Regional gravity setting of the Sudbury Structure

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1680-1690 ◽  
Author(s):  
R. B. Hearst ◽  
W. A. Morris
Keyword(s):  
Numerical Methods ◽  
Gravity Anomaly ◽  
Gravity Field ◽  
Downward Continuation ◽  
Gravity Models ◽  
Gravity Modeling ◽  
Meteorite Impact ◽  
Sudbury Structure ◽  
Regional Gravity ◽  
Impact Origin

In the vicinity of Sudbury, Ontario, Canada, the boundary between the Southern and Superior tectonic provinces is overlain by the elliptical Sudbury Structure. On the basis of gravity modeling, genesis of the Sudbury Structure has been attributed to either a magmatic origin (having a dense hidden differentiate zone) or a meteorite impact origin (there being no dense hidden mass). The difference between the two gravity models centers on the problem of regional‐residual separation. As shown by numerous previous studies, any such separation of components is nonunique. This becomes especially problematic when, as in Sudbury, a portion of the near‐surface geology has a similar orientation and dimension to more deep‐seated source. In this paper, several numerical methods (upward continuation, downward continuation, wavelength filtering, trend‐surface analysis) for determining the regional component of the gravity field associated with the Sudbury Structure have been applied and evaluated. Of the numerical methods used, the upward and downward continuation operators provided the most insight into the deep structural controls of the Sudbury Basin. Our preferred interpretation of the regional gravity field invokes a two‐component structure. Underlying the southern half of the Sudbury Structure is a laterally continuous gravity anomaly that is probably associated with a zone of uplifted Huronian volcanics. The gravity anomaly under the northern portion of the Sudbury Structure has a more restricted spatial extent. The close association between the northern limit of the gravity anomaly and the surface outcrop of the Levack Gneiss suggests the source of this anomaly is probably a slab of dense Levack Gneiss. This interpretation favors a meteorite impact origin for the Sudbury Structure.

Towards an updated, enhanced regional gravity field solution for Antarctica

2021 ◽  
Author(s):  
Mirko Scheinert ◽  
Philipp Zingerle ◽  
Theresa Schaller ◽  
Roland Pail ◽  
Martin Willberg
Keyword(s):  
Gravity Anomaly ◽  
Gravity Field ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Data Set ◽  
Gravity Field Model ◽  
Terrestrial Gravity ◽  
Field Solution ◽  
Gravity Disturbances ◽  
Regional Gravity

<p>In the frame of the IAG Subcommission 2.4f “Gravity and Geoid in Antarctica” (AntGG) a first Antarctic-wide grid of ground-based gravity anomalies was released in 2016 (Scheinert et al. 2016). That data set was provided with a grid space of 10 km and covered about 73% of the Antarctic continent. Since then a considerably amount of new data has been made available, mainly collected by means of airborne gravimetry. Regions which were formerly void of any terrestrial gravity observations and have now been surveyed include especially the polar data gap originating from GOCE satellite gravimetry. Thus, it is timely to come up with an updated and enhanced regional gravity field solution for Antarctica. For this, we aim to improve further aspects in comparison to the AntGG 2016 solution: The grid spacing will be enhanced to 5 km. Instead of providing gravity anomalies only for parts of Antarctica, now the entire continent should be covered. In addition to the gravity anomaly also a regional geoid solution should be provided along with further desirable functionals (e.g. gravity anomaly vs. disturbance, different height levels).</p><p>We will discuss the expanded AntGG data base which now includes terrestrial gravity data from Antarctic surveys conducted over the past 40 years. The methodology applied in the analysis is based on the remove-compute-restore technique. Here we utilize the newly developed combined spherical-harmonic gravity field model SATOP1 (Zingerle et al. 2019) which is based on the global satellite-only model GOCO05s and the high-resolution topographic model EARTH2014. We will demonstrate the feasibility to adequately reduce the original gravity data and, thus, to also cross-validate and evaluate the accuracy of the data especially where different data set overlap. For the compute step the recently developed partition-enhanced least-squares collocation (PE-LSC) has been used (Zingerle et al. 2021, in review; cf. the contribution of Zingerle et al. in the same session). This method allows to treat all data available in Antarctica in one single computation step in an efficient and fast way. Thus, it becomes feasible to iterate the computations within short time once any input data or parameters are changed, and to easily predict the desirable functionals also in regions void of terrestrial measurements as well as at any height level (e.g. gravity anomalies at the surface or gravity disturbances at constant height).</p><p>We will discuss the results and give an outlook on the data products which shall be finally provided to present the new regional gravity field solution for Antarctica. Furthermore, implications for further applications will be discussed e.g. with respect to geophysical modelling of the Earth’s interior (cf. the contribution of Schaller et al. in session G4.3).</p>

