Seismic influence on the last 1500-year infill history of Lake Sapanca (North Anatolian Fault, NW Turkey) Suzanne A.G. Leroy ⁎ ,1 , Markus J. Schwab 2 , Pedro J.M. Costa 3 Department of Geography and Earth Sciences, Brunel University, Uxbridge UB8 3PH, UK abstract article info Article history: Received 23 September 2009 Received in revised form 2 February 2010 Accepted 7 February 2010 Available online 13 February 2010 Keywords: Lake Sapanca Earthquake North Anatolian Fault Zone Palynology Lake sediment Mass-movement events Lake Sapanca is located on the North Anatolian Fault Zone in NW Turkey. It occupies a pull-apart basin at the junction between the İzmit–Sapanca fault segment, the Sakarya segment and the westernmost end of the Mudurnu Valley fault. Multiproxy analyses (lithology, loss-on-ignition, geochemistry, magnetic susceptibility and palynology) of a 586-cm-long sediment core taken in the centre of the lake revealed a complex history of at least five mass-movement events. The radiocarbon chronology suggests that the sediment sequence spans approximately the last 1500 years. The bottom metre of the sequence, before c. AD 580, is a gley soil resulting from a large sublacustrine landslide, whose origin is a collapse of the floodplain between the lake and River Sakarya. Sedimentation related to this eastern floodplain decreases progressively until c. AD 910. Sedimentological and palynological indicators from sediments younger than c. AD 910 document four major episodes of mass-movement originating most likely from the southern slopes of the lake. The landslide and the following four mass-movement events are suggested to be linked to earthquakes. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In the last decades lake sediment has increasingly been used as an archive for the history of ancient earthquakes. Using a combination of high-resolution seismic surveys, radiocarbon-dated sediment cores, historical documents and even submersible crafts, the chronology, magnitudes and epicentres of some large prehistoric earthquakes have been reconstructed for example in Lake Biwa (Japan), in Lake Yellowstone (USA), in Lake Puyehue (Chile) and in Lake Como (Italy) (Shiki et al., 2000; Morgan et al., 2003; Moernaut et al., 2007; Fanetti et al., 2008). In Switzerland by combining the results from two lakes, Strasser et al. (2006) have even highlighted the existence of large earthquakes in the region of Zürich so far believed to be free of major seismic hazards. In lake sediment, mass-movement events may be distinguished by their characteristic structures such as turbidites, homogenites or more simply by reworked sediment, and/or by the increased soil content (Schwab et al., 2009; Leroy et al., 2009). Lake Sapanca in NW Turkey is a key area of interest to earth scientists. It is located at a possible palaeo-connection between the Black Sea and the Marmara Sea, bypassing and predating the Bosphorus, i. e. in the İzmit–Sapanca–Sakarya corridor (Ryan and Pitman, 1998; Gürbüz and Leroy, 2010)(Fig. 1). The lake is located on an active strand of the North Anatolian Fault Zone (NAFZ) on which the last major destructive earthquakes occurred in 1999 (Akinci, 2004). The sediment fill in the lake is a potential archive of earthquakes on the Sakarya, İzmit–Sapanca and Mudurnu Valley segments of the NAFZ (Neugebauer et al., 1997; Lettis et al., 2002) (Fig. 2). Previous work on short Kajak cores taken from Lake Sapanca has demonstrated that a multiproxy approach can successfully reveal historic earthquakes in the region (Schwab et al., 2009; Leroy et al., 2009). We use a multiproxy approach to highlight the main mass- movement events in Lake Sapanca and therefore extend the history of strong earthquakes in the region. This involves the analysis of lithology, magnetic susceptibility, loss-on-ignition, geochemistry and palynology, including non-pollen palynomorphs, on a long (586 cm) percussion core taken from the centre of the lake. 2. Setting and previous studies Lake Sapanca is located in NW Turkey at 40° 43′ N, 30° 15′ E and at an altitude of 31 m asl (Figs. 1 and 2). As two other papers deriving from the same research project than this paper have been published (Schwab et al. 2009; Leroy et al., 2009), much of the setting descriptions, such as climate, vegetation, geology, relief and limnol- ogy, can be found there. Tectonophysics 486 (2010) 15–27 ⁎ Corresponding author. Tel.: +44 1895 266087; fax: +44 1895 269761. E-mail address: suzanne.leroy@brunel.ac.uk (S.A.G. Leroy). 1 Present address: Institute for the Environment, Brunel University, Uxbridge UB8 3PH, UK. 2 Present address: GFZ-German Research Centre For Geosciences, Section 5.2 Climate Dynamics and Landscape Evolution, Telegrafenberg, 14473 Potsdam, Germany. 3 Present address: Departamento de Geologia, Universidade de Lisboa, Campo Grande, Edifício C6, 1749-016 Lisboa, Portugal. 0040-1951/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2010.02.005 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto