Abstract
The North Anatolian fault (NAF) is a similar to 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 (M-w > 7) earthquakes that occurred during the twentieth 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 twentieth century that covers much of the last 2000 yr. 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, similar to 6: 5 km east of Lake Ladik (40.868 degrees N, 36.121 degrees E). The trenched fault strand forms an uphill-facing scarp and associated sediment trap below a small catchment area. 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 C-14 ages that were too old (by similar to 900 yr), we obtained highly reliable C-14 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 yr prior to the 1943 Tosya earthquake, including event ages of (2 sigma error): A. D. 1437-1788, A. D. 1034-1321, A. D. 549-719, A. D. 17-585 (1-3 events), 35 B. C.-A. D. 28, 700-392 B. C., 912-596 B. C. Our results indicate an average interevent time of 385 +/- 166 degrees yr (1 sigma).