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ANALISIS SPASIAL BERBASIS SISTEM INFORMASI GEOGRAFIS (SIG) UNTUK PEMETAAN BAHAYA DAN RISIKO TANAH LONGSOR DI KABUPATEN LAMPUNG UTARA Efriyanti, Annisa; Farduwin, Alhada; Styawan, Yudha
JOURNAL ONLINE OF PHYSICS Vol. 11 No. 1 (2025): JOP (Journal Online of Physics) Vol 11 No 1
Publisher : Prodi Fisika FST UNJA

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22437/jop.v11i1.49284

Kabupaten Lampung Utara termasuk daerah rawan tanah longsor yang telah mengalami kejadian dalam beberapa tahun terakhir. Penelitian dilakukan untuk menganalisis tingkat risiko tanah longsor melalui pendekatan Sistem Informasi Geografis (SIG) melalui komponen ancaman (hazard), kerenatan (vulnerability), dan kapasitas (capacity). Setiap komponen dibentuk berdasarkan parameter fisik dan social seperti curah hujan, kemiringan lereng, jenis tanah, tutupan lahan, geologi, kepadatan penduduk, serta ketersediaan sarana dan prasarana umum. Parameter tersebut diberikan skor dan bobot sesuai tingkat pengaruhnya, kemudian diolah menggunakan metode overlay spasial. Hasil analisis menunjukkan bahwa nilai indeks risiko tanah longsor berkisar antara 0,933-2,3 dan terbagi menjadi tiga kelas yaitu risiko rendah seluas 1.664,436 km², risiko sedang 754,743 km², dan risiko tinggi 39,820 km². Wilayah dengan risiko tinggi terindentifikasi di Kecamatan Tanjung Raja, Bukit Kemuning, dan sebagian Abung Tengah, sedangkan risiko rendah umumnya berada di bagian timur dan utara Kabupaten Lampung Utara. Secara umum, semakin tinggi tingkat ancaman dan kerentanan serta rendahnya kapasitas masyarakat di suatu daerah, maka semakin besar tingkat risiko tanah longsor yang berpotensi terjadi.

Pemodelan 3D Perubahan Coulomb Stress Pasca-Gempa Seram Pada 5 Mei 2024 Dengan Magnitudo 6.1 Mw Riski Wahyudi; Laila Auliya; Purwaditya Nugraha; Nugroho Prasetyo; Yudha Styawan
Geosfera: Jurnal Penelitian Geografi Vol 4, No 2 (2025): Geosfera : Jurnal Penelitian Geografi
Publisher : Universitas Negeri Gorontalo

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.37905/geojpg.v4i2.34961

This study aims to analyze Coulomb stress changes following the Mw 6.1 earthquake in Seram on May 5, 2024, in order to identify potential subsequent seismic hazards. The methodology employed numerical modeling using Coulomb 3.4 to calculate stress distribution, which was then visualized through spatial interpolation in both 2D maps and 3D cross-sections. The 2D modeling results reveal zones of significant stress increase that spatially correlate with the locations of major earthquakes in 1993 and 1998. The 3D analysis further indicates stress concentration at shallow to intermediate depths (0–12 km), consistent with the distribution of recorded aftershocks, thereby validating the reliability of the model. Additionally, stress transfer was detected toward surrounding faults, particularly the Seram strike-slip segment and the Bobot fault segment. In conclusion, this research demonstrates that Coulomb stress modeling provides a quantitative framework for assessing post-seismic stress evolution and constitutes a crucial basis for disaster mitigation efforts in the tectonically complex Maluku region.

Pemetaan Ancaman dan Risiko Bencana Tanah Longsor Menggunakan Sistem Informasi Geografis di Kabupaten Lampung Barat Maisyaroh, Siti; Farduwin, Alhada; Styawan, Yudha
(JITEK)Jurnal Ilmiah Teknosains Vol 12, No 1/Now (2026): Vol.12 No. 1 Mei 2026
Publisher : Universitas PGRI Semarang

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.26877/jitek.v12i1/Now.27319

