Complete Bouguer Anomaly Research Articles

3D Modeling of Subsurface Lawanopo Fault In Southeast Sulawesi, Indonesia Using Grablox and its Consequence to Geohazard

Lawanopo Fault is a horizontal shear fault (sinistral strike-slip) found in Southeast Sulawesi province and is thought to be active during Plio-Pleistocene or mid-late Miocene to the present. This study has been carried out which aims to find out the geometric shapes below the surface of the Lawanopo fault using complete Bouguer anomaly (ABL) data. The ABL data is projected onto a flat plane using the Dampney method at an altitude of 8 km, and the separation of local and regional anomalies is carried out using the upward continuation method at an altitude of 60 km. Three-dimensional (3D) modeling under the surface of the Lawanopo fault is done using the computer program Grablox. Data processing techniques using Singular Value Decomposition (SVD) and Occam inversion. The results showed that a high gravity anomaly of 190-225 mGal was caused by an igneous rock below the surface with a density of 2.7-3.33 gr/cm3 and a thickness of about 13 km, a moderate anomaly of 175-187 mGal caused by Paleozoic igneous rocks aged Carbon with a density of 2.6-2.9 gr/cm3 and a thickness of about 25 km. Low anomaly 115-160 mGal is caused by rocks with a density of 2.0-2.5 gr/cm3 and a thickness of about 22-23 km. The Lawanopo fault constituent rocks consist of alkaline rocks in the basement covered by sediment and metamorphic with a depth of Lawanopo fault more than 15 km and begin to be seen at a depth of 4.3 km of the surface. it is known that the area around the Lawanopo fault is an area prone to earthquakes. But, based on the soil and rock structure around the Lawanopo fault, the compactness and attenuation levels in reducing earthquake waves are quite good, so that land use around the Lawanopo fault tends to be safe.

Lineament Extraction using Gravity Data in the Citarum Watershed

Lineament is one of the most important features showing subsurface elements or structural weakness such as faults. This study aims to identify subsurface lineament patterns using automatic lineament in Citarum watershed with gravity data. Satellite gravity data were used to generate a sub-surface lineament. Satellite gravity data corrected using Bouguer and terrain correction to obtain a complete Bouguer anomaly value. Butterworth filters were used to separate regional and residual anomaly from the complete Bouguer anomaly value. Residual anomaly gravity data used to analyze sub-surface lineament. Lineament generated using Line module in PCI Geomatica to obtain sub-surface lineament from gravity residual value. The orientations of lineaments and fault lines were created by using rose diagrams. The main trends observed in the lineament map could be recognized in these diagrams, showing a strongly major trend in NW-SE, and the subdominant directions were in N-S. Area with a high density of lineament located at the Southern part of the study area. High-density lineament might be correlated with fractured volcanic rock upstream of the Citarum watershed, meanwhile, low-density lineament is associated with low-density sediment. The high-density fracture might be associated with intensive tectonics and volcanism.

Analysis of gravity anomaly decomposition and depth to basement, case study: Cenozoic Bogor Basin, Indonesia.

The Cenozoic Bogor Basin situated on the SE edge part of Sunda shelf is presumed to have hydrocarbon potential on its turbidite deep-water play. The deep subsurface geometry of this basin may play an important role, yet unexplored, to the hydrocarbon exploration. The gravity method is advantageous to illuminate the subsurface structure on the arbitrary depth and various sources. Eight-hundred-thirty-eight points of ground-based gravity survey were collected on roughly one kilometer spacing in the North of Bandung to Pamanukan region covering the Cenozoic Bogor Basin on the Subang-Purwakarta segment to generate complete Bouguer anomaly (CBA) map. This study examines the two robust methods of gravity anomaly decomposition (i.e., polynomial trend surface and upward continuation) by using multiple parameters to match the geological background. Radially averaged power spectrum was used to estimate the depth of anomalous source corresponds to the top of basement layer and resulting 4 km basement depth in North West Java basin and below 1 km on Tangkuban Parahu volcanic zone. The resulting estimated depth of Cenozoic Bogor Basin was evaluated by the matched a priori published data on those two areas and revealed the depth of depocenter (deepest sediment) on the Cenozoic Bogor Basin is up to 9 km, quite a deeper extent than previously assumed.

