Single-block rockfall dynamics inferred from seismic signal analysis

Clément Hibert,Floriane Provost,Franck Bourrier,Pascal Tardif,Frédéric Berger,Eric Mermin,Jean-Philippe Malet,Pierrick Bornemann

doi:10.5194/esurf-5-283-2017

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.

Highlights

Understanding the dynamics of rockfalls and other mass movements is critical to mitigate the associated hazards but is very difficult because of the limited number of observations of natural events
In this study we propose a new field experiment of controlled releases of single blocks to investigate the relationships between block properties and dynamics, and the features of the seismic signals generated by impacts with the slope
We have shown that correlations exist between several dynamic quantities and features of the seismic signal generated at each impact

Summary

Introduction

Understanding the dynamics of rockfalls and other mass movements is critical to mitigate the associated hazards but is very difficult because of the limited number of observations of natural events. C. Hibert et al.: Single-block rockfalls seismic signal mass (Favreau et al, 2010; Schneider et al, 2010; Moretti et al, 2012; Ekström and Stark, 2013; Allstadt, 2013; Yamada et al, 2013; Hibert et al, 2014a, c). Hibert et al.: Single-block rockfalls seismic signal mass (Favreau et al, 2010; Schneider et al, 2010; Moretti et al, 2012; Ekström and Stark, 2013; Allstadt, 2013; Yamada et al, 2013; Hibert et al, 2014a, c) These approaches are limited by the size of the events. The largest landslides will generate the long-period seismic waves used in the inversion and the modelling methods. These events constitute only a small proportion of the landslides that occur worldwide

Methods

Results

Conclusion