The Surface Rupture and Slip Distribution of the 17 August 1999 Izmit Earthquake (M 7.4), North Anatolian Fault

The 17 August 1999 I ˙zmit earthquake occurred on the northern strand of the North Anatolian fault zone.The earthquake is associated with a 145-km-long surface rupture that extends from southwest of Du ¨zce in the east to west of Hersek delta in the west.Detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step-overs; herein named the Hersek, Karamu ¨rsel-Go ¨lcu ¨k, I ˙zmit-Sapanca Lake, Sapanca-Akyazi, and Karadere segments from west to east, respectively.The Hersek segment, which cuts the tip of a large delta plain in the western end of the rupture zone, has an orientation of N80Њ.The N70Њ-80ЊE-trending Karamu ¨rsel-Go ¨lcu ¨k segment extends along the linear southern coasts of the I ˙zmit Gulf between Karamu ¨rsel and Go ¨lcu ¨k and produced the 470-cm maximum displacement in Go ¨lcu ¨k.The northwest-southeast-striking Go ¨lcu ¨k normal fault between the Karamu ¨rsel-Go ¨lcu ¨k and I ˙zmit-Sapanca segments has 2.3-m maximum vertical displacement.The maximum dextral offset along the I ˙zmit-Sapanca Lake segment was measured to be about 3.5 m, and its trend varies between N80ЊE and east-west.The Sapanca-Akyazi segment trends N75Њ-85ЊW and expresses a maximum displacement of 5.2 m.The Karadere segment trends N65ЊE and produced up to 1.5-m maximum displacement.The Karadere and Sapanca-Akyazi segments form fan-shape or splaying ruptures near their eastern ends where the displacement also diminished.