Characteristics of Magnetic Fabrics in Mass Transport Deposits in the Nankai Trough Trench Slope, Japan
Submarine landslides are a potential risk to coastal areas all over the world. Studies of mass transport deposit (MTD) contribute to our understanding of the nature and process of submarine landslides. Scientific drilling provides material containing geological records of past landslide events. However, MTDs may not always be uniquely discernible by visual inspection. We applied magnetic fabric analysis to the drilled cores to examine the potential of magnetic fabrics for use in identifying MTDs. Among the sites drilled in the framework of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), in Japan, of the Integrated Ocean Drilling Program (IODP), multiple occurrences of MTDs were observed in the recovered cores. We focused on the slope sediments in the footwall of the megasplay fault at Sites C0008 and C0018. The shape parameter (T) and the orientation of the axes of magnetic ellipsoids are distinctively scattered in MTDs at Site C0018. Downward increments in the lineation parameter (L) near the bottom of the MTDs may result from shear localization near the basal sliding plane. This, in combination with visual observation, suggests cohesive mass flow. By contrast, the results from sediments previously described as mass transport complexes at Site C0008 showed the opposite trend, suggesting a different process during transportation; i.e. the mass transport body evolved to become a complete debris flow. Our results show that magnetic fabric analysis is potent for describing MTDs and their internal structures. This finding may extend the methodology for describing MTDs and add to the discussion of the dynamic formation process.
KeywordsSubmarine landslide D/V Chikyu NanTroSEIZE Accretionary prism Megasplay fault IODP Expeditions 316 and 333
This research used samples and data provided by the Integrated Ocean Drilling Program. This work was partially supported by KAKENHI 19GS0211 and 21107001. We thank K. Tsuchida (Marine Works Japan Co. Ltd.) for providing technical support with regard to the AMS measurements. The IODP Expeditions 316 and 333 could not have been completed without the devoted contributions of those involved. Careful review and critical comments by David Völker and Yoshitaka Hashimoto improved this manuscript.
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