MONITORING OF JAKARTA SUBSIDENCE APPLYING 4D MICROGRAVITY SURVEY BETWEEN 2014 AND 2018

A study of time-lapse or 4D microgravity has been conducted to detect subsidence zones and the rate of subsidence between 2014 and 2018 in Jakarta. Jakarta city is mostly covered by a quaternary alluvium fan. Subsidence happened by several factors including excessive water exploitation, loss of recharge area, surface load, and the natural sinking properties of unconsolidated alluvium. By combining the complete Bouguer Anomaly (CBA) equation and gravity gradiometry methods, the Bouguer density of 2.33 g/cm3 can be obtained. Since subsidence occurred in the near-surface, the regional gravity anomaly has been separated from CBA by using combined spectrum analysis and moving average methods after implementing a Fourier Transform. The result shows that subsidence occurred all over the coastal area of Jakarta. In northern Jakarta, the average subsidence rate is more than 10 cm/year, and the highest rate happened in Tambora district with 15.9 cm/year. There is also a negative 4D microgravity anomaly in the southern part of Jakarta that seems to be related to ground level uplift and declining groundwater level.

Analisis Kedalaman Sumber Anomali Gravitasi menggunakan Spectral Statistical Technique di daerah Godean Yogyakarta

Depth analysis of the gravity anomaly source using Spectral Statistical Technique has been carried out in the Godean area, Yogyakarta. This research was conducted to determine the depth of the formation in the study area. This study used 56 gravity acquisition points spread over 2 lines along 12 km east-west direction. Depth analysis is carried out from the Complete Bouguer Anomaly profile. Spectral Statistical Technique is used as a method of determining depth by calculating the slope of the graph Ln (PS) vs k. The results of these calculations are obtained slope of 2 types of anomalies, namely deep anomalies and shallow anomalies. The deep anomaly has a slope of -9704, while the shallow anomaly has a slope of -279. The depth of the anomalous source in the study area has a value of 770 m for deep anomalies interpreted as Nanggulan formations, and 22 m for shallow anomalies interpreted as the Merapi Muda Volcano Deposition.

Determination of the Selected Gravity Field Functionals by the GGI Method: A Case Study of the Western Carpathians Area

In this paper, some features of the local disturbing potential model developed by the GGI method (based on Geophysical Gravity Inversion) were analyzed. The model was developed for the area of the Western Carpathians covering the Polish–Slovak border. A detailed assessment of the model’s property was made regarding the accuracy of the disturbing potential values (height anomalies), gravity values, complete Bouguer anomalies (CBA), and differences between geoid undulations and height anomalies (N−ζ). Obtained accuracies of the GGI quasigeoid model (in terms of standard deviation of the residuals to the reference quasigeoid models) were at the level of ±2.2 cm for Poland and ±0.9 cm for the Slovak area. In terms of gravity, there was shown dependence of the accuracy of the GGI model on the digital elevation model (DEM) resolution, the point height, the density of gravity data used, and used reference density of topography model. The best obtained results of gravity prediction were characterized by an error of approximately 1 mGal. The GGI approach were compared with classical gravity prediction methods (using CBA and topographic-isostatic anomalies supported by Kriging prediction), getting very similar results. On the basis of the GGI model, CBA and differences (N−ζ) were also determined. The strong dependence of resolution of the CBA model obtained by GGI approach, on the size of the constant density zones, has been demonstrated. This significantly reduces the quality of such a model. The crucial importance of the topographic masses density model for both determined values (CBA and (N−ζ)) was also indicated. Therefore, for determining these quantities, all available information on topographic mass densities should be used in modelling.

Gravity data inversion for the basement relief delineation through global optimization: a case study from the Aegean Graben System, western Anatolia, Turkey

SUMMARYAegean Graben System is a significant member of the complex geology of western Turkey. The depths to the metamorphic basement reliefs in two major grabens have been reported by many geophysical studies. However, the sediment thicknesses of these graben basins still remain controversial due to the findings differing from each other. Thus, we have inverted the gravity data of the sedimentary cover–metamorphic basement using a stochastic derivative-free vector-based metaheuristic named differential evolution algorithm (DEA). This is the first application of DEA adapted to the basement relief depth problem. Model parametrizations have been achieved by discretizing the basins using a group of juxtaposed vertical blocks. Before the inversion studies, mathematical nature of the inverse problem has been investigated via prediction cost function/error energy maps for some block pairs using a hypothetical basin model. These maps have shown the resolvability characteristic of the block thicknesses on such inversion problem. Parameter tuning studies for the optimum mutation constant/weighting factor have been performed to increase the efficiency of the algorithm. The synthetic data have been successfully inverted via the tuned control parameter and some smoothing operators. Probability density function (PDF) analyses have shown that the best solutions are within the confidence interval limits without uncertainties. In the field data case, long-wavelength anomalies caused by both crustal and deeper effects have been removed from the complete Bouguer anomalies through 2-D finite element method using the element shape functions. Some profiles extracted from the residual gravity anomaly map have been used for the inversion and obtained results have shown that the maximum depths to the metamorphic basement reliefs in the grabens are shallower than the findings of the previous studies. Information obtained from the lithological logs drilled in the grabens has supported our results. Moreover, PDF analyses have indicated the reliability of the obtained solutions without uncertainties.

