5:15 PM - 7:15 PM
[SCG59-P02] Sedimentological and geochemical analysis of piston cores from the outer rise of the Japan Trench
Keywords:Japan Trench, outer rise earthquake, turbidite
The outer rise is a key region where extensional normal faulting occurs as the oceanic plate bends before subducting beneath the overriding plate. Large-scale outer rise earthquakes are known to be triggered by major megathrust earthquakes. However, since the 2011 Tohoku earthquake (Mw 9.0), no significant outer rise earthquakes have been recorded. Despite extensive studies conducted in the Japan Trench, the mechanisms driving outer rise earthquakes, their recurrence intervals, and their sedimentary records remain poorly understood. Understanding these processes is essential for improving assessments of seismic hazard, especially tsunami hazard in subduction zones.
The sediments in the trench region serve as an important archive of seismic activity, particularly through turbidite layers formed by earthquakes and submarine landslides. This research aims to reconstruct the history of outer rise earthquakes, providing insights into their recurrence and underlying processes. Sedimentary records of grabens in the outer rise are expected to help distinguish outer rise earthquakes from megathrust earthquakes and improve our understanding of how stress accumulation and release occur within the subduction system.
In this study, piston cores from R/V Shinseimaru KS-15-3 cruise are used for sedimentological and geochemical analyses, including Muti-Sensor Core Logger (MSCL), CT scanning, and ITRAX X-ray fluorescence core scanning. As a result, multiple event deposits possibly caused by large earthquakes were identified. The findings from PC01 are as follows: most of the core consists of structureless layers (could be homogenite) and laminae with well-developed bioturbation. Laminated layers are relatively more abundant in the shallower sections of the core but are less frequent in the deeper sections. ITRAX data revealed distinct positive peaks of Ca, Mn, and Fe at the base of the laminated layers identified through CT image analysis. This suggests that the laminated layers and the overlying structureless layers represent event deposits formed by a series of depositional processes over a short period. The results from other cores also will be shown in the presentation.
The sediments in the trench region serve as an important archive of seismic activity, particularly through turbidite layers formed by earthquakes and submarine landslides. This research aims to reconstruct the history of outer rise earthquakes, providing insights into their recurrence and underlying processes. Sedimentary records of grabens in the outer rise are expected to help distinguish outer rise earthquakes from megathrust earthquakes and improve our understanding of how stress accumulation and release occur within the subduction system.
In this study, piston cores from R/V Shinseimaru KS-15-3 cruise are used for sedimentological and geochemical analyses, including Muti-Sensor Core Logger (MSCL), CT scanning, and ITRAX X-ray fluorescence core scanning. As a result, multiple event deposits possibly caused by large earthquakes were identified. The findings from PC01 are as follows: most of the core consists of structureless layers (could be homogenite) and laminae with well-developed bioturbation. Laminated layers are relatively more abundant in the shallower sections of the core but are less frequent in the deeper sections. ITRAX data revealed distinct positive peaks of Ca, Mn, and Fe at the base of the laminated layers identified through CT image analysis. This suggests that the laminated layers and the overlying structureless layers represent event deposits formed by a series of depositional processes over a short period. The results from other cores also will be shown in the presentation.