Journal of Applied Geology
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ESTIMATION OF SUBSURFACE STRUCTURE BASED ON MICROTREMOR, BORE HOLE OBSERVATIONS AND STOCHASTIC STRONG GROUND MOTION SIMULATIONS IN PALU CITY, CENTRAL SULAWESI, INDONESIA: A VALIDATION AND SENSITIVITY STUDY ON THE 23 JANUARY 2005 (PALU) EARTHQUAKE
Get PDFIn this study, we investigated the subsurface structure and strong ground motion parameters for Palu City. One of the major structures in Central Sulawesi is the Palu-Koro Fault system. Several powerful earthquakes have struck along the Palu-Koro Fault during recent years, one of the largest of which was an M 6.3 event that occurred on January 23, 2005 and caused several casualties. Following the event, we conducted a microtremor survey to estimate the shaking intensity distribution during the earthquake. From this survey we produced a map of the peak ground acceleration, velocity and ground shear strain in Palu City. We performed single observations of microtremors at 151 sites in Palu City. The results enabled us to estimate the site-dependent shaking characteristics of earthquake ground motion. We also conducted 8-site microtremor array investigation to gain a representative determination of the soil condition of subsurface structures in Palu. From the dispersion curve of array observations, the central business district of Palu corresponds to relatively soil condition with Vs ≤ 300 m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 0.4 to 1.8 s and the resonant frequency are in the range of 0.7 to 3.3 Hz. Three boreholes were throughout the basin especially in Palu area to evaluate the geotechnical properties of subsurface soil layers. The depths are varying from 1 m to 30 m. Strong ground motions of the Palu area were predicted based on the empirical stochastic green’s function method. Peak ground acceleration and peak ground velocity becomes more than 0.04 g and 30 kine in some areas, which causes severe damage for buildings in high probability. Keywords: Palu-Koro fault, microtremor, bore holes, peak ground acceleration and velocity
ESTIMATION OF S-WAVE VELOCITY STRUCTURES IN YOGYAKARTA BASIN, INDONESIA
Get PDFFor the theoretical simulation or prediction of strong ground motion, it is prime importance to get information of underground structures, especially for sedimentary layers overlying on bedrock, like in Yogyakarta Basin. The Standard Penetration Test, Spectral Analysis of Surface Wave (SASW) and other geotechnical properties are used to estimate S–wave velocity structures in this basin. SPT tests were conducted at nine sites and SASW measurements were performed at seventeen sites. As a result, the S-wave velocity structures of top 30 m depth had been evaluated in each site. The average shear wave velocity v30 s had been successful estimated and the sites are classified into three types; soft soil, medium dense soil and hard soil. All sites where SPT performed are on soft soil according to their v30 s . However, according to v30 s from SASW measurements, 10 sites are located on medium dense soils type, 5 sites on dense soils and 2 sites on soft soils. The acceptable equivalent S-wave velocitystructure is observed by comparing the results from SASW and geotechnical approach in Imogiri, Bambang Lipuro, Pundong (Watu, Pranti) and Pandak (Wijirejo) areas.
Keywords: Ground motion, underground structure, sedimentary layer, SPT, SASW, Pundon
Fluid Inclusion Study Of The Polymetallic Epithermal Quartz Veins At Soripesa Prospect Area, Sumbawa Island, Indonesia
Get PDFThe Soripesa prospect area is located at Maria village, Wawo district, Bima region in the eastern part of Sumbawa Island, Indonesia. This area is a part of Cenozoic Calc-alkaline volcanic inner Banda-Sunda Arc. The dominant lithology of Soripesa prospect area are a lithic-crystal tuff of andesitic and dacitic composition and bedded limestone. There have five main polymetallic epithermal quartz veins in the Soripesa prospect area, namely, Rini vein, Jambu air vein, Dollah vein, Merpati vein, and Arif vein. Those quartz veins are hosted mainly in andesitic volcaniclastic rocks. Fluid inclusion study on those quartz veins is vey important to know the condition of hydrothermal fluids and their origin. Fluid inclusion study is conducted at the laboratory of Earth Resources Engineering Department, Kyushu University, Japan. Homogenization temperature, freeze temperature, eutectic temperature, and melting temperature can be known from fluid inclusion study. Based on fluid inclusion study, formation temperatures of all veins are between 250–260◦C. Melting temperature is between -0.2 to -3◦C. Based on the melting temperature, salinity (wt.% NaCl equiv.) of fluid inclusions is calculated by using Bodnar’s equation. Paleodepth of formations and pressure of trapping are also estimated by using formation temperature and salinity. Based on Hass (1971) diagram, estimated paleodepths of formations are 270 m for Merpati vein, 400 m for Dollah vein, 480 m for Rini vein, 570 m for Arif vein, and 680 m for Jambu Air vein, respectively. Pressure of trapping can also be estimated from depth of formation, density of lithostatic overburden, and gravity; 72 bars for Merpati vein, 106 bars for Dollah vein, 127 bars for Rini vein, 151 bars for Arif vien, and 180 bars for Jambu Air vein, respectively. Keywords: Soripesa, polymetallic quartz veins, homogenization temperature, salinity
