## About

68

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Introduction

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April 1987 - present

## Publications

Publications (68)

Self-Adaptive Bare-Bones Teaching-Learning Based Optimization

Timor Island, located in the eastern Indonesian archipelago, has a complex tectonic evolution causing complex geological structures. Many hypothetical tectonic models are proposed mainly based on regional geological and geophysical data. Available geophysical data to support geological study at a more detailed scale are still very limited. Therefor...

Timor Island, Indonesia has complex geological structures related to its tectonic history. There is an existing subsurface geological model that is based on geophysical data. It is limited to the regional crustal scale and has a relatively low spatial resolution. The objective of our study was to delineate the sedimentary basin configuration of the...

We investigate the complex conductivity of 32 volcanic rock samples from two stratovolcanoes, La Soufrière Volcano (Guadeloupe Island, Caribbean) and Papandayan volcano (Java Island, Indonesia). These stratovolcanoes are characterized by high degrees of kaolinite-related alteration associated with the upwelling of acidic ground waters as well as th...

In gravity modelling, iterative refinement of 2D basement geometry is a classical problem where the density contrast has to be determined in advance. We present a relatively simple method to estimate 2D basement depth along with its density contrast. Known basement depths at several points and their associated gravity anomalies determine the gravit...

Gravity method is often used to estimate the sedimentary basin configuration at the preliminary stage of oil and gas exploration. This paper aims at the determination of 3D basement topography based on gravity data and known depth at several points. The gravity-depth relationship is used to determine the initial model and to adjust the model iterat...

A relatively new optimisation algorithm called symbiotic organisms search (SOS), which mimics survival efforts of organisms in an ecosystem, is presented. The interactions or synergy among organisms for survival involving mutualism, commensalism and parasitism phases are simulated as the stochastic search mechanism for optimum models in the search...

This work describes a subsurface basin configuration of the Lower Kutai Basin (hereinafter LKB) in East Kalimantan, Indonesia, as inferred from combination of magnetotelluric (MT), seismic, and gravity data. LKB is structurally controlled mainly by the Samarinda Anticlinorium extending in a NNE-SSW direction and is one of the most prolific hydrocar...

Symbiotic Organisms Search (SOS) is a global optimization algorithm inspired by the natural synergy between the organisms in an ecosystem. The interactive behavior among organisms in nature simulated in SOS consists of mutualism, commensalism, and parasitism strategies to find the global optimum solution in the search space. The SOS algorithm does...

Most earthquake studies focus mainly on offshore subduction zones that often produce high-magnitude earthquakes. However, onshore active fault earthquakes also common to cause significant devastation, due to their proximity to human activity and their relatively shallow depth. Most of active faults in Java show a west-east (W-E) trending direction....

Magnetotellurics (MT) can be applied to monitor resistivity change at depth that is for example due to fluid injection in enhanced oil recovery or CO2 storage. The observed MT data changes at the surface may be insignificant, but the effect can be enhanced using the layer stripping method, i.e. calculating MT data changes that would be observed at...

This paper discussed the investigation of the Sembalun-Propok geothermal system, West Nusa Tenggara Province, Indonesia. We analyzed the magnetotelluric data and its implication to the subsurface structure related to the system of Sembalun-Propok geothermal reservoir. In this study, information on the dimensionality of regional conductivity structu...

We present an interpretation of newly acquired audio-magnetotelluric data to reveal the subsurface geometry of Cimandiri Fault Zone, one of the major active faults in the western part of Java. The line section is 25 km long in a nearly north–south direction across the axes of CFZ with 24 stations of 750–1200 m spacing intervals. The 2D AMT inversio...

The magnetotelluric (MT) 1D modelling has been continuously receiving interest due to its effectiveness in obtaining overall subsurface resistivity image of an investigated area. The advances in computational resources allow increasing implementations of non-linear inversion using global search approach, such as Genetic Algorithm (GA). The genetic...

