Analysis of stress changes on the Poso fault caused by large inland earthquakes: Case study of the 2017 Mw 6.6 Poso and the 2018 Mw 7.5 Palu-Donggala earthquakes

The 2017 Mw 6.6 Poso and the 2018 Mw 7.5 Palu-Donggala represent significant seismic events in central Sulawesi Island. These events transferred the stress to the surrounding faults, which can promote or inhibit the critical condition in a fault, thus evaluating the stress transfer from these earthquakes is crucial for a comprehensive understanding of fault behaviour. In this study, we investigate the effect of these large events by resolving the accumulated Coulomb stress change onto a multi-strike segment of the Poso fault. Additionally, we also used GPS measurement (Global Strain Rate Model) to estimate the increase in tectonic stress rate due to coupling of triple-junction plate convergence. The 2017 Poso earthquake induces positive stress changes (7 kPa to 27 kPa) in the central segment, negative changes (–4 kPa to –10 kPa) in the northern segment, and less significant effects in the southern segment. The 2018 Palu-Donggala earthquake imparts a notably high negative Coulomb stress (–16 kPa to –27 kPa) across the entire northern segment. Cumulatively, both earthquakes reduce Coulomb stress predominantly in the northern part of the Poso fault, suggesting a delayed critical point. Furthermore, the analysis of the Coulomb stress changes time function indicates that stress accumulation in the northern Poso fault is more modulated by large earthquakes, while stress accumulation in the southern segments may be more controlled by longterm tectonic stress loading. The stress accumulation model developed in this study can provide a guidance in better understanding further earthquake risk mitigation in central Sulawesi.