Investigation of seafloor displacement, submarine landslide and sediment dynamics related to the 2011 Magnitude 9.0 Tohoku-Oki Earthquake along the Japan Trench, and ROV operations to ocean bottom instruments and observatories
Final Report Abstract
The giant Mw 9.0 Tohoku‐Oki earthquake caused seafloor displacements, triggered large submarine slumps and turbidity currents. Repeated bathymetric surveys revealed that changes in seafloor morphology are restricted to an area east of the epicenter (~38°N), where bathymetry anomalies of ± 50 m have been observed. Groundthruthing this structure by sediment coring revealed that the changes in seafloor morphology were indeed related to the Tohoku‐Oki earthquake. However, the structural changes were not caused by a submarine landslide, but by a large deep‐seated rotational slump. The dimensions of seafloor deformation, compared to (1) the shallow near‐trench earthquake rupture area and (2) the water depth of >7 km, is relatively small and may not have contributed significantly to tsunami generation. A more striking result, however, is that the forward growth of the prism and seaward advance of the deformation front by 2‐3 km can occur, episodically, within a single event during a period of seconds to minutes. Additionally, the creation of seafloor topography in the trench axis affects trench sedimentation patterns, which in turn, and on geologic time scales, may have further implications for the evolution of the trench and shallow‐most part of the seismogenic plate boundary system. Moreover, the deposits of the turbidity currents triggered by the 2011 Tohoku‐Oki earthquake have been identified in several records in the deep Japan Trench and along the continental slope. It has been observed that the sedimentary succession within the depression of the Japan Trench contains further prominent turbidite sequences, recording the earthquake activity along the Japan Trench subduction zone in the past. For example, the sedimentary fingerprint of the ancient AD 896 Jogan event (~Mw 8.6), suggested to be a predecessor of the Tohoku‐Oki event has been identified widespread along the Trench. It is the first time that turbidite‐based paleoseismological studies have been conducted in the Japan Trench setting, and highlights the suitability of this approach in this setting, in order to reconstruct the recurrence interval of large earthquakes, also beyond written historical documents. The scientific work onboard RV SONNE cruise was documented by a film crew of Radio Bremen/ARTE. Short film sequences have been shown directly after the cruise in the ARD‐Tagesthemen and local television programs of Radio Bremen. The entire documentation (52 minutes) of the cruise and post‐cruise sample analyses has been shown on ARTE on 28.02.2013 as “Expedition Tsunami ‐ Auf den Spuren einer Katastrophe”. Moreover, several national and international print‐ and online magazines, radio stations and television made reports on the cruise, like e.g. the Japanese television NHK, French press agency AFP, Nature News Blog, ZEIT‐online and Deutschlandfunk.
Publications
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(2013): A slump in the trench: Tracking the impact of the 2011 Tohoku‐Oki earthquake. Geology, 41(8): 935‐938
Strasser, M., Kölling, M., dos Santos Ferreira, C., Fink, H.G., Fujiwara, T., Henkel, S., Ikehara, K., Kanamatsu, T., Kawamura, K., Kodaira, S., Römer, M., Wefer, G. and the R/V Sonne Cruise SO219A and JAMSTEC Cruise MR12‐E01 scientists
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(2014): Evidence for Mass Transport Deposits at the IODP JFAST‐Site in the Japan Trench, In: Krastel et al (Eds.) Submarine Mass Movements and Their Consequences. Advances in Natural and Technological Hazards Research 37. Springer International Publishing, pp. 33‐43
Fink, H.G., Strasser, M., Römer, M., Kölling, M., Ikehara, K., Kanamatsu, T., Dinten, D., Kioka, A., Fujiwara, T., Kawamura, K., Kodaira, S., Wefer, G. and the R/V Sonne Cruise SO219A Cruise Participants
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2014. Report and preliminary results of R/V SONNE Cruise SO219A, Tohoku‐Oki‐Earthquake ‐ Japan Trench, Yokohama ‐ Yokohama, 08.03.2012 ‐ 06.04.2012. Berichte, MARUM – Zentrum für Marine Umweltwissenschaften, Fachbereich Geowissenschaften, Universität Bremen, No. 301, 83 pages, Bremen
Wefer, G., Strasser, M., Besuden, E. and Büttner, H., Diekamp, V., Dinten, D., dos Santos Ferreira, C., Fink, H., Franke, P., Fujiwara, T., Geprägs, P., Ikehara, K., Ishitsuka, K., Kanamatsu, T., Kawamura, K., Kimura, T., Kioka, A., Kitada, K., Klar, S., Kölling, M., Kopiske, E., Mai, H. A., Marcon, Y., Meinecke, G., Meyer, P., Osada, Y., Podszun, L., Ratmeyer, V., Renken, J., Römer, M., Sato, T., Schmidt, W., Seiter, C., Wangenheim, L., Zarrouk, M.
