Convergent margin accretionary prisms are structurally complex geological features. This is a proposal to conduct a walkaway Vertical Seismic Profile experiment at Oregon Margin site OM-3 to image the structural features within 3km of the borehole both perpendicular and parallel to structural strike. This should result in better definition of the frontal thrust and its associ- ated amplitude anomalies as well as part of the protothrust zone. Because the VSP's will be acquired in the drill hole using surface seismic sources, they should provide a better tie to surface seismic data. The walkaway VSP illumunates the zone below the borehole geophone, thereby imaging the structure below and laterally away from the drill hole. This lateral coverage will yield amplitude vs offset information, which will be used for inferring fluid contents of the frontal thrust and other layers that exhibit anomalous amplitudes. This award will support Dr. Moore's efforts to obtain Vertical Seismic Profiles (VSP) at the Oregon Margin drill site 3 (OM-3), which will be drilled on ODP Leg 146. This experiment will provide a more comprehensive three dimensional picture of the complex structural features of an accretionary prism within a three kilometer radius of the borehole. This will lead to a better understanding of the coupled structural and hydrogeologic system within the prism. VSP's will also allow direct comparison of seismic information to cored material and borehole logging data.
