Marine seismic refraction investigation over the Orpheus Gravity Anomaly off the East Coast of Nova Scotia

1966 ◽  
Author(s):  
G N Ewing ◽  
G D Hobson
Keyword(s):  
Nova Scotia ◽  
Gravity Anomaly ◽  
East Coast ◽  
Seismic Refraction ◽  
Marine Seismic

SEISMIC STUDIES ON THE EASTERN SEABOARD OF CANADA: THE ATLANTIC COAST OF NOVA SCOTIA

1964 ◽  
Vol 1 (1) ◽  
pp. 10-22 ◽  
Author(s):  
D. L. Barrett ◽  
M. Berry ◽  
J. E. Blanchard ◽  
M. J. Keen ◽  
R. E. McAllister
Keyword(s):  
Nova Scotia ◽  
Upper Mantle ◽  
Atlantic Coast ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Crust And Upper Mantle ◽  
Compressional Waves ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Eastern Seaboard

The results of seismic refraction profiles on the Atlantic coast of Nova Scotia and on the continental shelf off Nova Scotia are presented. Compressional and shear waves have been observed in the crust and mantle and suggest that the thickness of the crust is about 34 km. The compressional wave velocities recorded in the main crust and upper mantle are 6.10 and 8.11 km s−1 respectively. No compressional waves with values of velocity between these values can be identified, and this suggests that any "intermediate" layer is thin or absent. The corresponding shear wave velocities are 3.68 and 4.53 km s−1. Values of Poisson's ratio in the crust and mantle are 0.22 and 0.28. Alternative models of the crust which, on the evidence of travel times, might fit the observed results are discussed.

scholarly journals PROSPEK SUMBER DAYA ENERGI BERDASARKAN ANALISIS POLA ANOMALI GAYA BERAT DI DAERAH BIAK DAN SEKITARNYA, PAPUA

2016 ◽  
Vol 13 (2) ◽  
pp. 87 ◽  
Author(s):  
Saultan Panjaitan ◽  
Subagio Subagio
Keyword(s):  
Gravity Anomaly ◽  
Oil And Gas ◽  
East Coast ◽  
Gravity Anomalies ◽  
Source Rocks ◽  
Reservoir Rock ◽  
Ultramafic Rocks ◽  
Reservoir Rocks ◽  
Northern City ◽  
Fluid Reservoir

Hasil penelitian gayaberat di Pulau Biak menghasilkan anomali gayaberat yang dikelompokkan kedalam 2 (dua) satuan yaitu anomali gayaberat 50 mGal hingga 120 mGal membentuk rendahan anomali mencerminkan cekungan. Kelompok anomali gayaberat 120 mGal hingga 220 mGal membentuk tinggian anomali. Pola tinggian anomali sisa 0 mGal hingga 2 mGal diduga sebagai perangkap struktur migas yang terdapat di daerah Kota Biak utara, Mandon dan lepas pantai timur P. Pai. Batuan bertahanan jenis rendah antara 0 - 16 Ohm-meter yang mengindikasikan batuan reservoir jenuh fluida terbentuk di kedalaman 2500 meter. Kedalaman batuan dasar terbentuk antara 7000-8500 meter, dengan rapat massa batuan 2.9 - 3.1 gr/cm3 bertahanan jenis tinggi 1000-8200 Ohm-meter diduga sebagai cerminan dari batuan ultramafik kerak samudera. Batuan yang menyusun di daerah penelitian terdiri atas lapisan batuan Tersier dengan rapat massa 2.45 gr/cm3, batuan Pra-Tersier dengan rapat massa 2.75 gr/cm3 dan batuan dasar dengan rapat massa 3.1 gr/cm3. Batuan sumber adalah serpih Formasi Makat berumur Miosen dengan rapat massa batuan 2.45 gr/cm3, sedangkan batuan reservoir terdiri dari batupasir Formasi Mamberamo. Kata kunci Gayaberat, cekungan, migas, anomali sisa, rapat massa, sesar, antiklin, batuan sumber, tahanan jenis. Gravity research on the island of Biak gravity anomalies are grouped into two (2) units is a gravity anomaly 50 mgal up to 120 mgal is basin reflecting. Gravity anomaly 120 mgal up to 220 mgal formed heights anaomaly. Altitude residual anomaly from 0 mGal to 2 mgal is oil and gas as trapping structures contained in the northern City of Biak, off the east coast Mandon and P. Pai. The rocks is of low resistivity between 0 -16 Ohm-meter that indicates the saturated fluid reservoir rocks are in the depths of 2500 meter. The depth of the bedrock formed between 7000-8500 meters, with density 2.9 - 3.1 gr / cm3 is heights resistivity types of 1000-8200 Ohm-meter interpreted as a reflection of ultramafic rocks oceanic crust. The rocks in the study area consists of Tertiary rocks layers with a density 2.45 gr / cm3, the Pre-Tertiary rocks with density 2.75 gr / cm3 and bedrock with density 3.1 gr / cm3. The source rocks is of shale from Makat Formation Miocene age with density 2.45 gr / cm3, and the reservoir rock consists of sandstone Mamberamo Formation. Keywords: Gravity, basin, oil and gas, recidual anomaly, density, fault, anticline, source rocks, resistivity.

