IDENTIFICATION OF SUBSURFACE GEOLOGICAL STRUCTURES BASED ON DERIVATIVE AND GAUSSIAN FILTER METHODS FROM GRAVITY DATA IN THE GEOTHERMAL FIELD OF PARIANGAN

• Main Author: Azka Fauzan Siagian, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76584
• Institution: Institut Teknologi Bandung

The subsurface geological structure, particularly fault structures, play a significant role in the exploration of Earth's natural resources. There are several techniques that can be employed within the gravity method to identify these structures. These include the 2D Gaussian Filter method and the First Horizontal Derivative (FHD) method, as well as the Second Vertical Derivative (SVD) method using the Henderson & Zietz, Elkins, and Rosenbach filter operators. To comprehend these various techniques, this study conducts synthetic modeling and implements them in field data. Based on the anomaly responses generated from synthetic modeling, the FHD values show a maximum value at the center of the anomaly gradient body, while SVD has a value of "0" on the SVD anomaly curve. The Henderson & Zietz, Elkins, and Rosenbach techniques all exhibit almost identical anomaly pattern responses. However, the SVD Rosenbach filter operator performs relatively better than the other SVD filter operators. In the Henderson & Zietz filter operator, there is a reduction in the matrix count within the used constant, while Elkins filters out very high and low values, which may indicate the presence of Not A Number (NaN). Rosenbach employs a grid computation similar to Elkins, with the distinction that Rosenbach's calculations are more complex, aimed at avoiding the filtration of values referred to as (NaN) by Elkins. In addition to FHD and SVD, residual anomaly maps can also be used to determine structural continuity. Based on the results of filtering using the Gaussian Technique, it can be shown that the filtering process involves three stages: Fourier transformation, convolution/multiplication, and inverse Fourier transformation (IFFT). The values spread along the Gaussian curve are influenced by the standard deviation, where a larger standard deviation results in a more tapered Gaussian curve. Subsequently, the 2D Gaussian Filter will be applied to field data in the geothermal region of Pariangan. Complete Bouguer anomaly values in the Pariangan geothermal area range from 162 to 190 mGal. The residual anomaly values obtained from the Gaussian method range from -5 to 5 mGal, while the regional anomaly ranges from 164 to 190 mGal. The SVD Rosenbach values within the study area range from -14 to 10 mGal/m3. There is confirmed continuity with a northwest-southeast orientation.