Abstract
Detailed swath mapping of topography associated with other geophysical measurements has indicated that the outer wall of the western Kuril Trench is dissected by a number of normal faults which are parallel to the linear magnetic anomalies in the northwestern margin of the Pacific Ocean but slightly oblique to trend of the axis of the Kuril Trench by roughly 10°. It is inferred that about 130 million years old tectonic fabrics in the oceanic crust are rejuvenated when the lithosphere is bent downward under extensional stress at the trench outer wall to be subducted beneath the landward wedge. This pattern of faults shows a sharp contrast to alignment of faulted scarps found in the outer wall of the Japan and Izu-Ogasawara Trenches both trending by 60° oblique to the magnetic lineations. Majorities of outer wall scarps there are parallel to the trench axis, whereas some scarps trend subparallel to the axis forming zigzag pattern of escarpment. As direction of the extensional stress caused by downward bending of the lithosphere in these trench walls is nearly perpendicular to the old tectonic stresses, normal faultings seem to occur under the influence of the ongoing stress distribution alone irrespective of their old history.