The magnetotelluric (MT) method is commonly used to estimate the subsurface conductivity structure. From the point of view of computational resources availability, currently it is a common practice to perform a 2D MT inversion modelling of MT data measured along a profile. For that purpose, the geoelectric strike angle determination from MT data is...

Surveys with Controlled-Source Audio-frequency Magnetotellurics (CSAMT) are often performed in scalar mode for practical considerations. In such case, CSAMT data are obtained from electric and magnetic fields oriented along and perpendicular to the traverse line, respectively. With closely spaced sounding stations along a profile, layered or 1D mod...

In the Bayesian perspective, inference on model parameters from observed data is performed by calculating the likelihood of the data given prior model parameters, i.e. to estimate the posterior probability of model parameters. With the advent of computational resources, there are increasing interests in resolving full non-linear inverse problems us...

Papandayan (2665 m asl) is an Indonesian stratovolcano located at 50 km from Bandung in west Java and characterized by an intense hydrothermal activity. An advanced alteration takes place where acid fluids interact with rocks, weakening the edifice, so that even minor explosive eruptions threaten the stability of its flanks. The purpose of the curr...

Gravity data analysis and interpretation are based, among others, on their spatial variation represented by horizontal and vertical gradients. The gradient or derivative of a gravity field can be calculated either in the spatial domain or the wave-number domain. Historically, the second vertical derivative (SVD) of gravity data can be used to delin...

Electrical conductivity tomography is a well-established galvanometric method for imaging the subsurface electrical conductivity distribution. We characterize the conductivity distribution of a set of volcanic structures that are different in terms of activity and morphology. For that purpose, we developed a large-scale inversion code named ECT-3D...

In sedimentary basin studies, gravity data are typically used to estimate the basement topography. Gravity inversion methods are expected to be able to discriminate between continuous and discontinuous sedimentary basins. Most 3D gravity inversion methods require intensive computational resources (computer memory and processing time). MDR3D, a vari...

We have investigated the subsurface structure of the Sembalun-Propok Area, West Nusa Tenggara, by using the audio-frequency magnetotelluric (AMT) method. This area is one of the geothermal prospect areas in eastern Indonesia. There are 38 AMT observation points, which were deployed along three profiles. We applied the phase tensor analysis on all o...

Papandayan volcano in West Java, Indonesia, is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah, i.e. Mas, Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011, numerous volcano-tectonic B events are encountered and the volcano was set on alert status on...

Data processing is one of the essential steps to obtain optimum response function of the Earth’s subsurface. The MT Data processing is based on the Fast Fourier Transform (FFT) algorithm which converts the time series data into its frequency domain counterpart. The FFT combined with statistical algorithm constitute the Robust Processing algorithm w...

The subsurface structure of the Sembalun-Propok area, NTB, Indonesia, has been investigated using magnetotelluric method (MT). To obtain the information of the dimensionality of the regional structure and determine the regional strike of the study area, the phase tensor analysis has been performed in this study. The results show that most of the sk...

Particle Swarm Optimization (PSO) is one of nature-inspired optimization algorithms that adopts swarm (insects, school of fish, flock of birds etc.) behaviour in search for food or common target in a collaborative manner. The particles (or agents) in the swarm learn from their neighbours as well as themselves regarding the promising area in the sea...

The lack of computational tools, i.e. software, often hinders the proper teaching and application of geophysical data processing in academic institutions in Indonesia. Although there are academic licensing options for commercial software, such options are still way beyond the financial capability of some academic institutions. Academic community me...

Controlled-Source Audio-frequency Magnetotellurics (CSAMT) is a frequency domain sounding technique employing typically a grounded electric dipole as the primary electromagnetic (EM) source to infer the subsurface resistivity distribution. The use of an artificial source provides coherent signals with higher signal-to-noise ratio and overcomes the...

Vertical electrical sounding (VES) data are usually interpreted in terms of a 1D resistivity model using linearized inversion. The local approach of a non-linear inverse problem has fundamental limitations, i.e. the necessity of a starting model close to the solution and possible convergence to a local rather than a global minimum solution. We stud...

