Preliminary Results of the Paleoseismology of Aceh Fault in northern Sumatra, Indonesia

The Aceh Fault, part of Indonesia's Great Sumatran Fault System, exhibits recent faulting through prominent scarps along its 250-kilometer length. Running northwest-southeast, it spans northwestern Sumatra from Tripa to Banda Aceh, a city of over 268,000 residents. Understanding the complete faulting history is essential for assessing seismic risk, as instrumental records are too recent to capture long-term patterns. We study the fault by combining remote sensing using 8-m resolution DEM (DEMNAS) for the entire area and 15-cm resolution (LiDAR drone survey) for selected areas, field methods, and paleoseismology. We excavated two paleoseismic trenches across the fault and documented evidence of at least three well-dated ground-rupturing earthquakes from the upper 2 meters of strata spanning the last ~1000 years. The event chronology is constrained by 15 radiocarbon dates on detrital charchoal. This new paleoseismic data confirms that the Aceh Fault is active. Our study delineates the active trace of the fault zone and provides the first detailed information about significant prehistoric earthquakes along this fault. These findings improve seismic hazard maps and enhance understanding of the region's seismic risks.