Earthquake triggered rock falls and their role in the development of a rock slope: The case of Skolis Mountain, Greece I. Koukouvelas ⁎, A. Litoseliti, K. Nikolakopoulos, V. Zygouri Department of Geology, University of Patras, 265 00 Patras, Greece abstract article info Article history: Received 19 January 2015 Received in revised form 4 March 2015 Accepted 16 March 2015 Available online 28 March 2015 Keywords: Earthquake triggered landslides Rock falls Hazard zoning NW Peloponnese Greece Inventory of pre-earthquake and earthquake triggered landslides is used to provide insight into the interplay between climatic and tectonic forcing in the development of the rock slopes of the Skolis Mountain, in the NW Peloponnese. Aerial photograph analysis and surface mapping indicate that the Skolis Mountain is characterized by long-term climatically and tectonically controlled rock falls forming taluses. Temporally these taluses show a slow progressive inflation in surface area from 1945 to 2007. However, the post-earthquake surface area of the rock falls increased three times. Similarly 75 rock fall sites before the earthquake, increased into 89 after the Movri Mountain earthquake (Mw 6.4). In addition, during the earthquake a series of isolated rock falls descended Skolis slopes causing threat of the Santomerion village and blocking significant part of the dirt roads around it. These boulders are clustered in three areas beyond the base of taluses. The rock slope failures are controlled by a complex array of discontinuities that are conveniently related to rock mass classification following the geolog- ical strength index. These discontinuities are associated with joints and faults caused during the formation of the Hellenides fold- and thrust-belt, and/or related tectonic damage. We infer thata dense pattern of fractures in limestone plays a crucial role in the reactivation of movement within the rock falls during the 2008 Movri Moun- tain earthquake. All these data are used to define two borders, the taluses base and the rock fall hazard border beyond the base of taluses. For defining these borders we use the angle β drawn from the boulders' release zone down its maximal runout points. Our results indicate that the border defined by the β = 33° corresponds to the climatically driven rock falls while the β = 24° border is defined as the boulders' maximum runout during earthquakes. © 2015 Elsevier B.V. All rights reserved. 1. Introduction A strong feedback exists between geological history, tectonics, lithol- ogy and geomorphological evolution of slopes (Jaboyedoff et al., 2011); this is the reason why various types of landslides respond in many ways to tectonic processes. In addition most of the slope features can be considered as the result of long-term geomorphologic evolution under climatic forcing and/or in cases of geologically active areas by the tectonic forcing during earthquakes. Otherwise, topography, lithology and rock mass damage appear to promote or control the rock slope fail- ures (Reid and Iverson, 1992; Zêzere et al., 1999; Agliardi et al., 2013). Landslides are commonly triggered in the epicentral area of earth- quakes or in proximity with active faults (Keefer, 1984a,b; Bull et al., 1994; Tibaldi et al., 1995; Burbank and Anderson, 2001; Gallousi and Koukouvelas, 2007). Thus, mapping and analysis of the landslide distri- bution can be used for hazard assessments (Eisbacher and Clague, 1984; Keefer, 1984a). In addition, landslides in actively deforming areas often provide key data for understanding the delivering of material from hillslopes into valley bottom occupied by rivers, lakes, gulfs or glaciers (Molin et al., 2004; Korup, 2005a,b; Gallousi and Koukouvelas, 2007). For the Mediterranean and Greek climatic conditions, the relation- ships between landslides and extreme rainfall events have been exten- sively investigated (e.g. Crosta, 1998; Guzzetti et al., 2004; Koukis et al., 2005; Agliardi et al., 2013). However, the role of the earthquakes in landslides is poorly understood in Greece, since a limited number of case studies exist and information from historic data are limited (Koukouvelas et al., 1996; Christaras et al., 1998; Papadopoulos and Plessa, 2000; Ambraseys, 2009). In addition, landslide inventory data are poor for earthquake triggered landslides in terms of their dimen- sions and it is unlikely that very specific landslide-related parameters, such as material shear strength or phreatic surface levels, are mapped to the detail required for present day landslide susceptibility analysis. On the 8th of June 2008, a strong earthquake of Mw = 6.4 struck northwestern Peloponnese called hereinafter as the Movri Mountain earthquake (Fig. 1). Northwestern Peloponnese and its surroundings Io- nian Islands are located at the most tectonically and seismically active region of Greece (Papazachos and Papazachou, 1997; Ambraseys, 2009; Kokkalas et al., 2013 and references therein). The 2008 event Engineering Geology 191 (2015) 71–85 ⁎ Corresponding author at: University of Patras, Department of Geology, 26500 GR, Greece. E-mail address: iannis@upatras.gr (I. Koukouvelas). http://dx.doi.org/10.1016/j.enggeo.2015.03.011 0013-7952/© 2015 Elsevier B.V. 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