Bengkulu Province, Indonesia, is one of regions prone to earthquake hazards. Daily seismic activity, albeitminor, and imperceptible to humans is common place. Data from the Meteorology, Climatology, and GeophysicsAgency reveals an average of eight earthquakes per week. Earthquakes often trigger subsequent disasters such astsunamis, landslides, and liquefaction. However, liquefaction-related phenomena are often overlooked in researchs,particularly concerning subsurface layers. A notable event occurred on September 12th, 2007, when a powerful 8.6magnitude earthquake struck Indonesia, causing significant damage, particularly in Bengkulu City. This was followedby a liquefaction disaster in Tanah Patah Village, Bengkulu City. Consequently, the aim of this study is to assess thesubsurface conditions in the liquefaction-affected area using geophysical techniques, including microtremor and geoelectric surveys. The data was analyzed to evaluate soil conditions in the affected zone. The resistivity values indicate a predominance of water and sand mixtures at depths of 0 - 20 m (ranging from 1.46 to 15.5 Ω·m in Geo_TP-1 and from 4.64 to 15.1 Ω·m in Geo_TP-2). These conditions can facilitate processes like condensation and water flow, leading to sand compaction and increase susceptibility to liquefaction. The findings reveal that loose sand dominates the subsurface layers, rendering them highly vulnerable to liquefaction during intense seismic events. Furthermore, the environmental characteristics of the studied area exacerbate its susceptibility to liquefaction. This study provides a comprehensive analysis of soil conditions in the liquefied zone of Bengkulu City.
The Indonesian Archipelago is one dynamic volcanic arc region, where landslides frequently occur during the rainy season.Not only are geological conditions and high precipitation in the region, but also uncontrolled land use development and high social-vulnerability of the community living in landslide prone areas, that have become the major cause of landslide disasters in Indonesia.Accordingly, a strategic program for landslide risk reduction has been carried out by establishing an appropriate landslide risk management program with respect to social vulnerability.Such programs mainly emphasize the improvement of community resilience in landslide prone areas through community based landslide mitigation and early warning system, as well as public education.Geological investigations combined with social survey and analyses were also carried out to support the implementation of this risk reduction program in Central Java.Finally, it was concluded that the effectiveness of landslide disaster risk reduction was mainly driven by the community empowerment for disaster prevention and mitigation at the village level.
The 7.5 Mw tectonic earthquake that hit Palu City on 28 September 2018 was followed by tsunami and liquefaction that triggered massive mudflows in Balaroa, Petobo, and Jono Oge areas. Extensive damages to infrastructures occurred as the result of these earthquake-triggered disasters. This study explores the causing factors of the massive mudflow in Balaroa, Petobo, and Jono Oge areas as it is a quite rare phenomenon. This study focuses on the causing factors of liquefaction such as the condition of soil lithology, depth of water table, distance to the fo1cal mechanism, and the thickness of soft sediment.
Abstract. Landslides are one of the most widespread and commonly occurring natural hazards. In regions of high vulnerability, these complex hazards can cause significant negative social and economic impacts. Considering the worldwide susceptibility to landslides, it is necessary to establish a standard for early warning systems specific to landslide disaster risk reduction. This standard would provide guidance in conducting landslide detection, prediction, interpretation, and response. This paper proposes a new standard consisting of seven sub-systems for landslide early warning. These include risk assessment and mapping, dissemination and communication, establishment of the disaster preparedness and response team, development of an evacuation map, standardized operating procedures, installation of monitoring and warning services, and the building of local commitment to the operation and maintenance of the entire program. This paper details the global standard with an example of its application from Central Java, one of 20 landslide-prone provinces in Indonesia that have used this standard since 2012.
Abstract The utilization of v s30 data offers numerous applications within the geotechnical field, with one of its primary applications being the determination of site class and the microzonation of site class. v s30 data can be acquired through various methods, including Multichannel Analysis of Surface Waves (MASW), microtremor measurements, and N-SPT data. This study seeks to compare v s30 data and site class criteria based on measurements obtained from MASW, microtremor, and N-SPT data in the Opak River Basin. For the v s30 data analysis, a total of 27 data points from MASW and microtremor measurements, along with 3 data points from N-SPT measurements, were employed. These measurements were conducted across various geological formations, encompassing the young volcanic deposits of Merapi Volcano, alluvial deposits, and the Nglanggran, Sentolo, Wonosari, and Semilir Formations. It is worth noting that all N-SPT data were specifically collected within the young volcanic deposits of the Merapi Volcano Formation. The results of this analysis revealed v s30 values ranging from 159 to 192 m/s for MASW measurements, 156 to 789 m/s for microtremor measurements, and 241 to 249 m/s for N-SPT measurements. In accordance with the SNI 1726-2019 site class criteria, the site classes determined based on v s30 values from MASW and microtremor data included rock (SB), very dense soil (SC), stiff soil (SD) and soft soil (SE), while the site class based on v s30 N-SPT data fell under the stiff soil (SD) criteria. The correlation between v s30 values obtained from MASW and microtremor measurements yielded a strong correlation coefficient ( r ) of 0.98, and the correlation between v s30 values from MASW and N-SPT measurements demonstrated a very strong correlation coefficient ( r ) of 0.99.
