Search

Cibaliung merupakan daerah pertambangan mineral yang berada di Provinsi Banten. Hal ini, dibuktikan dengan adanya lubang tambang emas di daerah Cikoneng dan Cibitung. Penelitian tentang geofisika penting dilakukan guna menemukan cadangan emas baru di daerah Ciparay yang terletak di Sebelah Tenggara Cikoneng dan Cibitung. Metode geofisika yang digunakan di antaranya magnetik, resistivitas, dan induced polarization (IP). Metode magnetik digunakan sebagai survei pendahuluan untuk menggambarkan keberadaan struktur geologi pengontrol mineralisasi emas. Melalui peta reduce to pole dapat diketahui adanya tanda-tanda keberadaan struktur geologi yang ditunjukkan oleh anomali negatif (-220 hingga -135 nT) di Bagian Barat Daya daerah penelitian. Hasil teknik edge detectors menunjukkan adanya pola struktur dengan arah Northwest (NW) dan North-Northeast (NNE) yang dominan berada di Bagian Barat Daya sebelah Utara daerah penelitian. Metode resistivitas dan IP digunakan sebagai survei detail untuk menentukan keberadaan mineral yang terkandung dalam batuan. Hasilnya menunjukkan bahwa zona potensi mineralisasi ditunjukkan oleh anomali tinggi (resistivitas > 50 ohm.m dan chargeability > 40 msec). Resistivitas tinggi diduga sebagai respons batuan induk andesitic sedangkan, nilai chargeability tinggi merupakan respons dari hadirnya mineral-mineral bijih seperti emas dan perak. Zona potensi mineralisasi berada pada posisi patok 350-800 dengan arah persebaran mengikuti arah struktur geologi pengontrolnya yaitu NW dan NNE. Abstract. Cibaliung is a mineral mining area located in Banten Province. The area including gold mining in Cikoneng and Cibitung areas. Geophysical research is important to find new gold reserves at the Ciparay area, located in the Southeast of Cikoneng and Cibitung. Geophysical methods used include magnetic, resistivity, and IP. The magnetic method was applied as a preliminary survey to delineate the presence of the geological structure controlling the gold mineralization. Based on the RTP map, signs of the presence of geological structures are shown by anomalies -220 to -135 nT in the Southwestern part of the study area. The results of edge detector techniques show the existence of structural patterns in the direction of NW and NNE which are dominant in the Southwestern North of the study area. The resistivity and IP methods are employed for detailed investigation in order to obtain to determine the presence of minerals contained in rocks. The results show that the mineralized zones are indicated by high resistivity (> 50 ohm.m) and high chargeability (> 40 msec). High resistivity response is caused by andesitic source rock whereas, high chargeability response is related to the presence of ore minerals such as gold and silver. The mineralization prospect zone is indicated at the position of 350-800 and its direction corresponds to the direction of its geological structure namely NW and NNE. Keywords : New gold reserves, Negative magnetic anomalies , High resistivity , High chargeability .

At present there are many natural hazards in Indonesia especially landslides. Therefore, investigating landslides become essential due to their impacts on greater risk of destructions and loss of life. The mitigation approach for investigating landslide is to determine potential slip zones of vulnerable area. As we know that landslides occur mostly in a certain region of Bandung, Indonesia. Hence, geophysical measurements were carried out to investigate the potential slip zone in the research area, Cikahuripan Village, Parongpong Subdistrict, Bandung. We conducted Ground Penetrating Radar (GPR) and Direct Current Resistivity (DCR) measurements along six profiles. The geophysical survey of GPR was conducted using a 100 MHz GPR shielded antenna frequency and was obtained of two long profiles, whilst DCR was conducted using dipole-dipole configuration with four long profiles. Based on the integration of all GPR and DCR data were processed yielding the quasi 3D resistivity cross-section. The research area shows three lithology layers which are sandy tuff, clay tuff and lava breccia with range of resistivity value of 19,5–74 Ωm, 5–19,5 Ωm and more than 74 Ωm, respectively. The reimaging geological cross-section corresponds to GPR and DCR models indicating a potential slip zone. This appears as clay lithology at the depth of 4–16 meters beneath the surface. GPR and DCR results show that models are mutually supportive and consistent with each other.

