Probabilistic Seismic Hazard Assessment of Southern Offshore East Java Using Poisson and Gutenberg–Richter Models

Abstract

The southern offshore of East Java, situated along the active Sunda Subduction Zone, faces significant seismic threats from the convergence of the Indo-Australian and Eurasian Plates. This study evaluates earthquake probabilities in this region (8.5°S–12°S, 110°E–115°E) by combining the Gutenberg–Richter law with a stationary Poisson model. Seismicity data from the International Seismological Centre (1996–2025) were declustered using the Gardner and Knopoff method, yielding 1,348 mainshocks. A corrected completeness magnitude  filtered the catalog into a robust dataset of 888 events . The estimated seismic parameters ,  indicate a highly productive tectonic environment dominated by small-to-moderate events. The Kolmogorov–Smirnov test validated the stationary Poisson model  for annual mainshock counts. Temporal extrapolations indicate high seismic hazards over a 50-year horizon, with occurrence probabilities of 92.78% for , 15.42% for , and 1.06% for a megathrust event . These estimates provide a verified quantitative foundation for updating building codes and engineering practices along East Java's vulnerable coastline.