Evolution of the Sedimentary Infilling of the Hersek Lagoon (Turkey, Izmit Gulf): Possible Relationships with Tsunamis in the Marmara Sea
by
Sebastien Bertrand
Brunel University, West London, UK
Coauthors: Namik Çagatay, Lisa Doner, Ummuhan Sancar, Sena Akcer, Suzanne Leroy

The eastern part of the Marmara Sea is frequently affected by the seismic activity of the North Anatolian Fault (NAF). This activity is responsible for tsunamis and submarine landslides in the Marmara Sea (Öztürk et al., 2000; Altinok et al., 2001). During historical times (0-2000 AD) at least 9 major tsunamis have affected the Marmara Sea (Kuran & Yalçiner, 1993). They were mainly located in the vicinity of the Izmit Gulf (Altinok et al., 2001). The last high magnitude earthquake having affected the area (17th August 1999, Mw = 7.4) has induced a tsunami in the Marmara Sea with waves reaching 2.5 m (Altinok et al., 2001).

In the framework of the EU-funded RELIEF project (RELiable Information on Earthquake Faulting, www.ingv.it/paleo/RELIEF), ten sediment cores with a length varying between 1 and 4 meters have been collected in the Hersek lagoon (Izmit Gulf, eastern Marmara Sea, Turkey). The aim of this coring campaign was to reconstruct the evolution of the sedimentary infilling of the Hersek lagoon in relation with the tsunamis triggered in the Marmara Sea.

After having been scanned by x-rays, the cores have been opened, described and photographed. The physical properties of the sediment (magnetic susceptibility, g-density, p-wave velocity) have then been measured with high resolution (5 mm) on a GEOTEK multisensor core logger (GFZ, Potsdam). In order to interpret the variations of these high resolution signals, two long cores have been selected for complementary analyses: TOC, forams, grain-size by laser diffraction, and bulk- and clay-mineralogy by x-ray diffraction.

Results demonstrate that the sediment is mainly made of fine silt-sized particles containing dispersed Turitella and Cardium shells. The bulk mineralogy of the sediment is made of quartz, clays, plagioclase, calcite and halite. Some samples contain aragonite. The clay mineral assemblages are dominated by smectite and illite. Some reworked shell deposits (mainly Cardium) as well as sandy layers are intercalated in these fine sediments. These instantaneous deposits have probably been deposited in high energy environments, that may be in relation with tsunamis or storms in the Marmara Sea.

In order to reconstruct the sedimentation rates, radiocarbon dates have been obtained on non-reworked particles. These data allow us to estimate the age of the instantaneous deposits.

References

ALTINOK, Y., TINTI, S., ALPAR, B., YALÇINER, A.C., ERSOY, S., BORTOLUCCI, E. & ARMIGLIATO, A. (2001) - The tsunami of August 17, 1999 in Izmit Bay, Turkey. Natural Hazards, 24, 133-146.

KÜRAN, U. & YALÇINER, A.C. (1993) - Crack propagations, earthquakes and tsunamis in the vicinity of Anatolia, in S. Tinti (ed.), Tsunamis in the world, Kluwer Academic Publishers, pp. 159-175.

ÖZTÜRK, H., KORAL, H. & GEIST, E.L. (2000) - Intra-basinal water movements induced by faulting: the August 17, 1999, Gölcük (Izmit Bay) earthquake (Mw = 7.4). Marine Geology, 170, 263-270.

Date received: July 24, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-61.