| Popis: |
The compressional‐wave velocity in the uppermost sediments near the sea floor has been measured with high resolution, in deep water, by a variable‐offset technique in which source and receiver are at the sea floor. The receiver is a single hydrophone connected through a 300‐m length of seismic cable to an STD wire leading to a shipboard winch. The source is a 3.5‐kHz pinger clamped to the STD wire and transmitting 1‐ms pulses at 1‐s intervals. With the phone on the sea floor together with the piled‐up cable, the pinger drifts with the ship, moving away from the hydrophone until the cable comes taut, thus ending the run. Maximum offset is of the order of a few hundred meters (the length of the cable) and velocity structure can be obtained to depths of 100 or 200 m into the sediment. Interval velocities in layers as thin as 7 m in water depths in excess of 5000 m have been resolved by the method. |