Naturally existing electromagnetic (EM) fields recorded at the surface of the Earth can be used to infer the electrical conductivity distribution of the subsurface. In the magnetovariational sounding (MVS) technique, the transient variations of orthogonal components of the Earth’s magnetic field are measured. In the frequency domain, the magnetic t...

For this paper, we consider the resulting 3-D inversion using inversion modeling, which is motivated by developing theory and the recent application of the Magnetic Resonance Sounding (MRS) technique in detecting and mapping of subsurface groundwater. MRS is a non-invasive method which directly detects the groundwater's existence from surface measu...

A natural-source magnetotelluric (MT) survey was carried out in and around the Gede-Pangrango volcanic complex in the western part of Java island, Indonesia. This survey was intended to illus-trate the subsurface resistivity distribution beneath the volcano associated with geothermal po-tential in the area. For that purpose, we run two-and three-di...

Gravity gradiometry measurement allows imaging of anomalous sources in more detail than conventional gravity data. The availability of this new technique is limited to airborne gravity surveys using very specific instrumentation. In principle, the gravity gradients can be calculated from the vertical component of the gravity commonly measured in a...

The Markov Chain Monte Carlo (MCMC) algorithm has been successfully applied for inversion of 1D MT and VES data and also 3D EM (impedance tensor and tipper) data using thin-sheet approximation. This paper presents preliminary results of the MCMC inversion algorithm incorporating the full 3D MT modeling. In the MCMC inversion algorithm, a large numb...

Groundwater is an important economic source of water supply for drinking water and irrigation water for agriculture. Surface nuclear magnetic resonance (SNMR) sounding is a relatively new geophysical method that can be used to determine the presence of culturally and economically important substances, such as subsurface water or hydrocarbon distrib...

Vertical Electrical Sounding (VES) using Schlumberger electrode configuration is practical in the field with rough topography. With moderate investigation depth, VES technique is still commonly performed in preliminary surveys of a geothermal prospect. This paper presents the guided random search algorithm for VES data inversion leading to a quasi-...

The non-uniqueness in the solution of gravity inversion poses a major problem in the interpretation of gravity data. To overcome this ambiguity, "a priori" information is introduced by minimizing a functional that describes the geometrical or physical properties of the solution. This paper presents a 2D gravity inversion technique incorporating axe...

We investigate the possibility of application of the gravity method to delineate a typical coal-bed methane (CBM) bearing formation. We simulate gravity data corresponding to a realistic 3D gravity model associated with a thin coal layer in a sedimentary environment. The separate and combined gravity effects of the regional component and the coal l...

Motivated by the recent application of the surface nuclear magnetic resonance (SNMR) technique to detecting and mapping of subsurface groundwater, and making use of a recently developed theory of the method, we consider the resulting 3-D inversion modeling. SNMR is a new technology which just passed the experimental stage to become a promising surf...

Controlled-Source Audio-frequency Magnetotellurics or CSAMT typically employs a grounded dipole source in the range 1 Hz to 10 kHz. Most CSAMT data are still processed using the so-called near-field correction in order to apply MT modeling, especially in 1D. In this paper, we describe the inversion of CSAMT data using Markov Chain Monte Carlo (MCMC...

Surface Nuclear Magnetic Resonance (SNMR)is the geophysical method, which allows to determine water content and pore size distribution directly from the surface. A 3-D forward modeling code for SNMR amplitudes and decay times has been developed; after that improved 2-D and 3-D inversion algorithm has been investigated consist of model parametrizati...

Geo-electrical surveys employing Vertical Electrical Sounding (VES) technique are still commonly performed in preliminary surveys of a geothermal prospect. This paper describes the application of 1D VES data inversion using the Markov Chain Monte Carlo (MCMC) algorithm. Resistivities of a layered earth model with fixed thicknesses are biasly select...

