Kowanyama deep refraction seismic survey

1989 ◽  
Vol 20 (2) ◽  
pp. 303
Author(s):  
B.M. Haines ◽  
B.A. McConachie
Keyword(s):  
Gravity Data ◽  
Seismic Refraction ◽  
Cost Effective ◽  
Seismic Survey ◽  
Magnetic Data ◽  
Gravity And Magnetic ◽  
Refraction Seismic ◽  
Intermediate Section ◽  
Cape York ◽  
Gravity And Magnetic Data

The Carpentaria Basin in the west/central portion of Cape York Peninsula is largely unexplored for petroleum, and there is an apparent ambiguity in the basement depths interpreted from gravity and aeromagnetic data. It was decided that deep seismic refraction surveys at a variety of sites should prove cost-effective in defining the geologic model for the basin. Of particular interest is the possible existence of a north-south trending elongate infrabasin inferred qualitatively from a strong gravity low shown Figure 1. Results of the refraction work indicate that the magnetic and gravity data suggestive of the presence of an infrabasin are probably related to lithological variations within basement. Furthermore, it is improbable that the thickness of the sedimentary pile anywhere within the area of investigation exceeds 1100 metres. Basement velocities are high, from 5500m/sec to 6200m/sec, typical of fresh igneous and/or metamorphic lithologies. Carbonates could not be totally excluded on the basis of these velocities alone, but are improbable in view of the gravity and magnetic data. At some locations there is evidence for the presence of an intermediate section of higher velocity within the sedimentary sequence. This is thought to be quite thin, and possibly representative of the Toolebuc Formation.

scholarly journals Marine geophysical investigations offshore East Greenland

1983 ◽  
Vol 115 ◽  
pp. 93-100
Author(s):  
H.C Larsen
Keyword(s):  
Seismic Data ◽  
Seismic Refraction ◽  
Magnetic Data ◽  
Seismic Profiles ◽  
East Greenland ◽  
Gravity And Magnetic ◽  
Marine Gravity ◽  
Refraction Seismic ◽  
Regional Project ◽  
Gravity And Magnetic Data

During August and September 1982 a marine geophysical survey was conducted on the East Greenland Shelf. The survey was part of the ongoing regional project NAD (Larsen & Andersen, 1982; Andersen et al., 1981; Risum, 1980; Larsen & Thorning, 1980). In all 2794 km of 30-fold multi-channel seismic data and marine gravity and magnetic data were acquired (fig. 33). The object of the NAD programme is to acquire regional coverage of aeromagnetic, multichannel seismic refiection, seismic refraction (sonobuoy), marine gravity and magnetic data of the East Greenland Shelf between latitudes 60° N and 78°N. Aeromagnetic data comprising 63000 line kilometres were acquired in 1979 (Larsen & Thorning, 1980) and 5000 km of marine geophysical data were acquired in 1980 and 1981 (Larsen & Andersen, 1982; Andersen et al., 1981). This year the final data for the project were collected. Thus, a total of 7800 km of multi-channel refiection seismic data and 50 sonobuoy refraction seismic profiles of 20 to 70 km length have been acquired (fig. 33). In addition, marine gravity and magnetics were run at most lines.

Application of gravity and magnetic methods to assess geological hazards and natural resource potential in the Mosida Hills, Utah County, Utah

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1514-1526 ◽  
Author(s):  
Alvin K. Benson ◽  
Andrew R. Floyd
Keyword(s):  
Gravity Data ◽  
Magnetic Data ◽  
Geological Hazards ◽  
Mafic Lava ◽  
Subsurface Geology ◽  
Gravity And Magnetic ◽  
Geophysical Surveys ◽  
Utah County ◽  
Gravity And Magnetic Data ◽  
Hills Area

