UAV-enabled reconnaissance and trajectory modeling of a co-seismic rockfall in Lefkada

The paper presents the field evidence and the kinematical study of the motion of a rock block mobilised by an earthquake-induced rockfall in Ponti area in the island of Lefkada during a Mw 6.5 earthquake on 17th November 2015. A detailed field survey was deployed using an Unmanned Aerial Vehicle (UAV) with an ultra-high definition (UHD) camera, which produced a high-resolution orthophoto and a Digital Surface Model (DSM) of the terrain. The sequence of impact marks from the rock trajectory on the ground surface was identified using the orthophoto and verified through a detailed field survey. Additionally, the earthquake characteristics were determined in order to define the acceleration on the rock slope and the initial conditions of the detached block. Using the impact points from the actual rockfall trajectory, an analytical approach to reconstruct the trajectory was implemented, which led to some insights on the coefficients of restitution. In order to match the actual trajectory, 2D and 3D rockfall analyses were performed using the recommended set of parameters. However, the actual trajectory could not be accurately predicted, revealing limitations of existing models.