Identifying Subsurface Structures beneath the Sumani and Sianok Segments of the Great Sumatran Fault using Combined Geophysical Methods

Abstract The 1900 km long Great Sumatran Fault is a complex active fault system that is divided into segments that include the Sumani and Sianok segments in a rather densely populated area of the West Sumatra Province. Major earthquakes have occurred in these two segments that include the March 2007 Sumatra earthquake. Mitigating future risks requires a better understanding of these complex segments. To identify the subsurface structures beneath the Sumani and Sianok segments, we are conducting combined geophysical study that include gravity and magnetic. Gravity data were obtained from the published regional Bouguer anomaly map of the area around these two segments. The measurements from which the map was derived were rather sparse. Thus, more detailed magnetic measurements were carried out in this study. Magnetic measurements were also expected to be more sensitive as the predominant rocks in the study area are volcanic as well as other type of intrusive rocks. These gravity and magnetic analyses were complemented by seismicity data that include relocated seismicity data that will enhance the modelling of subsurface structures. Progress of this study will be reported. Challenges and obstacles will also be presented.

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Tectonic insight and 3-D modelling of the Lusi (Java, Indonesia) mud edifice through gravity analyses

Geophysical Journal International ◽

10.1093/gji/ggab020 ◽

2021 ◽

Vol 225 (2) ◽

pp. 984-997

Author(s):

Álvaro Osorio Riffo ◽

Guillaume Mauri ◽

Adriano Mazzini ◽

Stephen A Miller

Keyword(s):

Risk Mitigation ◽

Bouguer Anomaly ◽

Geological Model ◽

Resource Exploitation ◽

Subsurface Structures ◽

Central Java ◽

Geostatistical Interpolation ◽

Gravity Response ◽

Anomaly Map ◽

Bouguer Anomaly Map

SUMMARY Lusi is a sediment-hosted hydrothermal system located near Sidoarjo in Central Java, Indonesia, and has erupted continuously since May 2006. This mud eruption extends over a surface of ∼7 km2, and is framed by high containment dams. The present study investigates the geometry of the subsurface structures using a detailed gravimetric model to visualize in 3-D the Lusi system and surrounding lithologies. The obtained residual Bouguer anomaly map, simulated through geostatistical interpolation methods, supports the results of previous deformation studies. The negative gravity anomaly zones identified at Lusi are interpreted as fractured areas through which fluids can ascend towards the surface. A 3-D detailed geological model of the area was constructed with Geomodeller™ to highlight the main features. This model relies on the structures’ density contrasts, the interpreted residual Bouguer anomaly map, and geological data from previous authors. 3-D algorithms were used to calculate the gravity response of the model and validate it by inverse methods. The final output is a gravity constrained 3-D geological model of the Lusi mud edifice. These results provide essential details on the Lusi subsurface and may be useful for possible future geothermal resource exploitation and for the risk mitigation plans related to the maintenance of the man-made framing embankment.

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

Earth Science Research ◽

10.5539/esr.v7n1p94 ◽

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.

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

10.5194/egusphere-egu21-15769 ◽

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

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. &#160;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&#176; from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019).&#160;We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme. &#160;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-3 was found between the lapilli tuffs of the diatreme and the seafloor sediments.&#160; 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.&#160; The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores.&#160;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.&#160; 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.

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Upper crustal structure of Deception Island area (Bransfield Strait, Antarctica) from gravity and magnetic modelling

Antarctic Science ◽

10.1017/s0954102005002622 ◽

2005 ◽

Vol 17 (2) ◽

pp. 213-224 ◽

Cited By ~ 27

Author(s):

A. MUÑOZ-MARTÍN ◽

M. CATALÁN ◽

J. MARTÍN-DÁVILA ◽

A. CARBÓ

Keyword(s):

Crustal Structure ◽

Gravity Data ◽

Bouguer Anomaly ◽

Active Volcano ◽

Magnetic Data ◽

Deception Island ◽

Intrusive Body ◽

The South ◽

Bransfield Strait ◽

Gravity And Magnetic

Deception Island is a young, active volcano located in the south-western part of Bransfield Strait, between the Antarctic Peninsula and the South Shetland archipelago. New gravity and magnetic data, from a marine geophysical cruise (DECVOL-99), were analysed. Forty-eight survey lines were processed and mapped around Deception Island to obtain Bouguer and magnetic anomaly maps. These maps show well- defined groups of gravity and magnetic anomalies, as well as their gradients. To constrain the upper crustal structure, we have performed 2+1/2D forward modelling on three profiles perpendicular to the main anomalies of the area, and taking into account previously published seismic information. From the gravity and magnetic models, two types of crust were identified. These were interpreted as continental crust (located north of Deception Island) and more basic crust (south of Deception Island). The transition between these crustal types is evident in the Bouguer anomaly map as a high gradient area trending NE–SW. Both magnetic and gravity data show a wide minimum at the eastern part of Deception Island, which suggests a very low bulk susceptibility and low density intrusive body. With historical recorded eruptions and thermal and fumarolic fields, we interpret this anomaly as a partially melted intrusive body. Its top has been estimated to be at 1.7 km depth using Euler deconvolution techniques.