Gravity and magnetic data were collected in the Mosida Hills, Utah County, Utah, at over 1100 stations covering an area of approximately 58 km2 (150 mi2) in order to help define the subsurface geology and assess potential geological hazards for urban planning in an area where the population is rapidly increasing. In addition, potential hydrocarbon traps and mineral ore bodies may be associated with some of the interpreted subsurface structures. Standard processing techniques were applied to the data to remove known variations unrelated to the geology of the area. The residual data were used to generate gravity and magnetic contour maps, isometric projections, profiles, and subsurface models. Ambiguities in the geological models were reduced by (1) incorporating data from previous geophysical surveys, surface mapping, and aeromagnetic data, (2) integrating the gravity and magnetic data from our survey, and (3) correlating the modeled cross sections. Gravity highs and coincident magnetic highs delineate mafic lava flows, gravity lows and magnetic highs reflect tuffs, and gravity highs and magnetic lows spatially correlate with carbonates. These correlations help identify the subsurface geology and lead to new insights about the formation of the associated valleys. At least eight new faults (or fault segments) were identified from the gravity data, whereas the magnetic data indicate the existence of at least three concealed and/or poorly exposed igneous bodies, as well as a large ash‐flow tuff. The presence of low‐angle faults suggests that folding or downwarping, in addition to faulting, played a role in the formation of the valleys in the Mosida Hills area. The interpreted location and nature of concealed faults and volcanic flows in the Mosida Hills area are being used by policy makers to help develop mitigation procedures to protect life and property.

Gravity and Magnetic Methods

2000 ◽  
Author(s):  
Richard M. Carruthers ◽  
John D. Cornwell
Keyword(s):  
Large Scale ◽  
Gravity Data ◽  
Integrated Approach ◽  
Rock Properties ◽  
Magnetic Data ◽  
Satellite Gravity ◽  
Fully Integrated ◽  
Continental Shelves ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

Lateral variations in the density and magnetization of the rocks within the crust give rise to "anomalies" in the Earth's gravity and magnetic fields. These anomalies can be measured and interpreted in terms of the geology both in a qualitative sense, by mapping out trends and changes in anomaly style, and quantitatively, by creating models of the subsurface which reproduce the observed fields. Such interpretations are generally less definitive in themselves than the results from seismic surveys (see chapter 12), but the data are widely available and can provide information in areas where other methods are ineffective or have not been applied. As the different geophysical techniques respond to specific rock properties such as density, magnetization, and acoustic velocity, the results are complementary, and a fully integrated approach to data collection and interpretation is generally more effective than the sum of its parts assessed on an individual basis. Gravity and magnetic data have been acquired, at least to a reconnaissance scale, over most of the world. In particular, the release into the public domain of satellite altimetry information (combined with improved methods of data processing) means that there is gravity coverage to a similar standard for most of the offshore region to within about 50 km of the coast. Magnetic anomalies recorded from satellites provide global coverage, but the high altitude of the observations means that only large-scale features extending over many 10s of kilometers are delineated. Reconnaissance aeromagnetic surveys with flight lines 10-20 km apart provide a lateral anomaly resolution similar to that of the satellite gravity data. Oceanographic surveys undertaken by a variety of academic and research institutions are another valuable source of data in remote regions offshore which supplement and extend the more detailed coverage obtained over the continental shelves, for example, by oil companies in areas of hydrocarbon interest. Surveys over land vary widely in terms of acquisition parameters and quality, but some form of national compilation is available from many countries. A number of possible applications of the potential field (i.e., gravity and magnetic) data follow from the terms set out by UNCLOS. Paragraph 4(b) of article 76 states, "In the absence of evidence to the contrary, the foot of the continental slope is to be determined as the point of maximum change in the gradient at its base" (italics added).

Gravity and magnetic interpretation of the Deer Lake basin, Newfoundland

1984 ◽  
Vol 21 (1) ◽  
pp. 10-18 ◽  
Author(s):  
H. G. Miller ◽  
J. A. Wright
Keyword(s):  
Magnetic Data ◽  
Lake Basin ◽  
Magnetic Interpretation ◽  
Seismic Surveys ◽  
Reflection And Refraction ◽  
Gravity And Magnetic ◽  
Refraction Seismic ◽  
Gravity And Magnetic Data ◽  
Gravity And Magnetic Interpretation ◽  
Total Sediment

Detailed reconnaissance gravity surveys in the Deer Lake Carboniferous basin have been conducted using a station spacing of 2.5 km. The digitized aeromagnetic data for the basin were reduced to a 1:253 440 scale composite map. These two data bases were used to determine the configuration of major features and the total sediment thickness at various locations in the basin. Preliminary seismic results from reflection and refraction seismic surveys planned on the basis of these results are discussed. Modelling of gravity and magnetic data indicates that the Humber syncline contains approximately 1.2 km of sediments underlain on the west by rocks similar to the Long Range Complex. The eastern limb of the syncline is underlain by rocks similar to the Gull Pond Igneous Suite. The Howley Formation is deduced to be approximately 1.5 km thick and floored by rocks similar to the Topsails Igneous Suite.

