Along-trench structural variation and seismic coupling in the northern Japan subduction zone

Abstract

Large destructive interplate earthquakes, such as the 2011 M w 9.0 Tohoku-oki earthquake, have occurred repeatedly in the northern Japan subduction zone. The spatial distribution of large interplate earthquakes shows distinct along-trench variations, implying regional variations in interplate coupling. We conducted an extensive wide-angle seismic survey to elucidate the along-trench variation in the seismic structure of the forearc and to examine structural factors affecting the interplate coupling beneath the forearc mantle wedge. Seismic structure models derived from wide-angle traveltimes showed signi cant along-trench variation within the overlying plate. In a weakly coupled segment, (i) the sediment layer was thick and at, (ii) the forearc upper crust was extremely thin, (iii) the forearc Moho was remarkably shallow (about 5 km), and (iv) the P-wave velocity within the forearc mantle wedge was low, whereas in the strongly coupled segments, opposite conditions were found. The good correlation between the seismic structure and the segmentation of the interplate coupling implies that variations in the forearc structure are closely related to those in the interplate coupling.

Multiscale Seismic Tomography

“…Significant lateral velocity variations are revealed in the interplate megathrust zone, and most of the large megathrust earthquakes (M ≥ 7.0) which occurred between 1900 and 2013 are situated in or around high-V patches. These results indicate that the rupture nucleation of megathrust earthquakes is controlled by structural heterogeneities in the megathrust zone Zhao 2005, 2006a;Yamamoto et al 2011;Fujie et al 2013a;Huang and Zhao 2013a, b;Moreno et al 2014). A shallow high-V zone with large coseismic slip near the Japan Trench may account for the asperity of the 2011 Tohoku-oki main shock (Mw 9.0).…”

Seismic attenuation tomography of the Northeast Japan arc: Insight into the 2011 Tohoku earthquake (Mw9.0) and subduction dynamics

“…This feature is very similar to the results of velocity tomography (Figures d and e) that a significant high‐velocity (high‐ V ) patch exists off Miyagi, whereas low‐ V zones exist off Sanriku, Fukushima, and Ibaraki [e.g., Zhao et al ., ; Huang and Zhao , ; Tian and Liu , ]. Such a pattern of along‐arc velocity and Q variations is also consistent with the results of many two‐dimensional velocity profiles obtained from active‐source seismic experiments near the Japan Trench [e.g., Tsuru et al ., ; Fujie et al ., ].…”

Friction properties of the plate boundary megathrust beneath the frontal wedge near the Japan Trench: an inference from topographic variation

“…Based on bathymetry changes from before to after the earthquake, Fujiwara et al (2011) demonstrated that the seafloor of the outermost part of the landward trench slope moved approximately 50 m toward the trench and was uplifted by approximately 7 to 10 m. The large fault rupture and propagation might have been due to the essentially weak fault material and dynamic weakening ) and/or abnormal fluid pressure along the megathrust (Kimura et al 2012). Fujie et al (2013) researched the along-trench variation of the structure with seismic surveys in the northern Japan Trench, and their data suggest that there is a good correlation between the seismic structure and segmentation of the interplate coupling. This implies that the variations in the forearc structure are closely related to those in the interplate coupling.…”