Origins of diverse present displacements in a paleo-landslide area (Isiklar, Trabzon, northeast Turkey)

摘要

The Isiklar paleo-landslide area was reactivated in 1952, and today the spatial dimension of scarps is significantly different across the area. However, the steep slopes hamper the application of detailed in-situ methods, and the limited surficial field observations could not explain the complexity of the area so far. This paper aims to determine the origins of different displacements on two adjacent fields (Field-1 and Field-2) separated by woodland in the paleo-landslide area. The fields were imaged and monitored by multiple geophysical methods including seismic refraction and electrical resistivity tomography, surface waves analysis, and microtremors. Unified soil classification of six disturbed samples was carried out to define texture and grain size distribution. Up-to-date geographic maps were generated by GNSS measurements. The main findings show that the favorable conditions for the variation of displacements are controlled by the dissimilarity of landslide materials in terms of geological setting, S-wave velocity, and layer thickness. Also, the slope values higher than 30 are distinctive in fields regarding the development of scarps. Conversely, the seasonal changes and ground-water conditions do not influence the variability in displacements. The results suggest that the neighboring areas have been evolving differently on the same main-rock and the border of deforested woodland for agricultural purposes plays a crucial role in this process. The combination of different geophysical methods allowed imaging the subsurface at different spatial resolutions with various physical properties. Additionally, the integration of geophysical outcomes with geological and geodetic findings made it possible to restrict the spectrum of causal factors.