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INDONESIA
IJOG : Indonesian Journal on Geoscience
Published by Geological Agency of Indonesia
ISSN : 23559314     EISSN : 23559306     DOI : -
Core Subject : Science,
Earth & Planetary Sciences
The spirit to improve the journal to be more credible is increasing, and in 2012 it invited earth scientists in East and Southeast Asia as well as some western countries to join the journal for the editor positions in the Indonesia Journal of Geology. This is also to realize our present goal to internationalize the journal, The Indonesian Journal on Geoscience, which is open for papers of geology, geophysics, geochemistry, geodetics, geography, and soil science. This new born journal is expected to be published three times a year. As an international publication, of course it must all be written in an international language, in this case English. This adds difficulties to the effort to obtain good papers in English to publish although the credit points that an author will get are much higher.
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Articles 820 Documents
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High-Temperature Hydrothermal Fe-Ti Oxide Mineralization in The Arızlı Ophiolitic Mélange, Western Anatolia CİHAN YALÇIN; Adil Ozdemir
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.355-372

Abstract

The Arızlı Ophiolitic Complex in western Anatolia provides a distinctive geological context for comprehending Fe-Ti oxide mineralization processes in ophiolitic settings. This research examines the geochemical and mineralogical properties of Fe-Ti oxides using extensive fieldwork and laboratory investigations, including X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray diffraction (XRD). Ten samples were obtained from ultramafic and mafic rocks, displaying notable mineralization characteristics. The geochemical investigations indicated Fe₂O₃ concentrations between 10.52 % and 19.93 %, with TiO₂ contents ranging from 2.17 % to 13.63 %, suggesting hydrothermal and metasomatic processes. Discriminant diagrams, including Si-Al, Fe/Ti-Al/(Al+Fe+Mn), and Fe-Six2-Mn, validated the hydrothermal genesis of the deposit, supplemented by volcano-sedimentary processes Elevated Fe/Ti ratios and the clustering of samples within high-temperature hydrothermal domains (~300-500° C) suggest that hydrothermal fluids and metasomatic overprinting played a significant role in the formation of Fe-Ti oxide mineralization. A comparative analysis with other ophiolitic complexes, such as the Oman and Pindos ophiolites, underscores both common mineralogical-geochemical traits and unique attributes of Tthe Arızlı Ccomplex, notably its comparatively elevated aluminium enrichment. This work examines critical deficiencies in comprehending the genetic regulations and structural impacts on Fe-Ti oxide mineralization in ophiolitic environments. The findings offer a valuable foundation for subsequent research and resource evaluations, enhancing regional metallogenic models of hydrothermal Fe-Ti mineralization in ophiolitic environments.
Full Waveform Inversion (FWI) in 3D Synthetic Geological Modelling Indriati Retno Palupi; Wiji Raharjo; Oktavia Dewi Alfiani
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.189-197

Abstract

Modeling the Earth's subsurface is important in geophysics, for example, tomography and Full Waveform Inversion (FWI). Especially for FWI, it is a method in the geophysical field that is used to describe the subsurface with a high-resolution image by utilizing all parts of observation data (seismic traces) based on a velocity model. In this paper, the 3D synthetic geological modelling was generated as an initial model; then, based on it, seismic traces and also shot gathers were simulated by arranging sources and geophones, and finally, the FWI was done. After seismic traces (assumed as acoustic wave equations), complete with the smoothness, were obtained, then a hyperbolic partial differential equation between the time and space domains was applied before entering the inversion process. During the inversion process, the final seismic traces were obtained by velocity updating in the entire space and time until they reached zero misfit, so wave propagation and the final velocity model could be observed. The pattern changes of seismic traces, shot gather, wave propagation, and FWI could be described by modifying the seismic source and geophone location in the geological model. However, by generating a 3D synthetic geological model, there is much flexibility for getting various descriptions of acoustic wave simulations.
Creep-Overpressure Coupling in The Onshore of Northeast Java Basin: Structural and Field-Based Geological Constraints Eri S. Sitinjak; Benyamin Sapiie; Agus M. Ramdhan
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.269-296

