Rachman, Gazali (2023) Tomografi Seismik Waktu Tempuh Untuk Penentuan Struktur 3-D Vp, Vs, Dan Rasio Vp/Vs Di Zona Tumbukan Laut Maluku Dan Implikasinya Terhadap Aktivitas Tektonik Dan Gunungapi Di Halmahera. Doctoral thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Zona tumbukan laut Maluku dan area sekitarnya merupakan wilayah yang secara geologi dan tektonik sangat kompleks, terdapat subduksi ganda Lempeng Laut Maluku, Lempeng Sulawesi, Lempeng Filipina, sesar aktif, busur gunungapi Halmahera dan Sangihe, serta gempabumi yang kontinyu terjadi setiap tahunnya. Di area ini, terdapat beberapa riset terdahulu dalam penentuan lokasi dan relokasi hiposenter dengan menggunakan data lokal, regional, dan teleseismik. Sedangkan studi tomografi umumnya menggunakan gelombang P, dan baru beberapa tahun belakang, terdapat riset tomografi gelombang P dan S dari data teleseismik. Riset ini menggunakan data lokal dan regional gelombang P dan S untuk mengungkap sudut subduksi di bawah Lengan Utara Sulawesi, hubungan Lempeng Laut Maluku dengan aktivitas di Busur Gunungapi Halmahera, dan kedalaman lengkungan atas Lempeng Laut Maluku di utara dan selatan. Berdasarkan data dan latar belakang tersebut ditetapkan tujuan penelitian meliputi: (1) menentukan lokasi hiposenter gempa (2) relokasi hiposenter gempa (3) menentukan struktur 3-D Vp, Vs, dan rasio Vp/Vs tomografi seismik waktu tempuh (4) interpretasi berdasarkan relokasi hiposenter dan tomogram seismik waktu tempuh. Data waveform yang digunakan berasal dari website Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) mulai tanggal 1 Januari 2010 sampai 31 Desember 2017 sebanyak 1.691 event dengan magnitudo ≥ 4,0 dari 32 stasiun. Re-picking fase P dan S menggunakan Seisgram2K v7.0 diperoleh fase P sebanyak 18.578 dan S sebanyak 18.578. Jumlah fase ini berkurang setelah dilakukan penelusuran terhadap fase outliers dan residual time yang ≤ −10 detik dan ≥ 10 detik menjadi 17.628 fase P dan 17.628 fase S dengan jumlah event sebanyak 1.647. Selanjutnya, data ini digunakan untuk penentuan lokasi hiposenter, relokasi hiposenter, dan tomografi seismik waktu tempuh yang secara berurutan menggunakan metode non-linear location, teleseismik double-difference, dan simultaneous inversion. Lokasi hiposenter gempa berhasil ditentukan dengan rata-rata ketidakpastian lokasi arah x, y, dan z adalah 10,200 km, 14,082 km, dan 19,039 km. Hasil relokasi menjadi lebih baik yang dibuktikan dengan dispersi waktu residu yang lebih kecil dibandingkan sebelum relokasi. Event gempa mengalami pergeseran episenter dengan rata-rata 9,460 km dan pergeseran terbanyak mengarah ke barat daya, sedangkan pergeseran kedalaman didominasi pada kedalaman ±20 km. Seismisitas memperlihatkan pola yang berasosiasi dengan fitur-fitur utama di area ini yaitu pola subduksi ganda Lempeng Laut Maluku, pola Lempeng Sulawesi, pola Lempeng Filipina, gempabumi dangkal yang berasosiasi dengan sesar naik di sepanjang Punggungan Mayu-Talaut, gempabumi dangkal dan menengah di zona Palung Halmahera dan Sangihe berasosiasi dengan zona tumbukan antara Lempeng Laut Maluku dengan Lempeng Halmahera di timur dan Lempeng Sangihe di barat. Hasil uji resolusi checkerboard mempunyai resolusi yang dapat dipercaya sampai kedalaman 210 km, sedangkan pada penampang D-D’ bisa mencapai kedalaman 300 km. Hasil inversi tomografi yang sekaligus kebaharuan dalam penelitian meliputi: (1) Anomali Vp tinggi, Vs tinggi, dan rasio Vp/Vs rendah di bawah Lengan Utara Sulawesi dengan penampang dari selatan-utara berasosiasi dengan Lempeng Laut Maluku dengan perkiraan sudut subduksi ~40°. (2) Anomali Vp rendah, Vs rendah, dan rasio Vp/Vs tinggi di bawah busur gunungapi Halmahera di bagian selatan dan utara yang kemungkinan berasosiasi dengan sumber magma. Beberapa gunungapi yang terletak di utara telah mengalami erupsi dan berlangsung sampai sekarang, sedangkan gunungapi yang terletak di selatan dalam keadaan dormant. Gunung api ini terhubung dengan partial melting di atas Lempeng Laut Maluku menunjam ke timur. (3) Anomali Vp tinggi, Vs tinggi, dan rasio Vp/Vs rendah di bawah Laut Sulawesi, Laut Maluku, dan Halmahera diinterpretasi sebagai subduksi ganda Lempeng Laut Maluku. Di utara lengkungan atas lempeng ini tenggelam lebih dalam dibandingkan dengan di selatan. (4) Di Punggungan Mayu-Talaut terdapat batas tegas antara anomali kecepatan tinggi di bagian barat dan kecepatan rendah di bagian timur yang berasosiasi dengan densitas material atau sifat batuan yang berbeda.
