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All Journal Majalah Geografi Indonesia Sumatra Journal of Disaster, Geography and Geography Education Journal of Applied Geology
Gayatri Indah Marliyani
Department Of Geological Engineering, Universitas Gadjah Mada
Civil Engineering, Building, Construction & Architecture Earth & Planetary Sciences Education Energy Engineering Environmental Science

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Overview and Research Needs to Achieve Improved Understanding of Earthquake Hazards Affecting the Western Sumatra Coast Marliyani, Gayatri Indah
Sumatra Journal of Disaster, Geography and Geography Education Vol 1 No 2 (2017): Sumatra Journal of Disaster, Geography and Geography Education Volume 1 Number 2
Publisher : Sumatra Journal of Disaster, Geography and Geography Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (3059.592 KB) | DOI: 10.24036/sjdgge.v1i2.83

Abstract

Natural hazards that are affecting humans are mostly related to geological processes, for example earthquake, volcanic eruption, flooding and landslide. The geological processes itself is a naturally occurring event, it is only become hazardous in the presence of humans as it may cause loss of life and properties. Understanding aspects of geological-related hazards of a region is important to reduce the danger they may pose. Indonesia is located within an active and complicated tectonic setting. Three major tectonic plates: Eurasia, Indo-Australia and Philippine are collide and interact in the vicinity of Indonesia. The mechanism of plate interaction in Indonesia is dominated by subduction, where one plate is subducted beneath the other. The subduction processes are commonly associated with formation of volcanoes as well as active deformation in the crust associated with earthquakes.
Identifikasi Sesar Aktif di Pulau Bali dengan Menggunakan Data Pemetaan Geologi Permukaan dan Morfologi Tektonik Hurien Helmi; Gayatri Indah Marliyani; Siti Nur’aini
Majalah Geografi Indonesia Vol 35, No 1 (2021): Majalah Geografi Indonesia
Publisher : Fakultas Geografi, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/mgi.61928

Abstract

Pulau Bali dan sekitarnya berada dekat dengan zona subduksi sehingga rawan terhadap bencana gempa bumi. Struktur utama yang menyebabkan gempa bumi di Bali umumnya berada di zona subduksi di bagian selatan dan di zona sesar naik belakang busur di utara yang dikenal dengan sesar naik Flores. Selain potensi gempa dari kedua zona sesar ini, gempa yang berasal dari zona sesar di darat juga bisa menimbulkan bahaya yang signifikan. Penelitian ini bertujuan untuk melakukan pemetaan sesar aktif di darat dengan menggunakan kombinasi antara metode penginderaan jauh dengan survey lapangan. Data yang digunakan sebagai peta dasar adalah data digital elevation (DEM) model DEMNAS beresolusi 8 m serta data DEM beresolusi 0.5 m yang dihasilkan melalui proses fotogrametri dari foto udara. Analisis kelurusan menunjukkan adanya pola berarah baratlaut-tenggara dan timulaut-baratdaya. Validasi di lapangan menunjukkan bahwa kelurusan ini berasosiasi dengan keberadaan sesar-sesar geser, sesar oblique dan sesar turun. Sesar-sesar ini memotong batuan berumur Kuarter hingga endapan masa kini. Selain itu, data sebaran seismisitas menunjukkan adanya zona kegempaan dangkal yang berada pada area di sekitar kelurusan yang dipetakan. Kedua indikator ini menunjukkan bahwa sesar-sesar yang teridentifikasi dalam penelitian ini bisa dikategorikan sebagai sesar aktif. Hasil dari penelitian ini memberikan pemahaman baru mengenai geometri sesar aktif yang ada di Pulau Bali dan potensi kegempaan di masa yang akan datang yang memberikan kontribusi terhadap upaya mitigasi bencana gempa bumi di Pulau Bali. Bali and its surrounding region are located within proximity of the Sunda-Banda subduction zone making it prone to earthquake hazards. The structures that caused earthquakes in Bali are mainly from the front subduction faults and from the back-arc thrust fault known as the Flores Fault. In addition, earthquakes are frequently occur in the inland fault system. This study aims to map the inland active faults in Bali using a combination of remotely-based and field-mapping methods. We use the 8-m resolution digital elevation model (DEM) of DEMNAS and the 0.5 m resolution DEM from photogrammetry processing of aerial photo as our base maps. Our lineament analysis identifies northwest-southeast and northeast-southwest lineaments. Our field observation confirms these lineaments to be associated with strike-slip, oblique and normal faults. These faults dissect Quarternary to recent rock units. In addition, seismicity data indicate the occurrence of shallow earthquakes in the vicinity of these structures. All of these indicate that these structures are active. Results from this study provide a new understanding of the inland active fault geometry in Bali, useful in the seismic hazard analysis and may contribute to the earthquake mitigation efforts in Bali.   
Updated Segmentation Model of the Aceh Segment of the Great Sumatran Fault System in Northern Sumatra, Indonesia Aulia Kurnia Hady; Gayatri Indah Marliyani
Journal of Applied Geology Vol 5, No 2 (2020)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (11044.408 KB) | DOI: 10.22146/jag.56134

