Geophysical and numerical approaches to solving the mechanisms of landslides triggered by earthquakes: A case study of Kahramanmaraş (6 February, 2023)

Many landslides occurred in the 11 Turkish provinces affected by the earthquakes centered in Kahramanmaraş in February 2023, and many people lost their lives due to those landslides. To reduce the risks and hazards brought on by landslides induced by earthquakes, it is essential to identify the mechanisms causing landslides to arise in such situations. In this study, the geological strength index and both seismic refraction tomography and electrical resistivity tomography (ERT) geophysical methods were used to determine the failure mechanism of layered sedimentary units defined as flysch (claystone-siltstone-sandstone-marl). The shear strength reduction finite element method (SSR-FEM) was used with the RS2 computer program for model solutions. One of the geophysical methods, ERT, facilitated an interpretation of the cyclic failure mechanism that occurs in flysch, and it was found to be congruent with numerical models. Landslide slip circle depth, water-saturated layers, and resistivity values were determined with the ERT method. Seismic methods were employed to determine the velocity values (Vp, Vs) of the landslip mass. These velocity data, along with the elasticity modulus and Poisson ratios derived from them, were utilized in our numerical model. In the maximum shear strength and horizontal displacement analyses performed on the section line determined before the landslide, the natural state and the situation under the influence of groundwater were examined and the strength reduction factor (SRF) was determined as 1.35 and 1.24, respectively. In an evaluation conducted under the influence of the maximum horizontal ground acceleration (0.22 g) determined by taking into account the seismicity of the study area, it was concluded that instability occurred in the flysches and the SRF value was 0.72. An important finding of this study is that the results of geophysical methods used to determine the lithological properties of sedimentary rock masses and understand the causes of landslides align closely with those of numerical analysis methods, providing high accuracy. These methods also support new approaches, particularly in identifying landslip boundaries and detecting areas with high water saturation. It has been discovered that earthquakes actively contribute to the instability of these kinds of soils.