Abstract

The onshore Northeast Java Basin is one of the most important oil and gas basins in Indonesia. The active Kendeng Fault plays a significant role in hydrocarbon generation and earthquake activity in the region. Studying the Kendeng Fault activity and its relationship with overpressure and earthquake potential could improve oil and gas exploration activities as well as natural disaster mitigation efforts in the onshore areas of the Northeast Java Basin. Therefore, this research focuses on surface geological mapping and laboratory analysis of field samples. Fault creep in the onshore of the Northeast Java Basin has not been studied continuously. Active mud volcanoes, which result from subsurface overpressure, may influence the creep rate and activity of Kendeng Fault segments. The Kendeng Fault meets the criteria of a creeping fault due to its geology, subsurface overpressure conditions, and geometry. Manifestations of creep near fault planes are clearly visible through geological phenomena such as landslides or physical changes in buildings. The Central Java morphology (Grobogan area) is rougher than The East Java morphology (Surabaya area), which suggests a possible difference in creep rate. The focal mechanism of recent earthquakes in the Kendeng Fault Zone indicates strike-slip or thrust faulting. The Central Java Fault segment exhibits a faster creep rate than the East Java Fault segment. This is evident through swarms of earthquakes at Gunung Pandan and Rawa Bening. Elemental analysis of the fluid and mud, combined with gas analysis of all the mud volcanoes in the studied area, shows a positive correlation between possible halide minerals (Na, Mg, Ca, K, and Cl) and gas content (N₂ and O₂/Ar). There is also a slight relationship between these gas and fluid elements (R²). These parameters increase from the mud volcanoes in East Java to those in Central Java. CO₂ shows a negative correlation (r) and a slightly stronger relationship (R²) with CH₄. The mud volcanoes in Central Java are dominated by CO2, which may originate from volcanic activity in a deeper reservoir as a result of tectonic activity in the region. In contrast, the mud volcanoes in East Java are dominated by CH₄, which may originate from a highly overpressured hydrocarbon reservoir in a shallower area due to a high sedimentation rate. The very high sedimentation rate influences the slow-creeping fault segment in East Java (the Surabaya region) due to overpressure. Conversely, the faster creeping fault segment in Central Java (the Grobogan and Kesongo areas) may be influenced by volcanism due to tectonic activity in the region. These findings require further study, particularly the relationship of overpressure in each Kendeng Fault segment. The results will be useful for hydrocarbon exploration activities in the region as well as for natural disaster mitigation in general.
Extreme Drought Characteristics in Java (1960-1965) Muhshonati Syahidah; Rusmawan Suwarman; Dhara Brawijaya
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.409-422

Abstract

This study examines the characteristics of the extreme drought experienced in Java between 1960 and 1965, a period marked by consecutive years of dry conditions. The research employs the Standardized Precipitation Index (SPI) to quantify meteorological drought and to assess extreme events as defined by the World Meteorological Organization (WMO), focusing on magnitude, duration, and spatial extent. The analysis identifies extreme drought episodes in 1960 and 1965, with 1964 exhibiting the most extreme magnitude, indicated by SPI-12 values of ≤ -2. These droughts were notably prolonged, with a duration of up to thirty-nine months (from December 1960 to October 1964), and spatial analysis reveals that the southern half of Java was most affected, covering nearly half the region. Further analysis explores the influence of major climate anomalies, including El Niño (Niño 3.4), the Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO), and other climate indices. Spatial correlation analysis confirms that ENSO and IOD were the dominant drivers, with Niño 3.4 and DMI showing strong negative correlations with SPI-12, particularly across Central and East Java. In contrast, the PDO exhibited a positive correlation with SPI-12, suggesting it may have played a moderating role by enhancing rainfall during its positive phase. The study concludes that drought duration is a critical dimension in defining extreme drought in Java and that accounting for both interannual (ENSO, IOD) and decadal (PDO) variability is essential for improving drought risk forecasting and resilience strategies in vulnerable regions.
Geochemical Study of Water and Gas in The Wayang Windu Geothermal System Arif Susanto; Niniek Rina Herdianita; Dasapta Erwin Irawan; Prihadi Sumintadireja
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.423-440

