Along‐trench variations in the seismic structure of the incoming Pacific plate at the outer rise of the northern Japan Trench

• Published in: Geophysical research letters Vol. 43; no. 2; pp. 666 - 673
• Main Authors: Fujie, Gou, Kodaira, Shuichi, Sato, Takeshi, Takahashi, Tsutomu
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.01.2016
• Subjects: Crack propagation; Fracture mechanics; Marine; Ocean models; Oceanic crust; oceanic plate; Oceanography; outer rise; Plate tectonics; Plates (structural members); Propagation; pseudofault; Scars; Seismic engineering; Seismic surveys; Seismology; Transportation; Trenches; Vp/Vs ratio; Water content; wide‐angle seismic survey; Pacific Plate; INW, Pacific, Japan Trench
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL067363

To investigate along‐trench variations in the seismic structure of the incoming oceanic plate and their effect on water transportation by the oceanic plate, we conducted a wide‐angle seismic survey of a trench‐parallel transect 270 km long on the outer rise of the northern Japan Trench. The resulting seismic structure models show that the central part of the transect is characterized by rough topography, thick oceanic crust, low seismic velocities, and high Vp/Vs ratios, suggesting pervasive fracturing and high water content (hydration) there. These observations are consistent with the presence of an ancient fracture zone associated with ridge propagation. The trenchward extension of this fracture zone corresponds to an area of low interplate seismicity, low seismic velocities, and high Vp/Vs ratio around the depth of the subduction interface. Our results suggest that this ancient scar on the oceanic plate influences along‐trench variations in interplate seismic coupling through its effect on water transportation. Key Points Seismic structure study on the outer rise of Japan Trench showed along‐trench structural variations Observed variations can be explained by the presence of an ancient fracture zone The ancient scar on the oceanic plate determines the water transportation into the subduction zone