Typical Characteristics of the Earth’s Magnetic and Gravity Fields Related to Global and Regional Tectonics

2021 ◽  
Vol 62 (1) ◽  
pp. 6-24 ◽  
Author(s):  
N.L. Dobretsov ◽  
D.V. Metelkin ◽  
A.N. Vasilevskiy
Keyword(s):  
Geomagnetic Field ◽  
Extreme Values ◽  
Gravity Anomalies ◽  
Geologic History ◽  
Tectonic Processes ◽  
Igneous Provinces ◽  
Gravity Fields ◽  
Regional Tectonic ◽  
Qualitative Similarity ◽  
Free Air Gravity

Abstract —We present a summary and analysis of current views on the magnetic and gravity fields of the Earth as a reflection of global and regional tectonic processes. The discussion concerns the probable interconnection between the distribution of the geomagnetic field characteristics, gravity anomalies and the manifestations of mantle plume magmatism as the most remarkable geologic indicator of deep geodynamics. We demonstrate that the distribution of the characteristics of the main geomagnetic field has a qualitative similarity to anomalies of the gravity field. Brief variations of the geomagnetic field are due to high-frequency oscillations in the ionosphere, do not affect the general state of the field, and are useless when considering issues of global tectonics. On the contrary, variations with long periodicities, first of all geomagnetic reversals, can be among the main indicators of the evolution of the geodynamo – the heat mechanism controlling the entire series of global tectonic processes. The frequency of reversals is determined by the intensity of mantle plumes that cause the cooling of the core, increase the convection rate in the asthenosphere, and respectively, the periodic changes in the tectonosphere. We assume the existence of three modes of behavior for this system. The first one corresponds to steady convection, in which reversals are extremely rare or do not happen at all. These episodes – superchrons – compose no more than 20% of the duration of the Phanerozoic. The second mode occurs significantly more often in the geologic history and is characterized by active convection with frequent reversals happening at least once every 5 Myr. Finally, the third mode, which is rare for the Phanerozoic but was probably more prevalent in the early Precambrian, corresponds to hyperactive turbulent convection, when the frequency of reversals reached 20 and possibly more during one million years. Although the demonstrated qualitative similarity in the position of extreme values of the main geomagnetic field, the centers of free air gravity anomalies, and manifestations of large igneous provinces does not yet have a credible explanation, we consider it to be fundamental and requiring special study and detailed elaboration.

scholarly journals PREDICTING OF POTENTIAL PROPAGATION CHANNELS FOR ECOLOGICALLY HARMFUL SUBSTANCES IN GEOLOGIC MEDIA

2001 ◽  
Vol 1 ◽  
pp. 102
Author(s):  
B.H. Морозов ◽  
B.H. Татаринов ◽  
И.Ю. Буров
Keyword(s):  
Temporal Variations ◽  
Tectonic Processes ◽  
Hierarchical Levels ◽  
Regional Tectonic ◽  
Harmful Substances ◽  
Geologic Media

The questions o f assessment and prédiction of potential charnels o f infiltration of radionuclides in géologie environment are discussed. This is specially important for underground allocation of the nuclear objects. The method of allows for spatial-temporal variations in a geological massif at ail hierarchical levels from régional tectonic processes up top peri-contour zones of chambers.

scholarly journals On the accuracy of gravity fields obtained with Newton integrals on a hollow sphere

2020 ◽  
Author(s):  
Ludovic Jeanniot ◽  
Cedric Thieulot ◽  
Bart Root ◽  
John Naliboff ◽  
Wim Spakman
Keyword(s):  
Plate Tectonics ◽  
Mass Density ◽  
Plate Boundary ◽  
Spherical Geometry ◽  
Gravity Anomalies ◽  
Scaling Factor ◽  
Density Model ◽  
Satellite Gravity ◽  
Early Results ◽  
Gravity Fields

<p>The mass-density distribution of the Earth drives mantle convection and plate tectonics but is poorly known. We aim to predict gravity fields as a constraint for geodynamical modelling. In order to compute synthetic Earth gravity one must define a spherical geometry filled with a density model. Density models for the whole mantle down to the CMB come from tomographic models which therefore require converting speed waves velocities to density using a scaling factor.</p><p>We use a discretised integration method to compute globally gravity acceleration, gravity anomalies, potential and gradients, in the state of the art finite element code ASPECT.</p><p>Three density models are tested separately: a density field obtained from SL2013 and S40RTS tomographic models for the deep mantle, and the density model CRUST1.0 for the thin upper lithosphere layer. We combine these 3 datasets into one to create a composite model which is compared to the global seismic model LLNL-G3D-JPS of Simmons et al. (2015). We test the sensitivity of gravity prediction on the use of various conversion scaling factors of shear wave velocity to density. We find that the scaling factor profile also has a major impact on gravity prediction.</p><p>Finally, we present early results of the gravity field prediction for two local areas, the Indian-Tibet plate boundary and the Mediterranean Sea. Gravity predictions are compared to satellite gravity.</p>