Implementation 3D Inversion of Gravity Data to Identify Potential Hydrocarbon Reservoir Zones in West Timor Basin

A gravity survey has been carried out in the area of West Timor, East Nusa Tenggara to identify the existence of basin structures. The existence of reservoirs and trap structures are two important parameters in hydrocarbon exploration. Geologically, Timor possibly an area known to have a very complex geological structure. This complexity can be the main factor that causes the demotivation of geologists in exploring hydrocarbons. There are many indications of hydrocarbons in the form of oil and gas seeps on the surface, especially in East Timor. But most of them are not confirmed in the field, and only a few are even found in West Timor. The method used in this study is analyzing and 3D inversion modeling gravity data. The analysis was carried out using spectrum analysis and the second vertical derivative of the complete Bouguer anomaly (CBA). From the gravity parameters confirmed by geological data, the results indicate that in the study area there are basin and basement structures thought to be formed from unconformably of andesite igneous rock and tight send sediment with a density value of about 2.5 gr/cm3 . The average basement depth is about 5.5 km with its forming structure is the reverse/thrust fault with Northeast to Southwest its strike orientation. While in the southern part, especially in the central basin area, there is indicated a layer of sand sediment that is quite thick with a density value of about 2.2 gr/cm3 and has the potential to become a hydrocarbon reservoir.

Integration of gravity and magnetic inversion for geothermal system evaluation in Suli and Tulehu, Ambon, eastern Indonesia

The geothermal field of Suli and Tulehu is located in the eastern part of the Ambon Island, administratively situated in central Maluku regency, Maluku province, Indonesia. In the year 2017, the measurement of the Earth’s gravity and magnetic field has been done to evaluate the geothermal system in Suli and Tulehu. The application of gravity and magnetic methods was applied to determine the subsurface geological model describing geothermal sources, reservoirs, and faulting as a fluid conduit in the study area. Bouguer anomalies are positive in the range from 93 to 105 mGal, while magnetic anomalies are negative to positive in the range from − 656 to 310 nT, generally southwest to northeast. Geothermal manifestations in the form of hot springs associated with low residual Bouguer and magnetic anomalies positioned on the Banda-Hatuasa, Banda, and Huwe fault lines related to the alteration zone. Euler deconvolution analysis of the complete Bouguer anomaly data shows the maximum depth of fault detected at 1200 m. Gravity and magnetic inversion show high density and susceptibility contrast of rocks associated with Eriwakang and Simalopu pyroclastic rocks as geothermal sources. Low density and susceptibility contrast is estimated to be geothermal reservoirs due to interactions with geothermal source rocks below. A geological conceptual model based on the inversion modeling of gravity and magnetic data provides clear and comprehensive information on the geothermal systems in Suli and Tulehu, Ambon, the eastern part of Indonesia.

ANALISIS DATA GAYA BERAT DI DAERAH BENDAN DUWUR SEMARANG

This study was about the gravity in the area of ​​Bendan Duwur, Gajah Mungkur, Semarang. The method used in this research was gravity. The following steps in this activity were: calculating the value of Reader Gravity (gobs), Free Air Correction (FAC), Free Air Anomaly (FAA), Bouguer Correction (BC), Simple Bouguer Anomaly (SBA), Terrain Correction (TC), and Complete Bouguer Anomaly (CBA). The results of this research were listed as the Duwur bendan area, which can be seen from the shape of the points contained in the CBA, which is the smallest mGal value, 2.78 and the largest was 14.14. This can be assessed as an anomaly value, blue was the lowest value while pink the highest value, and yellow was the medium category. Based on the results of gravity measurements in the Bendan Duwur area, Semarang, the smallest mGal value was recognized by the TC compared to the gobs, FAC, FAA, and BC values. TC was producing 0.24 and the highest value was 1.13. The largest correction value was the FAC, the lowest value of mGal was 16.14, while the highest value of mGal was 26.33. Adapters for the Bendan Duwur soil structure based on CBA including the underground category generated were directly related to tectonic activity, but were more related to geology that requires special sedimentation and anthropogenic activities such as water needed.

