scholarly journals PEMODELAN GAYA BERAT 3D DAERAH PANAS BUMI DOLOK MARAWA KABUPATEN SIMALUNGUN, SUMATERA UTARA 3D GRAVITY MODELING OF DOLOK MARAWA GEOTHERMAL FIELD IN SIMALUNGUN REGENCY, NORTH SUMATERA

2015 ◽  
Vol 10 (2) ◽  
pp. 32-45
Author(s):  
Asep Sugianto ◽  
Tony Rahardinata
Keyword(s):  
Geothermal Field ◽  
Gravity Modeling ◽  
3D Gravity

Daerah panas bumi Dolok Marawa merupakan salah satu daerah prospek panas bumi di Sumatera bagian utara. Daerah panas bumi tersebut berada pada zona patahan Sumatera dengan manifestasi permukaan berupa sekelompok mata air panas yang memiliki temperatur antara 37o C hingga 65 o C. Serangkaian survei gaya berat telah dilakukan di daerah ini pada tahun 2006 dan 2015. Sebanyak 257 data gaya berat telah diukur dari daerah ini, dengan cakupan luas pengukuran sekitar 16 km x 13 km. Penelitian ini bertujuan untuk mengetahui distribusi densitas batuan melalui pemodelan 3D pada data gaya berat dengan menggunakan perangkat lunak Grablox. Hasil pemodelan memperlihatkan suatu blok berdensitas rendah yang bentuknya berarah baratlaut-tenggara dan berimpit dengan zona patahan. Densitas batuan rendah tersebut bernilai sekitar 2,4 g/cm 3 dan dianggap sebagai batuan rekahan yang mengisi zona patahan. Hasil pemodelan juga memperlihatkan suatu blok berdensitas tinggi di bawah bukit Dolok Bahtopu. Blok densitas tinggi ini diinterpretasikan sebagai suatu tubuh intrusi andesitik dan mungkin bertindaksebagai sumber panas bagi sistem panas bumi Dolok Marawa. 

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>

Joint optimization of vertical component gravity and P-wave first arrivals by simulated annealing

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. ID59-ID71 ◽  
Author(s):  
Kyle Basler-Reeder ◽  
John Louie ◽  
Satish Pullammanappallil ◽  
Graham Kent
Keyword(s):  
Simulated Annealing ◽  
Gravity Data ◽  
Vertical Component ◽  
Geothermal Field ◽  
P Wave ◽  
Joint Optimization ◽  
Gravity Modeling ◽  
Deep Basin ◽  
Data Set ◽  
Convolution Model

Joint seismic and gravity analyses of the San Emidio geothermal field in the northwest Basin and Range province of Nevada demonstrate that joint optimization changes interpretation outcomes. The prior 0.3–0.5 km deep basin interpretation gives way to a deeper than 1.3 km basin model. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts, flattening antiformal reflectors that could have been interpreted as folds. Furthermore, joint optimization provides a clearer picture of the rangefront fault by increasing the depth of constrained velocities, which improves reflector coherency at depth. This technique provides new insight when applied to existing data sets and could replace the existing strategy of forward modeling to match gravity data. We have achieved stable joint optimization through simulated annealing, a global optimization algorithm that does not require an accurate initial model. Balancing the combined seismic-gravity objective function is accomplished by a new approach based on analysis of Pareto charts. Gravity modeling uses an efficient convolution model, and the basis of seismic modeling is the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests found that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Restricted offset-range migration analysis provides insights into precritical and gradient reflections in the data set.

