Jurnal Geofisika Eksplorasi
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EARTHQUAKE VULNERABILITY MAPPING BASED ON MICROSEISMIC MEASUREMENTS IN THE CAMPUS AREA OF UNIVERSITAS SARJANAWIYATA TAMANSISWA YOGYAKARTA
Full text linkBuilding damage caused by earthquakes is more prevalent in the sedimentary areas of Yogyakarta City compared to the hilly regions of Wonosari and Kulonprogo, which have harder soil layers. The campus of Universitas Sarjanawiyata Tamansiswa (UST) is one of the campuses located in Yogyakarta City, where the regional geology is dominated by the Merapi Young Volcanic Deposits Formation. The UST campus area is vulnerable to earthquakes due to its proximity to an active seismic zone, making earthquake vulnerability mapping based on microseismic data an important necessity to support disaster mitigation efforts. The microseismic method was used in this study, while data analysis employed the Horizontal-to-Vertical Spectral Ratio (HVSR). Microseismic measurements were chosen because they have the advantage of not damaging the surface conditions of the ground, thus preserving the environment, and are easy to use in urban areas. The research method stages include survey design, field data collection, data processing and interpretation, and the creation of earthquake vulnerability maps. Data points were collected from 7 locations covering the Universitas Sarjanawiyata Tamansiswa campus area. The research results indicate that the study area has a dominant frequency value ranging from 1.10 to 2.74 Hz. Meanwhile, the amplification value ranges from 1.25 to 2.2. The sediment thickness of the study area ranges from 32 to 79 meters. The Seismic Vulnerability Index (Kg) of the study area ranges from 0.57 to 4 on a low to high scale. Based on the dominant frequency values, amplification, and seismic vulnerability index, the areas of the UST campus that are more vulnerable to earthquakes are the northern, eastern, and central parts, while the southern part is relatively safer
LANDSLIDE CHARACTERISTICS FROM CONCEPTUAL MODELLING OF WEATHERED LAYERS USING SUBSURFACE RESISTIVITY IN SANGON, DIY
Full text linkThe Sangon area is located in Kulonprogo Regency, which physiographically has landforms in the form of hills and mountains. Steep slope angles of the hills and weathered surface rock conditions increase the potential for landslides hazard in the Sangon area. This study aims to identify unstable layers that are prone to landslides in the Sangon, Kokap, and Kulonprogo areas. Information regarding the potential characteristics of landslides can significantly impact reducing losses caused by landslides hazard. Conceptual modelling of weathered layers that have the potential to trigger landslides has been carried out in the research area using resistivity distribution data of subsurface rocks using the geoelectrical method. Geoelectrical data from five measurement lines with a length of 290 m each line with a southeast-northwest orientation can delineate an image of the distribution of weathered layers in the subsurface. Based on the results of two-dimensional (2D) subsurface resistivity inversion modelling, it is known that the weathered layer as soil form andesite rock has a low resistivity value with a range of 7 m – 246 m with a depth of 0 - 12 meters in the subsurface. The distribution of resistivity value of the weathered layer is depicted in the 3D model to determine the distribution of the weathered layer, which is then made into a conceptual model that can describe the characteristics of landslides. The description of the 3D resistivity model of subsurface rocks produces a conceptual model of landslides in the research area, where the potential for landslides that may occur has characteristics in the form of debris flow or translational. The unstable layer volume was 947,000 m³, with a slope gradient ranging from 19% to 35%, with a moderate to steep slope
IMAGING DISPERSION CURVE OF DISPERSIVE WAVES USING SHORT-TIME FOURIER TRANSFORM: 2025 MYANMAR EARTHQUAKE M 7.7
