Sediment velocities and deep structure from wide-angle reflection data around Leg 116 sites

Abstract

The reduction of 6 wide-angle reflection profiles shot within the 2 fault blocks visited by Ocean Drilling Program (ODP) Leg 116 in combination with the ODP sonic logs has produced a velocity-depth structure for this area. The sediment velocity increases from 1.6-1.7km/s in the near surface to 3.4-3.5km/s immediately above basement with a velocity gradient of 0.75/s. A depth converted seismic reflection profile suggests that the pre-deformational basement surface was similar to the abyssal hill topography developed in the Pacific Ocean. A velocity for the top of oceanic layer 2 to 4.1km/s was identified as layer 2A. Assuming a velocity gradient of 0.7/s, an estimate of layer 2 thickness was obtained of 1.5km. It is possible to interpret residual depth anomalies in terms of a layer 3 that may be thinner than for normal oceanic crust. -Authors