Abstract

We study the Aceh Fault segment, the northernmost segment of the Great Sumatran Fault in western Indonesia. The Aceh Fault segment spans 250 km long, passing through three districts: West Aceh, Pidie Jaya, and Aceh Besar, a region of ~546,143 population. The current segmentation model assumes that the Aceh Fault segment acts as a single fault segment, which would generate closer to an M8 earthquake. This estimation is inconsistent with the ~M6–7 historical earthquake data. We conduct a detailed active fault mapping using an ~8 m resolution digital elevation model (DEM) of DEMNAS and sub-m DEM data from UAV-based photogrammetry to resolve this fault’s segmentation model. Our study indicates that the Aceh Fault is active and that the fault segment can be further divided into seven sub-segments: Beutong, Kuala Tripa, Geumpang, Mane, Jantho, Indrapuri, and Pulo Aceh. The fault kinematics identified in the field is consistent with right-lateral faulting. Our study’s findings provide new information to understand the fault geometry and estimate potential earthquakes’ maximum magnitude along the Aceh Fault segment. These are important for the development of seismic hazard analysis of the area.
Subsurface Geology and Hydrothermal Alteration of The “X” Geothermal Field, West Java: A Progress Report Peter Pratistha Utama; Pri Utami; Gayatri Indah Marliyani; Randy Wijaya Atmaja
Journal of Applied Geology Vol 6, No 1 (2021)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (9465.263 KB) | DOI: 10.22146/jag.63302

Abstract

“X” geothermal field is one of the geothermal fields in West Java. PT. Y (Persero) developed it since 2014. The geothermal field has produced electricity, with installed capacity amounted to 55 MWe. The “X” geothermal system is vapor-dominated. The geothermal manifestations are located at approximately 2,100 m asl. The “X” field consists of three main upflow zones: Kawah Putih, Kawah Ciwidey, and Kawah Cibuni. This study analyzed the drill cuttings from 3 wells as the primary data with total depths ranging from 1,581 to 2,166 m with the well’s highest stable temperatures measured of ±230°C. The three wells selected for this research—Well A, Well B, and Well C—were analyzed to describe the rock properties and estimate the prospect areas of present-day geothermal exploration in the “X” geothermal field.The paper aims to understand better of the subsurface geology and its correlation to the dynamic processes (i.e., hydrothermal alteration) in the “X” geothermal field. The hydrothermal minerals are formed by near-neutral pH fluids and are characterized by quartz, calcite, clays (smectite, illite, chlorite), wairakite, epidote, and actinolite. Acidic fluids are evident by forming acidic hydrothermal mineral, e.g., anhydrite at various depths of the studied wells, particularly at Well C which is located around Sugihmukti-Urug area. Moreover, the previous studies by Reyes (1990), Layman and Soemarinda (2003), Rachmawati et al. (2016), Elfina (2017) on hydrothermal minerals, geothermal manifestation characteristics, fluid geochemistry, and conceptual model are adapted to improve the analysis and interpretation of this paper.
Co-Authors Atmaja, Randy Wijaya Aulia Kurnia Hady Hady, Aulia Kurnia Hurien Helmi Peter Pratistha Utama Pri Utami Pri Utami Randy Wijaya Atmaja Siti Nur’aini