Publications of Research Center for Geotechnology, Indonesian Institute of Sciences
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Microzonation of Soil Resistance Based on Shear Wave Velocity Variation: Case Study of Kampung Melayu District, Bengkulu City
Full text linkThis research presents a unique microzonation map based on shear wave variations, specifically Vs10, Vs20, Vs30, Vs40, and Vs50. Microzonation is dividing a region into smaller zones based on specific characteristics, such as soil resistance to seismic waves. The method used in this research includes secondary data collection of shear wave velocity values and soil layers in the District of Kampung Melayu, then producing shear wave velocity distribution at various depths, soil site class distribution map, and Ground Amplification Factor (GAF) distribution map. The results of this study indicate that the variation in shear wave velocity at different depths provides an overview of the soil type resistance in Kampung Melayu District, Bengkulu City. The resulting microzonation map, a novel approach in this context, indicates an increase in the Vs value with increasing depth. Additionally, the Ground Amplification Factor (GAF) distribution reveals that areas with low soilspecific resistance exhibit higher amplification values, thereby increasing their susceptibility to seismic vibrations. These findings provide valuable and novel information for earthquake risk mitigation and the planning of safer infrastructure in this area, significantly contributing to civil engineering and urban planning
Reconstruction of Shear Surface Based on Joint Roughness Coefficient and Its Relation to Rock Shear Strength
Full text linkRock strength is a fundamental parameter in rock mechanics, serving as the basis for predicting rock behavior under different loading conditions. Among the various approaches to characterizing rock strength, shear testing of discontinuities plays a crucial role. The Joint Roughness Coefficient (JRC) provides an empirical link between joint surface roughness and shear strength parameters. In this study, joint surface profiles were reconstructed statistically based on JRC parameters and subsequently reproduced using three-dimensional (3D) printing technology. The printed molds were employed to cast laboratory specimens with pre-formed shear surfaces, which were then tested under direct shear conditions. The shear strength parameters obtained from the tests were analyzed in relation to their corresponding JRC values. The results demonstrate that the reconstructed and 3D-printed surfaces were successfully fabricated and accurately replicated joint roughness geometries. Direct shear tests confirmed the expected trend, with shear strength increasing alongside JRC. These findings indicate that shear surfaces can be prefabricated and manipulated with controlled roughness, providing a reliable and reproducible platform for investigating the mechanical behavior of rock joints
Volcanostratigraphy and Geological Hazard Potential of the Karaha-Sadakeling Volcano Complex, West Java, Indonesia
Full text linkThe purpose of this study is to determine the type and distribution of volcanic rocks both laterally and vertically and to analyze the potential hazards of the Karaha-Sadakeling Volcanic Complex. Volcanostratigraphically, the volcanic evolution from old to young is Cakrabuana Crown, Sadakeling Crown, Ewaranda Crown, and Talagabodas Crown. The recognizable landforms are crater traces, volcanic cones, lava flow ridges, and alluvial plains. The north-south oriented volcanic cone morphology of the study area parallels an approximate major fault that passes between the Cakrabuana Complex to the northeast, and the Karaha-Sadakeling Complex. The northern part is dominated by Sadakeling Crown volcanic deposits, the central part is composed of Ewaranda Crown deposits, and the southern part is dominated by TelagaBodas deposits. The magmatic evolution shows the process of magma assimilation and mixing with primitive magma. Potential volcanic disasters can include pyroclastic fall, pyroclastic flows, and lava flows. Primary eruptions are inferred to originate from Karaha Crater, which exhibits ongoing volcanic activity
Tectonic Geomorphology Analysis in Natural Hydrogen Exploration: A Case Study from Tanjung Api, Sulawesi
Full text linkNatural hydrogen exploration has been proven to be a challenging endeavor due to many factors. In this paper we present a new insight to hydrogen exploration by using tectonic geomorphology to identify key target area based on its tectonic activity in relation to the occurrence of active fault. Tectonic geomorphology analysis is performed using 3 morphometric indices such as mountain front sinuosity, basin shape index and drainage density to determine the index of relative tectonic activity in this region. Field observation shows that hydrogen seeps occurred in the area with high to very high tectonic activity (Class 1 – 2) that correlate with the present of active faults in this area. Tectonic geomorphology can be used to narrow down the potential area by identify active tectonic region which corelated to active faults in this area
