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

Abstract

We analyzed 21 rockfalls that occurred in limestone cliffs of the Chartreuse Massif (French Alps). These rockfalls were detected both by Terrestrial Laser Scanning or photogrammetry and by a local seismological network. The combination of these methods allowed us to study relations between rockfall properties (location of detachment and impacts areas, volume, geometry, and propagation) and the induced seismic signal. We observed events with different propagation modes (sliding, mass flow, and free fall) that could be determined from digital elevation models. We focused on events that experienced a free fall after their detachment. We analyzed the first parts of the seismic signals corresponding to the detachment phase and to the first impact. The detachment phase has a smaller amplitude than the impact phase, and its amplitude and duration increases with rockfall volume. By measuring the time delay between the detachment phase and the first impact, we can estimate the free‐fall height. We found a relation Es = aEpb between the potential energy of a rockfall Ep and the seismic energy Es generated during an impact, with a = 10−8 and b = 1.55 and with a correlation coefficient R2 = 0.98. We can thus estimate both the potential energy of a block and its free‐fall height from the seismic signals. By combining these results, we obtain an accurate estimate of the rockfall volume. The relation between the Ep and Es 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, https://doi.org/10.5194/esurf-5-283-2017, https://www.earth-surf-dynam.net/5/283/2017/).

Locating rock slope failures along highways and understanding their physical processes using seismic signals

“…6f), which may correlate to the seismic response from the hillslope. This leading phase could easily be detected in the slope-scale monitoring of rockfall (Roy et al, 2019). The total duration associated with the detachment to deposition of approximately 16 seconds is consistent with the signal duration identified from the spectrogram of station ELDB (50 to 66 seconds in the video shown in Fig.…”

“…Recently, a simple scaling between the source magnitude and volume has been well established, covering a wide range of source volumes from 10 0 to 10 6 m 3 . But, there is a scatter trend in the data distribution for volumes ranging from 10 2 to 10 5 m 3 (Roy et al, 2019), which is shown in this research.…”

“…Thus, it is essential to get precise information about the timing, location, and moving volume of such events within a short time for the purpose of issuing warnings and understanding the physical process of failures for assessment of hazard management, field survey, and slope protection after events. Recently, the seismic technique has been widely used for those purposes for RSF events, not only on a local scale (Vilajosana et al, 2008；Helmstetter & Garambois, 2010；Zimmer et al, 2012；Zimmer and Sitar, 2015Dietze et al, 2017;Roy et al, 2019), but also on a regional scale (Dammeier et al, 2011;Manconi et al, 2016;Fuchs et al, 2018). In the case of a free-fall event, the leading seismic signals corresponding to crack propagation and rock impact occupy a higher frequency band than do the signals induced by rock detachment and rebound (Levy et al, 2011;Dietze et al, 2017;Roy et al, 2019).…”

Rockfall and vulnerability of mountaineers on the west face of the Aiguille du Goûter (classic route up Mont Blanc, France), an interdisciplinary study

“…Quantifying rockfalls volumes from seismic signals is the subject of many studies (Dietze et al 2017;Hibert et al 2017;Le Roy et al 2019). Volumes can be derived from the characteristics of the seismic signal (duration, energy, amplitude) and are a function of the distance to the source, the type of ground impacted, the drop height, etc.…”

Reliability and Uncertainties of the Analysis of an Unstable Rock Slope Performed on RPAS Digital Outcrop Models: The Case of the Gallivaggio Landslide (Western Alps, Italy)

“…To determine the rock volume effectively involved in the landslide of May 29th 2018, it was decided to adopt a quantitative approach that minimizes the effect of the user-related bias (interpretation and manual delimitation of the sliding and the external surfaces of the rockfall), similar to those applied in [35][36][37].…”