Application of magnetic method to characterize Abaya campus building site, Southern Ethiopia

A geophysical survey involving magnetic method is conducted using ENVI-MAG proton precision magnetometer. The study is carried out with the aim of identifying the possible geological structures which may responsible for the failure of engineering structures. Three traverses having east –west orientation with a ten meters profile spacing and a readings station spacing and one traverse across the three traverses and randomly collected magnetic data were used. At each station three readings were taken and averaged out in order to increase the accuracy of data and diurnal and geomagnetic corrections were made. With the corrected data different anomalous maps were produced like total magnetic field anomaly map, residual magnetic anomaly map and analytical signal map using Oasis montaji6.4 software for further interpretation. The result of this research has shown that the area is affected by different geological structures which may be the cause for the crack and the failure of the building in the area.

New Perspective in Regional and Residual Separation of Gravity and Magnetic Data Processing

Separation between Regional and Residual anomaly in Gravity and Magnetic data processing is very important to get the best result in geological interpretation. Several method were used to solve this problem like upward continuation and polynomial fitting. With the same principle, 2D FFT is applied by make an interactive tools based on Matlab Language Programming, named “Oasis Ala-Ala”. It adopt the algorithm from software Oasis. It started with make visualization map or the original data, then the map divide into some grids. Each of grid contain gravity or magnetic data. Then it transformed from special to wavenumber domain. After that, it convolve with our own filter matrix. And the last step is inverse it to get the regional and residual anomaly map. However, Matlab is powerful in facilitate this process in the GUI Toolbox. One important thing is the size of gravity and magnetic data. It will improve to Filter matrix size before do inverse process.

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

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.

Basement and cover architecture in the Central Pyrenees constrained by gravity data

A new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from −18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth.

Correlation Of Residual Anomaly and Isoseismal Map by Using Power Spectral Density Method in Palu City Region

This research was conducted to see the correlation between residual anomaly map, geological map, and isoseismal map and how they contribute to the determination of earthquake-prone areas. Moreover, the area studied is an area that is difficult to obtain geophysical data such as urban areas. The residual anomaly is obtained by calculating the bouguer anomaly from elevation data and free-air correction satellite, which then through the FFT process changes the spatial domain to the frequency domain in MATLAB. Thus, it can separate regional anomaly maps with residuals. Using the overlaying technique on two maps, namely residual anomaly maps with isoseismal, a clear correlation was found between the residual anomaly value and the impact of the earthquake as well as the validation of the geological map in the area

Preliminary Study of Probolinggo Active Fault in East Java Based on Gravity Method

The Gravity Method based on TOPEX satellite data is a one of geophysical method which from satellite observations. The gravity method investigate the gravitational field from one to another observation point. The principle of this method has the ability to distinguish the mass material density from its environment, so that the subsurface structure can be identified. In this research, gravity method is used to identify subsurface structures that are suspected of Probolinggo Fault and identify the rock lithology. From TOPEX we get free air anomaly and then applied the correction process to obtain Complete Bouguer Anomaly (CBA) value. The CBA value is processed interpolation to create CBA map, and then the map is filtered by butterworth to obtain regional and residual maps. The value of high gravity acceleration is 0.076 - 19.74 mGal indicating compact rocks. Meanwhile, based on the residual anomaly map, the value of smaller gravity acceleration is -0.92 - 0.9 mGal indicates lower compacting rocks with smaller mass. The gravity acceleration contrast on the residual anomaly, on the north side of fault line (0.12 mGal to 0.45 mGal) and on the south side (-0.92 mGal to -0.043 mGal), is interpreted as normal fault. Furthermore, 3D modelling shows density value less than 2 gr/cm3 we can interpret as pyroclastic fall, in between 2 gr/cm3 until 2.4 gr/cm3 is sandstone and more than 2.4 gr/cm3 is igneous rock such as andesit. 2D slicing modelling show presence the shear fault, so we can suspect this area have oblique fault with west-east direction.

New Bouguer Anomaly Map for the Territory of the Slovenia

The existing Bouguer anomaly map, which covers the territory of the Republic of Slovenia is a few decades old. Since then, quite a few new gravimetric measurements (data) for the territory of Slovenia as well as high quality digital terrain models that are needed for creating such a map have been made available. The methodology and standards for creating gravity anomaly maps are also changing. Thus, the national Bouguer anomaly map was updated. There were some gross errors detected in the set of old gravimetric data. Additionally, the influence of new updated gravimetric data was analyzed. The comparison of the various maps and the analysis of the influence of input gravimetric data indicates that the new gravimetric data of Slovenia has a significant influence on the creation of the gravimetric anomaly maps for Slovenia (even over 30 mGals at some points).

Analysis of gravity anomaly and seismicity in Bali region

This study aims to determine the value of the gravity anomaly in the Bali region, identify the fault structure in the Bali region using gravity interpretation and analyze the relationship between gravity anomaly and seismicity in the Bali region. The data used is secondary data, namely satellite gravity anomaly data obtained from the topex website and earthquake data obtained from the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) catalog. Data processing in this study was done using gravity and Second Vertical Derivative (SVD) methods. We used Surfer15 software, Oasis Montaj, and the Generic Mapping Tool (GMT). The results of the complete Bouguer anomaly map show the anomalous value of the study area between 10-220 mGal, regional anomaly 40-190 mGal, and the residual anomaly between (-120)-60 mGal. Judging from the SVD contour map that has included earthquake data in the Bali region for the 2008-2020 period, the type of fault in the Seririt Fault, Tejakula Fault, and Fault around Mount Agung is a thrust fault. Judging from the value of the coefficient of determination, it shows that 99% of the seismicity value is influenced by gravity anomaly. The higher the value of the gravity anomaly, the higher the seismicity value.

Optimizing Matching Area for Underwater Gravity-Aided Inertial Navigation Based on the Convolution Slop Parameter-Support Vector Machine Combined Method

This paper focuses on the selection of matching areas in the gravity-aided inertial navigation system. Firstly, the Sobel operator was used in convolution of the gravity anomaly map to obtain the feature map. The convolution slope parameters were constructed by combining the feature map and the gravity anomaly map. The characteristic parameters, such as the difference between convolution rows and columns, convolution variance of the feature map, the pooling difference, and range of the gravity anomaly map, were combined. Based on the support vector machine algorithm, the convolution slope parameter–support vector machine combined method is proposed. Second, we selected the appropriate training sample set and set parameters to verify. The results show that compared with the pre-calibration results, the classification accuracy of the test set is more than 92%, which proves that the convolution slope parameter–support vector machine combined method can effectively distinguish between the suitable and the unsuitable area. Thirdly, we applied this method to another region. The navigation experiment was performed in the split-matching area. The average positioning error was better than 100 m, and the correct rate was more than 90%. The results show that sailing in the selected area can accurately match the trajectory and reduce the positioning error.

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

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.