Abstract

This study presents a comprehensive geochemical and hydrogeological characterization of the Wayang Windu Geothermal System in West Java, Indonesia. The research aims to identify water and gas chemistry patterns, to determine fluid origins, and to estimate reservoir temperatures to support conceptual modeling of the geothermal field. Field sampling was conducted on hot and cold springs and fumarolic gases, complemented by laboratory analyses of major ions (Cl⁻, SO42⁻, HCO3⁻; Na⁺, K⁺, Mg2+), stable isotopes (δ2H, δ18O), and gas compositions (CO2, N2, Ar). Data interpretation employed standard geochemical tools, including Cl-SO4-HCO3 and Na-K-Mg diagrams for water classification, δ2H-δ18O plots for recharge source identification, and N2-CO2-Ar ternary diagrams for gas origin assessment. The results indicate that sulphate-type hot springs mark upflow zones, while bicarbonate-type warm and cold springs reflect lateral outflow and mixing processes. The isotopic signatures confirm predominantly meteoric recharge with localized steam-heated and magmatic influences. The gas geothermometers estimate reservoir temperatures between 225° and 286° C, and Cl-Li-B relationships reveal three distinct reservoir clusters: Gambung, Wayang, and Windu. These findings provide critical insights into fluid pathways, reservoir structure, and recharge dynamics, forming a robust basis for sustainable geothermal resource management in volcanic settings.
Shear Wave Velocity Profiling: Comparing MASW and SPT for NEHRP Site Classification Erfan Syamsuddin; Alimuddin Hamzah Assegaf; Adi Maulana; Ulva Ria Irfan
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.441-453

Abstract

Discrepancies between shear wave velocity (Vs) profiles derived from Multichannel Analysis of Surface Waves (MASW) and the Standard Penetration Test (SPT) pose significant challenges for seismic site classification under the National Earthquake Hazards Reduction Program (NEHRP) standards. This study investigates the effects of velocity contrasts and irregular subsurface stratification on the alignment of MASW and SPT Vs profiles. A MASW survey was conducted using an active seismic source and an array of geophones, with data processing involving preprocessing, dispersion curve extraction, and shear-wave velocity inversion using a Monte Carlo approach. The extracted dispersion curve spans frequencies from 25 Hz to 80 Hz, with phase velocities ranging between 200 m/s and 500 m/s. The inverted Vs profile indicates a progressive increase in shear wave velocity with depth, suggesting a compacting sedimentary sequence transitioning into bedrock at greater depths. The computed Vs30 value of 541.7 m/s classifies the site as NEHRP Site Class C (very stiff soil or soft rock). The correlation with regional borehole data confirms the presence of clay and silty deposits in the upper layers, followed by claystones and sandstones at depth. Despite the reliability of the MASW for seismic site characterization, discrepancies with SPT-derived Vs profiles highlight the challenges posed by velocity contrasts, irregular stratification, and higher-mode Rayleigh waves. Refining inversion techniques and integrating multiple geophysical methods are crucial for improving subsurface characterization and seismic hazard assessments. These findings emphasize the importance of considering seismic design regulations for infrastructure development in Site Class C soils, which can exhibit moderate ground motion amplification.
Petrology and Geochemistry of Ciremai Volcano, West Java, Indonesia: Evidence of Open-System Magma Dynamics Keisha Prillia Qayyima; I Gusti Bagus Eddy Sucipta; Asep Saepuloh; Nurcahyo Indro Basuki; Very Susanto; Niniek Rina Herdianita; Mirzam Abdurrachman; Idham Andri Kurniawan; Prihadi Soemintadiredja; Emmy Suparka
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.473-486

Abstract

Ciremai Volcano is the youngest active volcanic system within the Ciremai Volcanic Complex (CVC), located on the northern coast of West Java. This study aims to further investigate the characteristics of the magmatic system as part of the Sunda Arc. The activity of the CVC is divided into four periods: Putri Volcano, Gegerhalang Volcano, Wurung Crater, and Ciremai Volcano with its parasitic cones. The magmatic evolution of the CVC is reflected in the characteristics of its lava throughout its volcanic history. Petrographic analysis reveals that the volcanic rocks of the CVC are predominantly composed of plagioclase, pyroxene, olivine, hornblende, and opaque minerals as phenocrysts. The magma exhibits calc-alkaline affinity, with Fe enrichment during the early stages of magma formation. The enrichment of incompatible elements (Sr, K, Rb, Ba, and Th), depletion of HFSE (Nb, P, and Ti), and the presence of xenoliths suggest a convergent margin setting, with a continental-derived sediment enrichment in the magmatic source. Both petrological and geochemical analyses indicate that the magmatic evolution of the CVC has an interconnected open-system magma dynamic. Major basaltic injections and mixing of basaltic magma likely triggered a significant eruption at the end of Gegerhalang and contributed to the development of new magma conduits. Besides fractional crystallization, the post-caldera magmatism of Wurung Crater, Ciremai, and its parasitic cones is affected by a prolonged basaltic influx and magma reheating.
Analytical Review of Natural Hydrogen Sources and Occurrence for Sustainable Hydrogen Future in Indonesia Andi Mardianza; Cindy Dianita; Adi Widyantoro
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.455-472

