Investigation of the probable trigger factor for large landslides in north of Dehdasht, Iran
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Investigation of the probable trigger factor for large landslides in north of Dehdasht, Iran Alireza Nilforoushan1 · Mashalah Khamehchiyan1 · Mohammad Reza Nikudel1 Received: 28 March 2020 / Accepted: 14 October 2020 © Springer Nature B.V. 2020
Abstract Charosa and Dehdasht is a part of folded Zagros that is located in the Kohgiluyeh and Boyer-Ahmad Province in southwestern Iran. This area is covered with several Zagros anticlines such as the Kuh-e-Sefid, Sartal, Nil, and Siah. From the geological perspective, the Ilam–Sarvak formation makes the major and high altitudes of the region. Numerous landslides have occurred in the highlands of this area, with the largest known landslides being the Mundan rock avalanche in the Nil anticline with an approximate volume of more than one billion cubic meters and the Almor rock avalanche in the Sartal anticline. This study explores the probable triggering factors of these landslides based on geological studies, seismotectonic studies, and numerical modeling methods. According to the results of this research, between earthquake and groundwater (as the two major landslide-triggering factors), the earthquake was able to cause instability and slip onset. Based on seismic investigations, the Mountain front fault in the vicinity of these anticlines has high seismic potential. So, the occurrence of earthquakes with a 1000-year return period and a minimum 7.3 momentum magnitude is likely triggered by these rock avalanches. The results show that due to favorable geological and topographic conditions of the study area, the earthquake has been able to cause large and catastrophic landslides in the region’s history. Keywords Rock avalanche · Deep-seated gravitational slope deformation · Triggering factor · Earthquake · Mountain front fault
1 Introduction Paleolandslides are pre-historic mass movements documented using geological and geomorphological evidence (Clague 2015). Studying these phenomena provides insights into unusual effects that are less visible in human life, such as giant rock avalanches, earthquakes with long recurrence, and rainfalls (Clague 2015). A comprehensive understanding of the hazards associated with landslides requires understanding many features, factors, and processes involved (Griffiths et al. 2012). Slope stability factors are classified into preconditioning, preparatory, and triggering factors (Glade and Crozier 2005). Preconditioning * Mashalah Khamehchiyan [email protected] 1
Department of Engineering Geology, Tarbiat Modares University, Tehran, Iran
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Natural Hazards
factors over human timescales are constant and affect the inherent strength of the slope. Factors that do not cause failure but change stability over time are preparatory factors, and those that change the status of the slope to unstable are triggering factors. Although there may be many causes for landslides, there is generally only one triggering factor (Varnes 1978). Examples of precondition, preparatory, and triggering factors are presented in WG/ WL
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