Structural characters of the Japan Trench subduction zone over the March 2011 Mw 9.0 Tohoku-Oki earthquake rupture, based on seafloor geomorphology and reprocessed multichannel seismic reflection data
Abstract
We collected and interpreted newly obtained bathymetric data and reprocessed, offshore multichannel seismic reflection data across the Japan Trench subduction zone to continental slope over the March 2011 Mw 9.0 Tohoku-Oki earthquake rupture. Bathymetric data gridded at 300 m (average) obtained after the 2011 event covers the 2011 rupture between 37.5N and 40N. Seafloor morphology illuminated by this topographic dataset shows that continental slope west of the subduction deformation front is deformed by (1) en echelon fold and fault scarps on a gently tapered accretionary wedge, (2) > 1500 m high east-facing escarpment that extends for at least 150 km along and subparallel to the trench axis, and (3) pairs of north-trending active normal faults that cut anticlinal crest of (1), each of which extends for about 20 km. Structural interpretation of reprocessed seismic data near the rupture area coupled with geomorphic interpretation shows that fault and fold scarps in accretionary wedge is underlain by shallowly dipping, emergent thrust faults that appear to sole into thin (~500 m thick) hemi-pelagic sediments on the subducting oceanic crust. Large escarpment is also underlain by a moderately dipping thrust fault, where Cretaceous and older rocks are thrust over Neogene sedimentary units comprising accretionary wedges; younger units onlapping onto the folded Neogene sediments at the base of the escarpment appear to be subtly folded upward, suggesting recent activity of the underlying thrust fault. Styles of deformation on the accretionary wedge and thrust trajectories may reflect bends of subducting oceanic crust, marked by reflectors of both overlying hemi-pelagic sediments and the oceanic moho, that is strongly deformed by normal faults presumably caused by extension of the outer-rise to form structural ramp on the basal decollement.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T13A2581I
- Keywords:
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- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 3060 MARINE GEOLOGY AND GEOPHYSICS / Subduction zone processes;
- 8015 STRUCTURAL GEOLOGY / Local crustal structure;
- 8170 TECTONOPHYSICS / Subduction zone processes