Aftershock activity from 17 August 1999 to 16 October 1999 depicting the fault rupture zone of the Izmit earthquake (Ito et al., 2002). The star indicates the hypocenter of the mainshock. The capital letters A–G are used to name the cluster zones (A, Çinarcik; B, Yalova; C, Gölcük; D, İzmit; E, Sapanca; F, Sakarya-Akyazı; G, Karadere). KB, Karamürsel basin; HP, Hersek peninsula; LSB, Lake Sapanca basin. The location names mentioned in the text are also shown. The surface slip data associated with the fault segments are numbered from 1 to 5 and originate from Aydın and Kalafat (2002). The upper dotted line indicates the co-seismic slip model for the mainshock based on GPS data (Reilinger et al., 2000). The upper right corner of the figure shows the Eurasian and Anatolian plates and the trace of the North Anatolian Fault Zone (NAFZ).