Kabupaten Lampung Barat termasuk daerah yang memiliki kondisi topografi berbukit hingga pegunungan dengan kemiringan lereng bervariasi dari datar hingga sangat curam, sehingga berpotensi tinggi terhadap kejadian tanah longsor ketika terjadi hujan. Penelitian ini bertujuan untuk memetakan tingkat ancaman dan risiko bencana tanah longsor di Kabupaten Lampung Barat menggunakan pendekatan Sistem Informasi Geografis (SIG). Analisis dilakuka dengan metode weighted overlay terhadap beberapa parameter yaitu curah hujan, kemiringan lereng, jenis batuan, tutupan lahan, jenis tanah dan keberadaan sesar. Masing-masing parameter diklasifikasikan, diberi skor dan bobot sesuai pengaruhnya terhadap terjadinya bencana tanah longsor.Pemetaan ancaman dilakukan dengan mengintegrasikan seluruh parameter melalui proses overlay yang kemudian diklasifikasikan menjadi tiga kelas yaitu rendah, sedang, dan tinggi. Analisis risiko dilakukan melalui integrasi peta ancaman dengan peta kerentanan dan kapasitas. Hasil penelitian menunjukkan bahwa tingkat ancaman longsor didominasi oleh kelas sedang dengan indeks (2,72-3,38) hingga tinggi dengan indeks (3,38-4,05). Sementara itu tingkat risiko longsor diperoleh indeks rendah (1,3-2,6), sedang (2,6-4), dan tinggi (4-5,3).kata kunci: ancaman; longsor; overlay; risiko; SIG

Spatial-Temporal Analysis of b-value Before and After the 2018 Lombok Earthquake Using OK1993 Based on Voronoi in the Bali-NTB Region Tata Dwi Hardi Yanti; Yudha Styawan; Rizki Wulandari
EKSAKTA: Berkala Ilmiah Bidang MIPA Vol. 27 No. 03 (2026): Eksakta : Berkala Ilmiah Bidang MIPA (E-ISSN : 2549-7464) In Progress
Publisher : Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Negeri Padang, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/eksakta/vol27-iss03/678

This study is motivated by the tectonic complexity of the Bali-NTB region, which results in a heterogeneous seismic distribution and active stress dynamics. The objective is to analyze the spatiotemporal evolution of the b-value using the Ogata-Katsura maximum likelihood estimation (OK1993), combined with Voronoi tessellation as an adaptive spatial partition and the Bayesian Information Criterion (BIC) for ensemble model optimization. Spatial analysis prior to the 2018 event revealed a contradiction in the form of high b-value (>1.0) in Lombok. However, the spatiotemporal analysis successfully explains the condition by identifying a zone of low b-value (<1.0) that developed following the 2007 intermediate sized earthquake through the 2018 mainshock distinct from the 2004 local anomaly that did not progress into a major earthquake. This indicates that the persistence of low b-values is a key indicator of high stress accumulation. Following the 2018 earthquake, the high stress zone expanded across Lombok and West Nusa Tenggara (NTB). This study emphasizes the importance of evaluating statistical reliability, such as N(b) and Median Absolute Deviation (MAD), to avoid misinterpretations due to data limitations, thereby providing a more reliable framework for regional seismic hazard assessment.

Peak Ground Acceleration Mapping of Indonesia Using Complementary Area Source and Smoothed Seismicity Approaches Eka Nioisa Br Surbakti; Ardian Saputra; Rizki Wulandari; Yudha Styawan
EKSAKTA: Berkala Ilmiah Bidang MIPA Vol. 27 No. 03 (2026): Eksakta : Berkala Ilmiah Bidang MIPA (E-ISSN : 2549-7464) In Progress
Publisher : Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Negeri Padang, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/eksakta/vol27-iss03/684

In Indonesia, the choice between area source and smoothed seismicity approaches has been driven by data availability rather than scientific evaluation, and no systematic comparison of both methods at the national scale has been conducted. This study compared both approaches across Indonesia to evaluate their differences in PGA estimation and assess the forecasting skill of the smoothed seismicity model. Both models were applied to the same declustered earthquake catalog with a Magnitude of Completeness of 4.7, b-value of 0.89, and a-value of 8.753, using identical Ground Motion Prediction Equations within a probabilistic seismic hazard analysis framework. Both models consistently identified North Sulawesi as the highest hazard region and Kalimantan as the lowest. The smoothed seismicity model produced higher maximum PGA values of 2.13 g compared to 1.1597 g and 1.5901 g from the area source model at 10% and 2% probability of exceedance in 50 years, respectively. Molchan Diagram validation yielded an Area Skill Score of 0.88 and R-score of 0.656, confirming strong forecasting skill. The two methods are complementary, and their integration within a logic tree framework is recommended for future national-scale PSHA in Indonesia.

