MODELLING AND SEISMIC OBSERVATION OF ROCKFALLS IN THE DOLOMIEU CRATER, PITON DE LA FOURNAISE, LA REUNION

Abstract:

The seismic and photogrammetric networks of the Piton de la Fournaise volcano (La Réunion Island), maintained by the OVPF, are well appropriate for the study of seismic signals generated by rockfalls occurring in the Dolomieu crater. In particular it makes it possible to relate the rockfall dynamics recorded by the cameras with the time change of the seismic energy. The aim of this study is to better extract the information contained in the seismic signal by comparing the force generated by the rockfall and the work rate, potential and kinematic energy changes calculated using numerical models of rockfalls with the generated seismic power during the rockfall propagation down the slope of the Dolomieu crater. A detailed comparison of the simulated dynamics with the movies of several rockfalls makes it possible to identify the different phases of the flow (initial collapse, impacts and interaction with the topography, stopping phase) and to relate them to the observed seismic signal. Simulations of rockfalls on 2D and 3D topographies obtained by laser-scanner survey of the crater are performed using the thin layer depth-averaged code SHALTOP. In particular we test the effect of the friction law (constant friction and volume or velocity weakening friction) on the simulated force and work rate to investigate if the signature of the friction law may be identified on seismic records.