Shallow and deep crustal structure of the western Sverdrup Basin, arctic Canada

1984 ◽  
Vol 21 (8) ◽  
pp. 902-919 ◽  
Author(s):  
L. W. Sobczak ◽  
A. Overton
Keyword(s):  
Gravity Data ◽  
Seismic Refraction ◽  
Sediment Accumulation ◽  
Density Control ◽  
Gravity Effects ◽  
Sverdrup Basin ◽  
Deep Crustal Structure ◽  
Crystalline Crust ◽  
Free Air Anomaly ◽  
Drill Holes

An analysis of gravity data along two detailed profiles over the western Sverdrup Basin in the Canadian Arctic supports a seismic refraction model. Drill holes as deep as 5.4 km near the profiles provide excellent density control. Mean densities in the thickest part of the basin exceed those in the thinner parts by an average of 0.13 Mg/m3.Bouguer anomalies corrected for the effect of water, sedimentary, and crystalline layers indicate significant anomalies that vary in width from 20 to 275 km and in amplitude from 3 to 46 mGal (30 to 460 μm s−2). These can all be explained by density structures within the sedimentary column. Sedimentary thickness along the profiles varies from 9 to 17.4 km, crystalline thickness varies from 18 to 33 km, and the total crustal thickness varies from 34 to 42 km. The analysis also shows: (1) negative gravity effects of about 60 to 120 mGal (600 to 1200 μm s−2) due to the mass deficiency of the water and sediments are offset by positive gravity effects of similar magnitude due to crustal thinning; (2) isostatic compensation of water and sediments by a mantle antiroot is evident from a regional free-air anomaly near zero and the apparent inverse variation of sedimentary thickness with the thickness of the crystalline crust; (3) in the thickest part of the basin, undulations at the sedimentary–crystalline boundary are in phase with and smaller in amplitude than undulations at the crust–mantle boundary; conversely, in the thinnest part of the basin, these undulations are out of phase and larger in amplitude.These effects may be explained by stretching of a crystalline crust and a general decrease in crustal rigidity with depth during sediment accumulation and subsequent orogenic events.

Crustal section across the polar continent–ocean transition in Canada

1986 ◽  
Vol 23 (5) ◽  
pp. 608-621 ◽  
Author(s):  
L. W. Sobczak ◽  
U. Mayr ◽  
J. F. Sweeney
Keyword(s):  
Transition Zone ◽  
Structural Model ◽  
Gravity Anomalies ◽  
The Arctic ◽  
Near Surface ◽  
Mafic Rocks ◽  
Gravity Effects ◽  
Sverdrup Basin ◽  
Crystalline Crust ◽  
Vertical Density

The Canadian Arctic Transect extends northwards from the Canadian Shield across a thick (about 18 km) and wide (over 800 km) sedimentary section consisting of four overlapping basins. These overlie a continental crystalline crust that thins from 48 to 8 km towards the Canada Basin. The latter overlies a relatively thin (5 – 10 km thick) oceanic crust below the Arctic Ocean. The calculated gravity effects of the upper sedimentary section were stripped away from the observed gravity anomaly, and the residual anomalies were used to determine the boundaries between sediment and crystalline crust and between crust and mantle. Residual anomalies with short wavelength and steep gradients were used to modify the initial near-surface structural model and to identify zones of evaporite and mafic rocks within the sedimentary rock column.Some interesting results emerge from this analysis: (1) analysis of the gradients of the shelf and slope suggests that shelf subsidence is hinged about a line near the central axis of the Sverdrup Basin; (2) continental crystalline crust thins oceanward from 48 km to 8 km at the transition zone over a distance of 825 km and appears to have stretched from an original width of 543 km, for an apparent stretch factor of about 1.5; (3) sediment thickness is usually inversely related to the crystalline crustal thickness; (4) the mantle below the ocean appears to be less dense than below the continental crust, with an assumed significant vertical density boundary between the two below the continental shelf (transition zone); (5) this analysis supports the concept that evaporites occur along the axis of the Sverdrup Basin, and mafic rocks appear to be concentrated along the flanks of the Sverdrup Basin; and (6) seismicity usually occurs over areas of relatively positive gravity anomalies that are considered to be the result of uncompensated sedimentary loads or mafic igneous intrusions or are areas of uplifted and folded rocks.

