Alternate number:

75 JUN

Platform:

R/V Asterias

Owner-Operator:

Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA

Center Principal:

Charles J. O'Hara

Area of Operations:

Rhode Island Sound, Rhode Island, Westport Harbor, Vineyard Sound, Cuttyhunk Island, No Mans Land, Martha's Vineyard, Massachusetts, United States, North America, North Atlantic

Bounding Coordinates (degrees)

North:

41.50

South:

41.25

West:

-71.25

East:

-70.70

Start and End Dates:

June 19, 1975, to June 30, 1975

Days at Sea:

12

Type of Activity:

Seismic profiling

Objectives:

The cooperative program is designed to provide detailed geological information and an assessment of mineral resources pertaining to that part of the continental shelf beneath the coastal waters of Massachusetts. In anticipation of the development of offshore natural resources of the Commonwealth, the major focus of the research effort is directed toward the occurrence, nature, and distribution of offshore deposits as well as the establishment of baseline data for the evaluation of environmental effects of exploitation. The subbottom-profiling surveys provide the foundation for a planned program of vibracoring and bottom sampling of geological features. Laboratory analysis of the vibracore and bottom samples will enable the evaluation of the economic importance of the deposits and, coupled with the seismic data, provide information about the geology and geologic history of the area.

Information to be derived:

Morphology of sea floor

Scientific Party
(USGS):

Charles J. O'Hara, Chief Scientist; Frank Jennings, Electronic Technician; Patricia Forrestal; Wayne Ferrebee; Elizabeth Winget; Susan Purdy; Barbara Tausey

Scientific Equipment:

EG&G Uniboom Catamaran with mounted Transducer
EG&G Capacitor Bank
EG&G Hydrophone Streamer
EPC Seismic Recorder (#151)
Epsco LORAN-C Receiver (recent model)
Epsco LORAN-C Repeater
Krohn-Hite Band Pass Filter

Navigation techniques used:

LORAN-C, radar, visual

Summary of Results:

Traverses: 33 (27 in a NW-SE orientation with a line spacing of 1 nautical mile, 6 in a SW-NE orientation with a line spacing of approximately 3 nautical miles); Seismic data: 368 nautical miles (682 kilometers) and penetration of up to 125 meters below the bottom were achieved

Continuous Data (in km):

682

Remarks:

All seismic tracklines were preplotted along LORAN-C navigation lines of position. This approach facilitated control of the survey vessel on the seismic tracks despite the course-setting influence of wind and currents. Cape Race, Newfoundland, and Dana, Indiana, LORAN-C slave transmitters were utilized as they are the most reliable and provide the best positional accuracy within the area. Navigational fixes were taken at 15-minute intervals, and ship speed over the bottom averaged 4.5 knots. The hydrophone array and catamaran float with mounted transducer were towed about 15 meters astern of the survey vessel. This configuration, coupled with ship speed, resulted in a sound source/receiver separation of approximately 10 meters. The transducer was triggered every 0.5 second, and the sweep rate of the recorder was set at 0.25 second. Only incoming seismic signals within the 200– to 4,000-Hz frequency range were fed to the recorder.

Contact:

Charles J. O'Hara