scholarly journals IDENTIFICATION OF BURIED ARCHEOLOGICAL OBJECTS WITH RADIAL DERIVATIVES OF MICRO GRAVITY DATA

2019 ◽  
Vol 2 (2) ◽  
pp. 84
Author(s):  
Muhammad Zuhdi ◽  
Bakti Sukrisna ◽  
Syamsuddin Syamsuddin
Keyword(s):  
Gravity Data ◽  
Synthetic Data ◽  
Gravity Anomalies ◽  
Density Contrast ◽  
Horizontal Distance ◽  
Radial Derivative ◽  
Horizontal Derivative ◽  
Almost All ◽  
Derivatives Of ◽  
Micro Gravity

The development of recent gravimetric technology allows us to measure gravity anomalies with accuracy of micro Gal. Micro gravity is able to detect very small gravity anomalies such as anomaly due to buried archeological objects below the earth surface. Radial Derivatives of gravity data is used to sharpen anomaly due to lateral changes of density contrast. Horizontal derivatives carried out by previous researchers have some weaknesses, i.e. the loss of derivative values in certain directions and inconsistence values at the source boundary of the same anomaly edge. To solve the horizontal derivative problem, a radial derivative is made. Radial derivative is derivative of gravity anomaly over horizontal distance in the radial direction from a certain point which is considered as the center of anomaly. There are two kind of radial derivative i.e. First Radial Derivative (FRD) and Second Radial Derivative (SRD). Blade Pattern is another way to enrich the ability of SRD to detect boundary of anomaly source. Synthetic gravity data of buried archeological object was made by counting the response of forward modelling. All of programs and calculation of the models in this research is performed based on Matlab® program. The results of the tests on the synthetic data of the model show that the radial derivative is able to detect the boundaries in buried temples due to density contrast. The advantage of radial derivatives which is a horizontal derivative in the direction of radial compared to ordinary horizontal derivatives is the ability to detect vertical boundaries of various anomaly due to horizontal layers and capable of showing density contrast in almost all directions.

Gravity interpretation using Fourier transforms and simple geometrical models with exponential density contrast

Geophysics ◽  
1993 ◽  
Vol 58 (8) ◽  
pp. 1074-1083 ◽  
Author(s):  
D. Bhaskara Rao ◽  
M. J. Prakash ◽  
N. Ramesh Babu
Keyword(s):  
Los Angeles ◽  
Fourier Transforms ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Sedimentary Basins ◽  
Density Contrast ◽  
Model Parameters ◽  
Exponential Density ◽  
Exponential Density Contrast ◽  
Gravity Interpretation

The decrease of density contrast in sedimentary basins can often be approximated by an exponential function. Theoretical Fourier transforms are derived for symmetric trapezoidal, vertical fault, vertical prism, syncline, and anticline models. This is desirable because there are no equivalent closed form solutions in the space domain for these models combined with an exponential density contrast. These transforms exhibit characteristic minima, maxima, and zero values, and hence graphical methods have been developed for interpretation of model parameters. After applying end corrections to improve the discrete transforms of observed gravity data, the transforms are interpreted for model parameters. This method is first tested on two synthetic models, then applied to gravity anomalies over the San Jacinto graben and Los Angeles basin.

Stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations

Geophysics ◽  
1999 ◽  
Vol 64 (3) ◽  
pp. 754-764 ◽  
Author(s):  
Valéria C. F. Barbosa ◽  
João B. C. Silva ◽  
Walter E. Medeiros
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
A Priori ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Sedimentary Basins ◽  
Upper And Lower Bounds ◽  
Density Contrast ◽  
Good Precision ◽  
Rift Basins

