Izmit Earthquake and Marmara Sea

Closeup of western part of  the North Anatolian Fault in the Marmara  Sea region. The fault segment to the west of the Marmara Sea ruptured in 1912.  The fault segment to the east of the Marmara Sea ruptured in a pair of earthquakes in 1999 shown in red and purple.  The Marmara Sea, shown with recent bathymetric mapping, is a seismic gap with an increased risk of an earthquake.  The city of Istanbul with a population of over 12,000,000 people lies to the north of the Marmara Sea near a strand of the NAF. Source: Armijo et al., 2002.
 

 
Modeling the effects of the 1999 earthquakes on the stress field by the USGS shows that they increased the stress (red in figure) on the next fault segment which is next to Istanbul.  Estimates of severe ground shaking in Istanbul are 62±15% over the next 30 years and 32±12% over the next decade . Sources: USGS, 2000; Parsons et al., 2000.

Photograph of destruction caused by the the Izmit earthquake in 1999 with an estimated loss of like of ~30,000 people.
Source: USGS, 2000

Map showing the major branches of NAF in Marmara Sea region in red. The NAF splits into several strands as it approaches the Marmara Sea.  The northern strand entering the Marmara Sea through the Gulf of Izmit (thicker line) has been the main focus of recent research efforts. However, offset markers only show half the expected motion. The remaining motion may be on the southern strands, particularly the strand along the southern margin of the Marmara Sea. 
Source: Okay et al., 2000.

Below: Multibeam bathymetry of the deep water parts of the Marmara Sea.  The northern part of the Marmara Sea consists of several 1200-m deep basins and separated by highs.  These were formed by bends and stepovers in the northern strand of the NAF.  The formation and history of these basins and whether they are still active is a major question about the Marmara Sea. .Most seismic and multibeam data acquisition has been concentrated in the deeper northern half of the Marmara Sea, in part, because of difficulty of obtaining good quality data in the shallow southern shelf. The basins and highs also preserve layers of sediment that record the history of the Marmara Sea. Source: Rangin et al., 2001.