Estimation of seismogenic depth and seismic coupling for improving seismic hazard assessment in Sulawesi

Sulawesi is characterized by complex interactions among major tectonic systems, producing strong spatial variations in seismicity and fault behavior. This study develops an integrated framework to characterize seismogenic depth, seismic coupling coefficient (SCC), and coupled thickness (CZ) across Sulawesi. A declustered earthquake catalog was grouped into 32 seismic clusters and analyzed to estimate cluster-specific magnitude of completeness, Gutenberg–Richter parameters, and frequency–magnitude distributions (FMD). Seismic moment rates were estimated by extrapolating the FMD toward alternative maximum-magnitude (Mmax) scenarios, whereas tectonic moment rates were evaluated using fault geometry, slip rate, rupture-width (W), and crustal-rigidity (μ) scenarios. The results reveal substantial spatial variability in seismogenic depth and SCC across different tectonic settings. Sensitivity and statistical analyses show that SCC estimates are systematically influenced by Mmax, rigidity, and rupture-width assumptions, demonstrating that representative coupling cannot be reliably defined from a single parameter combination. Representative SCC values were therefore identified using a rule-based framework integrating physical admissibility, sensitivity to rigidity, and stability across parameter ranges. Of the 32 seismic clusters, 22 yielded admissible SCC solutions and were subsequently used for SCC–CZ characterization. Combining the selected SCC with seismogenic depth yields CZ, enabling a classification that distinguishes tectonic zones according to relative coupling and coupled seismogenic thickness. Because the estimates remain conditional on catalog completeness, FMD extrapolation, fault geometry, rigidity, slip rate, and Mmax, SCC and CZ are interpreted as relative indicators rather than direct measures of fault locking or earthquake probability. The framework provides a reproducible basis for integrating seismic moment budgets and seismogenic structure into regional seismic-hazard characterization.