Controlled-source seismic experiment at Hole 581C.

Abstract

Seismic refraction lines fired to ocean bottom seismometers (OBS) and to the ocean sub-bottom seismometer (OSS) at Site 581 provide some of the highest quality refraction data yet obtained in the deep ocean. Excellent data with a shot spacing of less than 250 m are well recorded out to a range of 45 km. These data are analyzed with WKBJ, tau -p inversion, and reflectivity modeling which are used to obtain seismic models. The resulting model for the NW Pacific crust agrees with that obtained by Anosov et al. (1982) for the same region. It differs from 'standard' ocean crust models in that it contains a low-velocity zone for both P and S waves near the top of Layer 3. Strong shear conversion at the base of the sediments is easily identified on the different components, yielding an accurate sediment shear velocity of 210 m/s. -from Authors