FAULT PATTERN FROM SEABEAM PROCESSING - THE WESTERN PART OF THE BLANCO FRACTURE-ZONE (NE PACIFIC)

The Blanco Fracture Zone, which connects the Juan de Fuca and Gorda ri dges, is structurally complex and contains numerous pull-apart basins and accretion centers. It terminates at its western end in two troughs where the Juan de Fuca Ridge progressively dies out. This unusual str ucture is studied in detail using bathymetric analysis which allows th e fault pattern to be determined. The method developed to extract stru ctural information involves numerical treatment of the gridded bathyme try derived from image processing methods. The detailed mapping of the fault pattern shows that the active zone corresponds to a N 100 degre es E strike-slip zone which connects the southern end of the Juan de F uca Ridge with the northeastern edge of the Blanco Trough, via the nor thwestern wall of the Parks Plateau. The present day direction of the active zone comes after a previous one trending at N 115 degrees E, ap parently within the same area. The Parks Plateau results from a jump o f the plate boundary from the southern to northern limits of the plate au. Deformation over the past 2 Ma results from a northeastward displa cement of the junction between the transform zone and the ridge.