Evidence in support of a meteorite impact crater at Poplar Bay, Lac du Bonnet, southeastern Manitoba, Canada

1976 ◽  
Vol 13 (11) ◽  
pp. 1608-1612
Author(s):  
D. L. Trueman
Keyword(s):  
Gravity Anomaly ◽  
Impact Crater ◽  
Gravity Survey ◽  
Meteorite Impact ◽  
Maximum Value ◽  
Igneous Origin ◽  
Magnetic Signature ◽  
Geophysical Study ◽  
Impact Origin

Poplar Bay, in southeastern Manitoba, is a circular lake approximately 3 km in diameter, 21 m in depth, and is framed by radial and arcuate photolineaments. Geophysical study of Poplar Bay shows a unique magnetic signature, and results of a gravity survey indicate a profound deficiency of mass under the lake. The form of the gravity anomaly is circular, and it has a maximum value of −7 mGal.There is no evidence of an igneous origin for the feature and data indicate the plausibility of a meteorite impact origin for Poplar Bay.

Theoretical frame for the application of IOST in the downward continuation of GOCE SGG data

2021 ◽  
Author(s):  
Ilias N. Tziavos ◽  
Dimitrios A. Natsiopoulos ◽  
Georgios S. Vergos ◽  
Eleftherios A. Pitenis ◽  
Elisavet G. Mamagiannou
Keyword(s):  
Gravity Field ◽  
Heterogeneous Data ◽  
Theoretical Background ◽  
Geoid Determination ◽  
Downward Continuation ◽  
Geopotential Model ◽  
Correlated Errors ◽  
Satellite Gravity ◽  
The Earth ◽  
Regional Gravity

<p>Within the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, one of the main goals is the investigation of downward continuation schemes for the GOCE Satellite Gravity Gradiometry (SGG) data. It is well known that once the original SGG observations have been filtered to the GOCE Measurement Band Width (MBW), in order to remove noise and long-wavelength correlated errors, a crucial point for gravity field and geoid determination refers to the combination of GOCE data with local gravity field information. One possible way to exploit GOCE data is to use them in a Spherical Harmonic Synthesis (SHS) to derive a GOCE-only and/or a combined Global Geopotential Model. Our aim is to overcome the inherent smoothing of SHS and use directly the SGG data in order to investigate their contribution to regional gravity field and geoid determination. For that, methods based on the input-output-system-theory (IOST) are used for the combination of heterogeneous data at the Earth’s surface and at the satellite altitude or a mean sphere. The GOCE Level 2 gradients are first processed, transformed and reduced to a mean orbit using the IOST methods and then are downward continued to the Earth’s surface with an iterative Monte Carlo method (simulated annealing - SA). In this work we present the theoretical background of the proposed methodology and key-concepts for its implementation.</p>

scholarly journals Improved the Accuracy of Seafloor Topography from Altimetry-Derived Gravity by the Topography Constraint Factor Weight Optimization Method

2021 ◽  
Vol 13 (12) ◽  
pp. 2277
Author(s):  
Yongjin Sun ◽  
Wei Zheng ◽  
Zhaowei Li ◽  
Zhiquan Zhou
Keyword(s):  
Gravity Anomaly ◽  
Ordinary Kriging ◽  
Gravity Models ◽  
Weight Optimization ◽  
Kriging Method ◽  
Seafloor Topography ◽  
Constraint Factor ◽  
Topography Model ◽  
Regional Gravity ◽  
Better Than

