14:00 〜 14:15
[SCG55-25] 北海道東部沖におけるタービダイト古地震学
キーワード：古地震学、タービダイト、古地磁気永年変化、火山灰、千島海溝
To investigate paleoseismology along the Kuril Trench, we conducted several cruises offshore east Hokkaido, including MR17-16, KS-19-12, KM22-05, MR22-04, MR24-02, KS-24-7, and MR24-05. To ensure that each site within the slope and trench basins was suitable for paleoseismic coring, detailed surveys were performed, including bathymetry, Sub-Bottom Profiles (SBP), and Single-Channel Seismic reflection (SCS). A total of 28 piston cores and one giant piston core were retrieved from the Kuril Slope, Kuril Trench floor, and outer rise, at water depths ranging from 3,324 to 7,590 meters. Core description, Multi-Sensor Core Logger (MSCL) measurements, and X-ray Computed Tomography (X-CT) data acquisition have been completed. Age models will be developed using tephrochronology (volcanic ashes), Paleomagnetic Secular Variation (PSV), and radiocarbon dating of bulk organic carbon. Some core analyses, including paleomagnetic and geochemical measurements, are still ongoing.
Preliminary lithological results suggest that the study area can be categorized into four distinct zones: (1) Northeast of Kushiro Canyon: The slope basins northeast of Kushiro Canyon contain thin turbidites. Lithological observations indicate that these cores primarily consist of hemipelagic mud interbedded with turbidites, ranging from very fine sand to coarse sand. Event layers include both volcanic ash and turbidites, with individual event thicknesses ranging from about 5 to 30 cm. (2) Southwest of Kushiro Canyon: This area is characterized by slumping and chaotic deposits. Thick turbidite mud layers exhibit fluidized and distorted structures, with erosional features observed at the base of the coarse-grained layers. (3) Kuril Trench Floor: Thick turbidites (reaching up to 4 meters), are present in the trench basin and can likely be correlated along the Kuril Trench. This is likely due to the perpendicular connection between the mouth of Kushiro Canyon and the Kuril Trench, which can be transported of terrestrial and shallow-marine sediments into the deep sea via the canyon. (4) Outer Rise: The lithology of the outer rise is primarily composed of grayish-olive, bioturbated diatomaceous silt interspersed with several volcanic ashes. These preliminary findings provide valuable insights into turbidite recurrence for paleoseismology and contribute to a better understanding of sedimentation patterns offshore east Hokkaido.
Preliminary lithological results suggest that the study area can be categorized into four distinct zones: (1) Northeast of Kushiro Canyon: The slope basins northeast of Kushiro Canyon contain thin turbidites. Lithological observations indicate that these cores primarily consist of hemipelagic mud interbedded with turbidites, ranging from very fine sand to coarse sand. Event layers include both volcanic ash and turbidites, with individual event thicknesses ranging from about 5 to 30 cm. (2) Southwest of Kushiro Canyon: This area is characterized by slumping and chaotic deposits. Thick turbidite mud layers exhibit fluidized and distorted structures, with erosional features observed at the base of the coarse-grained layers. (3) Kuril Trench Floor: Thick turbidites (reaching up to 4 meters), are present in the trench basin and can likely be correlated along the Kuril Trench. This is likely due to the perpendicular connection between the mouth of Kushiro Canyon and the Kuril Trench, which can be transported of terrestrial and shallow-marine sediments into the deep sea via the canyon. (4) Outer Rise: The lithology of the outer rise is primarily composed of grayish-olive, bioturbated diatomaceous silt interspersed with several volcanic ashes. These preliminary findings provide valuable insights into turbidite recurrence for paleoseismology and contribute to a better understanding of sedimentation patterns offshore east Hokkaido.