The 12 November 1999 earthquake (M7.1) occurred on the Duzce fault, a splay of the North Anatolian fault in the Bolu basin approximately three months after the 17 August 1999 (M 7.4) earthquake. The surface rupture was 40 km long, and the maximum right-lateral offset was 500 5 cm, averaging 300 cm. The 9 km of the westernmost part of the rupture along the southern margin of the Eften Lake had a 350-cm maximum vertical displacement (normal faulting), some of which was already ruptured during the 17 August 1999 event with few tens of centimeters. The surface rupture has a generally simple narrow deformation zone of 0.5-5 m, however, in some places, it widens to 50 m. Transtensional and transpressional structures were observed within releasing and restraining step-over areas respectively. The larger dextral offsets on some streams indicate previous events. The dextral slip measurements along the rupture reflect a symmetric distribution. The eastern connection of this rupture zone with the main trace of North Anatolian fault remains unclear because the Bakacak and Elmalik fault, which are connecting faults, had no surface rupture.