Gravity geologic method is one of the important to derive seafloor topography by using altimetry-gravity, and its committed step is gridding of regional gravity anomaly. Hence, we proposed a topography constraint factor weight optimization (TCFWO) method based on ordinary kriging method. This method fully considers the influence of topography factors on the construction of regional gravity grid besides horizontal distance. The results of regional gravity anomaly models constructed in the Markus-Wake seamount area show that the TCFWO method is better than ordinary kriging method. Then, the above two regional gravity models were applied to invert the seafloor topography. The accuracy of derived topographic models was evaluated by using the shipborne depth data and existing seafloor topography models, including ETOPO1 and V19.1 model. The experimental results show that the accuracy of ST_TCFWO (seafloor topography model inverted by TCFWO method) is better than ST_KR (seafloor topography model inverted by kriging method) and ETOPO1 model. Compared with the ST_KR, the accuracy of the ST_TCFWO has improved about 26%. In addition, the accuracy of seafloor topography is affected by the variation of depth, the distribution of control points and the type of terrain. In different depth layers, the ST_TCFWO has better advantages than ST_KR. In the sparse shipborne measurements area, the accuracy of ST_TCFWO is better than that of V19.1, ETOPO1 and ST_KR. Moreover, compared to other models, ST_TCFWO performs better in flat submarine plain or rugged seamount area.

scholarly journals The Role Of High Degree Potential Coefficients And Satellite Altimeter Data In Gravity Field Aproximation In The Malaysian Region

1988 ◽  
pp. 1-9
Author(s):  
Majid Kadir
Keyword(s):  
Gravity Anomaly ◽  
Gravity Field ◽  
Peninsular Malaysia ◽  
Gravity Models ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Earth Gravity ◽  
Gravity Measurements ◽  
High Degree ◽  
Satellite Altimeter Data

Earth Gravity models (OSU81, OSU86E,and F) defined by a set of high degree potential coefficients were used to generate the geopotential geoid in the Malaysian region. In the very near future, land gravity measurements can be carried out where the station positioning in the survey will be by Global Positioning System (GPS) operating in differential mode. In areas with scarce height benchmark, especially in the remote areas of Peninsular Malaysia, the geopotential geoid can be utilized in conjunction with the satellite derived ellipsoidal heights to yield the orthometric heights of the gravity stations. Satellite altimeter data has the ability to provide high frequency gravity field information in the surrounding marine areas. The method of gravity anomaly recovery in the Tioman test area was based on the theory of least squares collocation. Gravity anomaly maps derived from satellite altimeter data can be used to scan large off-shore areas for detecting density contrasts within the oceanic's outer crust, and thus providing an indirect indication of potential hydrocarbon deposits.

Rb–Sr Study of Shock-metamorphosed Inclusions from the Onaping Formation, Sudbury, Ontario

1971 ◽  
Vol 8 (4) ◽  
pp. 435-443 ◽  
Author(s):  
Paul D. Fullagar ◽  
Michael L. Bottino ◽  
Bevan M. French
Keyword(s):  
Isotopic Composition ◽  
Granitic Rocks ◽  
Metamorphic Event ◽  
Meteorite Impact ◽  
Impact Melt ◽  
Sudbury Structure ◽  
Impact Origin

Sixteen inclusions from the Onaping Formation, a possible meteorite impact breccia at Sudbury, Ontario, were analyzed for Rb, Sr, and Sr isotopic composition. Inclusions ranged from weakly shocked granitic rocks to heterogeneous glassy inclusions (impact melt?). Strongly shocked and glassy inclusions yield separate isochrons of 1430 ± 65 m.y. and 1480 ± 55 m.y., respectively (λ 87Rb = 1.39 × 10−11 y−1). Twenty-eight samples, including data for Onaping Formation samples from the literature, have an isochron age of 1515 ± 65 m.y. Isochron initial 87Sr/86Sr ratios range from 0.714 to 0.717, The Onaping samples thus appear anomalously younger than the 1700 m.y. ages reported for the geologically younger Nickel Irruptive and Whitewater sediments. If the highly shocked granitic inclusions and glasses in the Onaping Formation are relatively susceptible to radiogenic Sr loss during subsequent thermal events, the data are compatible with an impact origin for the Sudbury structure. The whole-rock ages, combined with reported mineral ages, suggest a metamorphic event in the Sudbury area 1400–1500 m.y. ago.

