Emplacement kinematics of the Seymareh Rock-Avalanche Debris (Iran) inferred by field and remote surveying

Abstract

Understanding the kinematics of landslides helps us to better constrain failure mechanisms and it is useful to define hazard and consequent risk scenarios for mitigation strategies. According to the literature, between 10 and 11 ka, a huge landslide (up to 44 Gm3) occurred close to the Pol-e-Dokhtar city in the Lorestan region (west of Iran). As this landslide blocked the Seymareh River, it is known as Seymareh landslide. Seymareh giant landslide is the largest landslide documented on the Earth surface and is of great interest for earth scientists. We deepened the analysis of the emplacement kinematics of this enormous landslide, using remote and field surveying. The boundary of landslide debris, the ridges, gullies and clusters of blocks inside the debris area were recognized and then ridges curvature and direction and major block dimensions were measured also using GIS tools. Ridges directions inside the landslide debris preliminarily suggest the kinematics of the mass mobility. Furtheremore, soil samples were took from matrix of landslide debris at different places inside the rock avalanche debris area for their classification according to the USCS standard. The results of grain size analysis on the matrix of the soil samples in combination with Atterberg limits in different regions of the debris show that the most of the matrix is represented by ML while a more reduced part is represented by GC and GM soils. GC and GM soils were mainly distributed closer to the detachment zone of the Seymareh landslide, while ML soils are mainly distributed in middle and distal positions. The preliminary results of block distribution and some outcrops of Gachsaran Formation observed during field surveys led to recognition of the landslide debris basal contact that helped us to speculate on the paleo-valley hidden morphology.