Mapping of active major faults in the Mamasa and surrounding areas using satellite gravity data and topographic features

The mapping of active faults in Indonesia, especially in areas near the city center is very important to determine the building code. Mamasa Regency, West Sulawesi is one of the areas that have active faults, has not been mapped well in the 2017 seismic hazard book, which is a guidebook in creating building codes in Indonesia. A total of 762 earthquakes occurred in this area from November to December 2018. This study aims to map active faults associated with the source of these earthquakes. TOPEX satellite gravity data were processed to obtain the Complete Bouguer Anomaly. The residual and regional gravity values were separated using a Gaussian filter to identify the lineation of the fault and the existing fracture zone. The multiscale second vertical derivative was also implemented to identify and characterize the fault. Topographic contour mapping was carried out to confirm the presence of fault on the surface as well as to observe the direction of fault movement. We used seven focal mechanism data from Global CMT to support the interpretation result of gravity and topographic data. The result, the main fault is a sinistral strike-slip fault with N164E strike orientation. This strike-slip fault has two sides. The movement of the strike-slip fault on these two sides causes a pull-apart which results in normal faults in the pull zone between the two faults.

Urban Gravity Measurements for the Subsurface Mapping; Case Study Kaliawi

Gravity method is a passive geophysical method that can measure and obtain subsurface models based on rock density. Gravity method can be done in urban areas to obtain information about subsurface model as a reference in making urban policies related to disaster mitigation and urban development based on earth potential. Gravity research was conducted in Kaliawi, Bandar Lampung. Kaliawi has many problems including dense settlements and slums, areas prone to floods and landslides and has limited availability of fresh water. Based on the Complete Bouguer Anomaly results, the western area of Kaliawi has a low anomaly (36.8 – 38.2 mGal) with lithology of sandy-clay sedimentary rocks. Whereas the eastern area of Kaliawi has a high anomaly (38.4 – 40.8 mGal) with tuff lithology and can be bedrock. Based on the gravity anomaly and lithology, the western area of Kaliawi is a landslide area and recharge area while the eastern area of Kaliawi is good for settlement because it has bedrock.

Identification of Subsurface Structures of Geothermal Potential Area in East of Mount Lawu Using The Gravity Method

<p>Information about the eastern side subsurface stones of Mount Lawu regarding geothermal potential is limited. This research was conducted to provide information regarding geothermal potential in those area by using the gravity method. We did a 18 sites of gravity surveys in eastern flank of Mount Lawu where located in Magetan regency, Ngawi regency and Sragen regency, East Java. The principle of this method is to measure the earth's gravity field, then the value of gravity is corrected by some gravity corrections, i.e. height, tide, drift, normal gravity, free-air, Bouguer and terrain corrections. The Complete Bouguer Anomaly (CBA) shows the formation that related to the rock formation in the subsurface of Mount Lawu. Based on CBA modelling we found that in the eastern flank of Mount Lawu contains of tuff and breccia of volcanic rocks, breccia Jabolarangan and tuff Jabolarangan, lava andesite, igneous rock (pumice), and sedimentary rocks in the form of sandstone and clay. We found a fault structure on six tracks of a research area. Otherwise, we estimated that there is a geothermal potential on the southeast side of the research area</p>

Mapping of basement layer in field “X” petroleum system using ESA – MWT technique gravity data

Land gravity data acquired over part of North Sumatera Basin, Indonesia, was used to estimate depth to multiple horizons of density interface. Recently, gravitational data has difficulty to map the depth of subsurface layer structure except by using modeling. Here, we apply the energy spectral analysis-multi window test (ESA–MWT) technique to map the subsurface horizons. The estimated depth was computed from energy spectral analysis as the transformation of the gridded gravity data to 2D Fourier transform (Fast Fourier Transform). The energy spectrum analysis is performed at a test point by windowing the gridded complete Bouguer anomaly (CBA) at that test point with the square window size constantly increasing 1 km width from the previous window size. The distance between the test points is about 2 km on each of the gravity measurement lines. Plateau depths are then obtained which represents the density interfaces of the plot result between the depths of the anomaly to the window size. The results of the mapping of density interfaces correspond to sedimentary interfaces, those are the economic basement as Top Tampur Formation (Horizon 1), the top of several other sedimentary interfaces (Horizon 2-6), one of them is Top Belumai Formation (Horizon 2).

