Jurnal Geofisika Eksplorasi
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SITE EFFECTS IDENTIFICATION USING HVSR METHOD IN CISARUA HOT SPRING AREA, NATAR, SOUTH LAMPUNG
Full text linkCisarua, which contains a geothermal hot spring, is an intriguing area to investigate due to its location far from any known heat source or volcanic activity. Using the HVSR technique, this study aims to characterize the local site effects based on key parameters: natural frequency (fo), amplification factor (Ao), and average shear-wave velocity down to 30 meters depth (Vs30). Microtremor measurements were conducted at 25 locations across the Cisarua hot spring area, with an average spacing of 300 meters. Each site was recorded for 40–50 minutes, and the data were processed using Geopsy software to extract the HVSR curves, along with the fo and Ao values. The HVSR curves were then inverted using the Particle Swarm Optimization (PSO) algorithm to derive Vs30 values. The results show that fo values range from 0.6 to 1.1 Hz, and Vs30 values are generally below 175 m/s. These two parameters exhibit minimal spatial variation, indicating the presence of thick, soft, and relatively homogeneous sedimentary layers across most of the study area. The Ao values range from 2 to 5, with values below 3 dominating near the geothermal manifestation zone. The spatial distribution of fo and Ao reveals a northwest–southeast trend, which is strongly correlated with the presence of the Lampung–Panjang Fault that likely controls sediment accumulation and layer thickness in the area. Around point T13, Vs30 drops to 125–150 m/s, suggesting localized softening of the soil due to hydrothermal alteration processes. These findings emphasize the interplay between site effects, regional geological structures, and geothermal activity in shaping the dynamic properties of the subsurface in this area
STUDY OF ORE MINERALIZATION POTENTIAL IN METAMORPHIC ROCKS IN KAWATUNA AREA, PALU CITY, CENTRAL OF SULAWESI
No full textThe Kawatuna area has a complex geological structure and lithological condition of metamorphic rock, which is estimated to be a weak zone for hydrothermal solutions to rise and then accumulate as mineralization of veins in the metamorphic rock. Based on this, it makes this area interesting to research. This research aims to identify metal ore minerals and the mineralization characteristics of ores in the research area. The method used is a geological survey of the surface and laboratory analysis through ore microscopic as well as mineral chemistry tests. Based on the results of the research study, it was found that in metamorphic rocks in the Kawatuna area, sulfide metal ore minerals were found including argentite (Ag2S), pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite (ZnS), galena (PbS), and covelite minerals (CuS), Native elements ore minerals include gold (Au), silver (Ag), electrum (Au, Ag), and Oxide ore minerals in the form of hematite (Fe2O3). The mineralization formed is controlled by structures that produce fractures in the rock, which then produces mineralization as the veins of metamorphic rocks. The ore mineralization in the research area occurs through a hypogene process (the formation of a formation zone from primary ore minerals) and a supergene process stage (the formation of a formation or enrichment zone from secondary ore minerals)
PRELIMINARY ESTIMATION OF IGNEOUS ROCK RESERVE OF QUARRY MATERIALS USING GEOELECTRIC METHOD IN BIYUKU VILLAGE, BANGKO DISTRICT, JAMBI PROVINCE
No full textThe earth's subsurface can be composed of various rocks such as igneous rocks, sedimentary rocks, and metamorphic rocks. Determination of rock types below the surface is carried out using geophysical methods. This study aims to identify Rhyolite-Andesite Rock using the 2D geoelectric method of the Wenner-Schlumberger configuration used in determining the initial reserves of Rhyolite-Andesite mining materials by utilizing subsurface resistivity values based on 2D and 3D resistivity cross-section analysis. The results of the petrological analysis showed that the rock was rhyolite lava rock which was interpreted to come from the Rhyolite-Andesite Volcanic Formation of the Quaternary age. Interpretation of resistivity values is divided into 2 groups, namely values <350 Ωm interpreted as weathered igneous rocks due to structure and groundwater, then values> 350 Ωm interpreted as fresh igneous rocks of quarry mining materials (rhyolite). Initial reserve estimates based on 3D resistivity model blocks with a cutoff value of > 350 Ωm interpreted as rhyolite igneous rock have reserves volume 584,595.9461 m3
LAST GLACIAL MAXIMUM – HOLOCENE RAINFALL SHIFTS IN THE WESTERN SAVU STRAIT BASED ON GEOCHEMICAL PROXIES