scholarly journals Application of the nonlinear optimisation in regional gravity field modelling using spherical radial base functions

2021 ◽  
Author(s):  
Hany Mahbuby ◽  
Yazdan Amerian ◽  
Amirhossein Nikoofard ◽  
Mehdi Eshagh
Keyword(s):  
Gravity Anomaly ◽  
Gravity Field ◽  
Fundamental Equation ◽  
Physical Geodesy ◽  
Gravity Anomalies ◽  
Global Navigation Satellite Systems ◽  
Disturbing Potential ◽  
Gravity Field Model ◽  
Regional Gravity ◽  
Mean Square Errors

AbstractThe gravity field is a signature of the mass distribution and interior structure of the Earth, in addition to all its geodetic applications especially geoid determination and vertical datum unification. Determination of a regional gravity field model is an important subject and needs to be investigated and developed. Here, the spherical radial basis functions (SBFs) are applied in two scenarios for this purpose: interpolating the gravity anomalies and solving the fundamental equation of physical geodesy for geoid or disturbing potential determination, which has the possibility of being verified by the Global Navigation Satellite Systems (GNSS)/levelling data. Proper selections of the number of SBFs and optimal location of the applied SBFs are important factors to increase the accuracy of estimation. In this study, the gravity anomaly interpolation based on the SBFs is performed by Gauss-Newton optimisation with truncated singular value decomposition, and a Quasi-Newton method based on line search to solve the minimisation problems with a small number of iterations is developed. In order to solve the fundamental equation of physical geodesy by the SBFs, the truncated Newton optimisation is applied as the Hessian matrix of the objective function is not always positive definite. These two scenarios are applied on the terrestrial free-air gravity anomalies over the topographically rough area of Auvergne. The obtained accuracy for the interpolated gravity anomaly model is 1.7 mGal with the number of point-masses about 30% of the number of observations, and 1.5 mGal in the second scenario where the number of used kernels is also 30%. These accuracies are root mean square errors (RMSE) of the differences between predicted and observed gravity anomalies at check points. Moreover, utilising the optimal constructed model from the second scenario, the RMSE of 9 cm is achieved for the differences between the gravimetric height anomalies derived from the model and the geometric height anomalies from GNSS/levelling points.

scholarly journals Strategy for the realisation of the International Height Reference System (IHRS)

2021 ◽  
Vol 95 (3) ◽  
Author(s):  
Laura Sánchez ◽  
Jonas Ågren ◽  
Jianliang Huang ◽  
Yan Ming Wang ◽  
Jaakko Mäkinen ◽  
...  
Keyword(s):  
Gravity Field ◽  
Reference System ◽  
International Association ◽  
Accuracy Assessment ◽  
Equipotential Surface ◽  
Precise Determination ◽  
Gravity Models ◽  
Reference Network ◽  
Global Gravity Models

AbstractIn 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbersC(P) referring to an equipotential surface defined by the conventional valueW0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinatesXreferring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.

2-D gravity modeling with analytically defined geometry and quadratic polynomial density functions

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1730-1734 ◽  
Author(s):  
Beatriz Martín‐Atienza ◽  
Juan García‐Abdeslem
Keyword(s):  
Numerical Methods ◽  
Polynomial Function ◽  
Continuous Functions ◽  
Model Solution ◽  
Gravity Modeling ◽  
Density Functions ◽  
Gravity Effect ◽  
New Methods ◽  
Order Polynomial ◽  
Broad Variety

New methods for 2-D modeling of gravity anomaly data are developed following an approach that uses both analytic and numerical methods of integration. The forward‐model solution developed here is suitable to calculate the gravity effect caused by a 2-D source body bounded either laterally or vertically by continuous functions. In our models, the density contrast is defined by a second‐order polynomial function of depth and distance along the profile. We present several examples to show that our models are capable of accommodating a broad variety of geologic structures.

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