Tectonic features of the Japan Trench convergent margin off Sanriku, northeastern Japan, revealed by multichannel seismic reflection data

Abstract

Abstract. Near the Japan Trench convergent plate margin the seaward edge of the continental plate is deformed by subduction of the oceanic plate. We report the results of a multichannel seismic survey in the northern Japan Trench in which this deformed zone is demarcated from the rigid continental framework by a pronounced landward dipping reflector. The oceanic plate also undergoes deformation as the two plates interact in the subduction processes, resulting in a progressive deformation or destruction of a horst structure along the top of the subducting oceanic crust. This may eventually lead to the formation of a smooth plate boundary at the greater depth. More than 45 km landward from the trench axis, a smooth reflector suggesting a stable slip plane is visible along and above the oceanic crust. Our data indicate that the deformed zone pinches out landward --•60 km from the axis at 13 km depth and the slip plane becomes less obvious there. Seismicity of interplate earthquakes rapidly increases landward from this location, leading us to speculate that this is where coupling at the plate boundary becomes strong enough for earthquakes to occur. We conclude that the updip limit of the seismogenic zone of interplate earthquakes in the study area is characterized by the tectonic feature of a pinchout of the deformed sediments which overlie the subducting oceanic crust.

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

“…The frontal prism contains disrupted and chaotic seismic reflectors [e.g., Tsuru et al, 2000;Chester et al, 2013a] interpreted to represent shallowly landward dipping thrust faults that branch off the décollement and imbricate hemipelagic sediments [Scientific Party, 1980;von Huene et al, 1994;Tsuji et al, 2011;Kodaira et al, 2012;Nakamura et al, 2013]. Seismic surveys show a shallowly dipping (~8°) reflector interpreted as the décollement, around 821.5 m below sea floor (mbsf) between the frontal prism and downgoing Pacific Plate .…”

Simulation of Dynamic Earthquake Ruptures in Complex Geometries Using High-Order Finite Difference Methods

“…The problem is motivated by the recent magnitude 9.0 Tohoku-Oki, Japan, megathrust earthquake and the resulting tsunami. The specific geometry we consider is shown in Figure 6, and is loosely based on the subduction zone structure in the vicinity of the Japan trench (Tsuru et al, 2000;Takahashi et al, 2004). The Pacific Plate is being subducted to the west beneath the North American / Okhotsk Plate, with relative motion across the plate interface (the fault) occurring during megathrust earthquakes.…”

High‐resolution seismic imaging in the Japan Trench axis area off Miyagi, northeastern Japan

“…[3] Since the 1970s, seismic reflection studies of the Japan Trench [e.g., Nasu et al, 1980] have provided an understanding of the regional plate boundary structure [e.g., von Huene and Culotta 1989;von Huene et al, 1994;Tsuru et al, 2000;Tsuru et al, 2002]. The upper plate consists of a landward (inner) slope underlain by a continental framework, a tectonized middle slope, and a 10-km-wide frontal accretionary prism.…”