Co-detection of acoustic emissions during failure of heterogeneous media: new perspectives for natural hazard early warning

A promising method for real time early warning of gravity driven rupture that considers both the heterogeneity of natural media and characteristics of acoustic emissions attenuation is proposed. The method capitalizes on co-detection of elastic waves emanating from micro-cracks by multiple and spatially separated sensors. Event co-detection is considered as surrogate for large event size with more frequent co-detected events marking imminence of catastrophic failure. Using a spatially explicit fiber bundle numerical model with spatially correlated mechanical strength and two load redistribution rules, we constructed a range of mechanical failure scenarios and associated failure events (mapped into AE) in space and time. Analysis considering hypothetical arrays of sensors and consideration of signal attenuation demonstrate the potential of the co-detection principles even for insensitive sensors to provide early warning for imminent global failure

Co-detection of micro seismic activity as early warning of gravitational slope failure

We developed a new strategy for Disaster Risk Reduction for gravitational slope failure: We propose a simple method for real-time early warning of gravity-driven failures that considers and exploits both the heterogeneity of natural media and characteristics of acoustic emissions attenuation. This method capitalizes on co-detection of elastic waves emanating from micro-cracks by a network of multiple and spatially distributed sensors. Event co-detection is considered as surrogate for large event size with more frequent co-detected events marking imminence of catastrophic failure. In this study we apply this method to a steep rock glacier / debris slope and demonstrate the potential of this simple strategy for real world cases, i.e. at slope scale. This low cost, robust and autonomous system provides a well adapted alternative/complementary solution for Early Warning Systems.Comment: 11 pages, 8 figure

A Two-Threshold Model for Scaling Laws of Non-Interacting Snow Avalanches

The sizes of snow slab failure that trigger snow avalanches are power-law distributed. Such a power-law probability distribution function has also been proposed to characterize different landslide types. In order to understand this scaling for gravity driven systems, we introduce a two-threshold 2-d cellular automaton, in which failure occurs irreversibly. Taking snow slab avalanches as a model system, we find that the sizes of the largest avalanches just preceeding the lattice system breakdown are power law distributed. By tuning the maximum value of the ratio of the two failure thresholds our model reproduces the range of power law exponents observed for land-, rock- or snow avalanches. We suggest this control parameter represents the material cohesion anisotropy.Comment: accepted PR

Le déclenchement des avalanches de plaque de neige:<br />De l'approche mécanique à l'approche statistique.

The present work aims at understanding the mechanisms responsible forsnow slab avalanche formation.A first approach consists in applying to snow well known concepts of Fracture Mechanics. Experimental measurements of fracture toughness, are interpreted in terms of the particular structure of snow.A statistical approach is then used, based on databases provided by La Plagne and Tignes ski resorts. We show for the first time that avalanche sizes are scale invariant.Models used to describe such phenomena usually fail in correctly reproducing field data. We introduce a two-threshold stress-driven cellular automaton. We show that the statistical behaviour characteristic of snow avalanches, but also of other gravity-driven failures, can be easily reproduced acting on a single parameter that accountsfor the cohesion anisotropy of the material. The present approach may be considered as an alternative to Self Organised Criticality for gravity-driven systems.Ce travail est dédié à l'étude de la rupture du manteau neigeux, conduisantaux avalanches de plaques de neige.La détermination expérimentale de la ténacité de la neige, qui caractérise sa résistance à la propagation d'une fissure, nous a donné des résultats originaux que nous interprétons en tenant compte de la structure particulière de ce matériau.Une étude statistique basée sur les données de La Plagne et de Tignes nous a permis de montrer pour la première fois que les distributions des tailles d'avalanches sont invariantes d'échelle. Aucun modèle ne reproduisant correctement ces statistiques de terrain, nous avons créé un automate cellulaire à deux seuils, piloté en contrainte,qui reproduit le comportement statistique des avalanches mais aussi celui d'autres aléas gravitaires naturels à l'aide du réglage d'un unique paramètre reflétant l'anisotropie de cohésion du matériau. Cette approche peut être considérée comme une alternativeà la Criticalité Auto Organisée pour les ruptures gravitaires

Distribution, associated species and extent of biofouling “reefs” formed by the alien species Ficopomatus enigmaticus (Annelida, Polychaeta) in marinas

Artificial structures in ports are commonly colonized by non-indigenous epifauna that tolerate high pollution levels. Bioconstructions built by alien species may offer sheltered microhabitats for motile (vagile) animals but biofouling often becomes detrimental to human activities. In this context, the present study provides an inventory of 1) the extent of biofouling related to the alien Polychaeta Ficopomatus enigmaticus on hard structures of marinas in Normandy, France, and 2) the biodiversity of sessile (attached) or vagile (motile) fauna associated with these “reefs”, including both native and alien species. Reefs built by F. enigmaticus were found in 6 out of 12 marinas with oligohaline-mesohaline waters. Significant differences in the total volume of biofouling were found among sites, with maximum values observed in Honfleur's old basin (459.52 mL per 0.04 m2). Ficopomatus enigmaticus greatly dominated the sessile invertebrate community both in volume (74–100%) and weight (70–100%) in 5 out of 6 marinas. The fouling formed by 5 alien species was colonized by 15 motile invertebrate taxa, including 3 cryptogenic or alien species. The alien crab Rhithropanopeus harrisi displayed the highest frequency of occurrence (>80%) and mean density (>300 ind m−2), and the global densities of sessile (except F. enigmaticus) and motile fauna were significantly correlated (r = 0.824; p  0.05). In line with previous studies, these results suggest that F. enigmaticus acts as an engineer offering shelter for reef-associated organisms. In addition, results suggest that at the regional scale, inter-site differences in motile fauna may reflect differences in environmental parameters such as salinity. The presence of F. enigmaticus at low salinity levels led to assess its potential distribution at the scale of the European coasts, suggesting that in the context of climate change, favorable conditions for spawning (>18 °C) will likely expand towards the North, and particularly in the eastern and northern Baltic Sea