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. Plain Language Summary: Rockfalls are common natural hazards that threaten lives, local communities and infrastructures in mountainous areas. The movement of rockfalls may radiate seismic signals that can be captured by professional equipment. These seismic signals present useful information about the initial condition (e.g., volume, fall height) and movement process of rockfalls, which is important for disaster mitigation. We designed a series of laboratory experiments, modeling the process by which fragmental material freefalls and impacts a horizontal plate (simplified rockfall). By gathering and analyzing the seismic signals, empirical functions between the parameters calculated from seismic signals and fragmental rockfall properties are built. These empirical functions can be used to infer the rockfall properties (potential energy, volume, fall height, etc.) in real time based on the radiated seismic signals. Moreover, we focus on the effects of rock strength and rock fragmentation on the seismic signals. These factors are seldom considered before but are important, as illustrated in our experiments. Our results may help further understand the relationships between rockfall properties and the features of corresponding seismic signals. Key Points: Empirical functions between seismic parameters and fragmental rockfall properties are establishedA qualitative illustration of the variation in seismic characteristics caused by rock fragmentation is presentedThe relationship between the seismic energy and the potential energy of rockfalls follows a power law model at all scales [ABSTRACT FROM AUTHOR]