Evidence for Mass Transport Deposits at the IODP JFAST-Site in the Japan Trench
Several studies indicate that the 2011 Tohoku-Oki earthquake (Mw 9.0) off the Pacific coast of Japan has induced slip to the trench and triggered landslides in the Japan Trench. In order to better understand these processes, detailed mapping and shallow-coring landslides at the trench as well as Integrated Ocean Drilling Program (IODP) deep drilling to recover the plate boundary décollement (Japan Trench Fast Earthquake Drilling Project, JFAST) have been conducted. In this study we report sediment core data from the rapid response R/V SONNE cruise (SO219A) to the Japan Trench, evidencing a Mass Transport Deposit (MTD) in the uppermost section later drilled at this JFAST-site during IODP Expedition 343. A 8.7 m long gravity core (GeoB16423-1) recovered from ∼7,000 m water depth reveals a 8 m sequence of semi-consolidated mud clast breccias embedded in a distorted chaotic sediment matrix. The MTD is covered by a thin veneer of 50 cm hemipelagic, bioturbated diatomaceous mud. This stratigraphic boundary can be clearly distinguished by using physical properties data from Multi Sensor Core Logging and from fall-cone penetrometer shear strength measurements. The geochemical analysis of the pore-water shows undisturbed linear profiles measured from the seafloor downcore across the stratigraphic contact between overlying younger background-sediment and MTD below. This indicates that the investigated section has not been affected by a recent sediment destabilization in the course of the giant Tohoku-Oki earthquake event. Instead, we report an older landslide which occurred between 700 and 10,000 years ago, implying that submarine mass movements are dominant processes along the Japan Trench. However, they occur on local sites and not during each megathrust earthquake.
KeywordsJapan Trench Tohoku-Oki earthquake IODP-JFAST Mass-transport deposit Physical properties Geochemistry
We thank captain and crew of R/V SONNE for onboard assistance during cruise SO219A in 2012. The cruise and the research leading to this study were funded by the German Bundesministerium für Bildung und Forschung (BMBF) and the Deutsche Forschungsgemeinschaft (DFG-project WE 992/58-1) and was supported by the DFG-Research Center/Cluster of Excellence “The Ocean in the Earth System”. Vera Lukies is kindly thanked for lab assistance with the MSCL Core Scanner at MARUM-Center for Marine Environmental Sciences, University of Bremen, Germany. We further acknowledge B. McAdoo and J. Geersen for their constructive reviews. All data are available via the database Pangaea (http://www.pangaea.de).
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