Abstract

One transformative, inexpensive (~$0.5-1/kg), and low-carbon energy source is natural hydrogen produced by serpentinization and other geochemical processes. Global data on its accumulation, migration, and geological mechanisms have been collected in the present study. Temperature, pressure, and mineralogy all affect the rate at which hydrogen is generated. While very limited hydrogen is produced at low temperatures (0.01-1 mmol/kg), significant production (1-100 mmol/kg) is made possible by ideal hydrothermal conditions (200-315° C), with extremely high rates (100-360 mmol/kg) possible under extreme experimental conditions. The evaluation of Indonesia's enormous potential, situated within the vast East Sulawesi Ophiolite Belt, is a primary focus. The country's tectonic environment offers the three necessary components for a significant hydrogen play: a steady geochemical engine, a large supply of source rock, and efficient migration routes. Consequently, Indonesia stands poised to emerge as a potential leader in the regional hydrogen economy. To realize this potential, specific exploration and regulatory support must be initiated, and technical issues related to gas purity must be resolved. This work presents the scientific and financial justification for prioritising natural hydrogen in the global energy transition.
Subsurface Modeling Using Gravity Data in Southern Yogyakarta and Its Implications for The May 26th, 2006 Earthquake Muhammad Irham Nurwidyanto; Tony Yulianto; Rina Dwi Indriana; Adelia Nanda Pramudya
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.487-501

Abstract

The Yogyakarta region is one of the most seismically vulnerable areas in Indonesia, so detailed subsurface fault characterization is crucial for effective disaster mitigation strategies. Previous studies have recognized the Opak Fault as the main structure controlling seismicity in this area, but the geometry and existence of other fault systems remain less constrained. This study aims to delineate the subsurface density variations associated with fault zones and rock deformation. This study develops a two-dimensional gravity inversion model to refine the subsurface configuration of faults in southern Yogyakarta. Gravity data were processed through standard corrections and anomaly separation to generate a complete Bouguer anomaly and residual anomalies. The results show that residual anomalies (-60 to 100 mgal) successfully delineate lithological variations, where older volcanic units (Semilir, Nglanggeran, and Sambipitu Formations) produce positive density contrasts (0.4-0.85 g/cm³), while younger Merapi deposits display negative contrasts (-0.5 to -0.05 g/cm³). Importantly, the 2D model highlights not only the Opak Fault but also the Ngalang Fault to the east, spatially coinciding with the 26th May 2006 earthquake epicentre. This finding provides new evidence of the structural complexity in southern Yogyakarta and emphasizes the role of the Ngalang Fault in regional seismicity, offering an updated basis for seismic hazard assessment in the area.
Geospatial Analysis of LST and UHI Variability in Relation to Land Use/Land Cover Changes in Anambra State, Nigeria Okechukwu Ebuka Agbasi; Jude Steven Ejepu; Sunday Edet Etuk; Ubong Williams Robert
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.503-532

Abstract

Rapid urbanization and land use/land cover (LULC) changes have significantly altered land surface temperature (LST) patterns and intensified urban heat island (UHI) effects, particularly in rapidly developing regions of sub-Saharan Africa. This study aims to analyze the spatial variability of LST and UHI in relation to LULC changes across urban and rural areas of Anambra State, Nigeria. The study integrates Landsat 8 satellite imagery (2019 and 2024), Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), and geospatial analysis techniques. We classified LULC using a Support Vector Machine (SVM) algorithm and derived LST from thermal infrared bands using the Multi-Window Algorithm (MWA) with NDVI-based emissivity correction. UHI intensity was estimated using statistical threshold methods based on mean LST and standard deviation. Results indicate a 15.1% expansion of built-up areas, particularly in urban centres such as Onitsha, Nnewi, and Awka, leading to LST values exceeding 35.68°C and UHI intensities up to 30.59°C. In contrast, rural areas such as Ayamelum, Ogbaru, and Anambra West exhibited lower temperatures (below 31.37°C), attributed to higher vegetation cover and proximity to water bodies. However, ongoing deforestation and agricultural expansion have contributed to moderate temperature increases in rural regions. The study concludes that LULC changes are a primary driver of thermal variability in Anambra State. Sustainable land-use planning, afforestation, and climate-responsive urban design are essential for mitigating UHI effects and enhancing environmental resilience.

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