A geological interpretation of gravity and magnetic data, northwest Saskatchewan

1970 ◽  
Vol 7 (3) ◽  
pp. 858-868 ◽  
Author(s):  
R. H. Wallis
Keyword(s):  
Gravity Data ◽  
Magnetic Data ◽  
Early Proterozoic ◽  
Geological Interpretation ◽  
Metasedimentary Rocks ◽  
Lower Proterozoic ◽  
Gravity And Magnetic ◽  
Northern Saskatchewan ◽  
Gravity And Magnetic Data ◽  
Sedimentary Unit

The striking 'fit' of aeromagnetic and gravity data from the Precambrian of northwest Saskatchewan, combined with known and nearby analogous, geological relationships, suggests the presence of a northeast-trending belt, 250 × 20 miles (400 × 30 km), of early Proterozoic (?) metasedimentary rocks, probably magnetite-bearing meta-arkoses. This structural–sedimentary unit might have economic possibilities analogous to other northeast-striking, Precambrian, lower Proterozoic (?), metasedimentary belts of northern Saskatchewan, the Virgin River Belt, and the Wollaston Trend.

Seismic, gravity and magnetics, a complementary geophysical study of the Paqualin Structure, Timor Sea, Australia

1989 ◽  
Vol 20 (2) ◽  
pp. 25 ◽  
Author(s):  
P.M. Smith ◽  
M. Whitehead
Keyword(s):  
Seismic Data ◽  
Gravity Data ◽  
Seismic Survey ◽  
Magnetic Data ◽  
Data Sets ◽  
Intrusive Body ◽  
Geophysical Study ◽  
Timor Sea ◽  
Susceptibility Contrast ◽  
Gravity And Magnetic Data

The presence of a large anomalous structure in the northern part of Permit AC/P2 in the Timor Sea has been recognised ever since seismic data were first acquired in the area. Historically, however, sparse seismic coverage has always prevented a detailed and unambiguous interpretation of the complicated structure. In order to overcome this problem, some 2000 km of 3D seismic data were acquired over the feature. In conjunction with this seismic survey, detailed gravity and magnetic data sets were also recorded over the structure.Interpretation of the new seismic data indicated the presence of a piercement structure which is associated with a small negative Bouguer gravity anomaly and a magnetic intensity anomaly resulting from a positive susceptibility contrast. Modelling of the magnetic data indicated that an acidic or intermediate intrusive body was the most likely cause of the piercement structure. The presence of an acidic intrusive body was consistent with the gravity data which indicated that no large density contrast existed between the material of the piercement structure and the surrounding sediments.The combined interpretation of these three data sets was tested by a well, Paqualin-1, drilled on the flank of the piercement structure. The well encountered a thick evaporite sequence with associated thin bands of magnetitie and intermediate igneous rocks. It was logged with a three component downhole magnetic probe and forward magentic modelling work incorporating the results of the magnetic log gave good agreement with the observed aeromagnetic profiles.

THE ELECTRONIC COMPUTER AND GEOPHYSICS

Geophysics ◽  
1961 ◽  
Vol 26 (1) ◽  
pp. 40-44 ◽  
Author(s):  
L. S. Morrison ◽  
Robert Watson
Keyword(s):  
Digital Computer ◽  
Gravity Data ◽  
Number System ◽  
Magnetic Data ◽  
Memory Unit ◽  
Digit Number ◽  
Gravity And Magnetic ◽  
System Data ◽  
Electronic Computers ◽  
Gravity And Magnetic Data

