9411541 Bangs A deep multichannel seismic reflection survey of the Aleutian arc and the extensive Alaskina continental shelf will delineate and differentiate arc magmatism and terrain accretion. The high-quality images of the deep structure of the crust and uppermost mantle, when combined with the well-mapped onshore geology, should allow the principal investigators to constrain the mechanisms of accretion and magmatism.