** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its society members.
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Review
Solid earth sciences
202308202308
The nature of the Pacific plate as subduction inputs to the northeastern Japan arc and its implication for subduction zone processes
Fujie G, Kodaira S, Obana K, Yamamoto Y, Isse T, Yamada T, No T, Nakamura Y, Miura SGou Fujie, Shuichi Kodaira, Koichiro Obana, Yojiro Yamamoto, Takehi Isse, Tomoaki Yamada, Tetsuo No, Yasuyuki Nakamura, Seiichi Miura
Incoming oceanic plate, Oceanic crust, Controlled-source seismic survey, Japan Trench, Outer rise, Tohoku earthquake
(left) Map of the study area. Red lines show multi-channel seismic (MCS) reflection survey lines and white circles represent Ocean Bottom Seismometers (OBSs) deployed along some of survey lines to obtain wide-angle seismic reflection and refraction data. (right) Map of the crustal thickness in two-way time derived from all the MCS lines, showing notable regional variations.
Devastating megathrust earthquakes and slow earthquakes both occur along subducting plate interfaces. These interplate seismic activities are strongly dependent on the nature of the plate interface, such as the shape of the plate interface and the materials and physical conditions along the plate interface. The oceanic plate, which is the input to the subduction zone, is the first order control on the nature of the plate interface. To reveal the nature of the subduction inputs to the northeastern Japan arc, we have conducted large-scale controlled-source seismic surveys of the northwestern part of the oceanic Pacific plate. The obtained seismic data have revealed (1) oceanic plate structural evolution caused by plate bending prior to subduction, suggesting the promotion of the oceanic plate hydration; (2) spatial variation of the oceanic plate structure, such as variations in the thickness of sediment and crust; (3) that the spatial variations are caused by both ancient plate formation processes and more recent volcanic activities; and (4) that spatial variations of the nature of the subduction inputs show good correlation with the along-strike variations in the seismic structure and seismic activities after subduction, including the coseismic slip distribution of the 2011 Tohoku earthquakes and the structural differences between the northern and the southern Japan Trench. These observations indicate that the incoming oceanic plate structure is much more spatially variable than previously thought and also imply that the spatial variation of the subduction inputs is a key controlling factor of the spatial variation of various processes in subduction zones, including interplate seismic activities and evolution of the forearc structure.