Soil characterization for seismic vulnerability and preliminary subsidence assessment based on microtremor analysis in Sukarame District, Bandar Lampung Antosia, Risky Martin; Endryanti, Windy Meylana; Farduwin, Alhada; Rizki, Reza; Styawan, Yudha
Journal of Degraded and Mining Lands Management Vol. 13 No. 3 (2026)
Publisher : Brawijaya University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15243/jdmlm.2026.133.10439

This research estimated soil properties and land stability in Sukarame District, Bandar Lampung, using multi-parameter microtremor-derived H/V spectral ratio (HVSR) values and spaceborne InSAR deformation data. The study area is mainly composed of unconsolidated Quaternary volcanic deposits with an average natural frequency ( ) of about 2 Hz and a moderate amplification factor ( ) value of 4. Such parameters, together with an average seismic vulnerability index ( ), of 11s strongly point to substantial impedance contrasts in the sediments and a large overall sediment thickness. To validate the physical effects of these features, a Multi-Temporal InSAR analysis was applied using satellite observations. Results showed a strong land subsidence rate, with a difference in distance from the satellites up to -25 cm for certain sectors. Spatially problematic zoning corresponded to the area with higher near-surface stiffness ( ranges of 400-470 m/s) along the territories with large subsidence rates. This relationship showed that higher. and shallow material solidness are not sufficient conditions for stability against vertical deformation (also referred to as settlement), as substantial consolidation is likely to result from the significant load applied to the soil and groundwater extraction due to population pressure in these urban areas. These results highlight that must be used with caution and interpreted in conjunction with geodetic data for an integrated stability analysis. This integrated model is useful as a general guideline for land stability management, infrastructure hazard preparedness, and disaster-resilient spatial planning in the rapidly developing Sukarame District.

Analysis of Fault Plane and Distribution of Coulomb Stress Changes of the Mw 7.8 Earthquake Southwest of Sumatra Gabriela Gabriela; Kelly Lasofia Br Girsang; Rizki Wulandari Wulandari; Yudha Styawan
EKSAKTA: Berkala Ilmiah Bidang MIPA Vol. 27 No. 03 (2026): Eksakta : Berkala Ilmiah Bidang MIPA (E-ISSN : 2549-7464) In Progress
Publisher : Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Negeri Padang, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/eksakta/vol27-iss03/701

The Mw 7.8 earthquake that occurred southwest of Sumatra on March 2, 2016, at a depth of 24 km represents a major seismic event within the Sunda subduction zone, significantly influencing regional stress conditions. This study aims to analyze Coulomb stress changes (Δσc), examine stress distribution patterns, and evaluate the most representative fault plane controlling the earthquake source mechanism. The analysis was conducted using the Coulomb Stress Change method based on focal mechanism parameters and finite fault models obtained from the United States Geological Survey (USGS). The results indicate that Nodal Plane 1 (NP1) represents the true fault plane controlling the earthquake mechanism, with maximum stress increase of up to 0.1 bar and orientations from west–east to northwest–southeast. In contrast, Nodal Plane 2 (NP2) acts as a receiver fault, accommodating transferred stress from the main rupture, with similar stress magnitudes oriented north–south to west–east. The observed stress increases on both nodal planes highlight potential zones for aftershock occurrence. This study contributes to a better understanding of earthquake source mechanisms and stress redistribution patterns that may trigger subsequent seismic activity in the southwest region of Sumatra..

Integrating Time-Dependent and Time-Independent Earthquake Recurrence Models for Fault-Based Seismic Hazard Assessment in the Lampung Region, Southern Sumatra Rizki Wulandari; Yudha Styawan; Satria Bagus Prabowo
Spektra: Jurnal Fisika dan Aplikasinya Vol. 11 No. 1 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 1, April 2026
Publisher : Program Studi Fisika Universitas Negeri Jakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21009/SPEKTRA.111.05

