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

Abstract

Abstract The 2017 Mw 6.6 Poso and the 2018 Mw 7.5 Palu-Donggala earthquakes are the most recent large inland earthquakes (Mw ≥ 6.5) that occurred in the central part of Sulawesi Island. These large earthquakes 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 large events could give us a better understanding regarding the fault potential to be advanced towards rupture. In this study, we investigate the effect due to these two large events by resolving the accumulated Coulomb stress change onto a multi-strike segment of the Poso fault. The increase in tectonic stress rate is also estimated which comes from the geodetic measurement of the coupling of triple-junction plate convergence. Based on the stress changes of large earthquake and the tectonic stress rate, we analyse the Coulomb stress changes time function on the Poso fault. The coulomb stress changes on the Poso fault due to the 2017 Poso earthquake vary, ranging from positive values of 7 kPa to 27 kPa in the central segment of the Poso fault, negative values of -4 kPa to -10 kPa in the northern segment of the fault, and less significant effects in the southern segment. The 2018 Palu-Donggala earthquake transferred a relatively high negative Coulomb stress ranging from -16 kPa to -27 kPa in the entire northern segment of the fault. Additionally, the cumulative Coulomb stress of both earthquakes decreased the Coulomb stress mainly on the northern part of the Poso fault, suggesting a delay in reaching its critical point. Furthermore, the analysis of the Coulomb stress changes time function shows that the stress accumulation of some segments in the north of the Poso fault are more modulated by the stress release due to large inland earthquakes while stress accumulation in the southern segments of the Poso fault are more controlled by the long-term tectonic stress loading.