Ramadhanta, Athaya Harsya (2026) Pemodelan 3D Gayaberat untuk Memetakan Struktur Densitas di Kompleks Gunungapi Lamongan, Jawa Timur. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Kompleks Gunungapi Lamongan di perbatasan Kabupaten Lumajang–Probolinggo, Jawa Timur termasuk dalam gunungapi monogenetik yang memiliki sistem geologi bawah permukaan cukup kompleks. Adanya manifestasi mata air panas di sebelah timur dan di puncak Lamongan menngindikasikan adanya sistem panas bumi yang berasosiasi dengan struktur sesar.
Pemetaan kondisi bawah permukaan dengan inversi gayaberat di area ini masih terbatas dan belum berhasil mengorelasikan keberadaan mata air panas dengan sistem panas bumi Gunung Lamongan. Penelitian ini dilakukan untuk memetakan pola kelurusan struktur dengan analisis gradien gayaberat berupa Tilt Angle, Improved Normalized Horizontal Tilt Angle (INH), dan Euler Deconvolution yang diintegrasikan dengan model bawah permukaan hasil inversi 3D gayaberat. Digunakan data gayaberat lapangan sebanyak 144 titik tersebar di sekitar G. Lamongan–Tarub dan mata air panas Segaran. Inversi 3D gayaberat dilakukan pada data Complete Bouguer Anomaly (CBA) menggunakan pendekatan deterministik dengan metode Gradient-based least–squares pada tiga jenis norm regularisasi, yaitu L2 smooth (P2222) L1 sparse (P1111), dan L0 compact (P0111). Sebaran nilai CBA di area penelitian sebesar 1,63 hingga 23,73 mGal dengan anomali tinggi terpusat di sekitar G.Lamongan diinterpretasikan sebagai intrusi basaltik dan di sebelah timur berasosiasi dengan produk vulkanik Argopuro. Adapun anomali rendah berasosiasi dengan endapan maar dan piroklastik di sekitar mata air panas Segaran. Distribusi peta kerapatan kelurusan dan analisis gradien anomali menunjukkan orientasi struktur dominan NW–SE dan NE–SW dengan kerapatan tinggi berada di sebelah timur Kompleks Gunungapi Lamongan. Hasil pemodelan inversi 3D gayaberat dengan ketiga regularisasi menunjukkan kontras dan pola anomali yang identik. Model inversi L0 dipilih karena menghasilkan batas kontras densitas yang lebih tegas dengan rentang –0,24 hingga 0,40 g/cc relatif terhadap 2,67 g/cc sesuai kondisi geologi setempat. Kontras positif tinggi (0,32–0,40 g/cc) di bawah puncak G. Lamongan–Tarub diinterpretasikan sebagai intrusi basaltik yang teridentifikasi mulai kedalaman 50–3000 meter dengan dua jalur intrusi yang melebar hingga kedalaman 3000 meter berorientasi barat daya–timur laut. Sebanyak 9 (Sembilan) dugaan sesar teridentifikasi masing masing 2 segmen di sebelah timur laut G. Tarub, 3 segmen di sebelah selatan Ranu Agung, 1 segmen di utara mata air panas Segaran, dan 3 segmen di sebelah timur yang memotong endapan maar, piroklastik Lamongan, dan batuan vulkanik Argopuro pada kedalaman 0–1000 meter. Sesar-sesar baru yang teridentifikasi diduga menjadi pengontrol terbentuknya sistem panas bumi G. Lamongan.
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The Lamongan Volcanic Complex (LVC) on the border of Lumajang and Probolinggo Regencies in East Java is a monogenetic volcano with a fairly complex subsurface geological system. The presence of hot springs to the east and at the summit of Lamongan indicates a geothermal system associated with fault structures. Subsurface mapping using gravity inversion in this area remains limited and has not yet successfully correlated the presence of hot springs with the Lamongan Volcano geothermal system. This study was conducted to map structural alignment patterns using gravity gradient analysis specifically Tilt Angle, Improved Normalized Horizontal Tilt Angle (INH), and Euler Deconvolution integrated with a subsurface model derived from 3D gravity inversion. Field gravity data from 144 points distributed around Mt. Lamongan–Tarub and the Segaran hot spring were utilized. The 3D gravity inversion was performed on Complete Bouguer Anomaly (CBA) data using a deterministic approach with the gradient-based least-squares method under three types of regularization norms: L2 smooth (P2222), L1 sparse (P1111), and L0 compact (P0111). CBA values in the study area ranged from 1.63 to 23.73 mGal, with high anomalies concentrated around Mt. Lamongan—interpreted as basaltic intrusions and to the east, associated with volcanic products from Mt. Argopuro. Low anomalies, meanwhile, are associated with maar and pyroclastic deposits around the Segaran hot springs. The distribution of the lineaments density map and the analysis of anomaly gradients indicate dominant NW–SE and NE–SW structural orientations, with high density located east of the Lamongan Volcanic Complex. The results of 3D gravity inversion modeling using all three regularization methods show identical contrast and anomaly patterns. The L0 inversion model was selected because it generated a more clear density contrast boundary with a range of –0.24 to 0.40 g/cc relative to 2.67 g/cc, consistent with local geological conditions. The high positive contrast (0.32–0.40 g/cc) beneath the summit of Mt. Lamongan–Tarub is interpreted as a basaltic intrusion identified starting at depths of 50–3,000 meters, with two intrusion zones extending to a depth of 3,000 meters and oriented southwest–northeast. A total of 9 (nine) possible faults were identified, respectively 2 segments northeast of Mt. Tarub, 3 segments south of Ranu Agung, 1 segment north of the Segaran hot spring, and 3 segments to the east that cross maar deposits, Lamongan pyroclastic deposits, and Argopuro volcanic rocks at depths of 0–1,000 meters. The newfound faults are expected to influence the structure of the Mt. Lamongan geothermal system.
| Item Type: | Thesis (Other) |
|---|---|
| Uncontrolled Keywords: | Gayaberat, inversi, struktur densitas, Kompleks Gunungapi Lamongan, Gravity, inversion, density structure, Lamongan Volcanic Complex |
| Subjects: | G Geography. Anthropology. Recreation > G Geography (General) > G70.217 Geospatial data Q Science > Q Science (General) > Q180 Gravitation. Q Science > QE Geology > QE601 Geology, Structural |
| Divisions: | Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Geophysics Engineering > 33201-(S1) Undergraduate Thesis |
| Depositing User: | Athaya Harsya Ramadhanta |
| Date Deposited: | 22 Jul 2026 02:30 |
| Last Modified: | 22 Jul 2026 02:30 |
| URI: | http://repository.its.ac.id/id/eprint/136140 |
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- Pemodelan 3D Gayaberat untuk Memetakan Struktur Densitas di Kompleks Gunungapi Lamongan, Jawa Timur. (deposited 22 Jul 2026 02:30) [Currently Displayed]
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