A marine deep seismic sounding system

Abstract

A marine seismic system for recording near-vertical incidence to wide-angle reflected waves and refracted waves with penetration from the ocean bottom to the upper mantle has been developed. Operations require two ships, one the receiving vessel, the other the shooting ship. Seismic signals are received by six individual hydrophone assemblies suspended at 45-m depth from a neutrally buoyant 610-m cable trailed from the receiving vessel. After filtering and amplification, the seismic data plus the WWVB radio time code are recorded on a multichannel, 14-bit digital data acquisition system. The shooting ship detonates explosive charges as it proceeds along a predetermined course. In order to calculate origin times and to monitor the source signature, the signal from a single hydrophone and the WWVB time code are recorded on a 2-channel chart recorder and 4-channel FM analog tape transport. The digital recording and multiple receivers provide increased dynamic range relative to analog methods, improve the capability for detecting subcritical incidence reflections, and enable the use of data processing techniques, including stacking of weak refraction arrivals. Examples of an expanding reflection record section from a deep water sedimentary basin west of Vancouver Island and of a refraction record section recorded across Explorer Ridge spreading centre show the quality of data which are acquired with the marine seismic system.