AN: T72A-06TI:     Images of the Initiation of a Transform Plate Boundary,     the Explorer Transform Zone    AU: Kristin M. M. RohrAF: Geological Survey of Canada  PO Box 6000  Sidney BC V8L    4B2EM: rohr@pgc.emr.caAU: Kevin P. FurlongAF: Geosciences  Penn State University Park PA 16802EM: kevin@geodyn.psu.eduAB:         Seismicity, deformed magnetic anomalies and dynamic    modelling suggest that a new transform plate boundary is     currently being established across the Explorer psuedoplate.    The new plate boundary accommodates Pacific-North America     relative motion and movesthe Pacific-North America-Juan de    Fuca triple junction to the northern end of the the Juan de    Fuca ridge. As a test of this hypothesis we have collected    approximately 3300 km of single-channel seismic reflection    data over the Explorer and  Pacific plates. In 1994 a     regional scale survey was conducted with lines 8-16 km     apart and in 1996 two grids of reflection lines 2 km apart    and 20 km long were conducted on what has been thought of     as the coherent rigid Explorer microplate.            In previous models of tectonic evolution the Pacific and     Explorer plates formed at the Explorer ridge at the same     time and should have similar morphologies. In the regional    survey we observed significantly  different morphologies     and structure in basement and sediments of each plate. In     the detailed grids we mapped subvertical faults that cut     the seafloor and basement; their length varies from 5 to    over 25 km long. Their azimuth ranges from 340 (parallel     to the Pacific-North America vector) to 050 degrees.     Sedimentary faults at a high angle to a crustal shear    formed in small-scale analogue models of shear deformation.    Small amounts of extension and compression adjacent to     these faults imply that strike-slip motion is occurring on    the  faults.    SC: TDE: 3025DE: 8150DE: 8164MN: Fall Meeting 1996