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Ramadhan Priadi
Sekolah Tinggi Meteorologi Klimatologi dan Geofisika

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Analysis of the Donggala-Palu Tsunami Characteristics based on Rupture Duration (Tdur) and Active Fault Orientation using the HC-plot Method Ramadhan Priadi; Angga Wijaya; Maria Annaluna Pasaribu; Riska Yulinda
Jurnal Geofisika Vol 17 No 1 (2019): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (2202.153 KB) | DOI: 10.36435/jgf.v17i1.392

Abstract

September 28th, 2018, Donggala-Palu earthquake M 7.5 occurred at depth of 12 km and generated tsunami to be released off the coast in Palu Bay. The tsunami that occurred in Palu was very interesting because the results of the earthquake source mechanism Palu had a type of strike-slip fault that should not have generated a tsunami. This study purpose to estimate the characteristics of the Donggala-Palu tsunami based on rupture duration ( and orientation fault activated using the HC-plot method. The data used in this study are data waveforms from 17 seismic stations and CMT Global catalog data with the area of research 0.87 0 N-1.78 0S dan 118.640E- 120.95 0E. The waveform data used is a phase P-PP vertical component signal with a Bandpass-filter 1-5 Hz for determination . The fastest rupture duration from the earthquake source is obtained from the calculation of each station. Delay time measurement after P wave for 90% (T0.9), 80% (T0.8), 50% (T0.5), dan 20% (T0.2) from its peak value. Then the HC-plot method is used to estimate the orientation of generator fault Palu earthquake and the direction of rupture from the focal mechanism. From the results of processing obtained 2 pairs of seismic stations with almost the same distance but with different azimuths. The fastest rupture duration is at BBSI station with value of 82.014 s and distance from station to epicenter . So that the rupture direction is in the azimuth from the north. The result of fault orientation was obtained hypocenter distance to the centroid for nodal plane 1 is 6.32 km and nodal plane 2 is 30.17 km with distance centroid to hypocenter is 31.22 km. So in Palu earthquake, the tsunami generator fault was in nodal plane 1 with direction north-south. Criteria obtained indicate that the Palu earthquake M 7.5 has potential for a tsunami because of its value has meet ≥ 65 s, but from the result of the focal mechanism direction field not passing through the Palu bay is thought to be another parameter that generates a tsunami and Palu koro fault line uncharted.
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