Single-block rockfall dynamics inferred from seismic signal analysis

Abstract

Abstract. Seismic monitoring of mass movements can significantly help to mitigate the associated hazards; however, the link between event dynamics and the seismic signals generated is not completely understood. To better understand these relationships, we conducted controlled releases of single blocks within a soft-rock (black marls) gully of the Rioux-Bourdoux torrent (French Alps). A total of 28 blocks, with masses ranging from 76 to 472 kg, were used for the experiment. An instrumentation combining video cameras and seismometers was deployed along the travelled path. The video cameras allow reconstructing the trajectories of the blocks and estimating their velocities at the time of the different impacts with the slope. These data are compared to the recorded seismic signals. As the distance between the falling block and the seismic sensors at the time of each impact is known, we were able to determine the associated seismic signal amplitude corrected for propagation and attenuation effects. We compared the velocity, the potential energy lost, the kinetic energy and the momentum of the block at each impact to the true amplitude and the radiated seismic energy. Our results suggest that the amplitude of the seismic signal is correlated to the momentum of the block at the impact. We also found relationships between the potential energy lost, the kinetic energy and the seismic energy radiated by the impacts. Thanks to these relationships, we were able to retrieve the mass and the velocity before impact of each block directly from the seismic signal. Despite high uncertainties, the values found are close to the true values of the masses and the velocities of the blocks. These relationships allow for gaining a better understanding of the physical processes that control the source of high-frequency seismic signals generated by rockfalls.

On the Link Between External Forcings and Slope Instabilities in the Piton de la Fournaise Summit Crater, Reunion Island

“…On the other hand, smaller R S∕P values ranging from 10 −6 to 10 −5 have been found by Levy et al (2015) for granular flows in Montserrat valleys and by Berrocal et al (1978) for a landslide in Peru. Free-fall laboratory experiments of beads and grains have shown that the seismic energy dissipated during an impact depends on the grain size and velocity, on the nature of the receiving plate, and on the slope angle (Farin et al, 2016, as confirmed by field measurements (Hibert, Malet, et al, 2017). Furthermore, Bachelet et al, (2016Bachelet et al, ( , 2018 have shown that the presence of an erodible bed can decrease the seismic energy transmitted to the ground for free-fall grains, in agreement with field observations of rock impact (Farin et al, 2015).…”

Seismic Analysis of the Detachment and Impact Phases of a Rockfall and Application for Estimating Rockfall Volume and Free‐Fall Height

“…These studies allowed relating the most energetic seismic phases to boulder impacts after a free fall and showed that impacts were characterized by waves packets with frequency contents over the range 1-50 Hz. Controlled releases of single blocks in a marl gully (Hibert et al, 2017) or in quarries (Saló et al, 2018) explored seismic amplitude and energy in relation to the kinetics of block impacts. Hibert et al (2017) inferred single block mass and velocity from local seismic records with a fair accuracy (median ratio between calculated and measured velocity of 0.2).…”

“…Controlled releases of single blocks in a marl gully (Hibert et al, 2017) or in quarries (Saló et al, 2018) explored seismic amplitude and energy in relation to the kinetics of block impacts. Hibert et al (2017) inferred single block mass and velocity from local seismic records with a fair accuracy (median ratio between calculated and measured velocity of 0.2). In contrast, Saló et al (2018) did not find a correlation between kinetic parameters of the blocks and measured seismic energies.…”

“…Finally, we compare our results with two other sites, in order to test whether our relation could be applied to both smaller and larger rockfall volumes and for different geological settings. In the Yosemite area, we analyze the Happy Isle and Ahwiyah Point rockfalls to investigate volumes larger than 10,000 m 3 , while the controlled releases of block of Hibert et al (2017) extend the range of volumes down to 0.03 m 3 .…”

“…By combining these results, we obtain an accurate estimate of the rockfall volume. The relation between the E p and E s was tested on different geological settings and for larger range of volumes using Yosemite, Mount Granier rockfalls, and with a data set of controlled releases of blocks (Hibert et al, 2017(Hibert et al, , https://doi.org/10.5194/esurf-5-283-2017(Hibert et al, , https://www.earth-surf-dynam.net/5/283/2017.…”