A 3000-year record of ground rupturing earthquakes along the central North Anatolian Fault near Lake Ladik, Turkey

The North Anatolian Fault (NAF) is a ~1500-km-long, arcuate, dextral strike-slip fault zone in northern Turkey that extends from the Karliova triple junction to the Aegean Sea. East of Bolu, the fault zone exhibits evidence of a sequence of large (Mw>7) earthquakes that occurred during the 20th century that displayed a migrating earthquake sequence from east to west. Prolonged human occupation in this region provides an extensive, but not exhaustive, historical record of large earthquakes prior to the 20th century that covers much of the last 2000 years. In this study, we extend our knowledge of rupture events in the region by evaluating the stratigraphy and chronology of sediments exposed in a paleoseismic trench across a splay of the NAF at Destek, ~6.5 km east of Lake Ladik (40.868°N, 36.121°E). The trenched fault strand forms an uphill-facing scarp and associated sediment trap below a small catchment. The trench exposed a narrow fault zone that has juxtaposed a sequence of weakly-defined paleosols interbedded with colluvium against highly-fractured bedrock. We mapped magnetic susceptibility variations on the trench walls and found evidence for multiple visually unrecognized colluvial wedges. This technique was also used to constrain a predominantly dip-slip style of displacement on this fault splay. Sediments exposed in the trench were dated using both charcoal and terrestrial gastropod shells to constrain the timing of the earthquake events. While the gastropod shells consistently yielded 14C-ages that were too old (by ~900 years), we obtained highly reliable 14C-ages from the charcoal by dating multiple components of the sample material. Our radiocarbon chronology constrains the timing of seven large earthquakes over the past 3000 years prior to the 1943 Ladik earthquake, including event ages (including 2 sigma error):1437-1788AD, 1034-1321AD, 549-719AD, 17-585AD (1-3 events), 351BC-28AD, 700-392BC, 912-596BC. Our results indicate an average inter-event time of 385±166yrs (1 sigma)Understanding the Irregularity of Seismic Cycles: A Case Study in Turke