Mineralogy of granites from Hukurila area, Ambon Island, Indonesia: An insight into petrogenesis
Full text linkThe Hukurila area in the Leitimor region of Ambon Island hosts one of the granite bodies. The granite is surrounded by Jurassic-Cretaceous peridotites. Although granites in Ambon Island have been intensively investigated, their origin remains interesting to study. This work offers petrography and X-ray diffraction data of granite from Hukurila area and contributes to understanding petrogenesis in Ambon Island. Granites from Hukurila area are white to light brown and have a medium- to coarse-grained holocrystalline texture, with quartz, potassium feldspars, plagioclase, biotite, and muscovite being the most common minerals. Potassium feldspars are sometimes found in aggregated larger crystals in the outcrops. While cordierite, zircon, apatite, and mullite were also observed as accessory minerals under the microscope. Mullite in granites from Hukurila area indicates that the rocks were subjected to high temperatures. Aluminium-rich minerals (i.e., cordierite and mullite) in granites from Hukurila area suggest S-type granite with significant crustal contamination during their formation
Petroleum System Risk Quantification for PSC Investment in Indonesia’s LNG Sector
Full text linkInvestment decisions in upstream oil and gas sector of Indonesia often involve acquiring stakes in existing Production Sharing Contract (PSC) areas. Such decisions require careful assessment of geological uncertainty, economic viability, and regulatory constraints. For investors evaluating PSC blocks, a robust understanding of regional geological risk within the petroleum system is critical. This study introduces a practical and scalable geological risk quantification framework to support upstream investment decisions in the LNG sector in Indonesia. The framework is designed for application under the current fiscal regime and can be effectively implemented even when data availability is limited, such as when relying on information from the Migas Data Repository (MDR). Recognizing that early-stage opportunities often involve significant geological uncertainty, we developed a tailored petroleum system risk metric comprising five parameters: source rock, trap, dynamic factors, reservoir conditions, and subsurface issues. The framework was applied to five PSC blocks using Multi-Attribute Utility Theory (MAUT), integrating operator-specific economic indicators (Net Present Value, Internal Rate of Return, Payout Time, and Profitability Index) alongside CO₂ emission intensity. Monte Carlo simulations were conducted to evaluate investment rankings under uncertainty. A key finding is that the proposed risk quantification approach is simple enough to be implemented with limited MDR data, yet robust enough to support investment strategy. Furthermore, the framework builds upon and complements existing standardization effortsby the regulator, SKK Migas, offering a practical tool for upstream investors in an evolving regulatory landscape
Land Subsidence due to Groundwater Extraction and Natural Consolidation in the Bandung Basin, West Java, Indonesia
Full text linkBased on GPS and InSAR data, it is known that there is land subsidence in the Bandung Basin of 1.1 - 16.9 cm/year (GPS) and 0.9 - 1.7 cm/year (InSAR). Several types of land subsidence can be expected to occur in the Bandung Basin. However, the detailed characteristics and exact mechanism of land subsidence from a geological perspective in the Bandung Basin are still unknown. Two factors that can cause land subsidence are groundwater extraction and natural consolidation. It is known that there has been a significant decrease in groundwater levels in Bandung since the 1970s due to the very high intensity of groundwater extraction. It is also known that the Bandung Basin comprises one of them, the Kosambi Formation, which consists of organic clays with very high compressibility and undergoes a natural consolidation. Based on these facts, we determine the distribution of land subsidence rates due to groundwater extraction and natural consolidation, along with the percentage of their respective contributions in the Bandung Basin. Research materials include groundwater level depth data and organic clay consolidation data from previous studies. The results showed that the average land subsidence rate due to groundwater extraction was 1.85 cm/year, with a contribution percentage of 44.30%. In comparison, the average land subsidence rate due to natural consolidation was 0.92 cm/year, with a contribution percentage of 15.76%
