Characteristics of the Seismic Signal Generated by Fragmental Rockfalls: Insight from Laboratory Experiments

Continuous seismic signals are proposed as a useful quantitative information source for the estimation of rockfall properties. However, few studies have examined the characteristics of the seismic signal of fragmentation-related rockfalls. In this study, a series of laboratory experiments designed with crushable analog blocks freefalling and impacting on a thin horizontal plate under different initial conditions (e.g., block volume, strength and fall height) were conducted. Strong correlations are observed between the rockfall properties and the seismic parameters when considering the rock fragmentation during impact. However, these relationships are observed only when the variation in potential energy spans over one order of magnitude, indicating that the application of seismic signals is limited by rockfall properties. In particular, the seismic energy calculated by the diffuse method is the most stable seismic parameter that is highly correlated with the potential energy of rockfalls. By compiling the available data of the seismic signals of both natural and experimental rockfalls from previous studies and our experiments, we found that the relationship between the seismic energy and the potential energy of rockfalls follows a power law model at all scales. The exponent of the power law function ranges from 1.11 to 1.69. Rock strength can significantly affect the seismic features, which are quantitatively discussed. Rock fragmentation acts as an intermediate variable, which is controlled by rockfall properties and consequently affects the corresponding seismic characteristics. Furthermore, rock fragmentation reduces the efficiency of the conversion of potential energy to seismic energy of rockfalls.