Baturagung Escarpment is an essential tectonic element of Java Island because it represents a transition from the Southern Mountain Block to the Kendeng Basin. This study has succeeded in producing a three-dimensional model of the Baturagung Escarpment subsurface using gravity anomaly data. The data are distributed along a regional scale transect, whose resolving capability has been tested using a checkerboard test. Our proposed geophysical model can fit the observed data very well, with a 0.77% RMS error. This model exhibits a structural depression bounded by high basement blocks below the Baturagung Escarpment, one of the basement block outcrops at Jiwo Hills. The maximum width of the depression is 10 km, with a depth exceeding 3 km in some places. The depression might be formed because of an extensional tectonic regime that prevailed during the Palaeogene, followed by volcanic arc loads' emplacement up to the early Miocene.

Cross-sections of volcanic structures are generally constructed using existing surface rock data. The detailed subsurface is not accessible because of a limited approach; as a result, precision is less accurate. Geophysical data obtained from surface gravity measurements will improve this phenomenon based on the response of density variation through forward and inverse modelling. The joint interpretation will make it possible to improve the subsurface model and to apply it in volcano deposits that experience a throw. Gravity data acquisition is 200 points over an area of 16 × 14 square kilometres. An anomaly study will focus on near-surface phenomena, where modelling shows that inversion needs to be enhanced by mesh refinement. In addition, forward modelling renders the model more realistic. The results show, the fault reaches a half km. It is not seen in the geology section, and the density variation shows 0.3 grams/cc. This density change is interpreted for the pyroclastic in the depression segment. Fumaroles may interpret as the water percolating pathway from the peak through the flank structure. The meteoric water flows inside the volcanic deposits and the fault plane is the ends of the meteoric water reaching the outside.

Mapping of subsurface infrastructure such as pipelines, pipe ducts as well as man-made objects located below the earth surface is a difficult task in geotechnical engineering due to the need to direct contact to the object. Ground-Penetrating Radar (GPR) method as one of geophysical methods is an appropriate technique to solve such problems due to its capability to effectively provide the existence, the location and the depth of buried shallow objects. Despite many advantages, the application of GPR method is limited by achieved depth and resolution range that is frequency dependent. To overcome such problems, the so-called multi-frequency compositing method with Optimal Spectral Whitening (OSW) technique is studied and applied on real data acquired in the Muarakarang Combined Cycle Power Plant area located in the Northern part of Jakarta, the Capitol of Indonesia. Datasets from GPR measurement with 100 MHz and 250 MHz was used. Each radargram from the same path was processed individually and then joined to become multiple composite radargram. The resulted composite radargram from a GPR line we studied has shown clearer image for interpretation rather than individual interpretation. The applicability of this multi-frequency compositing recommend further study to solve some facing problems in geotechnical engineering.

The study of field camp geophysics in Karangsambung has been done since 1996 until 2019 by geophysical engineering ITB. During the field activities, students was assigned with several data acquisition using various geophysical methods. One of the most common method to conducted alongside with surface geological mapping is gravity. Compilation of gravity data during the activities will be presented in this work. There are two categories of data compilation during 24 years: data compilation 1996-2004, and 2005-2019. The observation conducted using relative gravimeter with data distribution already cover geological surface map in the study area (Luk-Ulo Melange Complex, Karangsambung Formation, Totogan Formation, and Diabas Intrusion). The pattern of gravity observation shows correlated with topographic variation. Range gravity observation from this study is about 62 mGal.

We investigated a significant correlation between Ground-Penetrating Radar (GPR) combined with down-hole seismic technique and geotechnical data (boring log and Standard Penetrating Test) to examine geophysical data as an important aid tool in interpreting geotechnical parameter. GPR data provide geotechnical engineers with continuous layering information, whereas down-hole seismic test (DHT) delivers geotechnical parameters such as Poisson's ratio $\sigma$ , Young Modulus E, Shear modulus and Bulk moduli. By combining these data with boring log and standard penetrating Test (SPT) data, a comprehensive estimation about geotechnical parameters can be achieved. We conducted GPR measurement with 100 MHz shielded antenna in two profiles (inline and cross-line) centered at a borehole. We conducted also SPT to measure soil strength and boring to know the lithology. Intensive examination reveals that GPR technique should be applied to extend the meaning of geotechnical parameter value around and between boreholes. From case study at ITB site, we found some interesting result. Whereas both GPR and down-hole seismic data can reveal hard soils with SPT value of more than 60 corresponding to silty sand, GPR data can detect the interface between silty clay and clayey silt layers that cannot be detected from SPT. This study reveal the potential use of GPR technique as a tool for investigation of subsurface that can be elaborated to the exploration of shallow coal seams in subsurface as well to that of valuable minerals.