Geological model and development of the Cenozoic Wiang Pa Pao Basin, Chiang Rai Province, Northern Thailand, based on gravity data modelling and surface structural interpretation

3-D Inverse gravity modelling, constrained by surface geological data across the Neogene Wiang Pa Pao Basin (WPB), Northern Thailand, provides new subsurface models of the basin geometry and its structural development. The intermontaine WPB is seismically active and exhibits many geothermal sites; both are indicative of active fault zones. Six hundred thirty-six terrestrial gravity stations with ~500 m spacing were acquired. The residual Complete Bouguer Anomaly map (CBA) reveals an N–S elongate basin characterized by gravity lows bounded by gravity highs on the eastern margin of the basin (metasedimentary basement), and moderate gravity anomalies on the western margin (granitic basement). Structural edge detection revealed N–S trending faults along the eastern and western margins linked by NE–SW and NW–SE trending lineaments. The 3-D gravity model indicates an asymmetric graben; with a maximum depocenter depth of ~1300 m. Surface structure and seismicity confirm the gravity interpretation that the WPB is a dextral transtensional basin characterized by WSW–ENE trending R'-shears and NNE–SSW R-shears distributed in duplex-like geometries along the N–S trending principal displacement zone. The WPB displays unusually well-developed R’-shears, where Palaeozoic metasedimentary rocks in the basement and Cenozoic basin sediments are present, these faults disappear to the south, where the main N–S fault resides entirely within the granite. The WPB is associated with Cenozoic multi-phase rifting: in the Late Oligocene–Miocene, major rift basins formed under W–E extension, strongly influenced by WSW–ENE to NE–SW and NW–SE pre-existing trends. In the Latest Miocene–Recent, the younger basins, including the WPB, underwent dextral strike-slip along new and existing N–S dextral fault trends.

Gravity Anomaly in Kelud, Kasinan-Songgoriti, and Arjuno-Welirang Volcano Hosted Geothermal Area, East Java, Indonesia

This study aims to determine the relationship of heat reservoirs in the Kelud, Kasinan-Songgoriti, and Arjuno-Welirang geothermal systems based on gravity data analysis. Gravity data are obtained from Geodetic Satellite (GEOSAT) and European Remote Sensing-1 (ERS-1) Satellite which have been corrected to free air correction. The result of gravity data analysis is in the form of a complete Bouguer anomaly which represents the gravity anomaly below the surface. The results of the complete Bouguer anomaly value obtained were -15,238 mGal to 86,087 mGal. Based on these results, regional anomalies and residual anomalies will be separated to determine the depth of the two anomalies. 3D modeling was carried out based on the complete Bouguer anomaly data to determine the reservoir relationships in the Kelud, Kasinan-Songgoriti, and Arjuno-Welirang geothermal systems.

IDENTIFIKASI BAWAH PERMUKAAN LAPANGAN MINYAK“HUF” SUMATERA SELATAN UNTUK MENDELINIASI STRUKTUR CEKUNGAN HIDROKARBON BERDASARKAN DATA GAYABERAT

Oil field research in regional Banyuasin “HUF” , South Sumatra have been done by the gravity data with objective of knowing fault structure based on analysis of hydrocarbon SVD and knows hollow structure based on the 3D model of the Bouguer Anomaly and Residual Anomaly. Study areas had Bouguer Anomaly between 13 mgal up to 33 mgal to the interval 1 mgal, where the value of Bouguer Anomaly high have a range value 26 mgal up to 33 mgal which is in the direction of west. While the low value of Bouguer Anomaly have a range value 13 mgal to 20 mgal that is in the east. To knew the existence of structure fault, filtering Second Vertical Derivative (SVD) on a Bouguer Anomaly, Regional and Residua mapl.Pattern of structure fault indicated the contours of a zero value and between the high and low contours. From the results of the analysis SVD Complete Bouguer Anomaly and SVD Residual Anomaly there were 4 (four) fault, while from SVD Regional Anomaly there are 3 (three) fault. 3D modeling the Residual Anomaly were conducted to prove the existence of the fault SVD analyzed based on the results of the analysis and to know the hydrocarbon basin. Based on the results of the inversion of 3D the Residual Anomaly, basin was found in the depth of 1500 m – 3000 m with a value of the density ranges from 2.24 gram/cc until 2.32 gram/cc which identified as sandstone basin.