We present a new, stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast. The subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated. Any vertical line must intersect the basement relief only once, and the mass deficiency must be concentrated near the earth’s surface, subject to the observed gravity anomaly being fitted within the experimental errors. In addition, upper and lower bounds on the density contrast of each prism are introduced a priori (one of the bounds being zero), and the method assigns to each elementary prism a density contrast which is close to either bound. The basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts, the latter occupying the upper part of the discretized region. The method is stabilized by introducing constraints favoring solutions having the attributes (shared by most sedimentary basins) of being an isolated compact source with lateral borders dipping either vertically or toward the basin center and having horizontal dimensions much greater than its largest vertical dimension. Arbitrary laws of spatial variations of the density contrast, if known a priori, may be incorporated into the problem by assigning suitable values to the nonnull bound of each prism. The proposed method differs from previous stable methods by using no smoothness constraint on the interface to be estimated. As a result, it may be applied not only to intracratonic sag basins where the basement relief is essentially smooth but also to rift basins whose basements present discontinuities caused by faults. The method’s utility in mapping such basements was demonstrated in tests using synthetic data produced by simulated rift basins. The method mapped with good precision a sequence of step faults which are close to each other and present small vertical slips, a feature particularly difficult to detect from gravity data only. The method was also able to map isolated discontinuities with large vertical throw. The method was applied to the gravity data from Reco⁁ncavo basin, Brazil. The results showed close agreement with known geological structures of the basin. It also demonstrated the method’s ability to map a sequence of alternating terraces and structural lows that could not be detected just by inspecting the gravity anomaly. To demostrate the method’s flexibility in incorporating any a priori knowledge about the density contrast variation, it was applied to the Bouguer anomaly over the San Jacinto Graben, California. Two different exponential laws for the decrease of density contrast with depth were used, leading to estimated maximum depths between 2.2 and 2.4 km.

scholarly journals Depth and shape solutions from residual gravity anomalies due to simple geometric structures using a statistical approach

2017 ◽  
Vol 47 (2) ◽  
pp. 113-132 ◽  
Author(s):  
El-Sayed Abdelrahman ◽  
Mohamed Gobashy
Keyword(s):  
Gravity Data ◽  
Random Noise ◽  
Synthetic Data ◽  
Vertical Cylinder ◽  
Gravity Anomalies ◽  
Horizontal Cylinder ◽  
Random Errors ◽  
Residual Gravity ◽  
Characteristic Points ◽  
The Usa

AbstractWe have developed a simple and fast quantitative method for depth and shape determination from residual gravity anomalies due to simple geometrical bodies (semi-infinite vertical cylinder, horizontal cylinder, and sphere). The method is based on defining the anomaly value at two characteristic points and their corresponding distances on the anomaly profile. Using all possible combinations of the two characteristic points and their corresponding distances, a statistical procedure is developed for automated determination of the best shape and depth parameters of the buried structure from gravity data. A least-squares procedure is also formulated to estimate the amplitude coefficient which is related to the radius and density contrast of the buried structure. The method is applied to synthetic data with and without random errors and tested on two field examples from the USA and Germany. In all cases examined, the estimated depths and shapes are found to be in good agreement with actual values. The present method has the capability of minimizing the effect of random noise in data points to enhance the interpretation of results.

scholarly journals Seafloor Density Contrast Derived From Gravity and Shipborne Depth Observations: A Case Study in a Local Area of Atlantic Ocean

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaoyun Wan ◽  
Weipeng Han ◽  
Jiangjun Ran ◽  
Wenjie Ma ◽  
Richard Fiifi Annan ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Local Area ◽  
Density Variation ◽  
Mean Difference ◽  
Density Contrast ◽  
Data Sets ◽  
Marine Gravity ◽  
Band Pass

Marine gravity data from altimetry satellites are often used to derive bathymetry; however, the seafloor density contrast must be known. Therefore, if the ocean water depths are known, the density contrast can be derived. This study experimented the total least squares algorithm to derive seafloor density contrast using satellite derived gravity and shipborne depth observations. Numerical tests are conducted in a local area of the Atlantic Ocean, i.e., 34°∼32°W, 3.5°∼4.5°N, and the derived results are compared with CRUST1.0 values. The results show that large differences exist if the gravity and shipborne depth data are used directly, with mean difference exceeding 0.4 g/cm3. However, with a band-pass filtering applied to the gravity and shipborne depths to ensure a high correlation between the two data sets, the differences between the derived results and those of CRUST1.0 are reduced largely and the mean difference is smaller than 0.12 g/cm3. Since the spatial resolution of CRUST1.0 is not high and in many ocean areas the shipborne depths and gravity anomalies are much denser, the method of this study can be an alternative method for providing seafloor density variation information.