Full text linkUnderstanding of Earth's subsurface is crucial for mitigating geological hazards, particularly earthquakes. A key parameter for subsurface characterization is the surface wave dispersion curve, which strongly reflects shear wave velocity (Vs) at various depths. This study presents an extraction of dispersion curves from earthquake signals using the Short-Time Fourier Transform (STFT). The STFT method enables the analysis of non-stationary signals like earthquake signals by dividing them into small segment, assumed-stationary segments, then applying the Fourier Transform to each segment. This process generates a time-frequency spectrogram that represents the evolution of frequencies over time. Myanmar earthquake M 7.7 is one of the greatest earthquakes that have damaging impacts. We used three inline stations for evaluating the waveform at CHTO (Chiang Mai, Thailand), KAPI (Sulawesi, Indonesia), and WRAB (Tennant Creek, NT, Australia). Waveform for KAPI and WRAB stations categorized teleseismic event represented good penetration waves to image deeper subsurface layes. Surface waves clearly seen at KAPI and WRAB classified by very low frequency and high amplitude in wave group train. The spectrogram, energy peaks at each frequency can be identified, which directly correlate with the group velocity of the surface waves. STFT successfully extract dispersion curve of surface waves at KAPI and WRAB station. However, the dispersion curve could not be extracted at CHTO station because its too close to the epicentre resulted in significant interference of waves phase caused inseparable frequency spectrum on each wave phases. Remarks on the study is stations nearer to the epicenter exhibit a higher frequency and broader range of dominant frequency, while those farther away show a lower frequency and narrow frequency range. The advantage of the STFT method lies in its ability to enable the identification of dispersion modes with good time-frequency resolution
ANALYSIS OF THE SUITABILITY OF PHYSICAL DEVELOPMENT OF THE CITY TOWARDS SPATIAL PLANNING IN PEKANBARU CITY
No full textPekanbaru City is one of the cities appointed as a National Strategic Area. Therefore, urbanization and changes in land use occur in Pekanbaru City. This study aims to decide on land-use changes, obtain information on the direction of physical development in Pekanbaru City, and decide the suitability between physical development and the Pekanbaru City spatial planning plan. The method used in this study is quantitative descriptive, digitizing on screen to make land use maps and overlaying in 2017 and 2023 to see changes in land use. The direction of physical development is obtained using a standard deviational ellipse. The suitability of land use with RTRW was obtained using the intersect overlay method. The results of this study are 1) Changes in land use between 2017 and 2023 are dominated by settlements, industrial areas, and trade and services. For other land uses, there are also changes but not too significant. 2) The direction of physical development from the city center to the suburbs with a south and southwest direction. 3) The suitability between physical development and the Pekanbaru City Spatial Plan 2020 - 2040, as much as 33,6% is by the RTRW. Areas that are not following the RTRW are 63%. For areas that do not follow the RTRW, the figure is 3,4%. The conclusion of this study shows that most areas in Pekanbaru City have not been realized by the Pekanbaru City RTRW 2020-2040. With the increase in population, it is hoped that development will be achieved through the established development plan
OPTIMALISASI NILAI-B SEISMIK DI WILAYAH JAWA MELALUI PEMODELAN OK1993 BERBASIS VORONOI
Full text linkThe spatial variation of b-values in seismically active regions provides critical insight into the stress state and rupture potential of fault systems. This study focuses on the Java region and surrounding subduction zones, where detailed mapping of b-values remains uncertain despite high seismic risk. A Voronoi-based ensemble modelling framework is implemented, incorporating the Ogata-Katsura 1993 (OK1993) formulation and spatial sampling via Sobol sequences to ensure uniform partitioning. Earthquake data from 1995 onward were compiled and harmonized into moment magnitude (Mw) using conversion equations from the Indonesian Earthquake Source and Hazard Map 2017. The OK1993 model enables estimation of b-values optimized via trust-constr and initialized with maximum likelihood estimates. The results reveal that high b-values (b > 1.2) dominate offshore southwest Lampung and south of Bali, whereas low b-values (b < 0.8) appear parts of the Sumatra fault near the Sunda Strait, faults across Java, and thrusts north of Bali and Lombok. Moderate b-values (0.8–1.0) extend along the southern Java trench and may represent partially coupled megathrust segments. Interestingly, the low b-value zones may indicate locked asperities and potential seismic gap segments, especially along southern Java, where large ruptures have not occurred in recent decades. This study demonstrates the utility of spatially adaptive, data-driven approaches in capturing complex tectonic segmentation and supports their integration into future seismic hazard assessments in Indonesia, particularly in Java and its surrounding regions