Terjadi longsor di area tebing batu (Rocky Wall) jalan akses fasilitas produksi pipa penyalur uap dan brine Pembangkit Listrik Tenaga Panas bumi (PLTP) milik PT. Pertamina Gothermal Energy (PT.PGE) di Kabupaten Muara Enim, Provinsi Sumatera Selatan, yang menyebabkan terjadinya penurunan produksi (derating) di PLTP akibat rusaknya fasilitas produksi dari sumur produksi klaster 1 ke PLTP. Tujuan dari penelitian ini untuk mengidentifikasi struktur lapisan bawah permukaan longsoran di area rocky wall dan untuk memprediksi kedalaman bidang gelincir (slip surface) berdasarkan nilai resistivitas lapisan tanah dengan metode geofisika ERT, sehingga metode geoteknik yang dipilih untuk penanganan longsor adalah tepat. Penelitian ini dilakukan dengan metode geofisika Electrical Resistivity Tomography (ERT) konfigurasi Wenner, Schlumberger dan Dipole-dipole dengan Ares II (Automatic Resistivity System II) sebagai peralatan utama ERT yang digunakan dalam pengambilan data. Luas daerah penelitian adalah 150 m × 200 m dengan jumlah pengukuran sebanyak 4 lintasan. Dari hasil pengolahan data pengukuran resistivitas menggunakan perangkat lunak Res2dinv dan Zondres2D, hasilnya menunjukkan bahwa sebaran batuan di daerah longsor rocky wall didominasi oleh lapisan breksi andesit lapuk dan lanau berpasir berlempung. Berdasarkan back analysis dan analisis stabilitas lereng sebelum kondisi longsor terjadi dan setelah longsor terjadi menggunakan Slope/W, didapatkan lapisan yang berpotensi menjadi bidang gelincir berkesesuaian pada kedalaman 10,43 m di bawah permukaan lereng.
Wilayah Indonesia memiliki kondisi geomorfologi yang unik karena berada pada pertemuan empat lempeng yaitu Lempeng Eurasia, Indo-Australia, Philippine dan Pasifik. Kondisi ini menjadikan Indonesia memiliki berbagai potensi bencana alam seperti gunung api, gempa bumi, tanah longsor, banjir, tsunami dan lain-lain. Kejadian tsunami di Aceh 2004, gempa bumi di Yogyakarta 2006 dan di Padang 2009, banjir di Wasior 2010, letusan Gunung Merapi 2010 serta bencana alam lainnya telah membuka kesadaran semua pihak untuk meningkatkan kesiapsiagaan dalam menghadapi bencana.
Salah satu bagian siklus mitigasi bencana yang perlu mendapat perhatian adalah kegiatan rehabilitasi dan rekonstruksi pada infrastruktur fisik pasca terjadinya bencana. Kegiatan ini harus direncanakan dan dilaksanakan dengan baik, agar perbaikan infrastruktur fisik dapat mempercepat pemulihan kehidupan masyarakat. Di samping itu, infrastuktur fisik tersebut diharapkan memiliki ketahanan untuk menghadapi bencana alam yang mungkin terjadi di kemudian hari. Dalam rangka untuk melaksanakan upaya rehabilitasi dan rekonstruksi, Badan Nasional Penanggulangan Bencana (BNPB) telah mengeluarkan Peraturan Kepala BNPB tentang Pedoman Rehabilitasi dan Rekonstruksi Pasca bencana (Perka BNPB No. 11 Tahun 2008). Peraturan ini mengatur standar dan kebijakan dalam tahap rehabilitasi dan rekonstruksi. Rehabilitasi dan rekonstruksi bertujuan untuk mengembalikan kehidupan dan penghidupan korban kembali seperti kondisi normal. Dalam tataran pelaksanaan, diperlukan proses evaluasi untuk menyempurnakan prosesnya.
Pemulihan infrastruktur fisik umumnya baru dilakukan ketika bencana telah terjadi yang mengakibatkan banyak infrastruktur mengalami kerusakan. Cara pemulihan seperti ini tentunya lebih berisiko karena kerusakan dan kerugian (damages and looses) bisa jadi sangat besar dan pemulihan memakan biaya dan waktu yang tidak sedikit. Untuk menghindari kerusakan dan kerugian tersebut, dalam makalah ini juga akan dibahas suatu konsep perbaikan/penataan infrastruktur fisik yang dianggap rentan terhadap bencana. Karena perbaikan dilaksanakan sebelum bencana terjadi, diharapkan kerusakan dan kerugian serta timbulnya korban jiwa dapat dihindari.
Abstract The technique using microtremor measurements are cost-effective tools that rapidly acquire high resolution sedimentary layer information over a large area about site response, sedimentary thickness, and average S-wave velocity structures from the secondary drilling stations. In 2012, the 274 stations of single microtremor recording were conducted to the main path of NS and EW of the research area. Microtremors were recorded with 3-components by using a model of Mitutoyo-GPL-6A3P and processed by the horizontal-to-vertical (H/V) spectral ratio technique which was used by BIDO software. The results show that the seismic behaviors in Yogyakarta City vary significantly: both of T s and T d spans 0.10-1.00 sec and 0.15-4.00 sec, and the thickness of sedimentary layers ranges from a few meters to over 200 meters. Moreover, to predict the strong ground motion it was used the Empirical Green's Function technique (EGF) formulated by Irikura 1,2 , based on scaling law of fault parameters for large and small events and the ω 2 source spectra. The NS, EW and UD components of synthetic acceleration wave form or Peak Ground Acceleration (PGA) are calculated 392.30, 484.20 and 236.40 cm/s 2 by the EGF method respectively and the Fourier Spectrum is represented the three components by the target event and subevents for the studied area. Finally, this paper evaluates the applicability of the different techniques for seismic behaviors estimation from the H/V spectral ratio of microtremor recordings and EGF method based on the Opak River Fault.
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