Study of a Method for Calculating the Current Accuracy In Map-Aided Navigation Problem

2021 ◽  
Vol 29 (1) ◽  
pp. 52-69
Author(s):  
K. V. Dunaevskaya ◽  
◽  
L. V. Kiselev ◽  
V. B. Kostousov ◽  
◽  
...  
Keyword(s):  
Extreme Values ◽  
Search Algorithm ◽  
Computer Experiments ◽  
Gravity Anomalies ◽  
Navigation Problem ◽  
Measurement Systems ◽  
Mapping Process ◽  
Reference Map ◽  
The Given ◽  
Current Accuracy

The paper studies a previously proposed method for calculating the current accuracy characteristics of a correlation-extreme search algorithm for solving the map-aided navigation problem. The proposed method is based on the analysis of the ratio of the extreme values of the functional used in the search algorithm for comparing the measured field fragment, and the fragments obtained from a reference map, and on determining the diameter of the set of the given level for this functional. The study is carried out using an example of three spatial geophysical fields: the sea depth field, the field of gravity anomalies, and the anomalous magnetic field; it is focused on their application for underwater vehicle navigation. The specific features of the information and measurement systems used in the survey of these fields, done by means of an underwater robot are described, as well as the procedure simulating the mapping process taking these features into account. The results of computer experiments on comparison of the proposed method for calculating the current accuracy and the method used in the Bayesian algorithm for solving the navigation problem are presented.

5. Gravity and the figure of the Earth

2018 ◽  
pp. 69-91
Author(s):  
William Lowrie
Keyword(s):  
Accurate Determination ◽  
Measurement Techniques ◽  
Gravity Anomalies ◽  
Dynamic Processes ◽  
The Core ◽  
The Earth ◽  
Free Air ◽  
Figure Of The Earth ◽  
Free Air Gravity

‘Gravity and the figure of the Earth’ discusses the measurement of gravity and its variation at the Earth’s surface and with depth. Gravity is about 0.5 per cent stronger at the poles than at the equator and it first increases with depth until the core–mantle boundary and then sinks to zero at the Earth’s centre. Using satellites to carry out geodetic and gravimetric observations has revolutionized geodesy, creating a powerful geophysical tool for observing and measuring dynamic processes on the Earth. The various measurement techniques employed fall in two categories: precise location of a position on the Earth (such as GPS) and accurate determination of the geoid and gravitational field. Bouguer and free-air gravity anomalies and isostasy are explained.

Empirical Determination of the Gravity Anomaly Covariance Function in Mountainous Areas

1980 ◽  
Vol 34 (3) ◽  
pp. 251-264 ◽  
Author(s):  
Gerard Lachapelle ◽  
K. P. Schwarz
Keyword(s):  
Gravity Anomaly ◽  
Covariance Function ◽  
Physical Geodesy ◽  
Gravity Anomalies ◽  
Mountainous Areas ◽  
The North ◽  
Regression Parameters ◽  
Free Air ◽  
Vening Meinesz ◽  
Free Air Gravity

An evaluation of the empirical gravity anomaly covariance function using over 95 000 surface gravity anomalies in the North American Western Cordillera was carried out. A regression analysis of the data exhibits a strong and quasi-linear correlation of free air gravity anomalies with heights. This height correlation is removed from the free air anomalies prior to the numerical evaluation of the gravity anomaly covariance function. This covariance function agrees well with that evaluated previously by the authors for the remainder of Canada. A possible use for such a covariance function of ‘height independent’ gravity anomalies in mountainous areas is described. First, the height independent gravity anomaly at a point of known height is evaluated by least squares prediction using neighboring measured height independent gravity anomalies. Secondly, the part caused by the height correlation is calculated using linear regression parameters estimated previously and added to the predicted height independent gravity anomaly to obtain a predicted standard free air anomaly. This technique can be used to densify the coverage of free air anomalies for subsequent use in integral formulas of physical geodesy, e.g., those of Stokes and Vening Meinesz. This method requires that point topographic heights be given on a grid.

Free air gravity anomalies over the oceans from Seasat and GEOS 3 altimeter data

Eos ◽  
1987 ◽  
Vol 68 (2) ◽  
pp. 17 ◽  
Author(s):  
G. Balmino ◽  
B. Moynot ◽  
M. Sarrailh ◽  
N. Valès
Keyword(s):  
Gravity Anomalies ◽  
Altimeter Data ◽  
Free Air ◽  
Free Air Gravity
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