TEMPORAL AND DEPTH VARIATION OF SEISMIC PARAMETERS PRIOR TO MAJOR EARTHQUAKES IN PALU REGION, INDONESIA
Full text linkThe Palu region in Central Sulawesi is high tectonic activity area due to a subduction zone and major fault system, which resulted in high seismic intensity. The b value, as the seismic characteristic, is a valuable parameter for evaluating stress conditions and earthquake precursors. This study aimed to investigate the temporal and depth variations of the b-value in the Palu region. We observed earthquake distribution over 75 years from 1950 to 2025, which was obtained from the United States Geological Survey catalog. We applied the declustering analysis to isolate the mainshock events by using the space-time window method. We also conducted the magnitude completeness estimation and b-value calculation with ZMAP. This result showed that the average b-value was around 0.88, which was indicated as an intermediate level of seismic activity, influenced by subduction and the Palu-Koro Fault. Decreasing b-value was observed prior to the 1996 and 2018 earthquakes, followed by an increase in the parameter. This pattern exhibited stress accumulation and release, which was represented by the magnitude distribution. This lowering characteristic of b-value could be a long term precursor to major earthquakes. Furthermore, the depth variation of b-value revealed high values in the upper crust (0–10 km), a decrease around 20–30 km, and a secondary increase near 40 km, which corresponds to the Moho, as indicated by shear wave velocity profiles. These results provide insight into the crustal structure and seismic behavior in a tectonically complex and tsunami-prone region
IDENTIFICATION OF AQUIFER LAYERS USING THE ELECTRICAL RESISTIVITY TOMOGRAPHY (ERT) METHOD IN GUNUNG KASIH AREA
Full text linkThe varied physiographic conditions of Lampung, from the west to the center and east, are the main factors in determining the geological field campus as a suitable learning environment. Gunung Kasih is one of the areas located on the Bukit Barisan Range, which has unique geological conditions with exposed basement rocks on the surface, making it a key factor in determining the geological field campus. However, the presence of crystalline basement rocks in Gunung Kasih prevents water from penetrating below the surface, thereby affecting the availability of groundwater for the local community. This study aims to identify aquifer layers around the Gunung Kasih area, using the Electrical Resistivity Tomography (ERT) method. Stratigraphically, based on field observations of rocks, the study area has lithology consisting of schist, marble, and sandstone in the western part, with a landscape characterised by structural hills. On the eastern side, volcanic deposits such as tuff and andesitic lava were found, with a denudational plain landscape. The geophysical survey was conducted using Wenner-Schlumberger configuration, with four survey lines oriented relatively west to east and north to south. Low resistivity anomalies are indicated by layers with resistivity values of 0–20.7 Ωm, while moderate-to-high anomalies have resistivity values of 29.9–89.9 Ωm. Very high resistivity anomalies are indicated by layers with resistivity values of 61.9–128 Ωm. In comparison with observations of rock outcrops and rock resistivity values, the aquifer layer is interpreted as being indicated by low resistivity anomalies in the relatively eastern part of the study area, which is near the surface to a depth of 15 metres and 25 metres. This layer is interpreted as tuffaceousrock comparable to the Hulusimpang Formation. The aquifer layer in the study area is interpreted as a shallow unconfined aquifer
THE STRATIGRAPHY AND GEOLOGICAL STRUCTURE IN KOTAAGUNG TIMUR DISTRICT, TANGGAMUS, LAMPUNG
