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Jurnal Geofisika
Published by Himpunan Ahli Geofisika Indonesia
ISSN : 0854352     EISSN : 24776084     DOI : https://doi.org/10.36435/jgf
Core Subject : Science,
Earth & Planetary Sciences Energy Physics
Jurnal Geofisika [e-ISSN : 2477-6084] is a scientific journal published by Himpunan Ahli Geofisika Indonesia (HAGI). This journal is referenced, each paper was assessed and evaluated by editors and reviewers who are experts in the relevant fields and come from education institutions and industry, both from within and outside the country. The published article covers all science and technology including Geophysics, Meteorology, Oceanography, Geology and Geodesy.
Arjuna Subject : Ilmu Bumi dan Planet (semua kategori) - Geofisika
Articles 100 Documents
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Analysis and Zonation of Land Vulnerability Areas in Pekon Karangrejo Ulubelu Tanggamus Using Microzonation Method Eko Rananda; Lintang Prabowo; Arief Putih Prabowo; Syamsurijal Rasimeng; Ida Bagus Suananda Yogi
Jurnal Geofisika Vol 18 No 1 (2020): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v18i1.420

Abstract

Abstract.Ulubelu Tanggamus is an area that have geothermal energy potential. This region consists of a geological structure in the form of graben and reverse fault formed between Mount Rendingan and Mount Kukusan. Identifications that can be done include surveys to map soil characteristics in shaking responses using microzonation methods. This study aims to analyze the values ​​of dominant frequency, dominant period, Vs30 and amplification. The stages of the research carried out are processing data to obtain dominant frequency, calculating the value of the dominant period, calculating the value of Vs30 and the amplification value, and making a map of the soil vulnerability of the UlubeluTanggamus area. Based on the distribution of the dominant frequency values, the UlubeluTanggamus geothermal area is dominated by a dominant Frequency (F0) >0.5Hz which is expected to be a very thick surface thickness of sediments more than 30m. The distribution of the dominant period value obtained is (T0)>1 where the character of the sedimentary rock type is very soft consisting of alluvial material formed from sedimentation of deltas, top soil, and mud. The distribution of the Vs30 value is dominated by the value of 100 <Vs30<200 and obtains an amplification value of 2<A0<6 times where the area is an area with a moderate risk category to the danger of soil vulnerability.
Analisis Anomali Gaya Berat Menggunakan Metode SVD dan Pemodelan 3D (Studi Kasus Gempa di Kepulauan Togean, Kabupaten Tojo Una-Una, Sulawesi Tengah) Afra Kansa Maimuna; Elisabet A Pramesthi; Yan A Segoro; Relly Margiono; Kekey S Azzahra; M Akhadi; Denny V Siregar
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.466

Abstract

Abstrak Metode gaya berat adalah salah satu metode geofisika yang didasarkan pada pengukuran medan gravitasi. Metode ini dapat diaplikasikan untuk memetakan daerah yang mengalami deformasi struktural berupa sesar terutama pada kejadian gempabumi. Berdasarkan gempabumi yang terjadi di Kabupaten Tojo Una-Una Sulawesi Tengah pada periode 9 Oktober 2020 sampai dengan 15 Oktober 2020 yang bersumber di dasar laut, penulis tertarik untuk mengetahui kemungkinan adanya keberadaan sesar bawah laut dikarenakan belum terpetakannya sesar di wilayah tersebut. Data yang digunakan dalam penelitian ini adalah data gravitasi hasil observasi satelit TOPEX dengan koordinat 0,25 o LU – 1,15o LS dan 121,46 o BT – 123,30 o BT. Metode yang digunakan adalah metode Second Vertical Derivative (SVD) dan pemodelan 3D menggunakan software Grav3D. Hasil analisis kurva anomali SVD terdapat kontras nilai densitas yang mengindikasikan adanya dugaan keberadaan sesar. Dugaan sesar ini memanjang dengan orientasi barat - timur. Hasil pemodelan 3D hingga kedalaman 24 km menunjukkan adanya anomali gaya berat yang cenderung positif dengan nilai kontras densitas di bawah permukaan berkisar antara - 0,8 gr/cm3 sampai 1,1 gr/cm3. Kata kunci: Anomali Gaya Berat, SVD (Second Vertical Derivative), Pemodelan 3D, Sesar. Abstract The gravity method is a geophysical method based on the measurement of the gravitational field. This method can be applied to map areas that experience structural deformation in the form of faults. Based on the earthquakes that occurred in Tojo Una-Una Regency, Central Sulawesi from 9 October 2020 - 15 October 2020 that originated on the seabed, we have an intention to find a possibility of fault as no-fault has been mapped in this area. The data used in this study is the gravitational data from the TOPEX satellite observations with coordinates 0,2 o N – 1,15 o S and 121,4 o E – 123,3 o E. The method used is the second vertical derivative (SVD) and 3D modeling using the Grav3D software. The results of the SVD show a contrast density value that indicates the possibility of a fault. This fault extends in a west-east orientation. The results of 3D modeling up to a depth of 24 km show a gravity anomaly that tends to be positive with the value of the distribution density under the surface ranging between -0,8 gr / cm3 to 1,1 gr / cm3. Keywords: Gravity Anomaly, SVD (Second Vertical Derivative ), Grav3D, Faults.
Perbandingan Indeks Kerentanan Seismik Antara Instrumen Akselerometer ADXL345 Dengan REFTEK 130-SMHR Menggunakan Metode Horizontal-to-Vertical Spectral Ratio I Gede Boy Darmawan; Rahmi Mulyasari; Rian Amukti
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.452

