Large‐offset seismic surveying using ocean‐bottom seismographs and air guns: Instrumentation and field technique

Geophysics ◽  
1987 ◽  
Vol 52 (12) ◽  
pp. 1601-1611 ◽  
Author(s):  
Yosio Nakamura ◽  
Paul L. Donoho ◽  
Phillip H. Roper ◽  
Paul M. McPherson
Keyword(s):  
Seismic Refraction ◽  
Ocean Bottom ◽  
Large Capacity ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Seismic Surveying ◽  
Ocean Bottom Seismographs ◽  
Marine Seismic ◽  
Processing Techniques ◽  
Signal Sources

Repeatable, closely spaced signal sources from large‐capacity air guns and detection and recording of signals using highly flexible, microprocessor‐controlled, digital ocean‐bottom seismographs allow us to acquire high‐quality, large‐offset, marine seismic refraction and reflection data. The acquired data are readily adaptable to various processing techniques originally developed for seismic reflection data. There are several requirements and problems specific to the technique. For example, bubbly signals from one or two large‐capacity air guns are often preferable to bubble‐suppressed signals from tuned arrays in identifying weak arrivals at large offset distances. Recorded water‐wave signals at near ranges provide precise locations of detectors relative to shots.

scholarly journals Cambridge radio sonobuoys and the seismic structure of oceanic crust

2019 ◽  
Vol 74 (1) ◽  
pp. 55-72 ◽  
Author(s):  
Melvyn Mason ◽  
Robert S. White
Keyword(s):  
Oceanic Crust ◽  
Plate Tectonics ◽  
Seismic Refraction ◽  
Continental Margins ◽  
Ocean Bottom ◽  
Seismic Structure ◽  
Cambridge University ◽  
The Usa ◽  
Ocean Bottom Seismographs ◽  
Marine Seismic

The Cambridge University Department of Geodesy and Geophysics pioneered the development of radio sonobuoys which could be used from a single ship to study the structure of the submarine crust. By contrast, contemporaneous marine seismic research, mainly in the USA, used more expensive techniques requiring the use of two ships. For nearly three decades from the early 1950s several generations of Cambridge sonobuoys were used as the primary tool to study the structure of the oceanic crust and the adjacent continental margins by seismic refraction methods, until superseded by ocean-bottom seismographs. An early result was to confirm the ubiquity across the world of relatively thin (compared with continental crust), probably volcanic, oceanic crust. This in turn underpinned the subsequent recognition of seafloor spreading and plate tectonics.

EXTENDED ARRAYS FOR MARINE SEISMIC ACQUISITION

Geophysics ◽  
1978 ◽  
Vol 43 (1) ◽  
pp. 3-22 ◽  
Author(s):  
J. H. Lofthouse ◽  
G. T. Bennett
Keyword(s):  
Data Quality ◽  
Data Acquisition ◽  
Signal Amplitude ◽  
Eastern Canada ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Formed Part ◽  
Marine Seismic ◽  
Receiver Arrays

In‐line arrays for both source and receiver have been implemented for marine seismic reflection data acquisition. The in‐line array dimensions (variable within limits) are considerably greater than any previously used system of which we are aware. The arrays were designed to attenuate extremely strong sea‐bottom multiples during the data acquisition phase. The source comprised 25 airguns arranged in five identical in‐line subarrays. Each subarray produced a signal of better than 6 barmeters acoustic intensity with a primary‐to‐bubble ratio of approximately 4.4 from guns totaling 297 cu in. When this source was delivered in 1973, it constituted the most powerful production airgun source for which we had seen calibration measurements. Receiver arrays were implemented by a “weighting‐mixing” box (which formed part of the DFS IV instrument), the input to which comprised 53 channels of data each from a 50 m live section in the streamer cable. Processing techniques which are complementary to the field procedures have been developed. Comparisons with “conventional” data (and such data processed to simulate field arrays) show significant improvements in “data quality” from the new field techniques, that is, the new data are easier to interpret geologically because interfering multiples have been attenuated relative to desired energy. Whilst the large outgoing signal amplitude will have made some contribution to the data quality, the major improvement is believed to result from the use of arrays in the recording phase. This system, first used for production in August 1973, was subsequently used successfully during recording of 17,000 km of offshore seismic data from Eastern Canada, the North Sea, and the Mediterranean.

Labeling long‐period multiple reflections

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 122-126 ◽  
Author(s):  
R. J. J. Hardy ◽  
M. R. Warner ◽  
R. W. Hobbs
Keyword(s):  
Seismic Reflection ◽  
High Amplitude ◽  
Data Sets ◽  
Multiple Reflections ◽  
Multiple Series ◽  
Seismic Reflection Data ◽  
Long Period ◽  
Reflection Data ◽  
Zero Offset ◽  
Marine Seismic

The many techniques that have been developed to remove multiple reflections from seismic data all leave remnant energy which can cause ambiguity in interpretation. The removal methods are mostly based on periodicity (e.g., Sinton et al., 1978) or the moveout difference between primary and multiple events (e.g., Schneider et al., 1965). They work on synthetic and selected field data sets but are rather unsatisfactory when applied to high‐amplitude, long‐period multiples in marine seismic reflection data acquired in moderately deep (700 m to 3 km) water. Differential moveout is often better than periodicity at discriminating between types of events because, while a multiple series may look periodic to the eye, it is only exactly so on zero‐offset reflections from horizontal layers. The technique of seismic event labeling described below works by returning offset information from CDP gathers to a stacked section by color coding, thereby discriminating between seismic reflection events by differential normal moveout. Events appear as a superposition of colors; the direction of color fringes indicates whether an event has been overcorrected or undercorrected for its hyperbolic normal moveout.

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