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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. [ABSTRACT FROM AUTHOR]

Our study aims to understand the palaeohydrological history of Lake Iznik and unravel the complex interplay between climatic, tectonic, and environmental factors that have shaped this Turkish basin. Through the analysis of seismic stratigraphy and sediment cores, we reveal a significant lowstand, indicating a lake level 60 m lower than today at ∼70 ka BP. Subsequently, a major phase of stepwise transgression is evidenced by 13 buried palaeoshorelines between ∼70 and 45 ka BP. From 45 to ∼10 ka cal BP, strong currents controlled the sedimentation in the lake, as evidenced by the occurrence of contourite drifts. Between ∼14 and 10 ka cal. BP, a major lowstand indicating a drier climate interrupted the current-controlled sedimentation regime. From ∼10 ka cal. BP, the subsequent increase in lake level occurred at the same time as the reconnection between the Mediterranean and Black seas. Archaeological evidence, including submerged structures of a basilica, establishes a link between lake-level changes and human settlement during the last millennium. The level of Lake Iznik has since continued to fluctuate due to climate change, tectonic events, and human activity. • Seismic data and sediment cores revealed Lake Iznik's past level fluctuations. • Thirteen paleoshorelines show a stepwise transgressional phase (>45 ka cal. BP). • Strong currents lead to contourite drift deposits from ∼45 to ∼10 ka cal. BP. • A ∼50 m lowstand at ∼10 ka cal. BP indicates a much drier climate. • Ongoing lake-level fluctuations due to climate, tectonics, and human impact [ABSTRACT FROM AUTHOR]