A framework for temporal and spatial rockfall early warning using micro-seismic monitoring

Abstract

Rockfall risk is usually characterized by a high frequency of occurrence, difficulty in prediction (given high velocity, lack of noticeable forerunners, abrupt collapse, and complex mechanism), and a relatively high potential vulnerability, especially against people and communication routes. Considering that larger rockfalls and rockslides are generally anticipated by an increased occurrence of events, in this study, a framework based on microseismic monitoring is introduced for a temporal and spatial rockfall early warning. This approach is realized through the detection, classification, and localization of all the rockfalls recorded during a 6-month-long microseismic monitoring performed in a limestone quarry in central Italy. Then, in order to provide a temporal warning, an observable quantity of accumulated energy, associated to the rockfall rolling and bouncing and function of the number and volume of events in a certain time window, has been defined. This concept is based on the material failure method developed by Fukuzono-Voight. As soon as the first predicted time of failure and relative warning time are declared, all the rockfalls occurred in a previous time window can be located in a topographic map to find the rockfall susceptible area and thus to complement the warning with spatial information. This methodology has been successfully validated in an ex post analysis performed in the aforementioned quarry, where a large rockfall was forecasted with a lead time of 3 min. This framework provides a novel way for rockfall spatiotemporal early warning, and it could be helpful for activating traffic lights and closing mountain roads or other transportation lines using the knowledge of the time and location of a failure. Since this approach is not based on the detection of the triggering events (like for early warnings based on rainfall thresholds), it can be used also for earthquake-induced failures.

Numerical investigation of seismic source location using distributed acoustic sensing for rockfall monitoring

“…For small-scale monitoring, geophones can effectively record and locate the impact points of rockfalls. However, for larger-scale monitoring with sparsely installed geophones, weak seismic events might only trigger nearby geophones and they cannot be accurately identified or located (Feng et al 2021). The dense and continuous sensing features of DAS are in favour for such applications.…”

“…The impact points of rockfalls may not be accurately located, especially when the monitoring scale is large. Feng et al (2021) developed a framework to use microseismic monitoring to forecast slope failures at a limestone quarry in Italy. The location of impact points was carried out to determine the rockfall trajectories.…”

Spatiotemporal characteristics of ground microtremor in advance of rockfalls

“…When a rock slope becomes dangerous, the measured seismic response exhibits strong directional amplification 26 , 27 . Compared to displacement analysis, these results show that vibration analysis signal characteristics can be used to improve early warning approaches of rock collapse 2 , 3 . However, seismic monitoring has temporal and spatial limitations because it can record signals after a seismic event in only a seismic zone.…”

“…Rock cliffs are usually unstable and may lead to catastrophic collapse that seriously threatens the construction of slope engineering and the safety of passengers in vehicles on the slope 1 , 2 . Only a few papers about rockfall prediction have been published, and no clear precursors before rock collapses have been detected 1 , 3 – 7 .…”

New Approach for Photogrammetric Rock Slope Premonitory Movements Monitoring

“…These techniques are used to quantify detached rock masses on rock slopes over time to estimate the expected magnitude frequency of rockfall [9][10][11][12][13][14], which is required to evaluate risk quantitatively [15,16]. For early warning purposes, ground-based radar interferometry [17], seismic signals [18] and acoustic signals [19] have proven useful in a variety of hazardous scenarios. For better understanding of the rockfall process, some authors have recently used videogrammetric techniques to track blocks and fragments generated during breakage in controlled scenarios on real-scale tests [20,21] or laboratory tests [22,23] and seismic analysis techniques [24,25].…”