Proceedings of the International Conference of Geological Engineering Faculty

GRAVITY DATA ANALYSIS IN BOGOR WESTJAVA – INDONESIA

Andi Agus Nur — Fri, 11 Feb 2022 00:00:00 +0530

Gravity measurements have been conducted, 169 gravity measurement data points with varied heights at each measuring point from 16 to 595.1 meters above sea level which is divided into two measurement paths. With the distance between the measuring points at a certain variation interval (effective 750 meters), using a closed loop method that aims to map subsurface conditions to Identifiying Structural Geology in the Bogor, West Java-Indonesia region. Complete Bouguer Anomaly (CBA) values varies from 26 mGal to 66 mGal. The High Anomalous Area, has a value of > 46 mGal, occupies more than the southern half of the study area, extends in the southwest to the possibility of symmetry in the east, and there is the highest anomaly between them. This high anomaly area is produced by a rock mass that has a greater mass density (≥ 2.507647059 gr/cm³). The Low Anomaly Area, has a value of ≤ 46 mGal, occupying less than half of the research area in the north. Increasing the anomaly value in the north on the map, forming an indication pattern of an open basin. This low anomaly area is produced by a rock mass which has a lower mass density (≤ 2.507647059 gr/cm³). Rock density at the study area based on forward modeling shows values in the range of 1.8 gr / cm³ s.d. 2.67 gr/cm³. The results of the study using gravity method based on 2D cross section shows that the main fault in bedrock along the AA 'research path is relatively West - East, with stratigraphic direction of each constituent rock layer to the south. The direction of the fault forms block faulting, making this area graben.

IDENTIFICATION AND CONSERVATION OF GEOHERITAGE (GEOLOGY) BASED ON GEODIVERSITY ANALYSIS (ASPIRING GEOPARK): STUDY OF KALTARA AND SANGKULIRANG-MANGKALIHAT

Fri, 11 Feb 2022 00:00:00 +0530

Aspiring geopark of Krayan Highland (Kaltara) and Sangkulirang-Mangkalihat mountain range is a geoheritage located in Northeast Kalimantan. The diversity of its nongeological aspects is located at the forests with High Conservation Value. Based on its intrinsic value, geosite is grouped within geological hotspots into diverse value areas (geoarea), by compiling them into data of geodiversity, biodiversity, and culturediversity. This inventory establishes 16 geosite types that are possible in 10 geological frameworks: anthropogeny, sedimentology, paleontology, mineralogy, stratigraphy, igneous rocks, metamorphic rocks, structural geology, neotectonics, geomorphology, hydrology and hydrogeology, geochemistry, geothermal, economics, paleogeography, and geohistory. Some sites are worth extraordinary and amazing Sites of Special Scientific Interest (SSSIs) and Regionally Important Geological and Geomorphological Sites (RIGS). Several geoheritage sites hold valuable evidence of Cenozoic magmatism and obduction, atoll and modern carbonate landscape, as well as distinctive hydrological features. Scientific meaning is close to the true value of the potential aspect. Its’ geological and landscape structures affect cultural tradition and biodiversity, forcing them to adapt. The geoheritage sites of Kaltara and Sangkulirang-Mangkalihat are popular in local, regional and national as well as global tourism spot.

SOIL CLASSIFICATION FROM RESISTIVITY AND P-WAVE SEISMIC VELOCITY WITH SUPPORT OF PARTICLE SIZE DISTRIBUTION (PSD) ANALYSIS

NA Ismail, Sanusi NH Abdullah , IZ Roslan, Rosli Rosli — Fri, 11 Feb 2022 00:00:00 +0530

It is encouraged to use more than one geophysical method when conducting a field survey. It can help improve the subsurface interpretation and reduce the ambiguity inherent from inversion of geophysical method. 2D resistivity and seismic refraction methods were conducted to map and characterize the subsurface at Desasiswa Indah Kembara, Universiti Sains Malaysia, Pulau Pinang. The inversion profile shows that the subsurface has two zones with a resistivity value of 150-500 Ω m (Zone A) and 5-100 Ωm (Zone B). On the other hand, the subsurface velocity is 0.3-0.6 km/s (Zone A) and 0.75-1.5 km/s (Zone B). However, the standard reference tables of resistivity and velocity value of soil and rock show variation and overlapping values that can affect the interpretation process. Therefore, additional information is important to support geophysical interpretation. Geological method such as particle size distribution (PSD) analysis (hydrometer analysis and mechanical sieving) was conducted to assist the interpretation. Percentage of clay, silt, and sand can be obtained through the PSD graph and used for soil classification. The value of total dissolved solids (TDS) and salinity of the area are also taken on-site for the saturated area with resistivity value of 20 Ωm at a depth of 2 m. The area has TDS (138-146 mg/L), and salinity (0.007 PSU) values indicating the fresh pore-fluid characteristics. Resistivity and seismic inversion profile manage to show the underlying subsurface layers. Results from PSD analysis also has supported the interpretation of the geology of the study area where Zone A was identified as silty sand, and Zone B is identified as silt and clay.

