Summary for Field Activity Number 1975-025-FA

Alternate Leg ID: FAY 004

Area of Operations: Georges Bank, United States, North America, North Atlantic

Dates: October 20, 1975 to October 26, 1975

Objectives: Leg 4 of the R/V FAY was set up to obtain approximately three reversed refraction lines on Georges Bank and to collect two to four long geophysical profiles over the continental slope and rise.

Type of Activity: Seismic profiling

Information to be derived: Bathymetric maps

Summary: The seismic refraction velocities were obtained with both expendable and a new recoverable sonobuoy (with an internal digital recorder) in order to confirm velocity models for Georges Bank which had been developed on the basis of earlier reconnaissance refraction studies in the 1950s, and on the basis of interval velocities obtained from multichannel seismic systems. The gravity profiles into deep water were designed to supplement the gravity measurements over the shallow water portion of Georges Bank, which were collected on FAY 003, and to cover several USGS multichannel seismic lines where no or poor gravity data were available. The high velocity sedimentary rock layer was confimed and probably represents early Cretaceous or Jurassic limestones and dolomities. The 5.0-5.4 km/sec material beneath the outer edge of the shelf and upper continental slope probably also represents a carbonate bank or reef which existed at the shelf edge in the early or Middle Cretaceous period. Gravity data: 1640 km; Bathymetry Data: 500 km; Magnetics: 600 km; Refraction stations: 4 reversed profiles.

USGS Project Number: RA

Contact: John Grow ()