3D Gravity modeling of the volcanic island of Surtsey, Iceland

2021 ◽  
Author(s):  
sara sayyadi ◽  
Magnús T. Gudmundsson ◽  
Thórdís Högnadóttir ◽  
James White ◽  
Joaquín M.C. Belart ◽  
...  
Keyword(s):  
Sea Level ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Modeling ◽  
Gravity Station ◽  
Effusive Activity ◽  
3D Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Drill Cores

<p>The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.  Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35° from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019). </p><p>We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme.  Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m<sup>-3</sup> was found between the lapilli tuffs of the diatreme and the seafloor sediments.  Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.  The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores. </p><p>A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.  Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.</p>

scholarly journals Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

2017 ◽  
Vol 47 (1) ◽  
pp. 3-19
Author(s):  
João Gabriel Motta ◽  
Norberto Morales ◽  
Walter Malagutti Filho
Keyword(s):  
Bouguer Anomaly ◽  
Shear Zones ◽  
Magnetic Data ◽  
Gravity Modeling ◽  
West Gondwana ◽  
Fold And Thrust Belt ◽  
Fold Belts ◽  
Thrust Sheets ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

scholarly journals Geometrical Characterisation of the Mamfe Basin, Cameroon, from the Earth, Gravitational Model (EGM 2008)

2018 ◽  
Vol 7 (1) ◽  
pp. 94
Author(s):  
Anatole Eugene Djieto Lordon ◽  
Mbohlieu YOSSA ◽  
Christopher M Agyingi ◽  
Yves Shandini ◽  
Thierry Stephane Kuisseu
Keyword(s):  
Average Length ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Igneous Rocks ◽  
Average Depth ◽  
The Earth ◽  
Gravitational Model ◽  
Petroleum Generation ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Gravimetric studies using the ETOPO1-corrected high resolution satellite-based EGM2008 gravity data was used to define the surface extent, depth to basement and shape of the Mamfe basin. The Bouguer anomaly map was produced in Surfer 11.0. The Fast Fourier Transformed data was analyzed by spectral analysis to remove the effect of the regional bodies in the study area. The residual anomaly map obtained was compared with the known geology of the study area, and this showed that the gravity highs correspond to the metamorphic and igneous rocks while the gravity lows match with Cretaceous sediments. Three profiles were drawn on the residual anomaly map along which 2D models of the Mamfe basin were drawn. The modeling was completed in Grav2dc v2.06 software which uses the Talwini’s algorithm and the resulting models gave the depth to basement and the shape of the basement along the profiles. After processing and interpretation, it was deduced that the Mamfe basin has an average length and width of 77.6 km and 29.2 km respectively, an average depth to basement of 5 km and an overall U-shape basement. These dimensions (especially the depth) theoretically create the depth and temperature conditions for petroleum generation. 

SHEAR ZONES IN NORTH EGYPT INTERPRETED FROM GRAVITY DATA

Geophysics ◽  
1977 ◽  
Vol 42 (6) ◽  
pp. 1207-1214 ◽  
Author(s):  
S. Riad
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Shear Zones ◽  
Gulf Of Suez ◽  
Eastern Side ◽  
Fault Systems ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Transcurrent Faults

The Bouguer anomaly map for the northern part of Egypt was used for determining fault systems which are probably present in the area. These systems show the presence of a number of almost parallel shear zones, striking in a northwest‐southeast direction. Extrapolation of some of these zones is suggested in the Gulf of Suez area. The movement of the eastern side of each zone is thought to be right‐lateral to the southeast. The shear zones are probably related to the interaction between the European and African plates. They probably started developing in the Oligocene and are presently still active. The opening of the Gulf of Suez is thought to be mainly due to the action of these transcurrent faults.

Processing steps for the compiling AAGRG gravity maps

2020 ◽  
Author(s):  
Pavol Zahorec ◽  
Juraj Papčo ◽  
Roman Pašteka ◽  
Keyword(s):  
Gravity Data ◽  
Atmospheric Correction ◽  
Bouguer Anomaly ◽  
Taylor Series Expansion ◽  
Methodological Innovation ◽  
Atmospheric Effect ◽  
Free Air ◽  
Point Data ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