HYDROGEOLOGICAL CLUSTER ANALYSIS WITH AVERAGE LINKAGE AND WARD METHOD IN THE SOUTHERN SLOPE OF MERAPI MOUNTAIN

H Riswandi, Supandi, E Sukiyah , Tania D — Fri, 11 Feb 2022 00:00:00 +0530

This study aims to see the cluster analysis process using the average linkage method and the Ward method, and comparing thus results in analysis to clustering several related variables deciding to use the data of depth and hydro chemical character of groundwater. Processing cluster analysis with the average linkage method is pairing objects that combine into one cluster. Then, calculating the two proximity of the object to another variable, the next merging occurs in the most similar clusters than other variables, forming the second cluster. The second combination is to calculate using the average linkage method formula, forming a new distance matrix. The cluster analysis steps with the Ward method starts by the close look at N clusters, which have one respondent for each cluster (all variables consider cluster). The first cluster is formed by selecting two of these N groups, which, when combined, have the smallest value of Error Sum of Squares (SSE). N-1 clusters then consider again to determine which of these two clusters can minimize heterogeneity. Thus, N clusters are systematically reduced by N-1, become N-2, and so on until they become one cluster. The results of clustering the two methods compared with the criteria for standard deviation within groups (S_W) and standard deviation between groups (S_B). The best method has a smaller S_W and S_B ratio. The results showed that the average linkage method and the Ward method have an S_B and S_W ratio value. This result shows that the average linkage method has better performance than the Ward method.

INTEGRATION OF LANDSAT AND SRTM DATA FOR PRELIMINARY EXPLORATION OF BAUXITE DEPOSITS, CASE STUDY: SOUTH EASTERN BINTAN ISLAND, RIAU ISLANDS PROVINCE

M Zulfikar, E Sukiyah, Albab A A — Fri, 11 Feb 2022 00:00:00 +0530

Bintan and surrounding islands are well known for the vast reserves of bauxite deposits in Indonesia. In Indonesia, Bauxite is generally formed through a laterization process of rocks such as granite, granodiorite, diorite, gabbro, and andesite which are rich in aluminosilicate minerals containing aluminum oxide (Al2O3). At this time with very high exploration costs, a minimal cost exploration support method is needed to find new potential reserves. Thus, remote sensing techniques can be effectively used as tools to identify the potential areas that contain bauxite deposits. This study presents the use of Landsat 7 and 8 imagery data from years 2000 and 2020, integrated with SRTM to analyze the spatial distribution of bauxite deposits around the Southern Bintan Islands. These data were processed and analyzed by the response of soil reflectance which may be similar to the mining/ex-bauxite mining area. The interpretation keys such as color, morphology, texture, and geological knowledge are used as a guidance of visual interpretation. The results of this study show that the region with bauxite potential has a slightly dark red color characteristic and a small partition of dark white in band 457 (Landsat 7) and 567 (Landsat 8). In addition, the morphology shows a gentle slope with a smooth to slightly rough texture. One of the small islands located in the southeast of Bintan Island, namely Poto Island, has these characteristics. Thus, it can be concluded temporarily that Poto Island has bauxite potential until the detailed mapping is carried out in further research.

FLEXURER SUBSIDENCE OF MAKASSAR STRAIT

Fri, 11 Feb 2022 00:00:00 +0530

There were two types of hypothesis concerning formation of Makassar Strait and surrounding areas during the Tertiary periods namely, compressive and extensional tectonics. The compression is characterized by formation of Samarinda Anticlinorium in East Kalimantan and West Sulawesi Thrust Fold Belt in Sulawesi whereas the extension was characterized by formation of aulacogen occupied by widening of Mouth of Mahakam River in Makasar Streat and also the presence of block faulting and atenuation on pre Tertiary basement.

This study on the basis of analysis new surface and subsurface data of those areas including DEM , Field data and also seismics profiles suggest that the sedimentation cycles and tectonic evolution in the area were simultaneously related to compressional tectonic rather than the extensional tectonics and form flexure subsidence activities. The flexure subsidence itself is related to loading due to tectonic and denudation processes occured in the Tertiarry to Quarternary and this is usually generated during and post collisional activities.