Bathymetry estimation from altimeter - derived gravity data in the Adriatic Sea

2021 ◽  
Author(s):  
Ljerka Vrdoljak ◽  
Marijan Grgić ◽  
Tomislav Bašić
Keyword(s):  
Adriatic Sea ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Shuttle Radar Topography Mission ◽  
Measured Data ◽  
Eastern Coast ◽  
Bathymetric Data ◽  
Almost All

<p>Bathymetric models representing the topography of the seafloor are an important parameter in almost all maritime related research. Traditional bathymetric shipborne or airborne surveys are cost and/or time consuming, and access to the measured data is mostly limited or expensive. Alternative bathymetric data sources for marine researchers are publicly available bathymetric models whose quality is often unknown and/or uneven. This research presents the study on the bathymetric prediction for the Adriatic Sea from altimetry-derived gravity anomalies and in-situ soundings using the gravity - geologic method (GGM). Bathymetric soundings used to determine the density contrast between seawater and bedrock were derived from nautical charts, EMODnet (European Marine Observation and Data Network) bathymetric grid, and GEBCO (General Bathymetric Chart of the Oceans) One Minute grid. More than 3000 chart soundings distributed across the Adriatic Sea were used to estimate the quality of the predicted bathymetric model as well as the quality of the latest versions of publicly available bathymetric models: DTU10Bat (Technical University of Denmark), GEBCO 2020, EMODnet 2018, ETOPO1, Smith and Sandwell v.19.1, and SRTM (Shuttle Radar Topography Mission) 15+ V.2.1. The results show that the computed model represents an update to bathymetric data in the Adriatic Sea, especially along its eastern coast.</p>

Conjugate complex variables method for the computation of gravity anomalies

Geophysics ◽  
1989 ◽  
Vol 54 (12) ◽  
pp. 1629-1637 ◽  
Author(s):  
Yue‐Kuen Kwok
Keyword(s):  
Gravity Anomalies ◽  
Higher Order ◽  
Complex Variables ◽  
Gravity Potential ◽  
Gravity Gradient ◽  
Horizontal Distance ◽  
Contour Integrals ◽  
Vertical Gravity ◽  
Analytical Expressions ◽  
Derivatives Of

Using conjugate complex variables, a generalized method is presented to derive formulas to calculate first‐ and higher‐order derivatives of the gravity potential due to selected mass models. Double integrals in the computation of gravity‐gradient anomalies are transformed into complex contour integrals. Analytical expressions for higher‐order derivatives of the gravitational potential in arbitrary directions due to two‐dimensional (2‐D) polygonal mass models are derived. The method is extended to 2‐D polygonal bodies whose density contrasts vary with depth and horizontal distance and can be generalized to deal with 2‐D bodies of any shape. The vertical gravity field and its first derivatives due to a homogeneous radially symmetric body are also computed using conjugate complex variables. Derivation of gravity and gravity gradient formulas generally is greatly simplified by the use of complex variables.

scholarly journals Penerapan Persamaan Trend Surface Analysis untuk Pemisahan Anomali Residual dan Regional pada Data Gayaberat

2021 ◽  
pp. 102-115
Author(s):  
Purwaditya Nugraha ◽  
Nono Agus Santoso
Keyword(s):  
Surface Analysis ◽  
Gravity Data ◽  
Synthetic Data ◽  
Gravity Anomalies ◽  
Analysis Method ◽  
Trend Surface Analysis ◽  
Microsoft Excel ◽  
Trend Surface ◽  
Surface Analysis Method ◽  
Regional Gravity

