Field experiments: How well can seismic monitoring assess rock mass falling?

Rockfall tracking and mass estimation are critical for effective hazard response. While seismic techniques have been applied to the field, systematic analysis remains lacking. In this study, we conducted rockfall experiments using seismic networks to investigate tracking and mass estimation issues. Two methods, time-based and amplitude-based source location methods, were used to identify initial rock-ground impact points. The high-fitness areas (>0.95) overlapping between the two methods showed a location error of <8.7 m for initial rock-ground impact points. However, the combined methods could not track bounce points on the slope. To address the limitation, we further defined a seismic energy ratio, a ratio between target and reference stations. When a reference station was far away from rockfall, the rising or decreasing of high-frequency (70–99 Hz) seismic energy ratios reflected the rock approaching or departing from the target station, respectively. Additionally, the peak low-frequency (1–40 Hz) seismic energy ratio of ground stations indicated the timing of the initial rock-ground impact. Successful implementation of these methods depends on optimal station distribution. The study recommends that different source-to-station distances with triangular station geometry and stations at different elevations provide a reliable location determination and straightforward rockfall tracking. Furthermore, the lowest frequency(fL) satisfied the power spectral threshold of −100 dB during the rockfall moving process correlated with the rock mass(M), M = 38,989FL-2.03 with R2 of 0.62. The relation was practical for estimating rockfalls' mass for future monitoring in the same slope. Our experiments demonstrate that this seismic technique can effectively assist in rockfall assessment.