Seismic Energy Analysis as Generated by Impact and Fragmentation of Single‐Block Experimental Rockfalls

Abstract

The analysis of seismic signals obtained from near‐source triaxial accelerometer recordings of two sets of single‐block rockfall experiments is presented. The tests were carried out under controlled conditions in two quarries in northeastern Spain; in the first test (Foj limestone quarry, Barcelona), 30 blocks were released with masses ranging between 475 and 11,480 kg. The second test (Ponderosa andesite quarry, Tarragona) consisted of the release of 44 blocks with masses from 466 to 13,581 kg. An accelerometer and three high‐speed video cameras were deployed, so that the trajectories, velocities, and block fragmentation could be tracked precisely. These data were used to explore the relationship between seismic energy and rockfall kinetics (the latter obtained from video analysis). We determined absolute and relative values of seismic energy and used them to estimate rockfall volumes. Finally, the seismic signature of block fragmentation was assessed in both the frequency and time domains. The ratios of seismic energy after impact to kinetic energy before impact ranged between 10−7 and 10−4. These variables were weakly correlated. The use of seismic energy relative to impacting kinetic energy was preferred for the estimation of volumes. Block fragmentation impacts were dominated by higher acceleration spectrum centroid frequencies than those of nonfragmentation impacts: 56.62 ± 2.88 and 48.46 ± 4.39 Hz at Foj and 52.84 ± 12.73 and 38.14 ± 4.73 Hz at Ponderosa.

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

“…Hibert et al () 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 () did not find a correlation between kinetic parameters of the blocks and measured seismic energies. All these studies highlight the large uncertainties on rockfall properties (volume, velocity, location, etc.)…”

“…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, ) or in quarries (Saló et al, ) explored seismic amplitude and energy in relation to the kinetics of block impacts. Hibert et al () inferred single block mass and velocity from local seismic records with a fair accuracy (median ratio between calculated and measured velocity of 0.2).…”

Contributions of Rock Mass Structure to the Emplacement of Fragmenting Rockfalls and Rockslides: Insights From Laboratory Experiments

“…From direct observation of deposit orthophotos of experiments, we can see that the blocks fractured and fragmented into numerous fragments, leading to energy redistribution and cover area variation. Specifically, the fragmentation process will affect the number, magnitude, and intensity of falling rock blocks, eventually affecting rock fragment trajectories and runout, as well as the destructive potential (Agliardi & Crosta, 2003; Jaboyedoff et al, 2005; Corominas et al, 2012; Ruiz‐Carulla et al, 2017; Saló et al, 2018). Therefore, the fragmentation process is fundamental for rockfall analysis.…”

“…If we consider the inclined slab as an acceleration stage that allows jointed analog blocks to accumulate speed, these slab experiments can simply describe the rockfall processes in which rock masses impact at high speeds onto the slope foot and are deposited on the horizontal ground near the slope foot (Sanders et al, 2013; Ruiz‐Carulla et al, 2017; Saló et al, 2018). However, if we consider the inclined slab as a sliding surface, based on the classification of landslides in Hutchinson (1998), the slab experiments are all translational slides, which are very common in natural rockslides (Crosta et al, 2017, 2018).…”

Damaged Speleothems and Collapsed Karst Chambers Indicate Paleoseismicity of the NE Bohemian Massif (Niedźwiedzia Cave, Poland)

“…Hence, the collapses in Niedźwiedzia Cave, which are characteristic not only of the ceiling and walls but also of the floor, may suggest that they are earthquake‐triggered. Importantly, the horizontal acceleration required to break most of the speleothems in Niedźwiedzia Cave (see Figure 6) is comparable to that produced by an earthquake, as they are too high to be produced by block collapse, which does not exceed 1 m/s 2 (Saló et al., 2018). Consequently, we interpret that at least some of the collapses in Niedźwiedzia Cave are earthquake‐induced.…”