OCEANIC CRUSTAL THICKNESS AND SEISMIC CHARACTER ALONG A CENTRAL PACIFIC TRANSECT

Seismic reflection data along a flow line of crustal generation in the central Pacific that spans ages of zero to 85 Ma and spreading half rates of 30 to 100 km m.y.-1 shows a nearly constant travel time of 2 s through igneous crust to reflection Moho. The highest-amplitude and most laterally continuous Moho reflections were recorded over 20-30 Ma crust that was emplaced at ''superfast'' (75-95 km m.y.-1) spreading rates. The superfast spread portion also records the lowest scatter about the 2-s average travel time to reflection Moho. Seismic images show that lower crustal reflectors dip consistently eastward toward the ridge crest. These dipping reflectors are truncated by the reflection Moho.