Abstract

Makalah ini membahas hasil pengembangan prototip instrumen akselerometer menggunakan sensor ADXL345 yang berbasis Micro-Electrical Mechanical System-based (MEMS). Untuk mengetahui kehandalan instrumen tersebut, kami melakukan validasi dengan cara membandingkan terhadap hasil kerja akselerometer pabrikan REFTEK 130-SMHR dalam pengukuran indeks kerentanan seismik Kg (Nakamura dkk., 2000). MetodeHorizontal-to-Vertical Spectral Ratio (HVSR) digunakan untuk mendapatkan nilai frekuensi dominan fg dan nilai amplifikasi Ag terlebih dahulu dan selanjutnya menghitung nilai Kg. Akuisisi data lapangan menggunakan kedua instrumenakselerometer tersebut dilakukan pada 30 titik amat dengan cuplikan frekuensi 500 Hz dan periode pengukuran selama 30 menit. Hasil pengukuran menunjukkan adanya keselarasan antara akselerometer ADXL345 dengan akselerometer REFTEK 130-SMHR. Untuk total luas daerah studi, kami mendapatkan nilai Kg yang sama, yakni sekitar 57%, dengan perbedaan sedang sekitar 37% dan perbedaan tinggi 6%. Hasil penting lainnya adalah adanya keselarasan pada nilai pengukuran instrumen ADXL345 dengan hasil observasi lapangan, khususnya di Gedung L Fakultas Teknik UNILA. Keselarasan ini dicirikan dengan adanya retakan pada lantai gedung yang berada pada zona kerentanan seismik cukup tinggi. Studi perbandingan kedua instrumen akselerometer tersebut menghasilkan kesimpulan bahwa pengujian prototipe ini masih perlu dilakukan lebih lanjut, khususnya pada daerah dengan tingkat variasi kerentanan seismik yang berbeda
Pemetaan Daerah Rawan Longsor Menggunakan Machine Learning di Kecamatan Muara Tami, Kota Jayapura, Papua M Aldi; Indra Rivaldi Siregar; Alissa Bilqis
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.504

Abstract

One of the high landslide vulnerability areas in Indonesia is located in Muara Tami District, Jayapura City. The main factors triggering the landslide are steep slopes and high elevations. However, there are still several other factors that also influence the occurrence of landslides, such as vegetation, land cover, and curvature. Landslides that occur can cause damages to all parties, both material and non-material. Therefore, it is necessary to map landslide-prone areas as a non-structural mitigation planning. This planning is useful for identifying areas that are relatively safer from landslides so that the fatalities incurred can be minimized. In this mapping, several parameters are used that are thought to trigger landslides, then they are calculated by machine learning using the random forest method. Based on the parameters used, the eastern and northwestern areas have high slope and elevation values, high curvature contrast values, and dry land forest cover. These results indicate the high potential for landslide vulnerability in both parts of the study area. Meanwhile, areas with low potential for landslide vulnerability have a curvature of 0, a relatively low slope and elevation. The model accuracy value obtained by the random forest method is 0.9. This value is categorized as good enough because it shows that the parameters used are good enough in mapping landslide vulnerability in the study area. These results are also supported by the high sensitivity and specificity values ​​based on the ROC curve. Areas with high potential for landslide vulnerability are Mosso Village and the border between Skow Mabo, Skow Yambe, Koya Tengah, Koya Timur, and Holtekam. Meanwhile, areas with low landslide potential were Skow Sae Village, the central part of East Koya, the northern part of West Koya, and the southern part of Holtekam.
Identifikasi Struktur Tektonik Di Laut Pidie Aceh Dengan Survey Geo-Marine mahmud yusuf; Muhammad Hasan; M Taufik Gunawan; Hidayanti Hidayanti; Siswanto Siswanto
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.481

