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INDONESIA
BULLETIN OF THE MARINE GEOLOGY
Published by Marine Geological Institute of Indonesia
ISSN : 14106175     EISSN : 25278843     DOI : -
Core Subject : Science,
Earth & Planetary Sciences
Bulletin of the Marine Geology is a scientific journal of Marine geoscience that is published periodically, twice a year (June and December). The publication identification could be recognized on the ISSN 1410-6175 (print) and e-ISSN: 2527-8843 (on-line) twice a year (June & December) and it has been accredited by Lembaga Ilmu Pengetahuan Indonesia (Indonesian Institute of Sciences) by Decree Number: 818/E/2015. As an open access journal, thus all content are freely available without any charge to the user. Users are allowed to download, and distribute the full texts of the articles without permission from the publisher.
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Articles 5 Documents
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Search results for , issue "Vol 25, No 2 (2010)" : 5 Documents clear
SUBMARINE MASS MOVEMENT AND LOCALIZED TSUNAMI POTENTIALITY OF MENTAWAI BASIN, SUMATERA, INDONESIA Haryadi Permana; C. Singh
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (675.386 KB) | DOI: 10.32693/bomg.25.2.2010.25

Abstract

The new bathymetry and seismic data were acquired during the PreTI-Gap marine survey (February 15 to March 6, 2008). The survey was carried out along the NE margin of Mentawai Island using multi-beam swath bathymetry equipment, and 28-channels seismic streamer and four-airgun source. The first target was the Mega Island region near the epicenter of the 2007 great earthquake. The shallow bathymetry is characterized as a flat coral platform suggesting that 200 km elongated plateau is slowly subsiding without any active faults. Further north, from South Pagai to North of Siberut Islands, the seafloor morphology changes significantly. The deep and wide canyons or valleys produce very rough seafloor morphology between 50 and 1100 m water depth. In general, the submarine topography shows two break slopes at different depths. Between slope breaks, the undulating, hilly and circular features dominate, possibly caused by mass movement. A push-up ridge is observed that dams the sediments eroded within a steep slope northeastward side. The seismic reflection data acquired along 14 dip seismic lines at the NE flank of Mentawai Islands, from Siberut to the South of Pagai Islands. We observed a set of southwestward dipping back thrust bounding the NE margin of the Mentawai Island and the push-up ridge observed on bathymetric image, which suggest that Mentawai fault is not pure a strike slip fault, but consists of a set of back thrusts. Such kind of back thrust movement at the flank of Mentawai basin can trigger mass movement or landslide that can produce localized tsunami causing damages to Sumatera mainland such as Padang, Painan or northern Bengkulu provinces and Mentawai Islands. Therefore, it is important to re-design the tsunami warning system, especially in this region, in order to mitigate tsunami risk to coastal region of western Sumatera. Keywords: multi-beam swath bathymetry, 28-channels seismic streamer, seismic reflection, back thrust, mass movement or landslide, tsunami warning system, mitigate tsunami risk Data batimetri dan seismik baru telah didapatkan selama survey kelautan PreTi-Gap (15 Februari hingga 6 Maret 2008). Survei dilaksanakan sepanjang tepian timurlaut Kepulauan. Mentawai menggunakan peralatan multibeam batimetri, seismik saluran ganda 28 kanal dengan 4 sumber energi airgun. Sasaran pertama adalah memetakan kawasan perairan P. Mega dekat pusat gempa besar tahun 2007. Kenampakan batimetri dangkal dicirikan dengan adanya dataran paparan terumbu karang sepanjang 200km yang secara perlahan mengalami penurunan tanpa akifitas sesar. Lebih jauh ke utara dari P. Pagai Selatan sampai di utara P. Siberut, morfologi dasar laut memperlihatkan perubahan secara signifikan yaitu lembah dalam dan lebar membentuk morfologi dasarlaut yang kasar dengan beda kedalaman antara 50 hingga 1100 meter. Secara umum, topografi dasar laut memperlihatkan perhentian dua lereng pada kedalaman yang berbeda. Diantara batas lereng yang dicirikan adanya kenampakan perlipatan, perbukitan dan bentuk melingkar diperkirakan sebagai hasil gelinciran batuan/tanah. Punggungan terangkat yang teramati merupakan penahan endapan yang melongsor pada lereng curam pada sisi sebelah timurlaut. Sebanyak 14 lintasan sismik refleksi pada sayap bagian timurlaut Kepulauan Mentawai, dari P. Siberut hingga ke selatan P. Pagai. Patahan anjak belakang yang teramati dengan sudut kemiringan ke arah baratdaya memotong bagian tepian timurlaut dari Kepulauan Mentawai dan punggungan terangkat yang terekam pada peta batimetri menegaskan bahwa Patahan Mentawai bukan murni sebagai patahan geser mengkanan akan tetapi juga memiliki komponen patahan anjak belakang. Setiap pergerakan sesar anjak di sisi Cekungan Mentawai dapat memicu gerakan tanah atau longsoran bawah laut dapat membangkitkan tsunami lokal yang mengakibatkan kerusakan di daratan Sumatera seperti di Padang, Painan atau Propinsi Bengkulu bagian utara dan Kepulauan Mentawai. Oleh karena itu adalah sangat penting untuk merencanakan sistim peringatan tsunami khususnya di kawasan tersebut dengan tujuan untuk melakukan mitigasi resiko bencana tsunami di kawasan pantai barat Sumatera. Kata Kunci: multibeam batimetri, seismik saluran ganda 28 kanal, sismik refleksi, sesar anjak belakang, gerakan tanah atau longsoran, peringatan dini tsunami, mitigasi resiko tsunami
PALEO-CHANNELS OF SINGKAWANG WATERS WEST KALIMANTAN AND ITS RELATION TO THE OCCURRENCES OF SUB-SEABOTTOM GOLD PLACERS BASED ON STRATA BOX SEISMIC RECORD ANALYSES Hananto Kurnio; Noor C.D. Aryanto
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (912.18 KB) | DOI: 10.32693/bomg.25.2.2010.26

