Seismic hazard in the Marmara Sea region following the 17 August 1999 Izmit earthquake

On 17 August 1999, a destructive magnitude 7.4 earthquake occurred 100 km e ast of Istanbul, near the city of Izmit, on the North Anatolian fault. This 1,600-km-long plate boundary(1,2) slips at an average rate of 2-3 cm yr(-1 ) (refs 3-5), and historically has been the site of many devastating earthq uakes(6,7). This century alone it has ruptured over 900 km of its length(6) . Models of earthquake-induced stress change(8) combined with active fault maps(9) had been used to forecast that the epicentral area of the 1999 Izmi t event was indeed a likely location for the occurrence of a large earthqua ke(9,10). Here we show that the 1999 event itself significantly modifies th e stress distribution resulting from previous fault interactions(9,10). Our new stress models take into account all events in the region with magnitud es greater than 6 having occurred since 1700 (ref. 7) as well as secular in terseismic stress change, constrained by GPS data(11). These models provide a consistent picture of the long term spatio-temporal behaviour of the Nor th Anatolian fault and indicate that two events of magnitude equal to, or g reater than, the Izmit earthquake are likely to occur within the next decad es beneath the Marmara Sea, south of Istanbul.