Abstract

Tim peneliti yang tergabung dalam Cruise Indonesia PRIMA 2017 telah melakukan penelitian di perairan selat Malaka dengan menggunakan kapal riset Baruna Jaya. Penelitian ini bertujuan mengamati struktur tektonik di selat Malaka di sebelah utara kabupaten Pidie. Metode yang digunakan dalam penelitian ini meliputi pengamatan topographi dasar laut dengan alat Single beam echosounder, kondisi geologi dasar laut dengan alat Sub bottom profiler (SBP), ditambah dengan pemodelan anomali gayaberat dari data satellite . Dari penelitian ini diperoleh hasil kondisi kemiringan lereng perairan daerah penelitian setidaknya memiliki empat kemiringan yang berbeda yaitu relatife datar, agak curam, miring, dan sedikit miring. Sedangkan kondisi geologi diketahui dasar laut terdapat batuan yang keras dan sedimen yang tebal mencapai 30 meter, dan di daerah ini ditemukan juga struktur geologi berupa patahan turun. Dari hasil pemodelan gayaberat juga diperoleh informasi adanya patahan turun.
Fault Reassessment in Way Huwi Area, South Lampung using Gravity Method LUHUT PARDAMEAN SIRINGORINGO; Andri Yadi Paembonan; Virgian Rahmanda
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.492

Abstract

The Age majority of regional geological maps that have been referenced by geologists in Indonesia are about 20-30 years old. One of them is Tanjung Karang Geological Map. Our opinion is that the map is old enough. Some faults features are doubted in the aspect of existence and its trend. It is represented by the dashed line symbol in the maps. Therefore, this research was carried out to provide a more detailed reinterpretation of faults in the Way Huwi area using the Gravity method. This area was selected because it is the new education center and economy in the eastern part of Bandar Lampung. This research was also carried out as part of disaster mitigation. The faults within this research area were identified with Horst-Graben type and formed before Lampung Formation was deposited. The trend of these normal faults is Northeast-Southwest. it is very different from the fault interpretation on Tanjung Karang regional geology map with the Northwest-Southeast direction. The genesis of the Way Huwi Fault is indirectly part of the extensional Sunda Strait.
Analisis Gempabumi Lombok 2018 Berdasarkan Mekanisme Sumber, Distribusi Slip, Asperity, dan Perubahan Nilai (Coulomb Stress) Pada Bidang Sesar ramadhan priadi; Yusuf Hadi Perdana; Angga Wijaya; Imam Suardi
Jurnal Geofisika Vol 19 No 1 (2021): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v19i1.430

Abstract

Gempabumi signifikan yang terjadi di Lombok pada bulan Juli hingga Agustus 2018 dengan magnitudo yang berkisar antara M 5,8 hingga 7,0. Pada periode tersebut terjadi kejadian gempabumi yang terjadi secara berurutan yaitu Mw 6,5 tanggal 28 Juli 2018 (22:47:38 UTC), Mw 6,9 tanggal 5 Agustus 2018 (11:46:38 UTC), Mw 5,9 tanggal 9 Agustus 2018 (05:25:31 UTC), Mw 6,4 tanggal 19 Agustus 2018 (04:10:22 UTC) dan Mw 6,9 tanggal 19 Agustus 2018 (14:56:28 UTC). Fenomena tersebut sangat jarang terjadi karena gempabumi memerlukan waktu yang relatif lama untuk mengakumulasi energi sebelum dilepaskan. Berdasarkan keunikan tersebut, pemodelan slip di bidang sesar untuk mengetahui sebaran zona akumulasi energi yang direpresentasikan oleh asperity dengan menginversi gelombang body dari stasiun teleseismik pada frekuensi rendah. Hasil pemodelan slip ini dikonfirmasi oleh sebaran perubahan nilai Coulomb stress setelah gempa. Hasilnya menunjukkan bahwa zona asperity gempabumi Lombok berada pada bagian up-dip. Distribusi slip dominan mengarah hampir tegak lurus ke arah utara. Pada gempabumi Mw 6,4 tanggal 19 Agustus 2018, arah vektor slip mengarah ke gempabumi Mw 6,9 tanggal 19 Agustus 2018, hal tersebut mengindikasikan bahwa gempabumi Lombok sebenarnya saling memicu satu dengan lainnya. Hasil pemodelan juga menunjukkan bahwa gempabumi signifikan di Lombok tidak memiliki asperity tunggal, namun terdistribusi pada bidang sesar di dekat permukaan. Berdasarkan hasil penelitian ini, kami menduga bahwa wilayah utara pulau Lombok mengalami pelemahan batuan karena tidak mampu lagi menahan akumulasi energi sehingga gempabumi Lombok saling memicu. Berdasarkan perubahan nilai Coulomb stress dapat disimpulkan bahwa gempabumi Mw 6,9 tanggal 5 Agustus 2018 berada di zona peningkatan stress dari gempabumi Mw 6,5 tanggal 28 Juli2018
Analisis Hubungan antara Nilai Critical Porosity dan Pore Space Stiffness Terhadap Kualitas Reservoir Batupasir Lapangan ”N” Cekungan Sumatera Selatan Nahdah Novia; Handoyo Handoyo; Fatkhan Fatkhan; Agus Laesanpura; Harnanti Yoga Putri
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.509

