scholarly journals Identification of local sesars of tejakula buleleng bali with anomaly gravity data using second vertical derivative method

2020 ◽  
Vol 3 (1) ◽  
pp. 18-25
Author(s):  
Komang Ngurah Suarbawa ◽  
I Gusti Agung Putra Adnyana ◽  
Elvin Riyono
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Three Dimensional ◽  
Fault Model ◽  
Two Dimensional ◽  
Upward Trend ◽  
Gravity Method ◽  
Vertical Derivative ◽  
Subsurface Structures ◽  
Derivative Method

Research has been carried out related to subsurface structures in the Tejakula Buleleng Bali area and its surroundings using the gravity method. This study aims to identify the local Tejakula fault. The data used in this study is gravity anomaly data obtained from observations of Geodetic Satellite (GEOSAT). The method used in interpreting the type of disturbance uses the Second Vertical Derivative method, which then produces two-dimensional (2D) and three-dimensional (3D) fault model interpretations. Based on the results obtained in the study, the condition of the bouguer gravity anomaly value in the Tejakula area and its surroundings at the research location is in the range of 65 mGal to 185 mGal. Meanwhile, based on the Second Vertical Derivative method in determining the type of fault, the Tejakula Fault can be categorized as a mandatory fault with an upward trend.

On: “Inversion of gravity profiles by use of a Backus‐Gilbert approach” by William R. Green (GEOPHYSICS, October 1975, p. 763–772).

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 777-777
Author(s):  
Ramesh Chander
Keyword(s):  
Gravity Anomaly ◽  
Total Mass ◽  
Gravity Data ◽  
Unit Length ◽  
Three Dimensional ◽  
Density Model ◽  
Dimensional Case ◽  
Two Dimensional ◽  
Mass Excess ◽  
Seminal Paper

An important possible constraint on a density model obtained from inversion of gravity data has been overlooked in the seminal paper by Green. The computed density model should be such that the corresponding total mass excess or deficit per unit length in a two‐dimensional case, or total mass excess or deficit in a three‐dimensional case, should be comparable to the value obtained by applying Gauss’s theorem to the observed gravity anomaly data (Grant and West, 1965, p. 227–28 and p. 232).

scholarly journals Basin Depth Mapping Beneath Wellington City Based on Residual Gravity Anomalies

2021 ◽  
Author(s):  
◽  
Alistair Stronach
Keyword(s):  
Gravity Anomaly ◽  
Sedimentary Basin ◽  
Gravity Data ◽  
Three Dimensional ◽  
Maximum Amplitude ◽  
Central Business District ◽  
Gravity Anomalies ◽  
Depth Map ◽  
Capital City ◽  
Detailed Knowledge

<p><b>New Zealand’s capital city of Wellington lies in an area of high seismic risk, which is further increased by the sedimentary basin beneath the Central Business District (CBD). Ground motion data and damage patterns from the 2013 Cook Strait and 2016 Kaikōura earthquakes indicate that two- and three-dimensional amplification effects due to the Wellington sedimentary basin may be significant. These effects are not currently accounted for in the New Zealand Building Code. In order for this to be done, three-dimensional simulations of earthquake shaking need to be undertaken, which requires detailed knowledge of basin geometry. This is currently lacking, primarily because of a dearth of deep boreholes in the CBD area, particularly in Thorndon and Pipitea where sediment depths are estimated to be greatest.</b></p> <p>A new basin depth map for the Wellington CBD has been created by conducting a gravity survey using a modern Scintrex CG-6 gravity meter. Across the study area, 519 new high precision gravity measurements were made and a residual anomaly map created, showing a maximum amplitude anomaly of -6.2 mGal with uncertainties better than ±0.1 mGal. Thirteen two-dimensional geological profiles were modelled to fit the anomalies, then combined with existing borehole constraints to construct the basin depth map. </p> <p>Results indicate on average greater depths than in existing models, particularly in Pipitea where depths are interpreted to be as great as 450 m, a difference of 250 m. Within 1 km of shore depths are interpreted to increase further, to 600 m. The recently discovered basin bounding Aotea Fault is resolved in the gravity data, where the basement is offset by up to 13 m, gravity anomaly gradients up to 8 mGal/km are observed, and possible multiple fault strands identified. A secondary strand of the Wellington Fault is also identified in the north of Pipitea, where gravity anomaly gradients up to 18 mGal/km are observed.</p>