The Lampung region in southern Sumatra is exposed to significant seismic hazard due to its proximity to the Sunda megathrust and multiple active crustal faults. This study integrates time-independent (Poissonian) and time-dependent (Brownian Passage Time/BPT) earthquake recurrence models to evaluate fault-specific rupture probabilities and their implications for probabilistic seismic hazard assessment (PSHA). This approach systematically bridges the gap between traditional stationary models and the physical reality of seismic cycles, ensuring that the resulting hazard estimates reflect the current elapsed time since the last major rupture. Earthquake catalogs from USGS, BMKG, and historical sources were compiled for shallow events ( 50 km) between 1900–2023, and fault parameters were derived from national hazard maps and published geological studies. Recurrence intervals were estimated for 28 major fault segments across Sumatra, the Sunda Strait, and western Java. Results show strong temporal variability in seismic potential, with the Kumering South segment exhibiting the highest 50-year rupture probability (>50%) due to its elapsed time nearing the estimated recurrence interval. In contrast, segments such as Semangko West-A show markedly reduced short-term probability under the BPT model. PSHA simulations using OpenQuake reveal peak ground acceleration (PGA) values of 0.6–1.5 g for 2% exceedance in 50 years, indicating very high hazard levels in areas adjacent to the Sumatra Fault System. Incorporating time-dependent recurrence provides a more cycle-consistent spatial pattern compared to Poissonian results, reducing overestimation in early-cycle segments and enhancing hazard representation in late-cycle faults. While this study is constrained by uncertainties in historical recurrence intervals and fault slip-rates, these findings provide a more refined academic contribution to regional hazard characterization, supporting more robust risk mitigation strategies in Lampung Province.

Spatial-Temporal Analysis of b-value Before and After the 2018 Lombok Earthquake Using OK1993 Based on Voronoi in the Bali-NTB Region Tata Dwi Hardi Yanti; Yudha Styawan; Rizki Wulandari
EKSAKTA: Berkala Ilmiah Bidang MIPA Vol. 27 No. 03 (2026): Eksakta : Berkala Ilmiah Bidang MIPA (E-ISSN : 2549-7464)
Publisher : Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Negeri Padang, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/eksakta/vol27-iss03/678

This study is motivated by the tectonic complexity of the Bali-NTB region, which results in a heterogeneous seismic distribution and active stress dynamics. The objective is to analyze the spatiotemporal evolution of the b-value using the Ogata-Katsura maximum likelihood estimation (OK1993), combined with Voronoi tessellation as an adaptive spatial partition and the Bayesian Information Criterion (BIC) for ensemble model optimization. Spatial analysis prior to the 2018 event revealed a contradiction in the form of high b-value (>1.0) in Lombok. However, the spatiotemporal analysis successfully explains the condition by identifying a zone of low b-value (<1.0) that developed following the 2007 intermediate sized earthquake through the 2018 mainshock distinct from the 2004 local anomaly that did not progress into a major earthquake. This indicates that the persistence of low b-values is a key indicator of high stress accumulation. Following the 2018 earthquake, the high stress zone expanded across Lombok and West Nusa Tenggara (NTB). This study emphasizes the importance of evaluating statistical reliability, such as N(b) and Median Absolute Deviation (MAD), to avoid misinterpretations due to data limitations, thereby providing a more reliable framework for regional seismic hazard assessment.

Peak Ground Acceleration Mapping of Indonesia Using Complementary Area Source and Smoothed Seismicity Approaches Eka Nioisa Br Surbakti; Ardian Saputra; Rizki Wulandari; Yudha Styawan
EKSAKTA: Berkala Ilmiah Bidang MIPA Vol. 27 No. 03 (2026): Eksakta : Berkala Ilmiah Bidang MIPA (E-ISSN : 2549-7464)
Publisher : Faculty of Mathematics and Natural Sciences (FMIPA), Universitas Negeri Padang, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24036/eksakta/vol27-iss03/684

In Indonesia, the choice between area source and smoothed seismicity approaches has been driven by data availability rather than scientific evaluation, and no systematic comparison of both methods at the national scale has been conducted. This study compared both approaches across Indonesia to evaluate their differences in PGA estimation and assess the forecasting skill of the smoothed seismicity model. Both models were applied to the same declustered earthquake catalog with a Magnitude of Completeness of 4.7, b-value of 0.89, and a-value of 8.753, using identical Ground Motion Prediction Equations within a probabilistic seismic hazard analysis framework. Both models consistently identified North Sulawesi as the highest hazard region and Kalimantan as the lowest. The smoothed seismicity model produced higher maximum PGA values of 2.13 g compared to 1.1597 g and 1.5901 g from the area source model at 10% and 2% probability of exceedance in 50 years, respectively. Molchan Diagram validation yielded an Area Skill Score of 0.88 and R-score of 0.656, confirming strong forecasting skill. The two methods are complementary, and their integration within a logic tree framework is recommended for future national-scale PSHA in Indonesia.

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