Airborne gravity measurements over mountainous areas by using a LaCoste & Romberg air‐sea gravity meter

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 807-816 ◽  
Author(s):  
Jérôme Verdun ◽  
Roger Bayer ◽  
Emile E. Klingelé ◽  
Marc Cocard ◽  
Alain Geiger ◽  
...  
Keyword(s):  
Data Reduction ◽  
Classical Method ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Mountainous Areas ◽  
Free Air ◽  
Gravity Measurements ◽  
Free Air Anomaly

This paper introduces a new approach to airborne gravity data reduction well‐suited for surveys flown at high altitude with respect to gravity sources (mountainous areas). Classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western French Alps by using a LaCoste & Romberg air‐sea gravity meter. The part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra. Beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft. This finding is theoretically argued by solving the equation of the gravimetric system (gravity meter and stabilized platform). The transfer function of the system is derived, and a new formulation of airborne gravity data reduction, which takes care of the sensitive response of spring tension to observable gravity field wavelengths, is given. The resulting gravity signal exhibits a residual noise caused by electronic devices and short‐wavelength Eötvös effects. The use of dedicated exponential filters gives us a way to eliminate these high‐frequency effects. Examples of the resulting free‐air anomaly at 5100‐m altitude along one particular profile are given and compared with free‐air anomaly deduced from the classical method for processing airborne gravity data, and with upward‐continued ground gravity data. The well‐known trade‐off between accuracy and resolution is discussed in the context of a mountainous area.

scholarly journals A long-offset seismic reflection and refraction study of the Gippsland and Bass Basins from onshore recording of a marine air-gun source

1989 ◽  
Vol 20 (2) ◽  
pp. 293
Author(s):  
C.D.N. Collins ◽  
J.P. Cull ◽  
J.B. Willcox ◽  
J.B. Colwell
Keyword(s):  
Deep Structure ◽  
Seismic Refraction ◽  
Reflection And Refraction ◽  
Air Gun ◽  
Long Offset ◽  
Deep Crustal Structure ◽  
Basin Formation ◽  
Seismic Refraction Data ◽  
Marine Air ◽  
Refraction Data

Seismic refraction data were obtained for the Bass and Gippsland Basins during the 1988 cruise of the BMR research vessell "Rig Seismic". Seismic recorders were deployed on land by BMR and Monash University to record long-offset wide-angle reflection and refraction data using the ship's air-guns as the energy source. Preliminary results have now been obtained from these data providing information on deep crustal structure related to the basin formation. Two crustal layers have been detected with velocities of 4.5 km/s increasing to 7.4 km/s (unreversed) at depths exceeding 20 km. Additional data have now been obtained over a traverse length of 170 km to provide constraints on the deep structure of Bass Strait and the Lachlan Fold Belt in Victoria and Tasmania.

Receiver function analyses and joint inversion with gravity data: new constraints on the Ivrea geophysical body along a high-resolution profile

2020 ◽  
Author(s):  
Matteo Scarponi ◽  
György Hetényi ◽  
Jaroslava Plomerová ◽  
Stefano Solarino ◽  
Ludovic Baron
Keyword(s):  
Receiver Function ◽  
Joint Inversion ◽  
Gravity Data ◽  
Sampling Rate ◽  
Seismic Refraction ◽  
Western Alps ◽  
Transverse Component ◽  
Reference Points ◽  
Physical Parameters ◽  
S Wave

<p>We collected new seismological and gravity data in the Val Sesia and Lago Maggiore regions in NW Italy to constrain the geometry and properties of the Ivrea Geophysical Body. This piece of lower Adriatic lithosphere is known to be at anomalously shallow depth along the inner arc of the Western Alps, yet existing seismological constraints (vintage seismic refraction data, local earthquake tomography) are spatially sparse. With the aim to reach higher spatial resolution in imaging the structure of the IGB, we analyze the seismological data with various receiver function approaches to map the main velocity discontinuities, followed by joint inversion with gravity data to fill the bulk properties of bodies with densities.</p><p>The new data acquisition consisted of two type of campaigns. For seismology, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague) along a linear West-East profile at 5 km spacing along Val Sesia and across the Lago Maggiore. This network continuously recorded seismic data for 27 months at 100 Hz sampling rate. For gravimetry, we compiled existing datasets and then completed the spatial gaps by relative gravity surveys, tied to absolute reference points, to achieve 1 gravity point every 1-2 km along the profile.</p><p>The receiver function (RF) analyses aim at detecting velocity increases with depth: primarily the Moho and the shallow IGB interfaces and their crustal reverberations (multiples), together with their potential dip by analyzing the transverse component RFs. Furthermore, we aim at investigating the sharpness of the velocity gradient across the discontinuities by analyzing the frequency dependence of the corresponding RF peaks. We aim at reproducing the observations by simple synthetic models.</p><p>The 2D joint inversion combines S wave velocity V<sub>S</sub> and bulk density as physical parameters to match both the seismological and gravimetry data. The relationship between the two parameters is initially chosen from the literature, but depending on the first results the relation itself may be inverted for, considering the various high-grade metamorphic rocks observed at the surface in the area, whose properties may not align with classical V<sub>S</sub>–density equations. In conclusion, we propose new constraints on the IGB, demonstrating the advantage of using multi-disciplinary geophysical observations and improved data coverage across the study area.</p>