No full textKotaagung Timur region, Tanggamus Regency, Lampung, is the focus area of this research. In general, the area has a unique and complex geological setting such as the variety of volcanic rocks, granite, and the Sumatran Fault System that through this area. Geological research aims to obtain geology dynamics about stratigraphy and geology structure in the research area. Two analyses have been done to achieve these goals, i.e., field observation, petrography analysis, and structural geology analysis. The stratigraphy units of the study area are composed of volcanic rocks, plutonic rocks, and surface deposits and can be divided into eleven lithostratigraphic units. The stratigraphy of the research area can be grouped into 5 groups, i.e., the Mount Gisting volcanic group, the granitoid pluton group, the Cawang Haro Mountains volcanic group, the Mount Tanggamus volcanic group, and the alluvial deposit. Geological structures are well developed, and the research area is cut by ten faults, such as dextral strike-slip faults, sinistral strike-slip faults, and reverse faults. Based on these things, the geological history of the study area started in the Late Oligocene with three episodes of volcanism. The first episode was Mount Gisting’s volcanism during the Late Oligocene-Early Miocene, followed by the granitoid intrusion. The volcanic products of the Cawang Haro Mountains in the Middle Miocene mark the second episode. The last volcanic episode occurred in the Holocene, it came from Mount Tanggamus’s volcanism. The development of the structural geology happened before the previous volcanism episode
ESTIMASI SUMBERDAYA BATUGAMPING DI PT. SEMEN BATURAJA TBK KABUPATEN OGAN KOMERING ULU PROVINSI SUMATERA SELATAN
No full textLimestone is a rock that is generally whitish, fine-grained, composed of calcium carbonate, and formed below sea level. The Sumatra region, especially in the South Sumatra region, has potential mineral resources in the form of limestone located in the Ogan Komering Ulu district. The study area is included in the Baturaja Formation (Nmb) with the Baturaja limestone unit and the Gumai Formation (Nmg) with the Gumai limestone unit, which are stratigraphically deposited in harmony. The formation of origin in the study area is divided into 2, namely the form of structural origin consisting of structural valley landforms (S1), and the form of anthropogenic origin consisting of non-mine landforms (A1), mine slope landforms (A2) and sump landforms (A3). In the research area in the field observations, there is a geological structure in the form of a right horizontal fault. With field observations and the presence of limestone resources in the research area, mining can be carried out in the area. In limestone mining, estimation is needed to be able to calculate resources before the mining process takes place. In this study, the depth of the limestone layer is modelled with a block model with the aim of being able to see the distribution of layers to be estimated. The estimation of limestone resources uses the Inverse Distance Weighting (IDW) method by estimating the value of the area that does not have an inferred value.Batugamping atau batukapur adalah batuan yang secara umum berwarna keputihan, berbutir halus, tersusun oleh kalsium karbonat, dan terbentuk di bawah permukaan air laut. Wilayah Sumatera khususnya pada Daerah Sumatera Selatan memiliki potensi sumber daya mineral berupa batugamping yang terletak di kabupaten Ogan Komering Ulu. Pada Daerah penelitian ini termasuk kedalam formasi Baturaja (Nmb) dengan satuan batugamping baturaja dan formasi Gumai (Nmg) dengan satuan batugamping gumai yang secara stratigrafi terendapkan secara selaras. Bentukan asal pada daerah penelitian terbagi menjadi 2 yaitu bentuk asal struktural yang terdiri dari bentuk lahan lembah struktural (S1), dan bentuk asal antropogenik yang terdiri dari bentukan lahan bukan tambang (A1), bentukan lahan lereng tambang (A2) dan bentukan lahan sump (A3). Pada daerah penelitian secara pengamatan dilapangan terdapat struktur geologi yaitu berupa sesar mendatar kanan. Dengan pengamatan dilapangan dan keterdapatan sumberdaya batugamping di daerah penelitian dapat dilakukan penambangan di daerah tersebut. Dalam penambangan batugamping, diperlukan estimasi untuk dapat menghitung sumber daya sebelum proses penambangan berlangsung. Pada penelitian ini kedalaman lapisan batugamping dimodelkan dengan model blok dengan tujuan agar dapat melihat sebaran lapisan yang akan di estimasi kan. Untuk estimasi sumberdaya batugamping menggunakan metode Inverse Distance Weighting (IDW) dengan menaksir nilai pada area yang tidak memiliki sampel endapan batugamping berdasarkan data sekitar atau data terdekat