LANDSLIDE TRIGGERING AS AN INDIRECT CONSEQUENCE OF AN EARTHQUAKE - CASE STUDY FROM NORTHERN CROATIA

he landslide is the movement of soil and rocks down a slope, as a result of the loss of shear strength in the material that builds the slope. Although various human activities increase the risk of landslides, the most common causes for the loss of shear strength are geological and morphological. Thus, natural triggers for landslides can be the characteristics of the soil and rocks that build the slope, the slope angle, erosion, water, but this paper will analyse the triggering of landslides as indirect consequences of earthquakes. During 2020, two significant earthquakes hit central Croatia. First, a moderate earthquake was triggered in the area of Zagreb, and towards the end of the year, a strong earthquake hit the regions of Petrinja, Sisak and Glina. In addition to the enormous damage to buildings, the mentioned earthquakes indirectly activated numerous landslides, including in the area of Northern Croatia. The landslide in Petrovsko was activated immediately after the Zagreb earthquake. This instability potentially threatened the D206 state road corridor. Engineering geological and recent geotechnical-geophysical investigations were applied to define the boundaries of instability, the lithological composition of sediments in the subsurface and locating the sliding surface. The unfavourable geological structure was determined, as silty sands and clays predominate in the surface layers, and organic clays of low shear strength appear immediately before contact with marl. The mentioned location of the landslide was selected for microtremor measurements that will be carried out as part of Croatian Science Foundation (HRZZ) project IP-2022-10-1296, SIGMATOPCRO.