BGR Bundesanstalt für Geowissenschaften und Rohstoffe

Marine seismic survey area: Off North America - Reflection seismic data

Refraction seismic data

Working area: Off North America
(1) Labrador Sea (2) Off US East Coast (3) Off Bahamas
BGR89 (Prospekta) 1989
BGR77 (Explora) 1977BGR79 (Explora) 1979NAT81 (Prospekta/Moore) 1981

Working area: OFF North AmericaWorking area: OFF North America Source: BGR

Cruise BGR77 1977

Labrador Sea

Multichannel seismic data acquisition parameters:
Total length of lines5.931 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 48 channels

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Cruise BGR79 1979

Vessel Explora

US East Coast

Multichannel seismic data acquisition parameters:
Total length of lines11.489 km 
Sampling rate4 ms
Record length10 000 ms
Streamerdigital - 48 channels

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Cruise BGR89 1989

Vessel Prospekta

East-Kanada

Multichannel seismic data acquisition parameters:
Total length of lines3.568 
Sampling rate4 ms
Record length11 000 ms
Streamerdigital, 60 channels

Summary

In the time from 13 August to 13 September, 1989 a geophysical survey was carried out with S.V. PROSPEKTA in the Southeastern Newfoundland Basin and in the Sohm Abyssal Plain. Sixteen multichannel seismic lines with a total length of 3,568 km were surveyed.

The general aim of the survey was to study the structure of the oceanic crust formed during the period from 150 to 80 m.y.B.P.. The results we found that the magmatic-volcanic activity at the Mesozoic Atlantic spreading center was episodic, and there was some form of magmatic-tectonic cycling in the Mid-Atlantic Ridge processes.

Drastic changes of the oceanic crustal structure have been observed, and a volcanic basement unit characterized by an internally divergent pattern of reflection horizons having an eastward dip was found coinciding with magnetic anomalies M-4 to M-0.

This body consists probably of basaltic flows and volcanic clastic rocks extruded near or above sealevel, and it appears that this unit is continuous from the Eastern Newfoundland Basin to the New England Seamount Chain.

A doubling of the oceanic crustal thickness occurs around M-10 and is present in the area of the young end of the series of magnetic M-anomalies.

Doubling of the thickness of the oceanic crust is also present in the conjugate eastern central North Atlantic segment in the area of magnetic anomalies M-10 to about M-0.

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Cruise NAT81 1981

Vessel Prospekta/Moore

Bahamas

Multichannel seismic data acquisition parameters:
Total length of lines3.568 km Mooere
Sampling rate4 ms 4 ms
Record length12 000 ms 15 000 ms
Streamerdigital - 60 channelsdigital - 48 channels

Summary

During the period August, 9th to September 1st a multiple ship multichannel seismic investigation was conducted between the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, the University of Texas (UT), Galvestone, and the Lamont Doherty Geological Observatory (LDGO), Palisades N.Y., using the research vessels S/V PROSPEKTA and R/V FRED H. MOORE.

The object of the investigations was to obtain, in different modes, multichannel seismic data with very large synthetic receiving arrays. Two types of investigation were conducted:

  1. With the two vessels steaming together along track at a separation equal to twice the length of the cable of the lead ship (S/V PROSPEKTA during most of the investigation). Both ships alternately fired their airguns on a 60 sec schedule. Each ship recorded both its own shots and those of the other ship. By gathering the recordings from both ships during processing it will be possible to obtain stacked data over a synthetic aperture of really 10 km with a CDP spacing of about 80 m. Velocity analysis procedures have been devised to obtain highly accurate velocity structures from this wide aperture CDP data so that we can obtain a continuous stacked section with velocity resolution and depth of penetration which is much enhanced over that which is possible using single ship measurements.

  2. At selected locations we obtained Expanded Spread Profiles (ESP’s). In this experiment the two ships steam on reciprocal headings away from a common midpoint with S/V PROSPEKTA firing its guns and R/V FRED H. MOORE recording. The ships steamed apart up to 60 km separation. In this way it is possible to obtain very deep and high resolution structure at a single location.

We also collected some single ship normal CDP data with S/V PROSPEKTA in areas of critical in order to make comparisons with the conventional method against the newer methods. The area of study includes the Blake Plateau, the Bahama Outer Ridge and the Blake Outer Ridge (a large current-built sedimentary structure), the Hatteras Abyssal Plain (underlain by Mesozoic and younger oceanic crust), the East Coast Magnetic Anomaly (ECMA) and the Blake Spur Magnetic Anomaly and the edge of the Nares Abyssal Plain. Thus we employed the new techniques in widely different geologic settings to establish its reliability under various situations. The deeper penetration combined with enhanced resolution from the wide aperture - CDP data should help to resolve several important problems in the region including the structure associated with the East Coast Magnetic and the Blake Spur Anomalies, variations with age in oceanic crustal structure, the deep structure in the margin regions and especially the existence of wedges of oceanward dipping reflectors on the continental margin landward of the ECMA. In total, 2,542 km CDP wide aperture lines, 116,5 km ESP-lines, 225 km 30-fold CDP-lines were measured by S/V EXPLORA. 92 Sonobuoys (88 of type SSQ 41, 4 of type SSQ 57) were deployed.

Contact

    
Dr. Volkmar Damm
Phone: +49-(0)511-643-3226
Fax: +49-(0)511-643-3661

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