Land Subsidence due to Groundwater Extraction and Natural Consolidation in the Bandung Basin, West Java, Indonesia

Based 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

Purworejo 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

Mineralogy of granites from Hukurila area, Ambon Island, Indonesia: An insight into petrogenesis

The 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

Tectonic Geomorphology Analysis in Natural Hydrogen Exploration: A Case Study from Tanjung Api, Sulawesi

Natural 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

Earthquake Hazard Evaluation Study on the Central Area of Selebar District, Bengkulu City, based on Seismic Response Analysis

The Selebar District, a developing area in Bengkulu City, has been the site of at least two significant earthquakes with a magnitude of Mw 7.0 in the past two decades. This study, which presents a seismic hazard assessment for the central area of the Selebar District, is of paramount importance. The study commences with field investigations at three strategically chosen points in the central area of Selebar District, Bengkulu City, including the airport, educational center, and toll road. The analysis, which involves the propagation of seismic waves, aims to comprehend the seismic behavior during an earthquake. The potential impact of seismic waves on structures and the environment is a serious concern. Seismic response analyses, a critical component of this study, were constructed based on a one-dimensional wave propagation model using a non-linear method. These analyses offer valuable insights into the potential impact of seismic waves on structures and the environment, a matter of serious concern. The results of the field investigations were also examined for seismic response analysis. The PGA, spectral response acceleration, and amplification factors are presented in this study and analyzed to determine the seismic hazard. Based on the PGA values, two earthquake sources can cause very high damage to buildings, and one earthquake source has a high potential. The generated spectral acceleration has exceeded the design spectral acceleration, especially at short periods. Therefore, using local spectra in building structure design can be a recommendation for local engineers to consider the impact of earthquakes on the central area of Selebar District, Bengkulu City

DENSITY DISTRIBUTION OF SHEAR WAVE VELOCITY, CONE RESISTANCE AND CORRECTED SPT IN THE DOMINANT SOILS OF BENGKULU CITY, INDONESIA

This research is of significant importance as it discusses the modelling of a two-dimensional map of soil parameters in Bengkulu City, Bengkulu Province, Indonesia. The two-dimensional modelling was conducted to show the distribution of soil parameter values based on the research points strategically distributed throughout Bengkulu City. These research points were chosen to represent the diverse soil conditions in the city, making the modelled soil parameters particularly helpful for engineers and construction consultants when planning construction in the study area. The parameters to be discussed include shear wave velocity, cone resistance, and corrected standard penetration test. This modelling applies Inverse Distance Weighting as an interpolation method from 215 research points. Inverse Distance Weighting is used because it supports knowing the value of soil parameters around the review point, especially in two-dimensional modelling. The results showed that the distribution of the highest value of shear wave velocity of the clay layer is dominated in the Teluk Segara sub-district. The distribution of the highest value of cone resistance of the clay layer is dominant in the Kampung Melayu Sub-district. The distribution of the highest value of corrected standard penetration test of the clay layer is also dominated in Kampung Melayu Sub-district

A SYSTEMATIC REVIEW OF GEOLOGICAL RESOURCE CONTAINING NICKEL : RESOURCE, DISTRIBUTION, MINING, EXTRACTION AND ADVANCED MATERIAL SYNTHESIS

Nickel ore is the main source of nickel, an important metal used in many modern materials. This paper gives a brief overview of different aspects of nickel ore, such as its history, types, distribution, demand, and the technology used for mining and processing it. The two main types of nickel ore are nickel sulfide ore and laterite ore. Indonesia has significant nickel ore deposits, primarily in the form of laterite, due to its tropical climate with high temperatures and rainfall. Nickel is essential for making various important materials like stainless steel, special alloys, plating, and batteries. Laterite also contains other valuable elements like iron, magnesium, silicon, and oxygen, found in compounds such as goethite, nickel oxide, magnesium silicate, and quartz. Laterite ore can be processed to produce nickel matte, ferronickel, and nickel pig iron. The paper also discusses advanced materials made from laterite ore, including photocatalysts and batteries. Mining and processing activities have both positive and negative effects on local communities. To minimize negative impacts, it is important to consider the satisfaction of both the local community and the government in the initial planning of mining and processing projects

Assessing the Water Criticality Index of the Welaran Watershed in Kebumen Geopark, Central Java: Towards Good Water Resource Management

The water criticality index (WCI) is the ratio between water use and availability. The higher the WCI value, the more concerned the water conditions in the area will be. The water crisis can be handled if various parties manage water resources following good management. The Welaran area is a watershed that is part of the Lukulo Watershed, where the population often experiences water shortages. Therefore, by knowing the value of WCI, it is hoped that various parties can know the water conditions in this watershed. Based on research and calculation of the water balance in the Welaran Watershed, it is known that with total water needs in 2019-2020 of 746,937 m3 and total water availability of 1,555,318 m3, the WCI value of the Welaran Watershed is 48.02%. In 2020, Karangsambung was designated as a part of Kebumen Global Geopark, which will certainly increase the number of tourists visiting here. The increase in tourist visits will also increase the need for water, including in the Welaran Watershed. To overcome these conditions, the Kebumen regency’s government and stakeholders are expected to be able to formulate a water management step by effective management