<p>First unified complete Bouguer anomaly map of AlpArray area compiled from terrestrial gravity data is in preparation. The following steps to calculate the first version of the map were performed: 1. unification of different spatial, height and gravity systems, 2. getting available detailed (mainly LiDAR-based) elevation models and their transformation from physical to ellipsoidal heights, 3. calculation of mass corrections (gravity effect of the topography between the surface and ellipsoid level) with density 2 670 kg/m<sup>3</sup>, 4. calculation of bathymetric corrections for water masses below the ellipsoid (correction density -1 640 kg/m<sup>3</sup>), 5. calculation of lake correction for great alpine lakes (correction density -1 670 kg/m<sup>3</sup>), 6. calculation of the final complete Bouguer anomalies based on normal field (Somigliana formula with GRS80 parameters, free-air correction using Taylor series expansion to the 2<sup>nd</sup> order) and particular corrections including also the atmospheric correction.</p><p>The quality control of input data was performed based on the height differences between the point data and particular elevation models. Several thousand points with height residuals higher than chosen threshold (±50 m) were excluded. The available detailed local elevation models (resolution 10 – 20 m) were compared with global model MERIT (resolution 25 m).</p><p>The most significant methodological innovation is the ellipsoidal heights concept using straightforward calculation of mass/bathymetric corrections in respect to the ellipsoid instead of using the geophysical indirect effect computation. Our specially developed program Toposk was used for mass/bathymetric correction calculation (the standard distance of 166.7 km was used for the first version of the map) as well as for the calculation of lake corrections. Mass corrections amount to hundreds of mGal, while the lake corrections reach more than 5 mGal locally. Atmospheric effect taking into account topography was also calculated and compared with standard atmospheric correction.</p><p> </p>

scholarly journals 2D Forward Modeling Geothermal System Gravity Data in South Solok Region, West Sumatra

2021 ◽  
Vol 4 (1) ◽  
pp. 36-44
Author(s):  
Muhammad Nafian ◽  
Belista Gunawan ◽  
Nanda Ridki Permana
Keyword(s):  
Heat Source ◽  
Geothermal Energy ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Filter Method ◽  
Geothermal System ◽  
Geothermal Systems ◽  
West Sumatra ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Indonesia has the greatest potential for geothermal energy in the world. Geothermal has an important role as an alternative fuel because it is a renewable energy source, but its use has not been maximized. One of the areas that have the greatest potential for geothermal energy in South Solok, West Sumatra. Therefore, this study was conducted to determine the geothermal system in the South Solok area, West Sumatra by using the gravity method. The gravity data processing stage requires some software to get the CBA value(Complete Bouguer Anomaly), map contours of the CBA. Anomaly separation with the butterworth filter method, determination of residual anomaly slice points, and 2D modeling of geothermal systems. Based on modeling, the qualitative interpretation interprets the Complete Bouguer Anomaly map which is suspected as a geothermal prospect area is a low anomaly ranging from 7.9 mgal - 9.4 mgal which is marked in dark blue. Meanwhile, quantitative interpretation produces modeling of the AB and CD slicing with a total of four layers. This layer consists of clay rock as a cap rock, sandstone as a reservoir, granite as a heated rock as a heat source, and the last layer in the form of magma as a heat source. The anomaly modeling of these two sections is dominated by granite rock with a density value of 2500 kg/m3 for the AB section and 2550 kg/m3 for the CD section.

ANALYSIS OF GRAVITY DATA NEAR CONTINENTAL MARGINS

1974 ◽  
Vol 14 (1) ◽  
pp. 114
Author(s):  
A. J. Flavelle ◽  
Y. Yoshimura
Keyword(s):  
Continental Margin ◽  
Sea Water ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Sedimentary Basins ◽  
Continental Margins ◽  
Upper Crust ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Thickness Variations

In general large, thick sedimentary basins are delineated by negative gravity features. The gravity data are usually expressed in the form of Bouguer anomaly contours.Ordinary Bouguer anomaly data fail as a direct indicator of approximate sedimentary thickness in zones on and adjacent to the continental margin. Rapid variations in crustal and ocean thickness cause gravitational variations which are not removed during the computation of Bouguer anomaly values.If crustal thickness variations are known or can be calculated then gravitational corrections can be made which take this factor into account. Similar corrections for variations in sea water attraction can be made. The resultant Bouguer anomaly map, corrected for those variations, will indicate in more definite terms density variations in the material of the upper crust. In particular Bouguer anomaly patterns over continental areas adjacent to the continental slope can be more easily interpreted in terms of sedimentary thickness.

