North Anatolian Fault in the Gulf of Izmit (Turkey): Rapid vertical motion in response to minor bends of a nonvertical continental transform

Abstract

The catastrophic rupture of the North Anatolian Fault east of the Marmara Sea on 17 August 1999 highlighted a need for mapping the underwater extension of that continental transform. A new bathymetric map of Izmit Gulf indicates that the fault follows the axis of the gulf with a few minor bends. Submerged shorelines and shelf breaks that formed during the Last Glacial Maximum provide markers to quantify vertical deformation. Variable tilting of these horizons reveals that vertical deformation is highest just south of the fault. A correlation between vertical deformation of the southern fault block and distance to fault bends can be accounted for by a fault dipping steeply to the south. Hence subsidence (uplift) of the southern, hanging wall block would be expected where the fault strikes at a slightly transtensional (transpressional) orientation to relative plate motion. Subsidence reaches about 8 mm/yr west of the town of Golcuk and might be accommodated in 1–2 m subsidence events during large earthquakes. That scenario is compatible with the tsunami runups and the coseismic subsidence of the southern shore that occurred in 1999. Seafloor morphology also suggests that earthquakes are accompanied by widespread gas and fluid release. The periphery of the deepest basin displays a hummocky texture diagnostic of sediment fluidization, and mud volcanoes occur west of Hersek peninsula that might be activated by earthquakes. Finally, the backscatter imagery reveals a series of lineaments midway through the gulf that are interpreted as products of the 1999 surface rupture. The seafloor is undisturbed farther west, suggesting that surface slip decreased to an insignificant level beyond Hersek. Possibly, the stress shadow from the 10 July 1894 earthquake, which was felt strongly along the western Izmit Gulf, contributed to arrest the 1999 surface rupture.

Continental Transform Basins: Why Are They Asymmetric?

“…Subtle bends, rather than sharp jogs, control the western and eastern basins and a number of other basins along the western NAF [e.g., Emre et al, 2003;Cormier et al, 2006]. As expected, subsidence occurs on the trans tensive side of the bends, where the fault is oriented clockwise from the rightlateral plate motion.…”

Spatial variation of the stress field along the fault rupture zone of the 1999 Izmit earthquake

“…This length of time along with the observation of the extremely low coefficient of friction may be considered to be additional clues on the extent of the co-seismic rupture and the post-seismic dynamics. The debate on whether the Yalova segment (40-km-long fault extending between Yalova and the Hersek Peninsula) was ruptured on 17 August is still underway (Cormier et al, 2006). Taking into account the proximity of the Ç ınarcık and Yalova segments and the low friction coefficient on the Ç ınarcık segment, the 63-h delay in the appearance of aftershocks may indicate the absence of considerable co-seismic displacements on the Yalova segment and that stress loading by post-seismic displacement was the likely trigger of the activity of the Ç ınarcık swarm.…”

“…A recent study based on high-resolution bathymetry data provides strong evidence showing that no signi cant motion occurred on the 40-km-long offshore Yalova segment located to the west of the Gölcük segment (Cormier et al, 2006), though modeling of geophysical data suggests considerable displacements (Wright et al, 2001;Gülen et al, 2002).…”

“…The right step-over of the Gölcük segment to the Yalova segment created the 5-km-wide Karamürsel basin that arrested 4-to 5-m co-seismic displacements on the Gölcük segment and prevented major failure on the Yalova segment Cormier et al, 2006). On the other hand, the ruptures on the Gölcük segment propagated eastward through the 1-to 2-km-wide Gölcük step-over basin, triggering 2-to 3-m surface displacements on the Sapanca segment (Ç emen et al, 2000;Aydın and Kalafat, 2002;Barka et al, 2002;Gülen et al, 2002).…”

Continental Transform Boundaries: Tectonic Evolution and Geohazards

“…These were recorded from geophysical investigations (multichannel seismic reflection profiles, multibeam bathymetry, high-resolution sub-bottom profiles, side scan sonar), sediment sampling (piston cores up to 30 m long and many gravity cores), and explorations by manned and unmanned submersibles. The data were acquired during the following cruises and research vessels: Seismarmara, Marmarascarps, Marnaut, Marmesonet, R/V Marion Dufresene, R/V Urania (2002,2009), and R/V Piri Reis (project TAMAM: 2008(project TAMAM: , 2010) Le Pichon et al, 2001;Polonia et al, 2004;Armijo et al, 2005;Cormier et al, 2006;Steckler et al, 2008;Géli et al, 2008;Görür and Çağatay, 2010).…”