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.
Highlights
The economic and population development, increasing access and construction in mountainous areas, bring people and infrastructures to a higher exposure to slope hazards (Dammeier et al 2011)
Based on the observation that the number of rockfalls increases before a larger rockslide (Suwa 1991; Suwa et al 1991; Amitrano et al 2005; Huggel et al 2005; Rosser et al 2007; Szwedzicki 2003; Hibert et al 2017b) and the fundamental law for failure material proposed by Voight (1988) after Fukuzono (1985), here, we propose a framework for a rockfall spatiotemporal early warning using microseismic monitoring
In detail, considering the scales of the events classified as RF, there are 416 very local events, 8 local events (L), and 4 slope scale events (S)
Summary
The economic and population development, increasing access and construction in mountainous areas, bring people and infrastructures to a higher exposure to slope hazards (Dammeier et al 2011). There are several ways to perform landslide early warning. Future developments in the exploitation of interferometric satellites might lead to a bloom of regional scale early warning systems (Raspini et al 2018), displacements are normally exploited at slope scale. The lack of long-term prefailure deformations compatible with the acquisition frequency of even the most modern displacement monitoring systems makes this kind of measurement not suitable for rockfalls. More common, approach to perform landslide early warning is based on rainfall monitoring, which is mostly used for regional-scale systems. As the relation between rockfall occurrences and rainfall is not very clear, since many other factors are involved, such as rock temperature, rock moisture, wind intensity, and air temperature (Matsuoka 2019), this kind of monitoring is not optimal for a rockfall early warning system
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