Updated comprehensive probabilistic seismic hazard analysis of the Andaman-Nicobar and Sumatra regions

Abstract

The Andaman-Sumatra subduction zone is among the most seismically active regions on Earth and has generated several great earthquakes (M w ≥ 8.0) in recent decades. This study presents an updated probabilistic seismic hazard assessment (PSHA) for the Andaman-Nicobar and Sumatra regions using a homogenized earthquake catalog spanning 1881–2025 comprising 37,660 events compiled from multiple global and regional agencies. The catalog was homogenized to moment magnitude (M w ) using region-specific conversion relations, declustered using established techniques, and evaluated through temporal and magnitude completeness analyses. Seismic sources were represented using three complementary approaches: tectonically defined areal source zones, fault-based linear source zones, and a gridded point source model constructed on a 0.1° × 0.1° spatial grid. Seismicity parameters were estimated using source specific magnitude of completeness (M c ) values derived from frequency-magnitude distribution analysis. Four ground motion prediction equations (GMPEs) were selected from an initial set of eleven through statistical evaluation of strong motion records and weighted using a log-likelihood approach. Epistemic uncertainties were incorporated through a 72-branch logic tree framework. The resulting hazard maps indicate peak ground acceleration (PGA) values of 0.25–0.40 g for 10% probability of exceedance (PoE) in 50 years, increasing to 0.40–0.70 g for 2% PoE along the Sunda megathrust and Nicobar segment. The results highlight the significant seismic hazard associated with both megathrust and intraplate sources and provide an improved regional hazard framework for engineering design and seismic risk mitigation.