from the Japan Basin to the coastal area off the northwestern Hokkaido and in the Ishikari Bay in 2017. The seismic survey has 2 lines; one was conducted from the Japan Basin, the Okushiri Ridge, the Kamui Trough to the Ishikari Basin off Rumoi in the northwestern Hokkaido using 39 OBSs, 1 OBN set, and an air-gun array system (max., 10,000 cu. inch) and MCS system, and the other was conducted from the Ishikari Basin to Ishikari Bay using 19 OBSs and an air-gun array system (max., 5,300 cu. inch).
In record sections of several OBSs, not only the first arrived phases but also later phases reflected from interfaces in the crust and uppermost mantle are visible. Also, the MCS profile clearly images the sedimentary layer and the undulations of the basement. The crustal structure in the Japan Basin is similar to the typical oceanic crust (e.g., White et al., 1992). From the basin, the Okushiri Ridge, Kamui Trough to Ishikari Basin, the crustal thickness and the P-wave velocity distribution have a variation. Particularly, these variations are large between the Okushiri Ridge and Kamui Trough. On the other hand, from the Kamui Trough to the coastal area and in the Ishikari Basin, the upper crust has a P-wave velocity of 5.4-6.2 km/s corresponding to the continental upper crust.