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All Journal Eksakta : Berkala Ilmiah Bidang MIPA
Yudha Styawan
Department of Geophysical Engineering, Faculty of Industrial Technology, Institut Teknologi Sumatera, Lampung, Indonesia
Agriculture, Biological Sciences & Forestry Astronomy Biochemistry, Genetics & Molecular Biology Chemical Engineering, Chemistry & Bioengineering Chemistry Civil Engineering, Building, Construction & Architecture Computer Science & IT Energy Engineering Environmental Science Materials Science & Nanotechnology Mathematics Mechanical Engineering

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 1 
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

Abstract

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..
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

Abstract

 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.
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)
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

Abstract

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..
Co-Authors Ardian Saputra Eka Nioisa Br Surbakti Gabriela Gabriela Kelly Lasofia Br Girsang Rizki Wulandari Rizki Wulandari Wulandari