Kebumen area is located in central Java Province, Indonesia, where outcrop of Pretertiary rock of old accretion wedge presence. However, the subsurface of the area, limestone, igneous rock, and Conglomeratic-clay of Karangsambung Formation, is poorly understood in subsurface. The current survey of gravity and AMT data is executing to delineate this boundary. The gravity profile and three point AMT is measure for reconnaissance study. The field observations for rock formations are also scrutinized, but the soil is prohibiting to seen more deep in detail. The general result of interpretation and modeling, show reaching depth of one and half kilo meter, the gravity data cover the mayor rock, but the AMT is more significance in better delineating the boundary. Hence the lithology could be distinguished for melange rock (1000 Ohm.m) and Karangsambung Formation of clay-conglomerate (80 Ohm.m), but also diabase of volcanic-plutonic rock (4000 Ohm.m). The preliminary result shows two mayor results, for limestone and Diabase. Limestone is spread-out on this area, probably the olistolith, and its extensions is more pronounce in the sounding point than the surface observations only. The mysterious of diabase, is more possible as sill product rather than vertical dike.

Kendari is a town in south east Sulawesi (Celebes) where the old rock of Triassic age is superposed with younger rock as unconformable. The emerging people and development infrastructure, is demanding the available water for domestic needs, not only from the river but also the groundwater. The water basin and its aquifer is investigate by resistivity and gravimeter. The resistivity-IP imaging of Wenner-Schlumberger configuration in several sections, and the Wenner sounding in several site is also executed. The deepest part of basin is delineated by gravity data. Besides the geophysics data, the crop out of significance rock is also observed. Several section show the resistivity result in near surface is agree well with crop out observation, such as conglomeratic rock and the resistivity signal of chargeability layer. The oldest rock crop out in surface is also agree well with the high resistivity value. The IP data to determine the water contents inside the rock in aquifer layer is also show up, and agree with the water availability. The prediction of groundwater basin could be detected by several mGal of gravity value. As result, we could draw the conceptual model of groundwater basin and hydrology aquifer.

The Lembang fault considering vulnerable because of the site is near downtown Bandung. The west Lembang segment is the rural area of Cibodas. The two opinions is emerging, become normal fault or strike slip fault, based on recent earthquake (2010 onward). The geology data show the structure is observed by the outstanding topographic extended about 20 km, with volcanic rock very dominant. The seismology data is analysed for year 2011 in Mw less than 3, and classical fault plane solution is obtained. The gravity data is better acquired than 0.1 mGal, with elevation precision better than 60 cm. The upward Continuation, and second vertical derivative, is applied on data, as well as modelling 2.5D. The section is presenting in one section only, while data is getting in larger area. The seismology data show mostly for event is strike slip although in several parts having event normal. The gravity data is not ideal as graben like structure but rather locally low about 10 mGal amplitude. The combining the two methods suggested the slip zone or sag pond is more possible for the local anomaly. Besides, the Lembang fault is extended toward north rather to west or south.

Induced Polarization (IP) is one of the Geophysical methods that utilize the polarization properties of the rocks. This method is widely used in metallic mineral exploration. In this method, it is known a specific method that called as Time Domain Induced Polarization (TDIP). The physical modeling of IP is used to study the behavior of TDIP response to the subsurface parameters. The fieldscale physical modeling is the development of the laboratory physical model. This modeling is realized by burying objects with a specific geometry that have contrasting physical parameter to host medium in the area that is not too extensive. Soil is used as host medium, sphere and block object which has variation in metallic mineral content as a target. The extreme targets was also made to evaluate the electrodes measurements. Data acquisitions are using the Dipole-dipole and Wenner configurations. The purpose of this study is obtaining the relations between TDIP response to changes of metallic minerals content. Res2DInv inversion modeling is used to obtain true chargeability and resistivity value in subsurface. The relationship between them is obtained from depth slicing of all inversion results. Evidently, the geometry and position of subsurface objects with contrasting in chargeability and resistivity can be identified with physical modeling fieldscale. Dipole-dipole and Wenner configuration are able to determine the TDIP responses in subsurface. Dipole-dipole configuration has main advantage, it is able to separate chargeability laterally, while Wenner produces deeper penetration. In this research, the relation between chargeability (m) and the iron-ore content (x) of the sphere targets using Dipole-dipole and Wenner configuration are m = 0,07e0,033x and m = 0,87e0,008x, while on the block targets m = 0,21e0,009x and m = 0,79e0,007x respectively. In this research, correlation between the resistivity and the metalic mineral content in the target can not be obtained with good result.

