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A 24-fold seismic line is presented that traverses the widest part of the convergent margin off the east coast of North Island, New Zealand. The seismic data were collected in December 1983 as a cooperative project between the New Zealand Department of Scientific and Industrial Research and the United States Geological Survey (USGS). Data were collected aboard the S.P. Lee. The complete line extends approximately 275 km (5100 CDP points), of which a portion across the slope (CDP 2100 1/N 4500) is shown. A preliminary interpretation of the entire line has been published by Davey et al. (in press).

The convergent margin is formed by the westward subduction of the Pacific plate under the Indian plate. Between North Island and Chatham Rise, it corresponds to the western margin of the Hikurangi Trough. Convergence between the two plates in the vicinity of the seismic line is oblique (approximately 30° from normal) and rapid (45 mm/year) and has created an imbricate-thrust accretionary prism that extends for as much as 175 km to the edge of North Island (Lewis, 1980). This accretionary prism contains well-defined trench-slope basins and intervening ridges that lie subparallel to the slope.

The seismic source consisted of five Bolt air guns in a tuned array that were shot at 2000 psi manifold pressure. The gun depth was 8.5 m and the shot spacing was 50 m. The receiver system was a Seismic Engineering (SEI) Multidyne 24-fold streamer with a 100-m group interval and 100-m group length towed at an

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