THE SECOND DERIVATIVE METHOD OF GRAVITY INTERPRETATION

Geophysics ◽  
1951 ◽  
Vol 16 (1) ◽  
pp. 29-50 ◽  
Author(s):  
Thomas A. Elkins
Keyword(s):  
Horizontal Plane ◽  
Graphical Method ◽  
Gravity Data ◽  
Three Dimensional ◽  
Horizontal Cylinder ◽  
Resolving Power ◽  
Theoretical Formula ◽  
Second Derivative ◽  
Derivative Method ◽  
Second Derivative Method

The second derivative method of interpreting gravity data, although its use is justifiable only on data of high accuracy, offers a simple routine method of locating some types of geologic anomalies of importance in oil and mineral reconnaissance. The theoretical formula by which it is possible to compute the second (vertical) derivative of any harmonic function from its values in a horizontal plane is derived for both the two‐dimensional and the three‐dimensional cases. The graphical method of computing the second derivative is discussed, especially as to the sources of error. A numerical coefficient equivalent of the graphical method is also presented. Formulas and graphs for the second derivative of the gravity effect of such geometrically simple shapes as the sphere, the infinite horizontal cylinder, the semi‐infinite horizontal plane, and the vertical fault, are presented with discussions of their value in the interpretation of practical data. Finally, the gravity and second derivative maps of portions of some important oil provinces are presented and compared to show the higher resolving power of the second derivative.

scholarly journals Basin Depth Mapping Beneath Wellington City Based on Residual Gravity Anomalies

2021 ◽  
Author(s):  
Alistair Stronach
Keyword(s):  
Gravity Anomaly ◽  
Sedimentary Basin ◽  
Gravity Data ◽  
Three Dimensional ◽  
Maximum Amplitude ◽  
Central Business District ◽  
Gravity Anomalies ◽  
Depth Map ◽  
Capital City ◽  
Detailed Knowledge

<p><b>New Zealand’s capital city of Wellington lies in an area of high seismic risk, which is further increased by the sedimentary basin beneath the Central Business District (CBD). Ground motion data and damage patterns from the 2013 Cook Strait and 2016 Kaikōura earthquakes indicate that two- and three-dimensional amplification effects due to the Wellington sedimentary basin may be significant. These effects are not currently accounted for in the New Zealand Building Code. In order for this to be done, three-dimensional simulations of earthquake shaking need to be undertaken, which requires detailed knowledge of basin geometry. This is currently lacking, primarily because of a dearth of deep boreholes in the CBD area, particularly in Thorndon and Pipitea where sediment depths are estimated to be greatest.</b></p> <p>A new basin depth map for the Wellington CBD has been created by conducting a gravity survey using a modern Scintrex CG-6 gravity meter. Across the study area, 519 new high precision gravity measurements were made and a residual anomaly map created, showing a maximum amplitude anomaly of -6.2 mGal with uncertainties better than ±0.1 mGal. Thirteen two-dimensional geological profiles were modelled to fit the anomalies, then combined with existing borehole constraints to construct the basin depth map. </p> <p>Results indicate on average greater depths than in existing models, particularly in Pipitea where depths are interpreted to be as great as 450 m, a difference of 250 m. Within 1 km of shore depths are interpreted to increase further, to 600 m. The recently discovered basin bounding Aotea Fault is resolved in the gravity data, where the basement is offset by up to 13 m, gravity anomaly gradients up to 8 mGal/km are observed, and possible multiple fault strands identified. A secondary strand of the Wellington Fault is also identified in the north of Pipitea, where gravity anomaly gradients up to 18 mGal/km are observed.</p>

scholarly journals Reservoir Identification Based on Gravity Method at “AUN” Geothermal Field

2019 ◽  
Vol 125 ◽  
pp. 14008
Author(s):  
Annisa Dwi Hafidah ◽  
Yunus Daud ◽  
Alfian Usman
Keyword(s):  
Gravity Data ◽  
Geothermal Field ◽  
Gravity Inversion ◽  
Eurasian Plate ◽  
Gravity Method ◽  
Vertical Derivative ◽  
Horizontal Derivative ◽  
Sumatra Island ◽  
Result Show ◽  
Subsurface Layers