Induced Polarization (IP) method is one of geophysical method. This method is develop the resistivity method with additional measurement in ability of the ground to store electrical charge. Electrode polarization process is a major factor to the IP response in medium that contain metallic minerals. The relationship between the metallic mineral content and TDIP will be quantized. The TDIP response is influenced by porosity, grainsize, clay and metallic mineral content. Measurement is performed of artificial samples that made of iron ore mixed with quartz and cement. The samples are varied in iron ore content (0%-80%), grainsize (65-300) micron and clay content (0%-25%). If Fe-total content greather, then rise exponentially in chargeability M=1.53exp(0.029Fe). When the density becomes larger, chargeability rise exponentially M=0.347exp(0.852Dens). The presence of clay will enlarge the chargeability and minimize resistivity exponentially Rho=15.06exp(0.02C). Chargeability is lower and resistivity is higher for larger grainsize. Increasing water saturation will reduce the value of resistivity Rho=600,7exp(-0.028W) and Rho=191.4exp(- 0.025W) for Fe-total content of 28.3% and 21.2%, respectively.

International audience; We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N–S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20–30 m of vertical offset. The intersection of these N–S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N–S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, an unusual style in accretionary wedges worldwide. The N–S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence.

Modelling studies of Time Domain Induced Polarization (TDIP) performed to obtain the relationship between parameters responses to metallic mineral content. This study includes mathematical, forward, physical and inversion modelling. Mathematical modelling is done by solving the Laplace equation to obtain the IP responses. Forward modelling is done by developing a numerical workflow to generate theoretical curves. Physical modelling obtained the data from various parameters of target measurement. TDIP responses that compared with the theoretical curves are the results of mathematical modelling. The best response of IP can be obtained by inversion modelling. TDIP responses measurement by varying target’s metallic mineral content is done for understanding the relationship between them. The amplitude of IP responses in forward modelling is determined by target’s radius and depth ratio, and ratio of background resistivity and target’s resistivity. The higher target’s radius and depth ratio, the higher the amplitude. There is a good correlation between TDIP responses to the presence of the target and the possibility of metallic mineral content in target.

Since 1950s, several authors have reported the so-called anomalous gravity during the total solar eclipses through various experiments. To address this issue, in the moment of the total solar eclipse of 9 March 2016 passing most regions in Indonesia, we undertook microgravity measurements using two precise gravimeters. The measurements were made at two locations: (1) Poso (central Sulawesi), a location close to the centre passage of the total eclipse and (2) Lembang (West Java), the site of Bosscha Observatory, where the partial solar eclipse occurred. The two sites are selected to measure the possible different influence of the eclipse on aligning the three objects. The measurements were recorded three days before and one day after the eclipse at various intervals from 30 seconds to a short time at 5 seconds. The finer recording was performed several hours before and after the total eclipse. This measurement allowed detailed analysis, not only in time but also in frequency range. A detailed analysis is presented in this paper. We consider all possible geophysical as well as atmospheric effects. The residual data show that the shielding effect, usually thought as responsible factor on anomalous gravity, is not significant.

Wide-angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three-dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of La Réunion. The submarine part of the edifice has fairly low seismic velocities, without evidence for intrusives. An upper unit with a velocity-depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope. Between this unit and the top of the oceanic plate, imaged by normal incidence seismic reflection, a more homogeneous unit indicated by shadow zones on several wide-angle sections may correspond to lavas of a different nature, extruded underwater in the earlier phase of volcanism. Coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part, with limited evidence for some intracrustal intrusion. Deeper in the lithosphere, the presence of a layer of intermediate velocity between the crust and mantle is firmly established. It is interpreted as resulting from the advection of hotspot magmatic products, possibly partially molten, and of a composition for which the crust is a density barrier. The extensive wide-angle coverage constrains the extent of this body. It does not show the elongated shape expected from plate drift above a steady hotspot supply. Alternative propositions can hence be considered, for example, that La Réunion is caused by a solitary wave of hotspot material or by a young hotspot. The size of the underplate, 140 km wide and up to 3 km thick, corresponds to less than half the volume of the edifice on top of the plate. Copyright 1999 by the American Geophysical Union.