Timing of Late Holocene Earthquakes on the Eastern Düzce Fault and Implications for Slip Transfer between the Southern and Northern Strands of the North Anatolian Fault System, Bolu, Turkey

Authors: CHRISTOPHER HITCHCOCK, ERHAN ALTUNEL, A. AYKUT BARKA, JEFFREY BACHHUBER, WILLIAM LETTIS, JOHN HELMS, SCOTT LINDVALL

Abstract: Results of trenching across the eastern Düzce Fault document that surface rupture has occurred repeatedly on the fault prior to the 1999 Düzce earthquake, and that offset during previous earthquakes occurred at the same location and with similar amounts and type of slip as that of the 1999 earthquake. The most recent pre-1999 earthquake on the fault occurred about 300 years ago. At least four and possibly five earthquakes (including 1999) have occurred in the past 2100 years. The earthquake recurrence interval ranges from 300 to 800 years. Estimates of cumulative slip on the northern and southern branches of the North Anatolian Fault System (NAFS) (including the Düzce Fault) show that most, if not all, accumulated elastic strain on the fault has been coseismically released at this location. Based on our mapping and palaeoseismic data, it appears likely that the southern and northern strands of the NAFS are structurally and kinematically linked in the vicinity of Bolu by active secondary faults, including the Elmalık and Bakacak faults. These faults extend along the western boundary of the Bolu Basin, between the Düzce Fault and the southern strand of the NAFS. The documented 1999 rupture on the Bakacak Fault and palaeoseismic evidence of previous Holocene displacement strongly suggest that the Bakacak and Elmalık faults transfer slip between the strands of the NAFS.

Keywords: North Anatolian Fault System, slip transfer, active fault, palaeoseismology, Holocene

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