Investigation of the probable trigger factor for large landslides in north of Dehdasht, Iran

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.