Abstract

Strata box seismic records were used to analyze sub-seabottom paleochannels in Singkawang Waters, West Kalimantan. Based on the analyses, it can be identified the distribution and patterns of paleochannels. Paleo channel at northern part of study area interpreted as a continuation of Recent coastal rivers; and at the southern part, the pattern radiates surround the cone-shaped morphology of islands, especially Kabung and Lemukutan Islands. Paleochannels of the study area belong to northwest Sunda Shelf systems that terminated to the South China Sea. A study on sequence stratigraphy was carried out to better understanding sedimentary sequences in the paleochannels. This study is also capable of identifying placer deposits within the channels. Based on criterias of gold placer occurrence such as existence of primary gold sources, intense chemical and physical weathering to liberate gold grains from their source rocks of Sintang Intrusive. Gravity transportation that involved water media, stable bed rock and surface conditions, caused offshore area of Singkawang fulfill requirements for gold placer accumulations. Chemical and physical whethering proccesses from Oligocene to Recent, approximately 36 million, might be found accumulation of gold placer on the seafloor. Based on grain size analyses, the study area consisted of sand 43.4%, silt 54.3% and clay 2.3%. Petrographic examination of the sample shows gold grains about 0.2%. Keywords: paleochannels, strata box seismic records, gold placer. Rekaman seismik strata box digunakan untuk menganalisa sungai purba bawah permukaan di Perairan Singkawang, Kalimantan Barat. Berdasarkan hasil analisis data strata box dapat diidentifikasi sebaran dan pola sungai purba. Sungai purba di bagian utara daerah penelitian ditafsirkan sebagai kelanjutan sungai sekarang, dan di selatan sungainya berpola memancar yang berasal dari pulau-pulau bermorfologi kerucut, seperti Pulau Kabung dan Lemukutan. Sungai purba daerah penelitian termasuk pada sistem sungai purba Paparan Sunda barat laut berakhir di Laut Cina Selatan. Suatu kajian sekuen stratigrafi dilaksanakan untuk lebih memahami sekuen-sekuen sedimen dalam sungai purba. Kajian ini juga mampu mengidentifikasi endapan-endapan plaser dalam alur tersebut. Berdasarkan kriteria pembentukan emas plaser atau letakan, seperti terdapatnya sumber emas primer, pelapukan kimia dan fisika yang sangat intensif untuk membebaskan butiran-butiran emas dari batuan induknya yaitu Batuan Terobosan Sintang. Transportasi gaya berat yang melibatkan media air, kondisi batuan dasar dan permukaan yang stabil, membuat daerah lepas pantai Singkawang memenuhi kriteria untuk akumulasi emas letakan. Proses pelapukan kimia dan fisika mulai dari Oligosen hingga Resen, sekitar 36 juta tahun memungkinkan dijumpainya akumulasi emas letakan di dasar laut. Berdasarkan hasil analisa besar butir daerah penelitian terdiri dari pasir 43,4%, lanau 54,3% dan lempung 2,3 %. Uji petrogafi menunjukan kandungan emas sekitar 0,2%. Kata kunci: sungai purba, rekaman seismik strata box, emas letakan.
3D PROPERTIES MODELING TO SUPPORT RESERVOIR CHARACTERISTICS OF W-ITB FIELD IN MADURA STRAIT AREA Priatin Hadi Widjaja; D. Noeradi
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1406.328 KB) | DOI: 10.32693/bomg.25.2.2010.27

