Analisis Deformasi Tektonik Pascadua Dekade Gempa Sumatra-Andaman 2004 Dan Nias 2005 Menggunakan Data GNSS

Haryadi, Dinar (2026) Analisis Deformasi Tektonik Pascadua Dekade Gempa Sumatra-Andaman 2004 Dan Nias 2005 Menggunakan Data GNSS. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Gempa Sumatra-Andaman 2004 (Mw 9,1) dan Nias-Simeulue 2005 (Mw 8,6) merupakan dua peristiwa megathrust terbesar di zona subduksi Sumatra yang menghasilkan deformasi coseismic berskala besar dan memicu proses deformasi postseismic jangka panjang. Penelitian ini menganalisis pola deformasi postseismic selama dua dekade di zona subduksi Sumatra menggunakan data GNSS dari 14 stasiun jaringan Sumatran GPS Array (SuGAr) periode 2004-2023. Berkas RINEX harian diolah menggunakan GAMIT/GLOBK untuk menghasilkan time series koordinat harian dalam kerangka ITRF2014. Komponen postseismic diekstraksi dengan mengoreksi gerak rigid Blok Sunda menggunakan Euler Pole Alif dkk. (2024), kemudian dimodelkan menggunakan fungsi peluruhan logaritmik dan eksponensial satu komponen gempa per grup stasiun. Estimasi parameter dilakukan melalui metode kuadrat terkecil linear dengan grid search pada 100 nilai waktu karakteristik (τ) yang tersebar secara logaritmik antara 1 hingga 5.000 hari. Hasil penelitian menunjukkan bahwa displacement horizontal seluruh stasiun mengarah ke barat hingga barat laut, mencerminkan proses elastic rebound zona fore-arc pascagempa, dengan gradien spasial yang berkurang dari utara ke selatan sesuai distribusi slip coseismic kedua gempa. Pada komponen vertikal, sebagian besar stasiun menunjukkan uplift, sementara beberapa stasiun di zona transisi Simeulue menunjukkan subsidence yang berkaitan dengan kompleksitas deformasi di zona overlap kedua rupture. Model logaritmik memberikan kecocokan yang sedikit lebih baik terhadap data GNSS SuGAr periode dua dekade dengan rata-rata RMS horizontal 6,88 mm dibandingkan model eksponensial dengan RMS 7,29 mm, meskipun selisihnya kecil dan tidak konsisten di semua stasiun. Hasil ini menunjukkan bahwa pada skala waktu dua dekade, afterslip dan relaksasi viskoelastik berkontribusi secara bersamaan terhadap sinyal deformasi postseismic yang teramati. Analisis spasial menunjukkan keterkaitan antara distribusi slip coseismic gempa 2004-2005 dan konsentrasi seismisitas Mw 5,0-6,5 periode 2006-2023, dengan aktivitas tertinggi di zona overlap Simeulue. Kurva fitting model pada time series GNSS SuGAr yang hingga akhir periode pengamatan 2023 belum sepenuhnya mendatar mengindikasikan bahwa proses pelepasan tegangan pascagempa 2004-2005 di zona subduksi Sumatra masih berlangsung.
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The 2004 Sumatra-Andaman earthquake (Mw 9.1) and the 2005 Nias-Simeulue earthquake (Mw 8.6) are among the largest megathrust events recorded in the Sumatra subduction zone, producing large-scale coseismic deformation and triggering long-term postseismic processes. This study analyzes two-decade postseismic deformation patterns in the Sumatra subduction zone using GNSS data from 14 stations of the Sumatran GPS Array (SuGAr) network covering the period 2004-2023. Daily RINEX files were processed using GAMIT/GLOBK to produce daily coordinate time series in the ITRF2014 reference frame. The postseismic component was extracted by correcting for the rigid motion of the Sunda Block using the Euler Pole parameters of Alif et al. (2024), then modeled using single-earthquake-component logarithmic and exponential decay functions per station group. Parameters were estimated through linear least squares with a grid search over 100 logarithmically spaced characteristic time (τ) values ranging from 1 to 5,000 days. The results show that horizontal displacements at all stations are oriented westward to northwestward, reflecting elastic rebound of the fore-arc zone, with a spatial gradient decreasing from north to south consistent with the coseismic slip distribution of both earthquakes. For the vertical component, most stations show uplift, while several stations in the Simeulue transition zone exhibit subsidence associated with the complexity of deformation in the overlap zone of both ruptures. The logarithmic model provides a slightly better fit to the two-decade SuGAr dataset with a mean horizontal RMS of 6.88 mm compared to 7.29 mm for the exponential model, although the difference is small and not consistent across all stations. This finding indicates that over two decades, afterslip and viscoelastic relaxation contribute simultaneously to the observed postseismic signal. Spatial analysis reveals a correspondence between the coseismic slip distribution of the 2004-2005 earthquakes and the concentration of Mw 5.0-6.5 seismicity during 2006-2023, with the highest activity identified in the Simeulue overlap zone. The model fitting curves on the SuGAr GNSS time series that have not fully flattened by the end of the 2023 observation period indicate that the postseismic stress release process following the 2004-2005 earthquakes in the Sumatra subduction zone is still ongoing.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Decay rate, Postseismic Deformation, GAMIT/GLOBK, GNSS, Megathrust, Sumatra
Subjects:	G Geography. Anthropology. Recreation > G Geography (General) > G109.5 Global Positioning System
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Geomatics Engineering > 29202-(S1) Undergraduate Thesis
Depositing User:	Dinar Haryadi
Date Deposited:	23 Jul 2026 04:21
Last Modified:	23 Jul 2026 04:21
URI:	http://repository.its.ac.id/id/eprint/136541

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