Paleoearthquakes of the Düzce fault (North Anatolian Fault Zone): Insights for large surface faulting earthquake recurrence

The 12 November 1999 M_w 7.1 earthquake ruptured the Düzce segment of the North Anatolian Fault Zone and produced a ∼40-km-long surface rupture. To improve knowledge about earthquake recurrence on this fault, we undertook paleoseismological trench investigations. We found evidence for repeated surface faulting paleoearthquakes predating the 1999 event during the past millennium. Dating was based on radiocarbon, ²¹⁰Pb analyses, and archaeological considerations. In addition to the 1999 earthquake, prior surface faulting earthquakes are dated as follows: A.D. 1685-1900 (possibly end of 19th century), A.D. 1495-1700, and A.D. 685-1020 (possibly A.D. 890-1020). The A.D. 967 and A.D. 1878 historical earthquakes are good candidates to have ruptured the Düzce fault correlating with the oldest and penultimate paleoearthquakes. No obvious correlation for the third paleoearthquake (A.D. 1495-1700) exists. These results shows that the Düzce fault considerably participates, along with the parallel Mudurnu fault sections, in the seismogenic deformation taking place along this part of the North Anatolian Fault. Four events since A.D. 685-1020 (possibly A.D. 890-1020) would yield an average recurrence time for the Düzce fault of 330-430 years (possibly 330- 370 years). The three most recent earthquakes, including 1999, occurred within 500 years. Merging results from other paleoseismological studies along the Düzce fault show a consistency of results and yields average recurrence times for the past 2000 years of 320-390 years. Assuming that the 1999 slip (2.7 m average, 5 m maximum) is representative of the behavior of this fault, the above recurrence times yield a reference figure of fault slip rate in the range 6.9-15.6 mm/a.