AN: T72A-04TI: Crustal Structure of the Queen Charlotte Transform Fault    Zone from Deep Crustal Multichannel Seismic Reflection DataAU: Maren ScheidhauerAU: A. M. TrehuAF: both at COAS, Oregon State University, Corvallis, OR    97331EM: mscheid@oce.orst.eduAF: Pacific Geoscience Centre, Sidney, B.C. V8L4B2, CanadaEM: rohr@pgc.emr.caAF: Lamont-Doherty Earth Observatory, Palisades, NY 10964EM: johnd@ldeo.columbia.eduAB:             Approximately 300 km of multichannel seismic reflection data    on the Queen Charlotte fault system were collected as part of    the ACCRETE experiment in September 1994 near the US-Canada    border.        The Queen Charlotte fault system is a segment of the North    America and Pacific plate boundary. Prior to late Eocene    plate motion was convergent; since then relative plate    motion has been primarily tranlational with small amounts    of tranpression and transtension.  The new profiles are    located in a region where the fault bends and changes from    a transpressive regime to the south to a purely translational    regime to the north.        The Queen Charlotte fault plate boundary is characterized by    an approximately 50-km wide terrace flanked to the west by a    topographic trough and to the east by the seismically active    inner fault. Line 1264 was shot along this inner edge of the    terrace; lines 1262 and 1250 cross the fault and terrace; and    line 1263 is oriented along the axis of the trough. Stacked    and migrated seismic profiles reveal the presence of a N-S    trending fault that is oblique to the plate boundary and    shows decreasing amounts of compression across and east    of it as distance from the main strand of the QCF increases.    The amount of compression in the terrace increases down-section    and to the north along this fault. This implies that the seaward    boundary of the terrace is not simply a relict trench and that the        oceanic plate seaward of the main plate boundary is deformed by    transpression during oblique plate motion. This deformation is    preserved as the plate migrates along the transform.        Gravity modeling using the interpreted reflection profiles    and constraints on density distribution derived from velocity    functions will provide more insight to the question wheather    oceanic crust extends beneath the terrace.    SC: TDE: 8150 Plate boundary structuresDE: 3025 Marine seismicsDE: 3010 GravityMN: Fall Meeting 1996