Summary for Field Activity Number 1976-030-FA

Alternate Leg ID: FAY 020

Area of Operations: Mid-Atlantic Continental Margin, North Atlantic Continental Margin, United States, North America, North Atlantic

Dates: August 10, 1976 to August 24, 1976

Objectives: Primary objectives were to look for geophysical evidence for the continuation of fracture zones from the Mesozoic sea-floor spreading anomalies into the continental margin, investigate the source of lineated magnetic anomalies in the Jurassic Quiet Zone, and obtain additional seismic data on the continental rise and slope.

Type of Activity: Seismic profiling

Information to be derived: Morphology

Summary: FAYs depature from Norfolk was delayed for 2 days while Hurricane Belle passed just off the coast. We finally departed at 0800 on August 10th with good weather and calm seas. Airgun, magnetometer, minisparker and 3.5 kHz were deployed at 1900Z near the edge of the continental shelf. The 3.5 kHz proved almost worthless in deep water, so after a few hours the system was turned off and the recorder used as a spare for the airgun system. The other systems ran smoothly for the entire cruise with only brief shutdowns of the airgun system to fix the guns and of the minisparker for regular maintenance. Heading into port on August 24th, we pulled the airgun and magnetometer at the 50 fathom contour but left the minisparker out as we crossed part of Nantucket Shoals. The only major problem was the high noise level on the Geometric gradiometer. Scatter in field readings (+/-2 gammas) made small gradients in the quiet zone impossible to see. The bottles were examined several times and the depressors adjusted to no avail. It appeared the ship has a rather large permanent magnetic field. Problems with LORAN-C reception were eliminated by replacing the corroded terminal box. Gravity: 3950 km; Airgun: 3700 km; Magnetics: 3700 km; Minisparker: 3700 km; 3.5 kHz: 60 km; Sidescan sonar: 0.

USGS Project Number: EA-RA

Contact: Kim Klitgord ()