The well-known non-uniqueness in modeling of potential-field data results in an infinite number of models that fit the data almost equally. This non-uniqueness concept is exploited to devise a method to transform the magnetic data based on their equivalent-source. The unconstrained 3D magnetic inversion modeling is used to obtain the anomalous sour...

Magnetotelluric (MT) method is a frequency domain sounding technique that uses naturally existing electromagnetic (EM) fields as the source to infer the subsurface resistivity distribution. Controlled-Source Audio-frequency Magnetotellurics (CSAMT) is derived from MT and uses an artificial EM source (typically grounded electric dipole) in the range...

Vertical Electrical Sounding (VES) using Schlumberger electrode configuration has relatively deep investigation depth and is practical in the field with rough topography. This paper discusses the Markov Chain Monte Carlo (MCMC) algorithm for 1-D VES data inversion. Layered model is formed by a number of layers with fixed thickness and the model par...

2-D resistivity imaging is now routinely employed for diverse application, especially for shallow or near-surface studies in groundwater prospecting, environemtal and geotechnical studies etc. This development is highly correlated with significant advances in equipment for measurement and software for modeling. However, Vertical Electrical Sounding...

Geophysical field method of surface
nuclear magnetic resonance (SNMR) allows a direct determination of hydrogeological parameters of the subsurface. The amplitude of the SNMR signal is directly linked to the amount of mobile water. The relaxation behaviour of the signal correlates with pore sizes and hydraulic conductivities of an aquifer. For impr...

In the last two decades, electromagnetic (EM) methods have been widely adapted for hydrocarbon exploration. Hydrocarbon saturated reservoir rock is typically electrically resistive relative to brine filled host rocks and or seal rocks. This work examines the applicability of electromagnetic methods consisting of passive magnetotelluric (MT) and act...

Earthquake is one among most disastrous natural hazards, and yet the earthquake prediction is still at the research stage. Important effort for earthquake hazard mitigation and prediction has been done so far to minimize casualties, i.e. monitoring seismicity, deformation using geodetic and GPS measurements, and also electric and magnetic fields va...

A magnetotelluric (MT) survey has been carried over the Kawengan field and the Banyuasin prospect to assess the potential of the deep reservoir in the Kujung carbonate and to clarify an indication of a shale diapiric mass in the core of the Kawengan anticlinal structure. The MT response data in terms of apparent resistivity and phase difference wer...

A fully non-linear inversion scheme based on bayesian Markov Chain Monte Carlo (MCMC) algorithm has been developed for magnetotelluric (MT) 1-D and thin-sheet models. Application for both synthetic and field data from various scale showed satisfying results with reference to synthetic models and local geology. The paper describes an attempt to appl...

Magnetotelluric (MT) method has been used for petroleum exploration MT worldwide, especially in reconnaissance stage of an exploration program and also in difficult areas due to topographic and structural complexity. However, application of MT in Indonesia is very limited due many restraining circumstances. The paper describes the basic principles...

The magnetotelluric response of a given conductivity model is obtained from the solution of Maxwell's differential equations. In the case of a one-dimensional model, the response function is usually expressed as a recursive formula connecting the impedance at the surface of two successive layers. The present paper describes an alternative algorithm...

A simple impedance tensor analysis of four magnetotelluric soundings recorded over the ECORS section of the Rhine Graben shows that for periods shorter than about 30 s, induction dominates over channelling. For longer periods, 2-D induction galvanically distorted by surface heterogeneities and/or current chanelled in the Graben can explain the obse...

Abstrak Pada masalah inversi dalam konsep inferensi Bayes solusi dinyatakan oleh fungsi densitas probabilitas (PDF) posterior pada ruang model. Estimasi PDF pada ruang berdimensi banyak dilakukan berdasarkan rantai Markov yang konvergen dengan probabilitas invarian identik dengan PDF model posterior. Eksplorasi ruang model secara ekstensif mengguna...