Full text linkThe Indo-Pacific Warm Pool significantly influences global atmospheric circulation, with tropical rainfall patterns highly sensitive to glacial–interglacial climate changes. During the Last Glacial Maximum (LGM), approximately 26,500 years before present, lower insolation, expanded ice sheets, and reduced sea levels weakened the Australian–Indonesian Monsoon (AIM) due to a southward shift of the Intertropical Convergence Zone (ITCZ). In contrast, the Holocene period experienced intensified monsoon systems and increased precipitation. However, high-resolution hydroclimate reconstructions from the western Savu Strait remain scarce. This study reconstructs rainfall variability from the LGM to the Holocene using geochemical proxies from sediment core ST10 (at 1 cm interval), located in the western Savu Strait. Three elemental ratios (Ti/Ca, K/Ca, and Rb/Sr) from X-ray fluorescence (XRF) core scanning were used to indicate terrigenous input, chemical weathering, and fluvial discharge. The age model was established using radiocarbon dating and stable isotope alignment with the Greenland ice core δ¹⁸O record. Log-transformed elemental ratios reveal four intervals of increased rainfall: the LGM, Heinrich Event 1 (HE1), Younger Dryas to Early Holocene, and the Late Holocene. These periods are characterized by elevated Ti/Ca, K/Ca, and Rb/Sr values, suggesting enhanced monsoonal rainfall and continental runoff. Conversely, lower proxy values during the Early Deglaciation, Bølling–Allerød, and Mid-Holocene indicate drier climatic conditions. These patterns align with regional proxy records from southwest Sumba and the Timor Sea, confirming the reliability of elemental ratios in reconstructing past hydroclimate variability. This study provides the first continuous record of rainfall shifts in the western Savu Strait from the LGM to Holocene and contributes to understanding long-term monsoon dynamics in southeastern Indonesia, highlighting the complex response of tropical hydroclimate to global climate forcing
DELINEATION OF ERUPTION PRODUCTS AND GEOTHERMAL PROSPECT ZONES IN MOUNT SLAMET, CENTRAL JAVA USING LANDSAT 8 AND GEOCHEMICAL DATA
Full text linkMount Slamet, located in Central Java, Indonesia, is one of the promising geothermal prospect areas due to its active volcanic system and distinct surface manifestations such as hot springs and altered grounds. This study aims to identify potential geothermal zones around Mount Slamet by integrating geochemical analysis and remote sensing data. Geochemical measurements from hot springs show temperatures ranging from 48–89 °C, pH values between 6.2–7.1, and elevated concentrations of SiO₂ (90–145 mg/L) and Cl⁻ (18–42 mg/L), indicating high-temperature fluid interaction. Remote sensing techniques, including thermal anomaly detection and alteration mineral mapping using multispectral and hyperspectral satellite imagery, were employed to delineate surface manifestations and hydrothermal alteration zones. The results indicate that the most prospective geothermal area is located in the southwestern part of Mount Slamet, characterized by strong thermal anomalies and geochemical signatures consistent with a high-enthalpy geothermal system. The integration of these methods provides a comprehensive assessment of geothermal potential, revealing key prospect areas with significant thermal anomalies and geochemical signatures indicative of a high-enthalpy geothermal system. These findings enhance understanding of Mount Slamet’s geothermal potential and offer valuable
UTILIZATION OF MULTIBEAM ECHOSOUNDER DATA FOR BATHYMETRY MAPPING: EVALUATION WITH INTERNATIONAL STANDARD
No full textBathymetric mapping is crucial for understanding seabed conditions, especially in maritime countries like Indonesia. This study evaluates the quality of bathymetric data acquired using Multibeam Echosounder (MBES) in Jakarta waters. The acquired data was processed and analyzed based on the international standard IHO S-44. The results show that most acquired bathymetric data met the specified accuracy standard. However, some data did not meet the standard, especially in areas with varying depths. Bathymetric maps and seabed slope classification maps were successfully produced. The bathymetric map shows the complex morphology of the seabed, while the slope classification map indicates the dominance of flat areas. This research contributes significantly to efforts to improve the quality of bathymetric data in Indonesia
CONTROLLED-SOURCE ELECTROMAGNETIC (CSEM) DATA PROCESSING WITH HIGH ELECTROMAGNETIC NOISE LEVELS
No full textThe Controlled-Source Electromagnetic (CSEM) method is one of the electromagnetic methods utilized in geophysical exploration. This method provides a subsurface image through the resistivity anomalies of materials encountered by electromagnetic waves. The research area is located near a major city, resulting in high electromagnetic noise. Electromagnetic noise can be categorized into two types of the noise namely periodic noise and sporadic noise. Eliminating noise is a crucial objective to enhance data quality, as it can introduce uncertainty into interpretations. Three noise removal techniques are employed: pre-stack to filter the harmonic noise, stacking to remove the sporadic noise, and post-stack for smoothing. The CSEM data used consists of signals in the time domain with a 10-second period and a 50% duty cycle. The results of applying these noise removal techniques indicate that all three methods are highly effective in noise reduction. The pre-stack technique can remove periodic noise, while sporadic noise is addressed by the stacking technique, and signal smoothing can be achieved using the poststack technique