Pemodelan 3D Gradien Gayaberat Vertikal dan Subsiden Tektonik pada Zona Konvergensi Tiga Lempeng Tektonik di Indonesia

Prakoso, Mikael Nicholas (2026) Pemodelan 3D Gradien Gayaberat Vertikal dan Subsiden Tektonik pada Zona Konvergensi Tiga Lempeng Tektonik di Indonesia. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Indonesia terletak pada zona konvergensi tiga lempeng tektonik utama (Australia, Eurasia, dan Pasifik) yang menjadikan Banda Arc sebagai salah satu kawasan geodinamika paling kompleks di dunia, dengan subduksi ganda dan kolisi busur-benua yang masih aktif hingga saat ini. Subsiden tektonik akibat pembebanan tektonik dari slab Australia yang menunjam di kawasan ini belum pernah dianalisis secara kuantitatif melalui inversi densitas tiga dimensi yang terintegrasi dengan data Vertical Gravity Gradient (VGG). Penelitian ini bertujuan menganalisis distribusi dan karakteristik VGG di zona konvergensi Banda Arc serta memodelkan distribusi densitas bawah permukaan secara tiga dimensi untuk mengidentifikasi mekanisme subsiden tektonik dan deformasi fleksural litosfer. Data yang digunakan meliputi GGMplus, SIO Marine Gravity v33, BATNAS, DEMNAS, GlobSed, GEMMA, dan SL2013sv. Anomali Bouguer diolah pada resolusi grid 10 menit busur, kemudian VGG diturunkan melalui Fast Fourier Transform (FFT). Densitas awal dihitung per lapisan menggunakan persamaan empiris Gómez-García dkk. (2019) untuk air laut dan sedimen, serta konversi Brocher (2005) untuk kerak dan mantel, kemudian diinversi tiga dimensi menggunakan GRABlox2 dengan model delapan lapisan hingga kedalaman 125 km. Hasil penelitian menunjukkan bahwa model densitas tiga dimensi mampu mereproduksi data observasi dengan sangat baik, ditandai dengan koefisien determinasi R² = 0,911 dan RMSE = 31,241 mGal untuk anomali Bouguer, serta R² = 0,944 dan RMSE = 3,830 Eötvös untuk VGG. VGG terbukti lebih sensitif dibandingkan anomali Bouguer dalam mendelineasi struktur dangkal, ditunjukkan oleh anomali negatif kuat hingga -128,050 Eötvös di zona Timor Trough, sementara anomali Bouguer dan VGG sama-sama mencapai nilai paling negatif pada sekitar bujur 132°BT, mengonfirmasi adanya satu sumber defisit massa yang menerus dari lapisan dangkal hingga struktur kerak yang lebih dalam. Variasi lateral Moho teridentifikasi dengan kedalaman 20-25 km di bawah kerak oseanik Laut Banda dan 35-40 km di bawah Outer Banda Arc. Model densitas tiga dimensi mengonfirmasi bahwa subsiden tektonik di Banda Arc didominasi oleh deformasi fleksural litosfer Australia akibat pembebanan tektonik dari slab yang menunjam, dengan subsiden maksimum diperkirakan mencapai 3.000-4.000 meter sebagai ekspresi kolisi busur-benua yang masih aktif.
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Indonesia is situated at the convergence zone of three major tectonic plates (Australia, Eurasia, and the Pacific), making the Banda Arc one of the most geodynamically complex regions in the world, characterized by double subduction and an ongoing arc-continent collision. Tectonic subsidence resulting from the tectonic loading of the underthrusting Australian slab in this region has not previously been quantitatively analyzed through three-dimensional density inversion integrated with Vertical Gravity Gradient (VGG) data. This study aims to analyze the distribution and characteristics of VGG in the Banda Arc convergence zone and to model the three-dimensional subsurface density distribution in order to identify the mechanisms of tectonic subsidence and lithospheric flexural deformation. The datasets used include GGMplus, SIO Marine Gravity v33, BATNAS, DEMNAS, GlobSed, GEMMA, and SL2013sv. Bouguer anomalies were processed at a 10 arc-minute grid resolution, and VGG was subsequently derived using the Fast Fourier Transform (FFT). Initial layer densities were calculated using the empirical equations of Gómez-García et al. (2019) for seawater and sediment, and the Brocher (2005) conversion for crust and mantle, followed by three-dimensional inversion using GRABlox2 with an eight-layer model extending to a depth of 125 km. The results show that the three-dimensional density model reproduces the observed data very well, with a coefficient of determination of R² = 0.911 and RMSE = 31.241 mGal for the Bouguer anomaly, and R² = 0.944 and RMSE = 3.830 Eötvös for VGG. VGG proved more sensitive than the Bouguer anomaly in delineating shallow structures, as indicated by a strong negative anomaly reaching -128.050 Eötvös in the Timor Trough zone, while both the Bouguer anomaly and VGG reached their most negative values at approximately 132°E, confirming the presence of a single mass deficit source extending continuously from shallow to deeper crustal levels. Lateral variation in Moho depth was identified, ranging from 20-25 km beneath the oceanic crust of the Banda Sea to 35-40 km beneath the Outer Banda Arc. The three-dimensional density model confirms that tectonic subsidence in the Banda Arc is dominated by flexural deformation of the Australian lithosphere driven by tectonic loading from the underthrusting slab, with maximum subsidence estimated at 3,000-4,000 meters as an expression of the ongoing arc-continent collision.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Anomali Bouguer, Banda Arc, GRABlox2, Inversi 3D, Subsiden Tektonik, Vertical Gravity Gradient, 3D Inversion, Banda Arc, Bouguer Anomaly, GRABlox2, Tectonic Subsidence, Vertical Gravity Gradient.
Subjects:	G Geography. Anthropology. Recreation > G Geography (General) > G109.5 Global Positioning System G Geography. Anthropology. Recreation > GB Physical geography > GB651 Subsidences (Earth movements) G Geography. Anthropology. Recreation > GC Oceanography > GC101.2 Seawater--Analysis Q Science > QC Physics Q Science > QC Physics > QC851 Coordinates--Measurement. Q Science > QC Physics > QC871 Meteorology--Observations.
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Geomatics Engineering > 29202-(S1) Undergraduate Thesis
Depositing User:	Mikael Nicholas Prakoso
Date Deposited:	24 Jul 2026 00:28
Last Modified:	24 Jul 2026 00:28
URI:	http://repository.its.ac.id/id/eprint/136620

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