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The seismic signals generated by rockfalls can provide information on their dynamics and location. However, the lack of field observations makes it difficult to establish clear relationships between the characteristics of the signal and the source. In this study, scaling laws are derived from analytical impact models to relate the mass and the speed of an individual impactor to the radiated elastic energy and the frequency content of the emitted seismic signal. It appears that the radiated elastic energy and frequencies decrease when the impact is viscoelastic or elastoplastic compared to the case of an elastic impact. The scaling laws are validated with laboratory experiments of impacts of beads and gravels on smooth thin plates and rough thick blocks. Regardless of the involved materials, the masses and speeds of the impactors are retrieved from seismic measurements within a factor of 3. A quantitative energy budget of the impacts is established. On smooth thin plates, the lost energy is either radiated in elastic waves or dissipated in viscoelasticity when the impactor is large or small with respect to the plate thickness, respectively. In contrast, on rough thick blocks, the elastic energy radiation represents less than 5% of the lost energy. Most of the energy is lost in plastic deformation or rotation modes of the bead owing to surface roughness. Finally, we estimate the elastic energy radiated during field scale rockfalls experiments. This energy is shown to be proportional to the boulder mass, in agreement with the theoretical scaling laws.

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This paper is published under the terms of the CC-BY-NC license.

Abstract. Rocky coast erosion (i.e., cliff retreat) is caused by a complex interaction of various forcings that can be marine, subaerial or due to rock mass properties. From Sunamura's seminal work in 1992, it is known that cliff retreat rates are highly variable over at least four orders of magnitude, from 1 to 10 mm yr−1. While numerous local studies exist and explain erosion processes at specific sites, there is a lack of knowledge at the global scale. In order to quantify and rank the various parameters influencing erosion rates, we compiled existing local studies into a global database called GlobR2C2 (which stands for Global Recession Rates of Coastal Cliffs). This database reports erosion rates from publications, cliff setting and measurement specifications; it is compiled from peer-reviewed articles and national databases. In order to be homogeneous, marine and climatic forcings were recorded from global models and reanalyses. Currently, GlobR2C2 contains 58 publications that represent 1530 studied cliffs and more than 1680 estimated erosion rate. A statistical analysis was conducted on this database to explore the links between erosion rates and forcings at a global scale. Rock resistance, inferred using the criterion of Hoek and Brown (1997), is the strongest signal explaining variation in erosion rate. Median erosion rates are 2.9 cm yr−1 for hard rocks, 10 cm yr−1 for medium rocks and 23 cm yr−1 for weak rocks. Concerning climate, only the number of frost days (number of day per year below 0 ∘C) for weak rocks shows a significant, positive, trend with erosion rate. The other climatic and marine forcings do not show any clear or significant relationship with cliff retreat rate. In this first version, GlobR2C2, with its current encompassing vision, has broad implications. Critical knowledge gaps have come to light and prompt a new coastal rocky shore research agenda. Further study of these questions is paramount if we one day hope to answer questions such as what the coastal rocky shore response to sea-level rise or increased storminess may be.

ABSTRACT:Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (http://cloudcompare.org/) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects.For further details: http://www.cloudcompare.org/doc/wiki/index.php?title=Facets_%28plugin%29

ABSTRACT:Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (http://cloudcompare.org/) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects.For further details: http://www.cloudcompare.org/doc/wiki/index.php?title=Facets_%28plugin%29

No abstract