Sumatra Island has the largest geothermal potential in Indonesia spread along the subduction zone between the Indian-Australian plate and the Eurasian plate. “AUN” geothermal field located in Sumatra Island and considered to be one of the largest potential geothermal prospects in Indonesia. This study is focused on identifying the prospect of “AUN” geothermal field using gravity method. First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) analysis were applied in order to determine a more accurate boundary of the fault. 3D inversions of gravity data were used to reconstruct subsurface model. The result show that analysis of First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) can confirm southwest-northeast fault and caldera structure as a boundary of geothermal reservoir and 3D gravity inversion can show subsurface layers with density 2.5 gr/cc to 2.8 gr/cc inside the boundary which is determined as a heat source in “AUN” geothermal field.

scholarly journals PENDUGAAN PATAHAN DAERAH “Y” BERDASARKAN ANOMALI GAYABERAT DENGAN ANALISIS DERIVATIVE

2020 ◽  
Vol 5 (1) ◽  
pp. 75-88
Author(s):  
Yasrifa Fitri Aufia ◽  
Karyanto Karyanto ◽  
Rustadi Rustadi
Keyword(s):  
Gold Mineralization ◽  
Gravity Data ◽  
Three Dimensional ◽  
Research Area ◽  
Two Dimensional ◽  
Fault Structure ◽  
Fracture Structure ◽  
Low Sulfidation ◽  
Dip Slope ◽  
Made In

The research area "Y" is an area of gold mineralization with low sulfidation epithermal type deposit. The existence of this type of mineralization on the path marked by the presence of mineral deposits, which form the quartz veined below the surface of the deposited within the structure of the fault. In this study, analysis of gravity data using derivatives analysis, i.e. First Horizontal Derivative (FHD) to determine the boundary fault structure and Second Vertical Derivative (SVD) to determine the type of fault. The existence of the fault structure integrated with subsurface modeling results in two-dimensional and three-dimensional. The results showed three line slice made in the area of research, identified structure of down faults (normal) trending northeast - south on slice 1 with an estimated dip (slope) is 22° and expected of strike on this fault is N 158° W and thrust fault structure trending northwest - south on slice 2 also slice 3 with an estimated dip (slope) is 22° and expected of strike on this fault is N 158° E. The results of the modeling of two-dimensional and three-dimensional show fracture structure is at the density of 2 g/cc – 2,67 g/cc in the depth of around 100 m - 250 m that consists of sedimentary rocks (clay and sandstone) with a density of 2,2 g/cc – 2,3 g/cc at the age of Tertiary Pliocene, tuff rock with a density of 2,4 g/cc – 2,5 g/cc at the age of Early Miocene and bedrock (basement) in andesite form with a density of 2,67 g/cc.

A FILTERING TECHNIQUE FOR INTERPRETING THE GRAVITY ANOMALY GENERATED BY A TWO‐DIMENSIONAL FAULT

Geophysics ◽  
1971 ◽  
Vol 36 (3) ◽  
pp. 554-570 ◽  
Author(s):  
Thomas M. Davis
Keyword(s):  
Gravity Anomaly ◽  
Fault Model ◽  
Quantitative Interpretation ◽  
Two Dimensional ◽  
Characteristic Parameters ◽  
Characteristic Curves ◽  
Long Wavelength ◽  
Spectral Components ◽  
Dimensional Gravity ◽  
Filtering Technique

In order to combine the advantages of a direct quantitative interpretation with an efficient regional‐residual separation, an interpretation technique based on characteristic curves derived through digital bandpass filtering has been developed for the two‐dimensional gravity fault model. Although the two‐dimensional fault model suffers from the lack of characteristic parameters, reasonably accurate direct interpretations are possible even in the presence of regional fields whose long wavelength spectral components overlap those of the anomaly. The characteristic curves given here were designed for use on relatively large deep structures with depths and thicknesses ranging from 0.8 to 8 km; however, the slight modifications necessary to accommodate any range are presented in detail.

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