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AEROMAGNETIC AND GEOLOGICAL INTERPRETATION OF A SECTION OF THE APPALACHIAN BELT IN CANADA

Canadian Journal of Earth Sciences ◽

10.1139/e67-069 ◽

1967 ◽

Vol 4 (6) ◽

pp. 1015-1037 ◽

Cited By ~ 6

Author(s):

B. K. Bhattacharyya ◽

B. Raychaudhuri

Keyword(s):

Prince Edward Island ◽

Bouguer Anomaly ◽

Polarization Vector ◽

Fault System ◽

Aeromagnetic Data ◽

Eastern Canada ◽

Geological Interpretation ◽

Vertical Displacements ◽

Regional Tectonic ◽

Anomaly Map

Studies were made of total field aeromagnetic data over an area covering a section of the Appalachian belt in eastern Canada. This area is bounded by latitudes 45 °N and 47°40′ N and longitudes 62°30′ W and 67 °W. The residual magnetic values were filtered analytically in order to accentuate the effects of regional tectonic trends in the area. The second vertical derivative values were evaluated for outlining the contacts of magnetized geological formations with a reasonable degree of accuracy. Results of the analysis of the Bouguer anomaly map for the area seemed to correspond well with the tectonic trends indicated by the aeromagnetic data. Sixty-five anomalies were chosen from the residual and filtered maps to determine the following parameters of the causative bodies: (1) intensity of polarization; (2) direction-cosines of the polarization vector; and (3) depths to the top and bottom of the bodies.The picture of the pre-Carboniferous basement, as inferred from aeromagnetic data, is that of a valley and ridge configuration characterized by a series of subparallel, elongated basement blocks with relative vertical displacements. The basement blocks are bounded by major fault systems, known or inferred, mostly of pre-Carboniferous age. These blocks are aligned mostly in the direction of major tectonic trend in the area. The details of subsurface Basement topography are discussed on the basis of the results of interpretation of aeromagnetic data. Most interesting of all is a belt of high magnetic intensity running roughly in a NW–SE direction over the Gulf of St. Lawrence and Prince Edward Island. It has been suggested that this belt is caused by a pre-Taconic topographic high, or alternatively, by a pre-Carboniferous basement high bounded by fault zones subparallel with the fault system under the Cabot Strait.

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SHEAR ZONES IN NORTH EGYPT INTERPRETED FROM GRAVITY DATA

Geophysics ◽

10.1190/1.1440785 ◽

1977 ◽

Vol 42 (6) ◽

pp. 1207-1214 ◽

Cited By ~ 24

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.

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Processing steps for the compiling AAGRG gravity maps

10.5194/egusphere-egu2020-16484 ◽

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

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/m3, 4. calculation of bathymetric corrections for water masses below the ellipsoid (correction density -1&#160;640 kg/m3), 5. calculation of lake correction for great alpine lakes (correction density -1&#160;670 kg/m3), 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 2nd order) and particular corrections including also the atmospheric correction.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 (&#177;50 m) were excluded. The available detailed local elevation models (resolution 10 &#8211; 20 m) were compared with global model MERIT (resolution 25 m).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.&#160;

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A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques

Geological Magazine ◽

10.1017/s0016756800020884 ◽

1993 ◽

Vol 130 (5) ◽

pp. 583-591 ◽

Cited By ~ 22

Author(s):

B. C. Chacksfield ◽

W. De Vos ◽

L. D'Hooge ◽

M. Dusar ◽

M. K. Lee ◽

...

Keyword(s):

Large Scale ◽

Gravity Data ◽

Bouguer Anomaly ◽

Digital Processing ◽

Integrated Modelling ◽

Magnetic Data ◽

Gravity Gradient ◽

The North ◽

Anomaly Map ◽

Shaded Relief

AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.

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

Al-Fiziya: Journal of Materials Science, Geophysics, Instrumentation and Theoretical Physics ◽

10.15408/fiziya.v4i1.20235 ◽

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.

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ANALYSIS OF GRAVITY DATA NEAR CONTINENTAL MARGINS

The APPEA Journal ◽

10.1071/aj73014 ◽

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.

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