Paleoearthquakes of the Düzce fault (North Anatolian Fault Zone): insights for earthquake recurrence

Abstract

The November 12, 1999, Mw 7.1 earthquake, ruptured the Düzce segment of the North Anatolian Fault Zone and produced a ca. 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 pre-dating 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: AD1685-1900 (possibly end of 19th century); AD1495-1700; AD685-1020 (possibly AD890-1020). The AD967 and AD1878 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 (AD1495-1700) 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 AD 685-1020 (possibly AD890-1020), would yield an average recurrence time for the Düzce fault of 330-430 yr (possibly 330-370 yr). The three most recent earthquakes, including 1999, occurred within 500 yr. Merging results from other paleoseismological studies along the Düzce fault show a consistency of results and yields average recurrence times for the past 2000 yr of 320-390 yr. 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/yr.