ALBERT

Description: SUMMARY We investigate by means of a 3-D geomechanical model the relationship between structural elements and contemporary kinematics in the Marmara Sea region, northwest Turkey. The recently imaged fault system beneath the Marmara Sea is incorporated into the model as frictional surfaces with varying strike and dip. The Main Marmara Fault is implemented as through-going and is accompanied by mostly non-vertical second-order faults. Topography, basement-topography and the Moho become mechanically effective through changes in density and elastic parameters across these horizons. The model is subjected to gravity and kinematic boundary conditions. The ultimate goal of this study is to set up a 3-D model that is consistent with both, kinematic observations and stress data. The stress results are presented in a complementary paper. In this paper we present the modelled long-term 3-D kinematics in terms of fault slip rates, rotations, vertical motion and sense of fault slip. The model results agree with Global Positioning System velocities, geological fault slip rates, palaeomagnetic measurements and with the observed pattern of subsidence and uplift. Furthermore, our tectonically driven vertical velocities can be linked to landscape and basin evolution and to features of sedimentation. Our results indicate that the Main Marmara Fault can be interpreted as a through-going fault that slips almost purely in a strike-slip sense. Nevertheless, and not contradictory to the previous statement, there is significant dip-slip motion at some sections of the Main Marmara Fault. The agreement of the modelled 3-D kinematics with model-independent observations supports that the main structural details of the fault system are accounted for. Sensitivity analysis of model parameters reveals that changes in rock properties and the initial stress state have minor influence on the 3-D kinematics. We conclude that the 3-D structure of the fault system is the key control of the kinematics. The slip rate of the Main Marmara Fault from our model is lower than previous estimates and shows high variability along strike (12.8–17.8 mm a –1 ). The latter indicates that stress accumulation is non-uniform along strike.