scholarly journals Deep crustal structure of the Tuamotu plateau and Tahiti (French Polynesia) based on seismic refraction data

2002 ◽  
Vol 29 (14) ◽  
pp. 1-1-1-4 ◽  
Author(s):  
Martin Patriat ◽  
Frauke Klingelhoefer ◽  
Daniel Aslanian ◽  
Isabelle Contrucci ◽  
Marc-André Gutscher ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Seismic Refraction ◽  
French Polynesia ◽  
Deep Crustal Structure ◽  
Seismic Refraction Data ◽  
Refraction Data

scholarly journals GRAVIMETRIC GEOID MODELLING OVER PENINSULAR MALAYSIA USING TWO DIFFERENT GRIDDING APPROACHES FOR COMBINING FREE AIR ANOMALY

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 515-522
Author(s):  
M. F. Pa’suya ◽  
A. H. M. Din ◽  
J. C. McCubbine ◽  
A. H. Omar ◽  
Z. M. Amin ◽  
...  
Keyword(s):  
Gravity Data ◽  
Reference Signal ◽  
Digital Terrain Model ◽  
Peninsular Malaysia ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Anomaly

Abstract. We investigate the use of the KTH Method to compute gravimetric geoid models of Malaysian Peninsular and the effect of two differing strategies to combine and interpolate terrestrial, marine DTU17 free air gravity anomaly data at regular grid nodes. Gravimetric geoid models were produced for both free air anomaly grids using the GOCE-only geopotential model GGM GO_CONS_GCF_2_SPW_R4 as the long wavelength reference signal and high-resolution TanDEM-X global digital terrain model. The geoid models were analyzed to assess how the different gridding strategies impact the gravimetric geoid over Malaysian Peninsular by comparing themto 172 GNSS-levelling derived geoid undulations. The RMSE of the two sets of gravimetric geoid model / GNSS-levelling residuals differed by approx. 26.2 mm. When a 4-parameter fit is used, the difference between the RMSE of the residuals reduced to 8 mm. The geoid models shown here do not include the latest airborne gravity data used in the computation of the official gravimetric geoid for the Malaysian Peninsular, for this reason they are not as precise.

scholarly journals Regional Seafloor Topography by Extended Kalman Filtering of Marine Gravity Data without Ship-Track Information

2021 ◽  
Vol 14 (1) ◽  
pp. 169
Author(s):  
Lucía Seoane ◽  
Guillaume Ramillien ◽  
Benjamin Beirens ◽  
José Darrozes ◽  
Didier Rouxel ◽  
...  
Keyword(s):  
Gravity Data ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Seafloor Topography ◽  
Single Beam ◽  
Beam Depth ◽  
Marine Gravity ◽  
Gravity Measurements ◽  
Polynomial Series ◽  
Free Air Anomaly

An iterative Extended Kalman Filter (EKF) approach is proposed to recover a regional set of topographic heights composing an undersea volcanic mount by the successive combination of large numbers of gravity measurements at sea surface using altimetry satellite-derived grids and taking the error uncertainties into account. The integration of the non-linear Newtonian operators versus the radial and angular distances (and its first derivatives) enables the estimation process to accelerate and requires only few iterations, instead of summing Legendre polynomial series or using noise-degraded 2D-FFT decomposition. To show the effectiveness of the EKF approach, we apply it to the real case of the bathymetry around the Great Meteor seamount in the Atlantic Ocean by combining only geoid height/free-air anomaly datasets and using ship-track soundings as reference for validation. Topography of the Great Meteor seamounts structures are well-reconstructed, especially when regional compensation is considered. Best solution gives a RMS equal to 400 m with respect to the single beam depth observations and it is comparable to RMS obtained for ETOPO1 of about 365 m. Larger discrepancies are located in the seamount flanks due to missing high-resolution information for gradients. This approach can improve the knowledge of seafloor topography in regions where few echo-sounder measurements are available.

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