Yildiz Altinok

Tsunamis in the Sea of Marmara: Historical documents for the past, models for the future

Abstract More than 30 tsunami events have impacted the coasts of the Sea of Marmara in the past two millennium, clustering in Izmit Bay, the shores of Istanbul, Gemlik Bay, the shores of the Kapidag and Gelibolu Peninsulas. With respect to the last well-known tsunami, the Izmit tsunami of 17 August, 1999, available field survey run-up data and marine surveys provide an opportunity to evaluate how these events were triggered. The main purpose of this study is to determine the slope failure potential as a possible tsunamigenic source in the Sea of Marmara by utilising multi-beam bathymetry, shallow and deep seismic reflection data. On the basis of the landslide geomorphology, the generation, propagation and coastal amplifications of tsunamis related to earthquake and slope failure scenarios were tested by using tsunami simulation model TWO_LAYER. The maximum water surface elevations near the shores along the north and south coasts are obtained according to the selected scenarios of tsunami generation by using available data.

Tsunamis Observed on and Near the Turkish Coast

For centuries, inhabitants of coastal areas have suffered from the effects of tsunamis. Turkey, with a coastline of 8333 km, has experienced many tsunamis.Historical records reveal that, during the observation period over 3000 years, the coastal and surrounding areas of Turkey have been affected by more than ninety tsunamis. These tended to cluster around the Marmara Sea, the city of Istanbul and the gulfs of Izmit, Izmir, Fethiye and Iskenderun. Each of the tsunami occurrences surveyed in this paper deserves further individual study. The most extensive available information concerns the tsunamis associated with the Istanbul Earthquakes of 1509 and 1894, the Eastern Marmara Earthquake in 1963 and that of Izmit in 1999,which disturbed the Marmara Sea; the Earthquake of 1939 in Erzincan ineastern Anatolia; and the 1968 Bartın Earthquake, which affected Fatsa and Amasra on the Black Sea. In addition to these, it is known that a tsunami occurred in 1598 on the shores of the Black Sea in connection with an earthquake at Amasya in northern Anatolia.

The Tsunami of August 17, 1999 in Izmit Bay, Turkey

The Kocaeli 1999 Earthquake with an Mw = 7.4 caused major hazards throughout the NW of Turkey from Tekirdag to Bolu. Historical data indicates that some of the earthquakes around Izmit Bay have caused tsunamis. In this study, tsunami research for the Kocaeli 1999 Earthquake has been made also taking into consideration historical data. In this research more than about 70 data at 35 localities have been used to determine the tsunami evidences in the bay. Coastal observations indicated runups which were ranging from 1 to 2.5 m along the shores. However, the wave runups are more complex along the south coast due to the presence of coastal landslides (Değirmendere, Halidere, Ulasli, Karamürsel) and subsided areas (Kavakli to Yeniköy) along the shore. West of Yalova, evidence of tsunami rapidly diminished. In addition, possible tectonic mechanism has been determined by using 33 single-channel high-resolution digital seismic reflection profiles which were acquired following the Kocaeli 1999 Earthquake. As a result it has been determined that the Kocaeli Earthquake has created tsunami in Izmit Bay.

Seismotectonic database of Turkey

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time.

New approaches in assessment of tsunami deposits in Dalaman (SW Turkey)

Some earthquakes in the Eastern Mediterranean are tsunamigenic, and some of their tsunamis affected the coastal area of the Gulf of Fethiye, SW Turkey. Recent trenching surveys on the low-lying coastal areas of Dalaman delta beach across the Rhodes Pass revealed three probable tsunami impacts as a result of the historical earthquakes of 1303, 1481, and 1741. Yet there have been relatively few studies of the processes associated with tsunami sediment transport, their deposition, and nature in geological record. In addition to the interpretation of sedimentary features, accurate palaeo-environmental assessments might be possible by distinctive biogeochemical researches on marine-sourced organic matters, geochemical properties, quantitative amounts of marine biomarkers, and deterministic ratios. The identification of major lipid biomarkers (fatty acids and sterols) in the samples recovered from the sidewalls of the studied trench, for example, indicated biogenic contributions due to the presence of phytoplankton, zooplankton, bacteria, and dinoflagellates. Quantitative estimation of biomarkers and deterministic ratios also indicated some evidences for marine-sourced organic matters, implying that biomarkers can be used to answer the open questions in tsunami and palaeo-tsunami researches.