Determination of suitable groundwater quality for agriculture by using GIS application in Bantul Regency, Yogyakarta Special Province, Indonesia
Get PDFirrigation purposes within Bantul area which is located on Yogyakarta Volcanic Groundwater Basin, 47 existing data points were used complementary with the results of 30 groundwater samples analysis which were collected from dug and tub wells in various locations of study area. ECw, TDS, pH and major cations: Na+, Ca2+, Mg2+, K+,and anions: Cl, HCO 3 , SO2 4 , NO 3 were analyzed as evaluation index. The relative tendency of ion in epm shows Ca2+>K+>Na+>Mg2+ and HCO 3 >Cl>SO2 4 . Variations in groundwater composition by using Mg/Ca vs. Na/Ca molar ratio indicates that the groundwater is close to silicate rock with influence of clastic carbonate rock. Higher salinity approach to the west of the Bantul indicates that groundwater quality is controlled by clastic carbonate rock and expose limestone of Sentolo hills. Groundwater samples fall under class I suggested that groundwater is good and suitable for irrigation based on Doneen’s classification of permeability index and 78.37% is in excellent category by Wilcox classification on N%. According to the SAR values plotted in the USSL diagram, the majority of the groundwater samples belong to C2-S1 and C2-S2 class, indicating medium salinity and low sodium water which can be used for irrigation with little danger. The suitability of groundwater quality for agriculture is determined by thematic maps produced from ArcGIS Spatial Analyst based on FAO guideline. Salinity is the significant problem that has slight to moderate restriction effect on crops productivities in this area. The ECw map indicates that good groundwater quality for crops is at the middle to the east of study area close to Opak River, while at the western irrigation water is affected but yielding no reduction on rice productivity. However, it has slight to moderate restriction on sensitive crops indicated in thematic map of crops land with different yield potential. The agricultural land in which has yield potential of 100%, 90% and 75% is about 2727.90 ha (38.56%), 735.49 ha (10.39%) and 208.98 ha (2.95%) of the study area respectively. Key words: Irrigation groundwater quality, total dissolved solids (TDS), electrical conductivity (EC), evaluation index, ArcGIS Spatial Analyst, FAO guideline, yield potential
ESTIMATION OF THE GEOLOGICAL STRENGTH INDEX SYSTEM FOR CAVITY LIMESTONE LAYER IN QUARRY AREA, REMBANG, CENTRAL JAVA PROVINCE, INDONESIA
Get PDFLimestone mining needs a good mine design which is safe for the environment. Mine design is determined by the rock mass quality. The rock mass quality in each mine location is not necessary the same depending on the geological conditions. The research area is located in limestone quarry of Sale District, Rembang Regency, Center Java Province-Indonesia. In the limestone quarry area, there is cavity zone which consists of cavity limestone layer at the wall of quarry bench. This cavity layer in limestone quarry has occurred by solution process. The cavity layer zone is a potentially weak zone which has caused bench failures in the limestone quarry area. The objective of this research is to analyze the rock mass quality in the cavity limestone layer using Geological Strength Index (GSI) system. Final result of the research is a rock mass characterization, specifically for cavity limestone layer. Keywords: geological strength index, limestone, cavity laye
ROCK MASS RATING OF CAVITY LIMESTONE LAYER IN REMBANG, CENTRAL JAVA, INDONESIA
Get PDFmine design. Mine design is determined by the rock mass quality, which varies from one mine location to another, depending on the geological conditions. The research area is located in limestone quarry of Sale District, Rembang Regency, Central Java Province, Indonesia. In the study area, a cavity zone is exposed at the wall of quarry bench and occurs by a solution process. The cavity layer zone is a weak zone which has caused bench failures. The objective of this research is to evaluate the quality of the cavity limestone layer for a safe mine design using Rock Mass Rating (RMR) system. Final result of the research is a rock mass characterization, specifically for the cavity limestone layer. Keywords: Rock mass rating, limestone, cavity laye
GEOCHEMICAL VARIATIONS ON HOSTED VOLCANIC ROCKS OF CIBALIUNG EPITHERMAL GOLD MINERALISATION, BANTEN – INDONESIA: IMPLICATIONS FOR DISTRIBUTION OF SUBDUCTION COMPONENTS
