REJUVENATION OF 130 MY-OLD FABRICS ON THE OUTER WALL OF THE WESTERN KURIL TRENCH

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