Abstract

Kualitas batuan reservoir yang baik adalah reservoir yang memiliki nilai porositas dan permeabilitas tinggi. Parameter utama dalam menentukan kualitas batuan reservoir adalah permeabilitas. Permeabilitas dipengaruhi oleh grain size, tortuosity, dan surface area yang pada praktiknya sulit untuk dihitung. Sebagai penghubung, parameter critical porosity dan pore space stiffness digunakan untuk mengetahui kualitas reservoir yang juga berkaitan dengan elastisitas batuan. Karakterisasi parameter-parameter tersebut dilakukan dengan menggunakan data logging, data XRD, dan permeabilitas. Dengan menggunakan persamaan Zimmerman dan model Nur untuk mendapatkan nilai pore space stiffness dan critical porosity. Penelitian ini menganalisis hubungan parameter petrofisika dengan parameter elastik untuk menentukan kualitas reservoir batuan. Hasil penelitian menunjukkan bahwa hubungan permeabilitas terhadap critical porosity dan pore space stiffness mampu merepresentasikan grain size dan tortuosity suatu batuan. Kualitas reservoir yang baik menunjukkan hubungan permeabilitas berbanding terbalik dengan tortuosity dan sebanding dengan grain size berdasarkan hasil nilai dari pore space stiffness dan nilai critical porosity besar berdasarkan hasil nilai pore space stiffness dan critical porosity sumur “N1” yaitu 0.1-0.3 dan 0.28-0.45, dan nilai permeabilitas berada pada range 2-46 mD.
Utilization of Bayesian Framework in Lithology and Fluid Prediction by Using Inverted Elastic Parameter from Seismic Data Rizky Adityo Prastama; Ignatius Sonny Winardhi
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.514

Abstract

Development stage of a hydrocarbon field usually aims to discover additional reserves within the working area. In this stage, more data, such as well log and core sample, are available to be included in the development plan compared to early exploration stage. Incorporating the information from well to know the distribution of the prospective zone could be done in many ways. In this paper, the workflow of how information in producing well is utilized to predict the distribution of gas-filled sand by using Bayesian framework is presented. Bayesian frameworks use prior statistical information of the gas sand itself, such as prior probability and likelihood function, in calculating the posterior probability. From the available well data, three lithology and its fluid content are classified as gas sand, brine sand, and shale. The likelihood function of these lithology is computed using Gaussian distribution and the prior probability is estimated by Markov-chain approach. Based on the prior information, the posterior probability is iteratively calculated by using values from elastic parameter section that is inverted from seismic data. The resulting probability section of each lithology will have value ranging from 0 to 1. The maximum-a-posteriori (MAP) in every location in the section is concluded as the most probable lithology to be discovered. The result shows that the distribution of gas sand can be predicted quite well by using acoustic impedance and Vp/Vs ratio. This is proven by a good fit between the predicted lithology section and the well.
Slope of Spectral Amplitude: Simple Yet Effective Hydrocarbon Indicator Gadang Gentur Wihardy; Hilfan Khairy
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.523

Abstract

Spectral decomposition has been developed and used for many years to help understanding the subsurface condition. Numerous different approach and specific application of this methodology have been proposed and each of the approach has its own advantages. Slope of Spectral Amplitude is a new spectral decomposition based methodology, which is developed based on the intrinsic seismic attenuation phenomenon affecting the seismic spectrum. The difference of spectrum will be characterized by Intercept and Gradient parameters. These parameters can be used to identify the presence of hydrocarbon from seismic data. Further extension of this concept, transformed the Intercept and Gradient result into Gas Probability data which indicates high probable gas occurrence. Good relationship between gas occurrences confirmed by wells with the resulted Intercept, Gradient and Gas Probability data is shown through several examples presented in this study. These examples cover different seismic data environment and different interval of analysis.

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