With the advent of electronic computers a revolution in data handling has been brought about. As yet few people outside of scientific research or accounting fields are familiar enough with these computers to know how they can be applied in their particular type of work. Electronic computers consist of three basic elements: an operations register, a digital computer and a memory unit. The memory unit retains information in numeric form in locations that are identified by a coordinate system. Data stored in memory may be retrieved and processed in the digital computer and the results of the computation may be stored for later use. Computations are carried out in the binary or two‐digit number system. The operations register controls the operation of the digital computer and the memory unit and acts as a link between the intent of the programmer and the internal operation of the system. An object, given the proper code numbers describing its shape, size, color, etc., can be identified from other objects by comparison of code numbers. The speed and ability of electronic computers to compare and identify makesn possible the solution of very exacting problems that otherwise would be humanly next to impossible from time considerations. Electronic computers have been used in geophysical exploration to compute and contour derivative maps of gravity and magnetic data. They have been used to reduce gravity data to datum, compute interval and average velocities from velocity profile data and have been used to solve many non‐recurring problems.

Joint and constrained inversion of magnetic and gravity data: A case history from McArthur River area, Canada

Geophysics ◽  
2020 ◽  
pp. 1-76
Author(s):  
Mehrdad Darijani ◽  
Colin G. Farquharson ◽  
Peter G. Lelièvre
Keyword(s):  
Joint Inversion ◽  
Gravity Data ◽  
Real Life ◽  
Magnetic Data ◽  
Airborne Gravity ◽  
Uranium Deposits ◽  
Athabasca Basin ◽  
Compositional Approach ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

Magnetic and gravity data are used in the early stages of exploration for uranium deposits in the Athabasca Basin of Canada, just as for many other mineral exploration scenarios. Uranium mineralization in the Athabasca Basin is located where faults in the basement intersect the unconformity between the basement and the overlying sandstones. Both the gravity and magnetic data are dominated by signatures from the basement and an overburden of glacial sediments. The gravity and magnetic data are effective at mapping the basement geology. Any subtle gravity signal from the mineralization related to the formation of the uranium deposits is masked by the signal from the variable thickness overburden. 3D joint inversion of gravity and magnetic data, first without and then with constraints, is evaluated as a means of better determining the structure of the three main lithologies (overburden, sandstones, basement) in the Athabasca Basin. A significant amount of physical property information is available for the main rock units (and overburden), which makes the use of the compositional approach to joint inversion appropriate. For the joint inversion, the fuzzy c-mean clustering method is used. Results from representative synthetic examples show that the joint inversions can construct the overburden and basement structures better than the independent inversions of gravity and magnetic data. Furthermore, constrained joint inversion allows delineation of all three major layers in the area. The same inversion strategies were then applied to the real airborne gravity and magnetic data from the McArthur River area in the eastern Athabasca Basin. The results obtained demonstrate the capabilities of joint inversion for real-life situations.

scholarly journals Marine geophysical investigations offshore East Greenland

1982 ◽  
Vol 110 ◽  
pp. 81-86
Author(s):  
H.C Larsen ◽  
M.S Andersen
Keyword(s):  
Seismic Refraction ◽  
Geophysical Survey ◽  
Magnetic Data ◽  
East Greenland ◽  
Reflection Seismic ◽  
Denmark Strait ◽  
Gravity And Magnetic ◽  
Marine Gravity ◽  
Regional Project ◽  
Gravity And Magnetic Data

During August and September 1981 a marine geophysical survey was conducted on the shelf of East Greenland. The survey consisted of two programmes, one being part of the ongoing regional project NAD (Andersen et al., 1981; Risum, 1980, and Larsen & Thorning, 1980), and the other being a small programme in the Denmark Strait (fig. 26). In all 2388 km of 24-fold multi-channel seismic data and marine gravity and magnetic data were acquired. The objective of the NAD programme is to acquire regional coverage of aeromagnetic, multi-channel seismic reflection, seismic refraction (sonobuoy), marine gravity and magnetic data of the East Greenland Shelf between latitudes 60°N and 78°N. Aeromagnetic data comprising 63000 line kilometres were acquired in 1979 (Larsen & Thorning, 1980) and 2610 km of marine geophysical data were acquired in 1980 (Andersen et al., 1981). It is anticipated that the NAD acquisition programme will be completed in 1982 after a further four weeks marine geophysical survey. The objective of the Denmark Strait programme is to map the deeper structure and subsurface configuration of what is assumed to be the basaltic basement of this region (Larsen, 1980), and to obtain stratigraphic information of the overlying sedimentary succession with special emphasis on the evaluation of the subsidence history of the region.

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