The separation of regional anomalies and residual anomalies in gravity data is an important part in interpreting gravity data. This process aims to obtain gravity anomalies that have been associated with exploration targets. The Trend Surface Analysis method is a mathematical approach to the earth field that can be used to separate maps into regional components and local components. The application of this method into gravity data can be used to separate regional anomalies and residual anomalies. The process of processing the trend surface analysis method can be done using Microsoft Excel. This method is tested first on synthetic gravity data, the purpose of this test is to determine the performance of the trend surface analysis method in performing anomaly separation. Based on the test results of the trend surface analysis method on synthetic gravity data, it was found that this method was quite good at separating regional anomalies and residual anomalies. This is evidenced by the anomalous pattern that is already the same between the regional gravity anomaly resulting from the separation of the anomaly using the trend surface analysis method and the regional anomaly resulting from synthetic data. The same anomaly pattern can also be seen in the residual anomaly resulting from the separation of the anomaly using the trend surface analysis method with the residual anomaly resulting from synthetic data. The application of the trend surface analysis method to field data has been carried out by producing regional anomalies and residual anomalies. This method is very good at separating regional anomalies and residual anomalies, especially in regional anomalies located at deep depths.Pemisahan anomali regional dan anomali residual pada data gayaberat merupakan bagian penting dalam melakukan interpretasi data gayaberat. Proses ini bertujuan untuk mendapatkan anomali gayaberat yang sudah berasosiasi dengan target eksplorasi. Metode Trend Surface Analysis merupakan teknik pendekatan matematika pada bidang kebumian yang dapat digunakan untuk memisahkan peta kedalam komponen regional dan komponen lokal. Penerapan metode ini ke dalam data gayaberat dapat digunakan untuk memisahkan anomali regional dan anomali residual. Proses pengolahan metode trend surface analysis dapat dilakukan dengan menggunakan microsoft excel. Metode ini diuji terlebih dahulu pada data gayaberat sintetis, tujuan pengujian ini adalah untuk mengetahui performa metode trend surface analysis dalam melakukan pemisahan anomali. Berdasarkan hasil pengujian metode trend surface analysis pada data gayaberat sintetis didapatkan bahwa metode ini cukup baik dalam memisahkan anomali regional dan anomali residual. Hal ini dibuktikan pada pola anomali yang sudah sama antara anomali gayaberat regional hasil pemisahan anomali metode trend surface analysis dengan anomali regional hasil data sintetis. Pola anomali yang sama juga dapat dilihat pada anomali residual hasil pemisahan anomali metode trend surface analysis dengan anomali residual hasil data sintetis. Penerapan metode trend surface analysis pada data lapangan telah dilakukan dengan menghasilkan anomali regional dan anomali residual. Metode ini sangat baik dalam memisahkan anomali regional dan anomali residual terutama pada anomali regional yang berada pada kedalaman dalam

scholarly journals Marquardt inverse modeling of the residual gravity anomalies due to simple geometric structures: A case study of chromite deposit

2019 ◽  
Vol 49 (2) ◽  
pp. 153-180 ◽  
Author(s):  
Ata Eshaghzadeh ◽  
Alireza Dehghanpour ◽  
Sanaz Seyedi Sahebari
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Synthetic Data ◽  
Vertical Cylinder ◽  
Gravity Anomalies ◽  
Horizontal Cylinder ◽  
Inversion Method ◽  
Chromite Deposit ◽  
Different Shapes

Abstract In this paper, an inversion method based on the Marquardt’s algorithm is presented to invert the gravity anomaly of the simple geometric shapes. The inversion outputs are the depth and radius parameters. We investigate three different shapes, i.e. the sphere, infinite horizontal cylinder and semi-infinite vertical cylinder for modeling. The proposed method is used for analyzing the gravity anomalies from assumed models with different initial parameters in all cases as the synthetic data are without noise and also corrupted with noise to evaluate the ability of the procedure. We also employ this approach for modeling the gravity anomaly due to a chromite deposit mass, situated east of Sabzevar, Iran. The lowest error between the theoretical anomaly and computed anomaly from inverted parameters, determine the shape of the causative mass. The inversion using different initial models for the theoretical gravity and also for real gravity data yields approximately consistent solutions. According to the interpreted parameters, the best shape that can imagine for the gravity anomaly source is the vertical cylinder with a depth to top of 7.4 m and a radius of 11.7 m.

