Tectonics of the Marmara Sea

Conflicting models of deformation and hazard


 Summary of different models for the formation and current tectonics of the Marmara Sea grouped into three major kinematics classifications.  Which model is correct has significant implications for the seismic hazard at Istanbul.  Depending upon the model, the Marmara seismic gap could be ruptured by a single large earthquake or multiple smaller earthquakes with corresponding large differences in ground shaking and damage.


The most prominent models are the “pull apart” model (A) proposed by Armijo et al. (2002) and the “single fault” model (B)  proposed by Le PIchon et al. (2001).  The kinematics of each are presented in diagram (C) below (from Flerit et al., 2003).  In the top, the Sea consists of several pull apart basins with northwest-trending normal faults and ENE-trending strike-slip faults.  In the bottom, a single master strike-slip fault has cut through all of the previous basins, inactivating some of the previous structures. Depending on which is correct the Marmara Sea could fail in a single great earthquake or multiple major earthquakes.




 Over the last 60 years, the North Anatolian Fault has ruptured in a series of destructive earthquakes with an overall propagation from east to west. The Marmara Sea is the only major gap along the North Anatolian Fault.



Finally, we note the most of the research effort has focused on the northern Marmara Sea where deeper water makes data acquisition easier.  However, offset markers indicate up to half the Holocene slip expected may be missing.  Less intensively studied branches of the NAF farther south, such as the one shown above in Gemlik Bay in the SE Marmara Sea may contain the missing slip.
Source: Yaltirak and Alper, 2003.