Abstract

The gas field, initial named W-ITB Field, is located at the southwestern part of the East Java sedimentary basin in Madura Strait area. W-ITB Field was discovered by W-ITB#1 well in 2006. In W-ITB#1 well gas reservoir layer was just only found at Selorejo and Mundu Formation, on the other hand, on W- ITB#2 the gas reservoir is not found in Mundu Formation. Determination of reservoir characteristic including the distribution and quality at W-ITB Field, was done by using 3D geological modelling both for structure and stratigraphy. This model was executed based on integration of well data (petrophysics) and cross section seismic interpretation. The results, at Zone 2 and Zone 3 for vertical V-shale distribution shows as a good quality reservoir (0-15%). Laterally distribution, area at southwest of W-ITB 1 well has low V-shale or chatagorized as a good quality reservoir. While, porosity distribution, zone 1 and zone 2 have better reservoir (29-35% V-shale value) than Zones 3 and 4. NTG distribution result indicates that zone 2 and 3, with high value means a good reservoir. Due to only two exploration well, to guide lateral distribution, so that acoustic from seismic data is used for porosity distribution. Key words: modelling, reservoir, characteristic, V-shale, porosity, quality, Madura Strait Lapangan gas dengan nama inisial W-ITB terletak di bagian barat daya cekungan sedimen Jawa Timur yang termasuk di wilayah Selat Madura. Lapangan ini ditemukan dari Sumur W- ITB#1 pada tahun 2006. Pada sumur W- ITB#1 Lapisan reservoir yang mengandung gas hanya dijumpai pada Formasi Selorejo dan Mundu, namun dari hasil sumur W- ITB#2, lapisan reservoir gas dalam Formasi Mundu tidak diperoleh. Penentuan karakteristik reservoir termasuk distribusi dan kualitasnya di Lapangan W-ITB dilakukan dengan pemodelan geologi 3-Dimensi baik secara struktur dan stratigrafi dengan berdasarkan pada integrasi data sumur pemboran dan penampang seismik yaitu analisis petrofisik dan interpretasi seismik. Berdasarkan pemodelan 3-Dimensi, pada Zone-2 dan Zone-3 untuk distribusi V-shale secara vertikal merupakan zone dengan kandungan reservoir yang baik dengan nilai V-sh 0 – 15%. ecara distribusi lateral, wilayah di bagian barat daya dari sumur W- ITB#1 memiliki kandungan V-sh yang rendah atau dikategorikan reservoir dengan kualitas baik. Adapun pada distribusi porositas, Zona-1 dan Zona-2 mengandung reservoir yang lebih baik dengan nilai 29- 35% daripada Zona-3 dan Zona-4. Hasil distribusi NTG mengindikasikan bahwa Zona-2 dan Zona-3 dengan nilai tinggi mengandung reservoir yang baik. Karena hanya memilki dua sumur eksplorasi, untuk memandu distribusi lateral maka hasil impedansi akustik dari data seismik digunakan untuk distribusi porositas. Kata kunci: pemodelan, reservoir, karakteristik, V-serpih, porositas, kualitas, Selat Madura
THE SAFETY FACTOR ANALYSIS OF THE MARINE SLOPE STABILITY MODEL ON THE ACCESS CHANNEL OF MARINE CENTRE PLAN CIREBON, WEST JAVA. Franto Novico; Nur Adi Kristanto
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1474.746 KB) | DOI: 10.32693/bomg.25.2.2010.28