Thickness of the Earth's crust in the deep Arctic Ocean: Results of a 3D gravity modeling

2013 ◽  
Vol 54 (3) ◽  
pp. 247-262 ◽  
Author(s):  
V.Yu. Glebovsky ◽  
E.G. Astafurova ◽  
A.A. Chernykh ◽  
M.A. Korneva ◽  
V.D. Kaminsky ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Earth’S Crust ◽  
Gravity Modeling ◽  
3D Gravity ◽  
Earth's Crust

scholarly journals 3D GRAVITY MODELING OF IMPACT STRUCTURES IN BASALTIC FORMATIONS IN BRAZIL: PART II – VISTA ALEGRE, PARANÁ

2019 ◽  
Vol 37 (1) ◽  
pp. 69
Author(s):  
Júlio Cesar Ferreira ◽  
Emilson Pereira Leite ◽  
Marcos Alberto Rodrigues Vasconcelos ◽  
Alvaro Penteado Crósta
Keyword(s):  
Impact Crater ◽  
Lower Layer ◽  
Mass Density ◽  
Density Model ◽  
Gravity Modeling ◽  
Impact Structure ◽  
Central Uplift ◽  
Subsurface Layers ◽  
3D Gravity ◽  
Density Modeling

ABSTRACT. This study characterized the subsurface framework of the Vista Alegre impact structure in terms of a 3D mass density model obtained from forward gravity modeling, constrained by petrophysical and geological data from a previously published work. Like the nearby Vargeão impact structure, Vista Alegre is a complex impact structure formed in basaltic lava flows of the Serra Geral Formation with a central uplift exposing sandstones of Piramboia/Botucatu Formations and impact breccias. A 3D mass density model is proposed, consisting of five subsurface layers: polymictic breccias, shocked/fractured basalts, basalts (Serra Geral), shocked sandstones (Piramboia/Botucatu) and a lower layer of pre-Triassic sedimentary rocks. The central region containing the fractured polymictic breccias and shocked target rocks (basalt and sandstone) is_100 m thick. The target rocks are deformed at depths of up to_1 km, which represents the basal contact of the sandstones of the Piramboia/Botucatu Formations with Pre-Triassic strata. Values of structural uplift (_650 m), central uplift diameter (_3.5 km) and depth of excavation (_400 m) inferred from our model are fairly consistent with theoretical values, thus supporting a meteoritic impact nature. The Vista Alegre model is in agreement with the density model for the nearby Vargeão impact crater and provides new insights into the formation of impact structures in basaltic targets, with potential implications for the study of other planetary surfaces.Keywords: density modeling, impact crater, central uplift, Serra Geral Formation.RESUMO. Este estudo apresenta uma caracterização em subsuperfície da estrutura de impacto Vista Alegre em termos de um modelo 3D de densidade de massa obtido a partir de uma modelagem direta de dados gravimétricos, vinculada à dados petrofísicos e dados de mapeamento geológico previamente publicados. Assim como a cratera de Vargeão, Vista Alegre é uma estrutura de impacto complexa, formada em fluxos de lava da Formação Serra Geral, com elevação central expondo arenitos das Formações Piramboia/Botucatu e brechas de impacto. Foi proposto um modelo constituído por cinco camadas em subsuperfície: brechas polimíticas, basaltos fraturados, basaltos (Serra Geral), arenitos (Piramboia/Botucatu) e uma camada inferior de rochas pré-Triássicas. A região central contendo as brechas polimíticas e as rochas-alvo fraturadas (basaltos e arenitos) tem _100 m de espessura. As rochas da região do impacto estão modificadas até profundidades de _1 km, onde ocorre o contato entre as camadas pré-Triássicas e os arenitos das formações Piramboia/Botucatu. Valores de soerguimento estrutural (_650 m), diâmetro do núcleo central soerguido (_3,5 km) e profundidade de escavação (_400 m) são consistentes com valores teóricos que podem ser inferidos do nosso modelo, reforçando a origem por impacto meteorítico. Em geral, o modelo de Vista Alegre está de acordo com o modelo de densidades da cratera de impacto de Vargeão e fornece novos conhecimentos sobre a formação de estruturas de impacto em alvos basálticos e para estudos de geologia planetária. Palavras-chave: modelo de densidades, cratera de impacto, núcleo soerguido, Formação Serra Geral.

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