The large-magnitude earthquake potential of an active strike-slip fault system in Lake Poso, Central Sulawesi, Indonesia

Earthquakes along the Ring of Fire are considered among the most destructive on Earth. In Indonesia, 19 earthquakes with a magnitude greater than 7.5 have been recorded in the last 20 years, all causing devastating catastrophes. As witnessed by the 2018 magnitude 7.5 Palu earthquake, extensive areas on the island of Sulawesi are particularly prone to seismic hazards due to the converging Australian, Eurasian, Pacific, and Philippine tectonic plates. However, instrumental records show that extensive areas in the central part of the island appear to be seismically quiet in the last century regarding larger magnitude ≥ 7 earthquakes. Lake sediments are excellent sentinels for environmental changes occurring in its near surroundings, hence they serve as a natural archive for events, including seismicity, thus allowing the investigation of the notion of absence of large-magnitude earthquakes. In 2022, we conducted a geophysical and high-resolution bathymetric survey at Lake Poso to provide insight into seismic activity in Central Sulawesi beyond the instrumental record. The survey allowed us to image large subaquatic slides and lake-bottom offsets, which indicate high-intensity earthquakes, possibly related to the presence of an active local fault system. Our paleoseismological assessment suggests a recurrence of large-magnitude earthquakes every 1600 ± 1450 years over the last 11,000 years. Based on our subsurface observations, the evolution of the tectonic Poso basin indicates that large-magnitude earthquakes are also possible in this region. The consequences of such an event may have devastating consequences for local populations and infrastructures in Sulawesi.