5:15 PM - 6:30 PM
[SCG45-P05] Multibeam bathymetric and single-channel seismic surveys of the Mid-Slope Terrace off Sanriku in the northern Japan Trench
Keywords:Japan Trench, Mid-Slope Terrace, Multibeam Bathymetric Survey, Single-Channel Seismic Reflection Survey
We conducted JAMSTEC R/V Kaimei KM19-03 cruise in 2019. During the research cruise, we carried out mulibeam bathymetry and single-channel seismic reflection surveys in the Mid-Slope Terrace (MST) off Sanriku in the northern Japan Trench (39-40°N).
The Mid-Slope Terrace (MST) is a flat to gentle slope with an average slope angle of about 0-2°. The MST is situated at a depth of 4000-6000 m and is a slope break between the steep upper and the lower trench landward slopes. The MST has the regional variation in the depth and width of the terrace from south to north along the trench. It may reflect regional differences in the dynamics of the upper plate in the subduction zone exerting on the landward slope, or differences in the stage of the tectonic evolution. Our study area is located at a depth of 4600-4800 m and has one of the largest east-west (trench to landward) widths of the MST, about 20 km, and is a region where the MST is well developed.
The Kaimei bathymetric data were obtained using a KM122 multibeam echo sounder. And also, cross-track bathymetric data were collected using a KM122 echo sounder by the German R/V Sonne SO251A cruise and using a SeaBeam 3012 echo sounder by the JAMSTEC R/V Mirai MR16-09 Leg 4 cruise, respectively. These bathymetric data have higher resolution compared with previous data, because the data were measured using recent echo sounders. Therefore, the complex topography of co-existing slope failures, steep scarps, minor ridges, and small sedimentary basins covering the MST (e.g., Sasaki, 2003) were mapped more clearly.
The slope failures suggest erosion and landslides, the steep scarps suggest faulting, the minor ridges suggest uplift, and the small sedimentary basins suggest subsidence. The single-channel reflection record shows that the thickness of sediment basin is about 75 m even in the thickest deposits. Considering the sedimentation rate of about 36-109 cm/kyr estimated from sediment cores obtained by piston coring in the sedimentary sub-basin in the study area, the sedimentary sub-basin on the MST has been formed within about 70-200 ka. The sedimentary layers located on the western and landward sides of the MST are inclined toward the landward in the lower part of the layer, suggesting that the western side of the MST has been tilted toward the landward while subsiding.
In this paper, we will describe features and relations of the seafloor and the sub-surface structures, and discuss the tectonic evolution of the upper plate in the Japan Trench.
We thank the officers and crew of R/V Kaimei for outstanding professionalism and dedication that made the cruise successful. We are indebted to marine technicians from Nippon Marine Enterprises, M. Takaesu, Y. Ohwatari, H. Iwamaru, and M. Morioka for their invaluable help to acquire data at sea.
Figure: Bathymetry of the Mid-Slope Terrace off Sanriku in the northern Japan Trench. Contour interval is 50 m.
The Mid-Slope Terrace (MST) is a flat to gentle slope with an average slope angle of about 0-2°. The MST is situated at a depth of 4000-6000 m and is a slope break between the steep upper and the lower trench landward slopes. The MST has the regional variation in the depth and width of the terrace from south to north along the trench. It may reflect regional differences in the dynamics of the upper plate in the subduction zone exerting on the landward slope, or differences in the stage of the tectonic evolution. Our study area is located at a depth of 4600-4800 m and has one of the largest east-west (trench to landward) widths of the MST, about 20 km, and is a region where the MST is well developed.
The Kaimei bathymetric data were obtained using a KM122 multibeam echo sounder. And also, cross-track bathymetric data were collected using a KM122 echo sounder by the German R/V Sonne SO251A cruise and using a SeaBeam 3012 echo sounder by the JAMSTEC R/V Mirai MR16-09 Leg 4 cruise, respectively. These bathymetric data have higher resolution compared with previous data, because the data were measured using recent echo sounders. Therefore, the complex topography of co-existing slope failures, steep scarps, minor ridges, and small sedimentary basins covering the MST (e.g., Sasaki, 2003) were mapped more clearly.
The slope failures suggest erosion and landslides, the steep scarps suggest faulting, the minor ridges suggest uplift, and the small sedimentary basins suggest subsidence. The single-channel reflection record shows that the thickness of sediment basin is about 75 m even in the thickest deposits. Considering the sedimentation rate of about 36-109 cm/kyr estimated from sediment cores obtained by piston coring in the sedimentary sub-basin in the study area, the sedimentary sub-basin on the MST has been formed within about 70-200 ka. The sedimentary layers located on the western and landward sides of the MST are inclined toward the landward in the lower part of the layer, suggesting that the western side of the MST has been tilted toward the landward while subsiding.
In this paper, we will describe features and relations of the seafloor and the sub-surface structures, and discuss the tectonic evolution of the upper plate in the Japan Trench.
We thank the officers and crew of R/V Kaimei for outstanding professionalism and dedication that made the cruise successful. We are indebted to marine technicians from Nippon Marine Enterprises, M. Takaesu, Y. Ohwatari, H. Iwamaru, and M. Morioka for their invaluable help to acquire data at sea.
Figure: Bathymetry of the Mid-Slope Terrace off Sanriku in the northern Japan Trench. Contour interval is 50 m.