scholarly journals Seismic and Gravity Investigations of the Central Volcanic Region, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Timothy Andrew Stern
Keyword(s):  
Gravity Anomaly ◽  
Gravity Model ◽  
Upper Mantle ◽  
Seismic Data ◽  
Seismic Refraction ◽  
Volcanic Rocks ◽  
Low Density ◽  
Anomaly Field ◽  
Volcanic Region ◽  
Back Arc

<p>Gravity and seismic refraction studies were undertaken in order to investigate the geological structure of the Central Volcanic Region. A detailed analysis of density determinations from bore-hole rock samples, three seismic refraction surveys and a spectral analysis of the magnetic anomaly field are described. Interpretation of the observed gravity anomaly fie ld for the Central Volcanic Region is initially undertaken by analytically separating the observed anomaly field into its regional and residual components; the almost entirely negative residual anomaly field is then interpreted in terms of varying thicknesses of near-surface, low-density volcanic rocks. At Mangakino and just west of Taupo, however, it is found that the calculated gravity anomaly effect of the seismically determined thickness of low-velocity, and hence low-density, volcanic rocks is less negative than the observed residuals; at both locations "secondary residuals" of about -200 μN/kg remain unexplained. Models are presented that account for these secondary residuals as being due to discrete volumes of low-density molten rhyolite emplaced within the seismic basement. The second method of gravity interpretation used in this study involves modelling all components of the observed gravity anomaly field . This necessitated giving consideration to both the gravity effect of the subducted Pacific plate and to seismic data bearing upon the variation of crustal thickness and mantle density throughout the central North Island. A gravity model for the central North Island is developed for which the important features are:  i) The crust of the Central Volcanic Region is deduced to be only about half the normal continental thickness, and underlying the crust is an "anomalous", low-density upper mantle. This finding from the gravity model is supported by the results of a previous study of upper mantle seismic velocities and from the interpretation of a longrange seismic refraction survey carried out within the Region. These seismic data indicate the depth to, and the velocity of the upper mantle beneath the Region to be 15 km and 7.4 km/s respectively. ii) The positive gravity anomalies that predominate over the western and northwestern North Island can largely be explained by gravity edge-effects associated with variations in the crustal thickness and mantle density within the back-arc areas of the North Island. The gravity model is interpreted as lending support for a previously made proposal that the Region is the site of asymmetric back-arc spreading, and that the crustal rocks now being created are transitional in character between typical oceanic and typical continental.</p>

The East Coast Onshore-Offshore Experiment, II. Seismic refraction measurements on the continental shelf between Cape Hatteras and Cape Fear

1968 ◽  
Vol 58 (3) ◽  
pp. 821-834
Author(s):  
John J. Dowling
Keyword(s):  
Continental Shelf ◽  
East Coast ◽  
Seismic Refraction ◽  
Crystalline Basement ◽  
Well Control ◽  
Depth Contour ◽  
Cape Hatteras ◽  
Near Shore ◽  
Cape Fear ◽  
Refraction Data

abstract During the East Coast OnShore-OffShore Experiment (ECOOE) two lines of instrumented buoys were anchored on the continental shelf between Cape Hatteras and Cape Fear. One line extended from near shore to the 100 fathom depth contour. The other line was parallel to and near the 100 fathom depth contour. Shots varying in size from 20 lbs. to 10 tons were fired along both lines. From the refraction data obtained and well-control available, crystalline basement is correlated with a layer of velocity 5.96 km/sec, the top of the Lower Cretaceous with a layer of velocity 3.54 km/sec and the top of the Upper Cretaceous with a layer of 2.44 km/sec. A contour map of the depth to crystalline basement under the shelf and structure sections are presented. The statistical uncertainties in the depths and velocities were determined.

Marine seismic refraction studies on the continental margin to the south of Australia

1965 ◽  
Vol 12 (4) ◽  
pp. 479-495
Author(s):  
L.V Hawkins ◽  
J.F Hennion ◽  
J.E Nafe ◽  
H.A Doyles
Keyword(s):  
Continental Margin ◽  
Seismic Refraction ◽  
The South ◽  
Marine Seismic
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