Scenario-based tsunami hazard assessment for the northwestern coast of Marmara Sea

Historical moderate-scale tsunamis have frequently impacted the Sea of Marmara, an inland sea to NW Turkey. In this study, three earthquake-induced tsunami scenarios are determined in the northwestern Sea of Marmara based on recent geophysical data, and numerical simulations are performed to assess the possible impact on the densely populated areas on the northwestern coast. The simulation results suggest that a broad coastal sector can be affected and the layout of the coastline in the study area and the alignment of the shelf slope with respect to tsunami direction are the main factors affecting the coastal amplification of tsunamis. The computed nearshore tsunami amplitudes according to the three scenarios range from 0.5 to 2 m along the coast of northwestern Marmara. Only a small coastal stretch between the villages of Gazikoy and Sarkoy seems less impacted due to its oblique position with respect to the propagation direction of the waves. As the physical characteristics of tsunamis are strongly correlated with the sea depth, the steep rise in bathymetry towards the coastal area between Kumbag and Gazikoy is the primary factor influencing the tsunami characteristics in this area. Additionally, the coastal morphology and energy attenuation must be the fundamental causes of the spatial and temporal distribution of modeled waves observed along the shore. The findings show that moderate-scale tsunamis, which could be triggered by moderate earthquakes, pose a threat to the seaports in the province of Tekirdag. Tsunami hazard assessment, risk and evacuation maps, and action plans need to be developed, and preparedness with stakeholders should be conducted for the coastline in the northwestern Sea of Marmara.