Rupture zones in the area of the 17.08.99 Izmit (NW Turkey) large earthquake (M-w 7.4) and stress changes caused by its generation

The M-w 7.4 Izmit earthquake of 17 August 1999 struck a part of the North A natolian fault in the area of Izmit Bay (NW Turkey). Historical information shows that the fault which moved during the generation of this earthquake consists of two fault segments moved during the generation of large (M simi lar to 7) earthquakes in 1719 and 1754, respectively. Since then only the c entral part (between Izmit and Lake Sapanca) of this fault ruptured by the generation of a smaller shock (M = 6.6) in 1878. The spatial stress variati ons based on the calculation of changes in the Coulomb Failure Function (De lta CFF) associated with this earthquake are supported by the distribution of strong aftershock foci. Large positive values of Delta CFF to the east a nd west of the mainshock epicenter are in agreement with the notion that se condary faults were triggered there by the generation of the main event. La rge positive values of Delta CFF are also observed in the adjacent western fault segment where the 1766 event was generated, evidencing the occurrence of the next strong earthquake in this segment.