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The Maluku Sea collision zone and the surrounding area are geologically and tectonically very complex. There is a double subduction of the Maluku Sea Plate, Sulawesi slab, and Philippine slab, active faults, the Halmahera and Sangihe volcanic arcs, and earthquake events that continuously occur every year. In this area, there have been several previous studies in determining the location and relocation of hypocenters using local, regional, and teleseismic data. Whereas tomographic studies generally use P waves, only in recent years have there been P- and S-wave tomographic studies from teleseismic data. This research uses local and regional data of P- and S-waves to reveal the angle of subduction beneath the North Sulawesi Arm, the relationship of the Maluku Sea Plate with activity in the Halmahera Volcano Arc, and the depth of the arc over the Maluku Sea Plate in the north and south. Based on the data and background, the research objectives are set to include: (1) determining the location of the earthquake hypocenter, (2) relocating the earthquake hypocenter, (3) determining the 3-D structure Vp, Vs, and Vp/Vs ratio of seismic tomography travel time (4) interpretation based on hypocenter relocation and travel time seismic tomograms. The waveform data was accessed from the Meteorology, Climatology and Geophysics Agency (BMKG) website from 1 January 2010 to 31 December 2017 for a total of 1,691 events with magnitude ≥ 4.0 from 32 stations. Re-picking the P- and S-phases using Seisgram2K v7.0 obtained 18,578 P- and 18,578 S-phases. The number of these phases decreased after tracing the phase outliers and residual time ≤ −10 s and ≥ 10 s to become 17,628 P- and 17,628 S-phases with a total of 1,647 events. Determination of the location of the hypocenter uses the non-linear location method, relocating the hypocenter utilises the double-difference teleseismic method, and seismic tomography of travel time applies the simultaneous inversion method. The location of the earthquake hypocenter is successfully determined with estimated mean location uncertainties in the x, y, and z directions of 10.200 km, 14.082 km, and 19.039 km. The relocation results are better, as evidenced by the dispersion of the residual time is smaller than before the relocation. The earthquake event experienced an epicenter shift with a mean of 9.460 km; most shifts are directed to the southwest, while the depth shift is dominated at ±20 km. Seismicity shows patterns associated with the main features in this area, that is, the double subduction pattern of the Maluku Sea Plate, the Sulawesi slab pattern, the Philippine slab pattern, shallow earthquakes associated with reverse faults along the Mayu-Talaut Ridge; the shallow and medium earthquakes in the trench zone of Halmahera and Sangihe are associated with the collision zone between the Maluku Sea Plate and the Halmahera Plate in the east and the Sangihe Plate in the west. The results of the checkerboard resolution test have a reliable resolution to a depth of 210 km, whereas in the cross-section of D-D' it can reach a depth of 300 km. The tomographic inversion results, which are also the novelty in this study, include (1) Anomaly of high Vp, high Vs, and low Vp/Vs ratio beneath the Sulawesi's north arm with a south-north section associated with the Maluku Sea Plate with an estimated subduction angle of ~40°. (2) Low Vp, low Vs, and high Vp/Vs ratio beneath the Halmahera volcanic arc, the volcanoes located in the southern and northern are associated with possible magma sources. Several volcanoes in the north have experienced eruptions and are continuing until now, while the volcanoes in the south are dormant. These volcanoes are connected to the partial melting above the Maluku Sea Plate, subducting to the east. (3) Anomalies of high Vp, high Vs, and low Vp/Vs ratio beneath the Celebes Sea, Maluku Sea, and Halmahera are interpreted as double subduction of the Maluku Sea Plate. In the north, the upper curvature of this plate submerged deeper than in the south. (4) On the Mayu-Talaut Ridge, there is a clear boundary between high-velocity anomalies in the west and low-velocity in the east, which are associated with different material densities or rock properties.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Uncontrolled Keywords: | Re-picking fase P dan S, lokasi hiposenter, relokasi hiposenter, tomografi seismik waktu tempuh, Laut Maluku, busur gunungapi Halmahera, Re-picking of P- and S-phases, hypocenter location, hypocenter relocation, travel time seismic tomography, Maluku Sea, Halmahera volcanic arc. |
| Subjects: | Q Science > QE Geology > QE538.8 Earthquakes. Seismology |
| Divisions: | Faculty of Science and Data Analytics (SCIENTICS) > Physics > 45001-(S3) PhD Thesis |
| Depositing User: | Gazali Rachman |
| Date Deposited: | 01 Mar 2023 07:24 |
| Last Modified: | 01 Mar 2023 07:24 |
| URI: | http://repository.its.ac.id/id/eprint/97715 |
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