Rockfalls seismic waves contain valuable information on event properties. However, as rockfalls predominately occur in mountainous regions, generated seismic waves are prone to be affected by strong surface topography. For this reason, the influence of topography on the wavefield, in particular surface wave propagation, is investigated using the Spectral Element Method on a 3D domain with realistic surface topography of Dolomieu crater on Piton de la Fournaise volcano, La Réunion. Topography induced ground motion modification is studied relative to a flat reference model. Peak Ground Velocity (PGV) and total kinetic energy can be (de-)amplified by factors up to 10 and 20, respectively. The spatial distribution of the amplification is strongly influenced by the underlying geology as shallow low velocities guide energy along the surface. Simulations on different topographies suggest that the wavefield is affected more by variations of crater curvature than crater depth. To reveal the effect of topography on recorded signals at Dolomieu crater, inter-station spectral ratios are computed. It is demonstrated that these ratios can only be simulated when taking into account surface topography while the comparisons suggest that the direction of the acting source and the resulting radiation patterns can be ignored. Finally, the seismic signature of single impacts is studied. Comparison with simulations help to associate signal pulses to impact sources. It is revealed that a single impact can provoke complex waveforms of multiple peaks, especially when considering topography. Impact forces derived from Hertz contact theory result in comparable magnitudes of real and simulated signal amplitudes.

Rockfalls generate seismic signals that can be used to detect and monitor rockfall activity. Event locations can be estimated on the basis of arrival times, amplitudes or polarization of these seismic signals. However, surface topography variations can significantly influence seismic wave propagation and hence compromise results. Here, we specifically use the signature of topography on the seismic signal to better constrain the source location. Seismic impulse responses are predicted using Spectral Element based simulation of 3D wave propagation in realistic geological media. Subsequently, rockfalls are located by minimizing the misfit between simulated and observed inter-station energy ratios. The method is tested on rockfalls at Dolomieu crater, Piton de la Fournaise volcano, Reunion Island. Both single boulder impacts and distributed granular flows are successfully located, tracking the complete rockfall trajectories by analyzing the signals in sliding time windows. Results from the highest frequency band (here 13-17\,Hz) yield the best spatial resolution, making it possible to distinguish detachment positions less than 100\,m apart. By taking into account surface topography, both vertical and horizontal signal components can be used. Limitations and the noise robustness of the location method are assessed using synthetic signals. Precise representation of the topography controls the location resolution, which is not significantly affected by the assumed impact direction. Tests on the network geometry reveal best resolution when the seismometers triangulate the source. We conclude that this method can improve the monitoring of rockfall activity in real time once a simulated database for the region of interest is created.