Gravity Survey of King Fahd University of Petroleum and Minerals Dammam Dome, Saudi Arabia

2021 ◽  
Author(s):  
Pantelis Soupios ◽  
Alexandros Stampolidis ◽  
Maurizio Fedi ◽  
SanLinn Kaka ◽  
Khalid Al-Ramadan ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
3D Models ◽  
Low Noise ◽  
Gravity Survey ◽  
Differential Gps ◽  
Gravity Measurements ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Abstract The study area is a part of Dammam Dome that is situated at King Fahd University of Petroleum & Minerals (KFUPM) campus, Dhahran, Kingdom of Saudi Arabia. The gravity survey was conducted as a pilot case study to explore part of Dammam Dome in greater detail. Gravity data were collected solely during night hours due to low noise levels. A significant part of the survey was conducted during the summer holiday period, , when there was no student are on campus. A total of 235 gravity measurements were made using a Scintrex CG5 gravitometer, while a Trimble R10+ differential GPS (DGPS) was used to measure the stations’ location and elevation with the highest accuracy. All gravity data were reduced using several algorithms, and their outcomes were cross-compared. The Complete Bouguer anomaly map for the campus was then generated. Several enhancement filters including edged detection and shallow to deeper source separation were applied. Data were inverted, and 2.5D and 3D models were created to image the subsurface conditions. The main purpose of this study is to better understand the subsurface geology, tectonic settings of the Dammam Dome by applying the high-resolution gravity method before carrying out any comprehensive geophysical (seismic) 3D survey.

Gravity characterization of the La Rioja Valley Basin, Argentina

Geophysics ◽  
2009 ◽  
Vol 74 (3) ◽  
pp. B83-B94 ◽  
Author(s):  
Mario Ernesto Gimenez ◽  
Myriam Patricia Martinez ◽  
Teresa Jordan ◽  
F. Ruíz ◽  
Federico Lince Klinger
Keyword(s):  
3D Model ◽  
Bouguer Anomaly ◽  
First Order ◽  
3D Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Basement High ◽  
La Rioja ◽  
Deconvolution Techniques

The La Rioja Valley is a sedimentary basin in the Pampean Ranges, a region of basement uplifts and broad valleys in the Andean foreland. The present study advances understanding of the genesis of the basin by providing subsurface data on its geometry and characteristics. Gravity and topographic data, including a newly completed gravity survey, were integrated to create a complete Bouguer anomaly map. Euler and Werner deconvolution techniques sum with traditional potential-fields methods and sparse independent data from seismic and magnetotelluric methods to test and constrain the subsurface geophysical characterization of the La Rioja Valley Basin. The residual anomaly, obtained through upward continuation, was inverted to obtain the best 3D gravity model of the La Rioja Valley Basin, which shows the first-order geometry of the basin. This reveals that the basin is asymmetric, with up to [Formula: see text] of low-density basin fill in a depocenter located in the west-central sector of the valley. Second-order features of the basin include a southeast-trending basement high, likely a fault zone that subdivides the basin, which has been revealed by a suite of analytical methods (3D model of depth to basement, a 2D inverse model, and Werner deconvolution solutions).

DETECTION OF GROSS ERRORS IN THE GRAVIMETRIC DATABASE OF THE RIO GRANDE DO SUL STATE

2012 ◽  
Vol 30 (3) ◽  
Author(s):  
Marilei Bender Xavier ◽  
Silvia Beatriz Alves Rolim
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Rio Grande ◽  
Shuttle Radar Topography Mission ◽  
Rio Grande Do Sul ◽  
Digital Elevation ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Elevation Model ◽  
Gravity Recovery

Since 1950, ground gravity data of the Rio Grande do Sul State (RS), Brazil, have been systematically collected by the Department of Geodesy of the Universidade Federal do Rio Grande do Sul (UFRGS) and other institutions in a total of 7.218 points. This paper proposes three methods for detection of gross errors in this database, based on: 1) the digital elevation model of Shuttle Radar Topography Mission (SRTM), 2) the Gravity Recovery and Climate Experiment (GRACE), and 3) the interpolated observations of ground gravity observations (Bouguer anomaly). The 1st method identified 217 points of altimetry, representing 3.00% of the database. The 2nd identified 645 points of gravity observations, representing 8.93% of the database. The3 rd method identified 60 points of land gravimetric observations, representing 0.83% of the database. The criterion to eliminate the observations was based on the recognition of coincident outliers in, at least, 2 methods. The matching points of coarse errors among altimetry, gravity and Bouguer anomaly were grouped in 177 points, representing 2.45% of the database. These points were considered gross errors and were erased from the database. After cleaning the database, we focused in the preliminary interpretation of the Bouguer anomaly map of the RS, recognizing a direct association of the main regional geologic units with four well-defined geophysical domains.

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