scholarly journals GEOPHYSICAL STUDIES OF BASIN STRUCTURES ALONG THE EASTERN FRONT OF THE SIERRA NEVADA, CALIFORNIA

Geophysics ◽  
1964 ◽  
Vol 29 (3) ◽  
pp. 337-359 ◽  
Author(s):  
J. H. Healy ◽  
Frank Press
Keyword(s):  
Sierra Nevada ◽  
Gravity Data ◽  
El Paso ◽  
Gravity Anomalies ◽  
Density Contrast ◽  
Seismic Velocities ◽  
Owens Valley ◽  
Eastern Front ◽  
Garlock Fault ◽  
Mohorovičić Discontinuity

A seismic and gravity survey along the eastern front of the Sierra Nevada, California, between southern Owens Valley and the Garlock fault, outlines a series of basins with maximum depths ranging from 5,000 to 9,000 ft. These basins follow the front of the Sierra Nevada in a continuous chain with one interruption of about 10 miles near Little Lake. The gravity anomalies indicate that the basins are bounded by a series of high‐angle faults rather than a single large fault. The seismic velocities in the basin deposits appear to correlate with the stratigraphy of the section exposed in the El Paso Mountains. A comparison of Bouguer anomalies with seismic depths indicates a density contrast of 0.35 g/cc in basins less than 3,000 ft deep, and an average but widely varying density contrast of 0.25 g/cc in basins 4,000 to 8,000 ft deep. A digital‐computer program for automatic computation of basin depths from gravity anomalies was evaluated and found to be useful in this type of analysis. Changes in the depth to the Mohorovičič discontinuity cannot produce regional gradients as large as the regional gradients observed in the area of the survey. Either structure on an intermediate crustal boundary or lateral changes in crustal densities, or a combination of these, is required to explain the gravity data.

Gravity inversion of basement relief constrained by the knowledge of depth at isolated points

Geophysics ◽  
1996 ◽  
Vol 61 (6) ◽  
pp. 1702-1714 ◽  
Author(s):  
Jorge W. D. Leão ◽  
Paulo T. L. Menezes ◽  
Jacira F. Beltrão ◽  
João B. C. Silva
Keyword(s):  
Linear Trend ◽  
Gravity Data ◽  
Synthetic Data ◽  
Effective Density ◽  
Density Contrast ◽  
Gravity Inversion ◽  
True Value ◽  
Isolated Points ◽  
The Media ◽  
Homogeneous Media

We present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media. It consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media. The knowledge of the interface depth at isolated points is used to estimate the depth [Formula: see text] of the shallowest point of the interface, the density contrast Δρ between the two media, and the coefficients [Formula: see text] and [Formula: see text] of a first‐order polynomial representing a linear trend to be removed from data. The solutions are stabilized by introducing a damping parameter in the computation of the downward‐continued anomaly by the equivalent layer method. Different from other interface mapping methods using gravity data, the proposed method: (1) takes into account the presence of an undesirable linear trend in data; (2) requires just intervals for both Δρ (rather than the knowledge of its true value) and coefficients [Formula: see text] and [Formula: see text]; and (3) does not require the knowledge of the average interface depth [Formula: see text]. As a result of (3), the proposed method does not call for extensive knowledge of the interface depth to obtain a statistically significant estimate of [Formula: see text]; rather, it is able to use the knowledge of the interface depth at just a few isolated points to estimate [Formula: see text], Δρ, [Formula: see text], and [Formula: see text]. Tests using synthetic data confirm that the method produces good and stable estimates as far as the established premises (smooth interface separating two homogeneous media and, at most, the presence of an unremoved linear trend in data) are not violated. If the density contrast is not uniform, the method may still be applied using Litinsky’s concept of effective density. The method was applied to gravity data from Recôncavo Basin, Brazil, producing good correlations of estimated lows and terraces in the basement with corresponding known geological features.

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