Get PDFSubduction of the Indo-Australian Plate beneath the Eurasian Plate formed at least seven magmatic arcs in Indonesia. One of the magmatic arcs is the Neogene Sunda-Banda arc hosts various style of gold mineralisation such as Cibaliung epithermal gold mineralisation. Major and trace element data for host volcanic rocks to the Cibaliung epithermal gold mineralisation is provided by this study to identify the magmatic arc system and the distribution of subduction components. Enriched LILE (Large Ion Lithopile Element) and LREE (Light Rare Earth Element) compositions for basaltic andesite – rhyodacitic samples from the Cibaliung district are characteristic of calc-alkaline arcs. In this typical volcanic arc, the subduction component can be shown to make a dominant contribution to its content of LILE such as Rb, K, Th, and Ba enriched (more than 88%) relative to the mantle and within plate inputs. The incompatible elements (Hf, Zr, and Nb) cannot be observed in the subduction component and thus assumed to be derived from trace element enriched sub-continental lithosphere. These incompatible elements are defined as conservative elements therefore it suggests that the magma occurrence is related to a hydrous slab component. Keywords: Subduction, Indo-Australian plate, magmatic arcs, volcanic rocks, Cibaliung, epithermal gold
GEOLOGICAL CONSIDERATION FOR CO2 STORAGE IN INDONESIA: A BASINAL SCALE OUTLOOK
Get PDFCarbon dioxide capture and storage (CSS) is alternative of reducing atmospheric emissions of CO2. The concepts of CO2 storage refer to the injection of carbon dioxide in dense form into aquifers, which basically must meet several conditions. Three types of geological formations that can be used for the geological storage of CO2 are oil and gas reservoirs, deep saline formations and unmineable coal beds. Indonesia has 60 Tertiary basins, however that great precautions must be taken for selecting particular sedimentary basin in Indonesia for carbon dioxide storage because of high possibility of leakage and the need to find deep formations as CO2 host since the geothermal gradient is high. One possibility to find proper basins is by selected “mature” basin as the detailed geological conditions are well known. Candidates are are North East Java or South Sumatra Basins.
Keywords: Carbon dioxide capture, storage, emission, basin
OVERVIEW OF DEEP GEOLOGICAL CO2 STORAGE AND ITS AREA SELECTION METHOD
Get PDFGeological sequestration of CO2 inside deep geologic formations is revolutionary among several other initiatives to combat the global warming. This method is already approved globally as a reliable and likely to be the only option that will allow removing CO2 in large enough quantities over short enough times to make a real difference. The first step of any geological CO2 storage projects is to select appropriate sedimentary basins in which CO2 will be injected and stored temporarily or permanently within permeable geological layers. The criteria for site selection methods are here explained based on summary from stateof-the-art research findings now exist. This method is planned to be applied for a more detailed mapping of potential sedimentary basins in Indonesia and neighboring regions.
Keywords: Sequestration, sedimentary basin, geological layers
MERCURY AND ARSENIC CONTAMINATION FROM SMALL SCALE GOLD MINING ACTIVITIES AT SELOGIRI AREA, CENTRAL JAVA, INDONESIA
Get PDFSmall scale gold mines discussed here are located at Selogiri area, Central Java, Indonesia which was mined by local community mainly during gold rush in 1990s. This Selogiri gold deposit genetically is characterized by porphyry mineralization overprinted by epithermal system. The ore minerals assemblage consists of pyrite, sphalerite, chalcopyrite, galena, chalcocite and rare arsenopyrite.
Chemical analysis of soil and stream sediment sampled over 1.5 km across at the Selogiri gold extraction site indicates that the site has been contaminated with mercury due to mining activities. The mercury concentrations in soil and stream sediments collected during dry season range from 0.01 to 481 ppm and 0.01 to 139 ppm, respectively, higher than background value of 0.05 ppm. In contrast, mercury concentration in stream sediments collected during rainy season from the same location as dry season sampling ranges from 0.01 to 13.42 ppm, and one sample has anomalous value of 331 ppm. This result show that rain water may disperse and decrease mercury concentration in stream sediments.
In case of arsenic, although the ore contains rare arsenic minerals, arsenic concentration in bulk rock and ore is high ranging from 8 to 59 ppm, while the arsenic concentration in tailing is much higher ranging from 5.8 to 385 ppm. Chemical analyses on pyrite reveal that the pyrite grains contain arsenic and might be the source of arsenic in Selogiri mine site. However, analysis of dug-well water demonstrates that the mercury and arsenic content is still lower than the maximum allowable concentration.
Keywords: Mercury, arsenic, contamination, Selogiri, gold min