Assessment of tsunami impacts on the Kocasu Region (Sea of Marmara, Turkey)

Aykurt Vardar H., Ünlü S., Altınok Y., ALPAR Ş. B., Özer N., Balkıs N., ...More

EGU General Assembly 2011, Austria, 1 - 04 April 2011, vol.13, pp.0-3241

  • Publication Type: Conference Paper / Full Text
  • Volume: 13
  • Country: Austria
  • Page Numbers: pp.0-3241
  • Istanbul University Affiliated: Yes


Some of the major historical earthquakes in the Sea of Marmara are tsunamigenic. The tsunamis registered in the
recent catalogues are small to moderate and co-seismic. Those were mostly reported from the big cities located
in the western and north-eastern parts of the region. Even the southern coastline is relatively far from the main
active faults passing through the Sea of Marmara from east to west, and partly sheltered by the islands, the tsunami
waves hit the region (e.g. 10.10.123, 06.09.543, 22.05.1766 and 18.09.1963). Along the coast of Mudanya, for
example, strong tsunami waves were particularly effective in 1766 and waves reached a height of 1 m in 1963.
The tsunami waves observed in Erdek Bay during the 543 event might have also been effective in Bandirma Bay
and the study area. The numerical wave models indicate that the moderately high tsunamis can be effective along
the coastal strip between the Gulf of Gemlik in the east and the Kapıda^g Peninsula in the west, and overcome the
natural sand barriers. Unfortunately urbanization spreads for the last 50 years and causing adverse environmental
effects on original sediment successions of coastal facies. A few only excavation sites, suitable for an extensive
paleoseismological investigation, were left far from artificial development. Considerably being low-energy depositional
environments far from post-depositional erosion, the coastal wetlands and lagoons in the Kocasu region
are the best places for tracking tsunami deposits. Under the scope of the EU project TRANSFER (Tsunami Risk
ANd Strategies For the European Region), a candidate tsunami deposit was observed in a trench at the Ballikaya
district. The trench is located on the Kocasu Delta, behind the natural sand barriers and 410 m far from the modern
shoreline. Soil samples were collected from sandy layers which show no grading structure, suggesting rapid
deposition of sediments from floods of water. In addition a piston core drilled on the trench site was logged by
multi-sensor core logger for every 0.5 cm using gamma density, resistivity, P-Wave, and magnetic susceptibility
sensors. Even the core is made up of coarse grained sediments without clear boundaries, some enigmatic stratification
was observed 48-51cm below the surface. Comparing to those of overlying layers these units have higher
magnetic susceptibility. In addition to the interpretation of sedimentary features, the depositional conditions are
often readily inferred from the presence and distribution patterns of biomarkers. In that sense paleoenvironmental
assessments were tried to have been elucidated by geochemical properties, marine biomarkers and deterministic
ratios. There were no meaningful correlations for major elements (Cu, Cr, Cd, Fe and Al) through the core samples,
while slightly increased concentrations of oxide groups (Al2O3, CaO, MgO, Na2O and K2O) were detected
for the enigmatic layers. FAMEs are most commonly analyzed using a gas chromatography equipped with mass
detection. In this way 30-35 fatty acids can be routinely separated. The identification of marine lipid biomarkers
indicates biogenic contributions due to the presence of phytoplankton, zooplankton, bacteria and dinoflagellates.
Quantitative estimation of biomarkers and deterministic ratios indicated some evidences for marine-sourced organic
matters. The higher ratios of C22:6w3/C20:5w3, for example, imply the presence of dinoflagellates in the
samples below 40 cm. Depending on these preliminary results we suggest that further studies are needed.