Depth Estimation of Geothermal Heat Structures by Euler Deconvolution of Gravity Data at Eburru Area, Kenya

Gravity survey was done at the Eburru area to estimate the source depth locations and delineate the fault boundaries using 3D Euler deconvolution. Gravity data was collected using CG-5 gravimeter. Gravity data reductions were done by applying drift correction, latitude correction, free air correction, Bouguer correction and terrain correction to the observed raw data to obtain complete bouguer anomaly (CBA). The CBA data was transferred to Oasis montaj software for Euler deconvolution processing. The 3D Euler deconvolution was carried out to determine and estimate the depth of the density bodies. Euler deconvolution locates the gravity anomaly source and estimates its depth from the gravity observation level. Euler deconvolution was preferred to other filtering methods in this study as solutions are only determined over identified analytic signal peaks, the window size varies according to anomaly size and the final solution involves only a few more precise depth estimates. The Euler deconvolution was performed using structural indices of 0.5, 1.0 and 2.0. Results from this analysis indicated that the CBA values in this study area range from gravity values of -272 mGal to -286 mGal and residual Bouguer anomaly amplitude range between -3 mGal and 3.4 mGal. The 0.5, 1.0 and 2.0 structural indices generated five solutions at depth range of 433 m - 2269 m, 801 m - 1433 m and 1170 m - 2246 m respectively occurring almost at the same locations on gravity highs. The deep structures were observed to occur in the northern part of the study area, and interpreted to be dense intruding masses likely to be trapped by the overlying cap rock at these depths. These could be geothermal heat sources that can be exploited to generate geothermal energy.

Subsurface Analysis Using Gravity Data at Lili Sepporaki Geothermal Area

Gravity survey plays an important role in early stage of subsurface imaging in geothermal system. The aim of this study is to understand the subsurface structure and possibly the heat source based on rock density distribution with three dimensional inversion modeling (3D). In 2010, Center of Mineral Resources, Coal and Geothermal of Indonesia was performed gravity survey at Lili Sepporaki geothermal area with 205 stations within a 10 x 10 km coverage area. The complete Bouguer anomaly was obtained with the density of 2.8 g/cm3 and this density was used to do 3D modelling. Bouguer anomalies ranging from 40 mgal to 62 mgal were observed in the study area with low anomalies values located in the northern part and high anomalies located in the southern part of the study area. Based on the 3D inversion modeling results, there are low density rocks with values between 2.0 - 2.3 g/cm3 around the hot springs of the research area with a depth of <1 km. These rocks are interpreted as rocks that associated with fractures forming a fault zone that controls the surface manifestation of the study area. High density rocks with values between 3.0 - 3.3 gr/cm3 are located south of research area with depth >2 km. This rocks are interpreted as intrusive igneous rocks and are thought as the heat source of geothermal systems in the study area.

The Subsurface Modelling of Karaha-Telaga Bodas Geothermal System using Gravity Method

The Complete Bouguer Anomaly (CBA) map from 1997 gravity survey at Karaha-Telaga Bodas, West Java, Indonesia is used to make a model of the subsurface geothermal system. A two-dimensional cross-section of the system is produced using a 2.5-D forward modeling. Initially, the print CBA maps of the Karaha-Telaga Bodas geothermal system is digitized. Next, the digital map is separated by using the moving average and spectral filtering methods, so a regional and residual anomaly maps are obtained. The subsurface modelling is made based on geological information of the area to produce a model that can represents the real condition as similar as possible. The line chosen for modelling has a North - South orientation, passing through Karaha and Telaga Bodas to foresee both of the geothermal system in one cross-section. Subsurface model interpretation shows that there are two separate granodiorite intrusion body with density contrast of 0.5 g/cc below Karaha - Telaga Bodas. This conclusion coincides with the intrusion body found during drilling operation. The intrusion body is possibly the heat source of the system. The reservoir of this system is interpreted as volcanic breccia with thickness of two kilometres in Telaga Bodas and keeps thinning towards Karaha. The fluids of the Karaha-Telaga Bodas Geothermal System are estimated to come from acid sulphate water and meteoric water entering from Telaga Bodas, as well as meteoric water entering from Karaha. There is an upflow in the South, Telaga Bodas.