Abstract

This study is focused on access channel model that safety factors of some slopes stability would be investigated. Plaxis version 8 is applied to analyze a magnitude of safety factors and displacements based on three different slopes of access channel there are 30°, 45° and 60°. Furthermore, parameters are adopted from geotechnical drilling and laboratory tests. A finite element is applied as a simple model to analyze within a Mohr-coulomb equation. Based on soil data analyses on Marine Center Plan, indicates low safety factor and high deformation. As results, 10 to 40 meters deformation of the slopes and 0.80 to 2.34 of safety factor are obtained of the models. For that reason, a combination between slope channel and infrastructure must be considered. Keywords: Safety factor, slope stability, access channel, Marine centre, Plaxis Kajian ini dilakukan terhadap faktor keamanan dari beberapa jenis kemiringan dinding alur pelayaran yang selanjutnya dilakukan pemodelan dengan menggunakan alur pelayaran Besarnya keruntuhan dan faktor keamanan pada beberapa sudut kemiringan yang berbeda telah dianalisis dengan menggunakan perangkat lunak geoteknik Plaxis Versi 8. Tiga jenis kemiringan yang berbeda telah dibuat yaitu sudut kemiringan 30°, 45° dan 60°. Sebagai data masukan, parameter diambil berdasarkan hasil pemboran geoteknik yang telah dianalisis di laboratorium. Model sederhana elemen terbatas telah dibuat dan dianalisis berdasarkan persamaan Mohr-Coulumb. Berdasarkan analisis data tanah pada rencana Marine Centre menunjukan faktor keamanan yang rendah dan deformasi yang besar. Total deformasi yang dihasilkan berkisar 10-40 meter dengan nilai faktor keamanan 0,80~2,34. Oleh karena itu, dari hasil tersebut perlu dipertimbangkan untuk mengkombinasikan kemiringan alur dengan infrastruktur. Kata kunci : faktor keamanan, kemiringan lereng, alur pelayaran, Marine centre, Plaxis
THE SEAFLOOR MORPHOLOGHY OF SUNDA STRAIT FOR LAYING THE UNDERWATER CABLES Yogi Noviadi
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (500.327 KB) | DOI: 10.32693/bomg.25.2.2010.29

Abstract

The coastal and offshore areas around the Sunda Strait will be developed to be a submarine cable corridor connecting between Java and Sumatra Islands. There are some requirements that should be considered before laying the underwater cables. One of these considerations is to understand the seafloor morphology of the Sunda Strait. The study was conducted based on six of track lines with 1 km line spacing and 4 Cross lines. The water depth obtained then was corrected to the depth of water from the Lowest Water Level (LWL). The seabed condition in the near shore area of Sumatra side is very flat and is influenced by 2 km offshore tide activity. The coast line is characterized by mangrove and fine fraction of sediments (mud and clay). At the Java side, the coastal morphology is characterized by the very steep slope and most of the area is occupied by the industrial activities. Keywords: seafloor morphology, under water cables, Sunda Strait Area pantai dan perairan Selat Sunda akan dikembangkan sebagai bagian dalam penempatan kabel bawah laut yang menghubungkan Pulau Jawa dan Pulau Sumatera. Rencana penempatan kabel bawah laut ini membutuhkan beberapa persyaratan teknis yang harus dipertimbangkan. Salah satu pertimbangan untuk peletakan kabel bawah laut adalah memahami morfologi dasar laut selat Sunda. Penelitian dilakukan berdasarkan 6 lintasan pemeruman dengan jarak antar lintasan 1 km, dan 4 lintasan memotong lintasan utama. Kedalaman laut yang diperoleh kemudian dikoreksi dengan muka laut terendah. Kondisi permukaan dasar laut di sisi pantai Sumatra sangat datar serta sejauh 2 km ke arah laut lepas masih dipengaruhi oleh aktifitas pasang surut. Garis pantainya dicirikan oleh tanaman bakau dan fraksi sedimen halus (lumpur dan lempung). Pada sisi Jawa, morfologi pantai dicirikan oleh kemiringan lereng yang curam dan kebanyakan area ditempati oleh aktivitas industri. Kata kunci: morfologi dasar laut, kabel bawah laut, Selat Sunda

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