Active fault map and paleoseismology results from the Aceh Fault in North Sumatra, Indonesia: Unravelling faulting dynamics along the Great Sumatran Fault system

Abstract

The Aceh Fault, a major strike-slip fault forming the northernmost segment of Great Sumatran Fault, exhibits recent faulting through prominent scarps along its 250-km length. Running northwest-southeast, it traverses northwestern Sumatra from Tripa to Banda Aceh, a city of over 268,000 residents that is more commonly associated with the 2004 tsunami, but also lies directly on this active fault zone. Understanding the earthquake rupture history, including pre-instrumental events, is essential to characterize long-term seismic patterns and to assess associated hazards. We investigated the fault using 8-m resolution DEM (DEMNAS) for the entire fault zone, 15-cm resolution lidar DEM for selected areas, field mapping, and paleoseismology. Two paleoseismic trenches excavated in the Geumpang area reveal evidence of at least three ground-rupturing earthquakes over the past ∼1000 years. Event timing was constrained by radiocarbon analysis of detrital charcoal, providing sufficient chronological control to identify two well-dated events and one older event with lower precision. These results confirm that the Aceh Fault is active, delineate its surface trace, and offer the first detailed record of prehistoric earthquakes along this fault. This information contributes to improved seismic hazard mapping and a clearer understanding of tectonic risk in the Banda Aceh region.