Lateral variations in the signature of earthquake-generated deposits in Lake Iznik, NW Turkey

Abstract

Using lake-sediment cores to document past seismicity requires a comprehensive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake-induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical analyses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1-T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of authigenic Fe-Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub-lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground-motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisations to the coring site.