Assessment of Bedrock PGA Values based on Probabilistic Seismic Hazard Analysis in Purworejo, Indonesia
Full text linkPurworejo Regency, Central Java, is directly adjacent to the Indian Ocean in the South, where there is a subduction zone between the Indo-Australian Plate and the Eurasian Plate. The movement of these plates has the potential to cause earthquakes, so for mitigation purposes with the design of earthquake-resistant buildings, PGA analysis and Earthquake Hazard Curve are needed. Data is sourced from the 2017 Indonesian Earthquake Hazard Source Map Book using Hazard Analysis software (USGS PSHA) GMPE modified. The attenuation function or GMPE (Ground Motion Prediction Equation) used is also the same as that used to create the Indonesian Earthquake Hazard Map of earthquake source mechanisms consisting of subduction, fault, and background earthquake with a return period of five hundred, one thousand, two thousand and five hundred, five thousand, ten thousand years. The results show that for a 2500-year return period, the most contributing earthquake source in the Purworejo Regency is a subduction earthquake source, with Kaligesing Subdistrict having the highest PGA value of 0.209 g and Bruno Subdistrict owning the lowest PGA at 0.186 g. The distribution of PGA values at this return period shows that the PGA values increase as the location approaches the subduction earthquake source from North (0.15 – 0.20 g) to South (0.20 – 0.25 g). Based on the PGA value, the Purworejo Regency area could feel the occurrence of earthquake vibrations. However, it is still necessary to mitigate the occurrence of earthquakes by building earthquake-resistant buildings to minimize losses when a major earthquake occurs in the futur
Comparing Numerical Methods for Infiltration Estimation: A Statistical Approach to Accuracy and Efficiency
Full text linkThis study evaluates four numerical methods—Euler, Heun, Runge-Kutta 4th order (RK4), and Adams-Bashforth—in terms of their accuracy and computational efficiency for solving the Horton infiltration model, which is crucial for hydrological studies. The methods were applied to simulate soil infiltration and cumulative recharge, with a focus on determining the most suitable method for practical applications in water resource management, agriculture, and soil conservation. An ANOVA (Analysis of Variance) test was conducted to assess the statistical significance of differences in the results obtained from the methods. The test revealed no significant differences between the methods (p-value = 0.9995), indicating that despite differences in computational complexity and accuracy, the methods produced similar results. The Euler method, being the simplest and fastest, provided acceptable results for shorter simulations or less critical applications, while RK4 and Heun, though more computationally expensive, yielded more accurate estimates. Adams-Bashforth offered a reasonable balance between accuracy and efficiency. This study highlights the importance of selecting the appropriate numerical method based on both accuracy and computational cost, particularly for real-time applications and large-scale simulations in hydrology. The findings suggest that simpler methods like Euler can be used for less critical tasks, while more accurate methods like RK4 should be employed for high-precision modeling in complex hydrological scenarios
Rock Mass Quality Analysis of Soko Cave, Temayang District, Bojonegoro Regency, East Java based on Q-System, Rock Mass Rating, and Geological Strength Index Methods
Full text linkThis study aims to analyze the rock mass quality of Soko Cave, located in Temayang District, Bojonegoro Regency, East Java, as a basis for evaluating geotechnical stability for tourism purposes. Three rock mass classification methods were used: Q-System, Rock Mass Rating (RMR), and Geological Strength Index (GSI). Data were obtained through field surveys, geological mapping, cave geometry measurements, and observation of discontinuities using the scanline method at 11 observation stations. The rock mass quality was generally classified as good to very good, with the Q-System method producing the highest score, followed by GSI and RMR. The differences in results were due to the different parameters used by each method. Basedon these findings, the rock mass in Soko Cave was considered naturally stable and did not require additional support structures, making it safe for geological tourism development. This study not only compares methods but also emphasizes the importance of using the three systems complementarily to provide a realistic and applicable picture of the stability of rock masses in carbonate caves. The GSI method shows potential as a reliable approach for this environment, although further validation with a broader data coverage is needed