High slip rate for a low seismicity along the Palu-Koro active fault in central Sulawesi (Indonesia)

Accurate chronological records are critical for understanding the landformsevolution, and, in particular, of alluvial fan sequences emplaced during glocal/global climatic changes. Toward this end, we measured in-situ-produced 10Be in quartz boulders exposed on top surfaces of Sulawesian Late Quaternary alluvial fans. Combined geomorphic study(SPOT image and field analyses) indicate that this site is composed of twoalluvial fan units. In situ-produced 10Be concentrations suggest that they were emplaced during two successive major climatic events. The calculated minimum exposure ages date the younger unit abandonment at 11,000±2,000 years and seem consistent with a Late Interglacial abandonment age (~120,000years) for the older unit. This study demonstrates that using both the neutron and muon components implicated in the production of in situ10Be, surficial erosion rates can be estimated (~6 m/Ma in Sulawesi )and alluvial fan surfaces dated. In particular, it shows that10Be may be used to date fan surface emplacement during the last 120 ka under humid tropical conditions, significantly helping to constrain continental paleo-climatology in these regions.