Morphotectonic evidence from the southern branch of the North Anatolian Fault (NAF) and basins of the south Marmara sub-region, NW Turkey H.H. Selim a, * , O. Tüysüz b , A. Karakas ¸ c , K.Ö. Tas ¸ d a Istanbul Commerce University, Faculty of Engineering and Design, Department of Jewellery Engineering, Istanbul 34840, Turkey b Istanbul Technical University, Eurasia Institute of Earth Sciences, Istanbul 34469, Turkey c Kocaeli University, Faculty of Engineering, Department of Geology, Kocaeli 41380, Turkey d Sakarya University, Faculty of Engineering, Department of Geophysics, Sakarya 54187, Turkey article info Article history: Available online 23 November 2012 abstract This study investigated the morphotectonic evidence from the southern branch of the North Anatolian Fault (NAF) and the south Marmara sub-region, NW Turkey. The south Marmara sub-region has two uplifts located in the south and north, and a depression between these uplifts. The uplifts are bounded by the southern branch of the NAF. The southern branch is divided into the YeniceeGönen (YGFZ), ManyaseMustafakemalpas ¸a (MMF), Uluabat (UFZ) and Bursa (BFZ) faults. The relation between the active tectonics and recent morphology were evaluated by using the geomorphic indices (GIs) (AF: asymmetry factor, T: topographic symmetry factor, SL: river lengthegradient index, S mf : mountain- front sinuosity). GIs were used to define the effects of tectonism on morphology and were used to calculate the relative tectonic activity index (Iat). The values obtained through the GIs indicate a young tectonism in the study area. The study area morphometrically presented two Iat classes; class 1 (high relative tectonic activity) and class 2 (moderate relative tectonic activity). The present GPS data and Iat classes of the southern branch faults of the NAFZ were correlated. All of the calculations and field data reveal that the southern branch of the NAF is the main tectonic element forming the geomorphology of the south Marmara sub-region. Ó 2012 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The North Anatolian Fault (NAF) is a right lateral strike-slip fault, which splays into northern and southern branches in NW Anatolia (Barka, 1992; Okay et al., 2000; S ¸ engör et al., 2004). Degree of the tectonic effect on morphology depends on the slip rates of each branch. Slip rates of the NAF vary among the branches of the NAF (Hubert-Ferrari et al., 2002). Gasperini et al. (2011) studied geological slip rates along the North Anatolian Fault in the Marmara Region. Meade et al. (2002) presented the recent GPS slip rates for the faults of the southern Marmara sub-region. Gürbüz and Gürer (2008) investigated tectonic geomorphology of the northern branch of the NAF in the Lake Sapanca Basin in the Eastern Mar- mara Region. The south Marmara sub-region is under the influence of the southern branch of the NAF. Morphology of the study area has been shaped by the southern branch of the NAF and its related segments. The investigation area is characterized by a depression area surrounded by two uplifts in the south of the Sea of Marmara. The depression area and uplifts were formed by the active faults in the region. An assessment of the seismicity of the South Marmara Region from a temporary seismic network was performed by Gök and Polat (2012). There are several basins located in the depres- sion. The active faults of the southern branch of the NAF, which morphologically border each basin, were the main tectonic and morphologic elements in forming the basins (Selim, 2004; Selim and Tüysüz, 2013). The basins were formed by the YeniceeGönen (YGFZ), ManyaseMustafakemalpas ¸ a (MMF), Uluabat (UFZ) and Bursa (BFZ) faults in the south Marmara sub-region of the Marmara Region. Geomorphology of the region is tectonically controlled by these faults extending approximately EeW and NEeSW (Fig. 1). The purpose of this study is to define the effective factors that were crucial on the morphological evolution of the four basins (Gönen, ManyaseKaracabey, Uluabat and Bursa) and to reveal that the sub-region was not formed based on the eustatic movements and that the morphology has been shaped by active tectonics. For this purpose, this paper applies a quantitative geomorphological method to the south Marmara sub-region to evaluate relative rates of tectonic activity (Iat). The GIs such as drainage basin asymmetry * Corresponding author. E-mail addresses: haluk.selim@gmail.com, hselim@iticu.edu.tr (H.H. Selim). Contents lists available at SciVerse ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2012 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2012.11.022 Quaternary International 292 (2013) 176e192