Investigating Stress Transfer and Fault Interaction in the July‑August 2025 Poso and Tokararu Earthquakes, Central Sulawesi, Indonesia

Abstract

The July‑August 2025 earthquake in Central Sulawesi, which consisted of the Mw 5.9 Poso strike‑slip event and the Mw 6.0 Tokararu thrust event, offers new insights into stress transfer and fault interaction in a tectonically complex setting. We combined Coulomb stress modeling, HypoDD aftershock relocation, and ascending‑track DInSAR analysis to investigate the sequence. Relocation of 669 events sharpened fault geometries, with aftershocks of the Poso earthquake clustering along the Poso‑West segment and those of Tokararu aligning on a shallow thrust plane. Coulomb stress modeling shows that aftershocks correlate well with positive ΔCFS lobes for both events, supporting static stress transfer as a key mechanism, though no significant positive stress was transferred from Poso to Tokararu. DInSAR results reveal both pre‑ and co‑seismic deformation, with uplift reaching +16 cm and subsidence –13 cm at Poso, and uplift up to +13 cm and subsidence –14 cm at Tokararu. These signals suggest strain accumulation and possible aseismic slip preceding rupture. Geological contrasts within the Pompangeo Complex, where weak alluvial sediments overlie stronger metamorphic basement rocks, further explain the differences in rupture style. Together, these multidisciplinary findings highlight the interplay of tectonic loading, fault mechanics, and lithological heterogeneity in shaping cascading earthquake hazards in Central Sulawesi.