Is Earthquake Triggering Driven by Small Earthquakes?

Using a catalog of seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this relation and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that seismicity triggering is driven by the smallest earthquakes, which trigger fewer events than larger earthquakes, but which are much more numerous. We propose that the non-trivial scaling of the number of triggered earthquakes emerges from the fractal spatial distribution of seismicity.Comment: 5 pages, 2 figure

Spectral analysis and correlation of ambient seismic noise. The case study of Madonna del Sasso (NW Italy)

Ambient vibrations recorded on potentially-unstable rock slopes show that the temporal variations in the spectral content and in the correlation of seismic noise can be related to both reversible and irreversible changes within the rock mass. In this work, we analyzed the seismic recordings acquired at the potentiallyunstable granitic cliff of Madonna del Sasso (NW Italy) from October 2013 to November 2014. The spectral content of noise systematically highlighted clear energy peaks at specific frequencies on the most unstable sector, interpreted as resonant frequencies of the investigated volume. Horizontal ground motion at the fundamental frequency was moreover found to be orthogonal to the main fractures observed at the site and consequently parallel to the potential direction of collapse. Cross-correlation was computed between the recordings of the sensors placed in the prone-to-fall compartment and a stable reference station. Both the temporal variations of the resonant frequencies and the results of cross-correlation showed seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from damage processes within the rock mass, were detected during the monitored period

The Forecasting Skill of Physics‐Based Seismicity Models during the 2010–2012 Canterbury, New Zealand, Earthquake Sequence

The static coulomb stress hypothesis is a widely known physical mechanism for earthquake triggering and thus a prime candidate for physics-based operational earthquake forecasting (OEF). However, the forecast skill of coulomb-based seismicity models remains controversial, especially compared with empirical statistical models. A previous evaluation by the Collaboratory for the Study of Earthquake Predictability (CSEP) concluded that a suite of coulomb-based seismicity models were less informative than empirical models during the aftershock sequence of the 1992 Mw 7.3 Landers, California, earthquake. Recently, a new generation of coulomb-based and coulomb/statistical hybrid models were developed that account better for uncertainties and secondary stress sources. Here, we report on the performance of this new suite of models compared with empirical epidemic-type aftershock sequence (ETAS) models during the 2010-2012 Canterbury, New Zealand, earthquake sequence. Comprising the 2010 M 7.1 Darfield earthquake and three subsequent M = 5:9 shocks (including the February 2011 Christchurch earthquake), this sequence provides a wealth of data (394 M = 3:95 shocks). We assessed models over multiple forecast horizons (1 day, 1 month, and 1 yr, updated after M = 5:9 shocks). The results demonstrate substantial improvements in the coulomb-based models. Purely physics-based models have a performance comparable to the ETAS model, and the two coulomb/statistical hybrids perform better or similar to the corresponding statistical model. On the other hand, an ETAS model with anisotropic (fault-based) aftershock zones is just as informative. These results provide encouraging evidence for the predictive power of coulomb-based models. To assist with model development, we identify discrepancies between forecasts and observations. © 2018 Seismological Society of America. All rights reserved

Écoute sismique et acoustique du mouvement de terrain de Séchilienne (massif de Belledonne)

Seismic monitoring can be used to detect micro-seismicity induced by the progressive damage and deformation of landslides, as well as rockfalls and debris flows. This method allows to monitor continuously the temporal evolution of a site and to identify the mechanisms responsible for the triggering of these instabilities. Séchilienne rockslide is instrumented since 2007 by three seismic antennas. This network has been temporarily completed by one microphone, which yields supplementary information to improve the classification and location of seismic sources.L’écoute sismique des mouvements gravitaires permet de détecter la micro-sismicité induite par l’endommagement et la déformation de ces objets, ainsi que les éboulements et les coulées de débris. Cette méthode permet de suivre en continu l’évolution temporelle d’un site et d’identifier les mécanismes responsables du déclenchement de ces instabilités. Le mouvement de terrain de Séchilienne a été instrumenté dès 2007 par trois antennes sismiques. Ce réseau a été complété temporairement par un microphone, qui apporte des informations complémentaires pour améliorer la classification et la localisation des sources.Helmstetter Agnes, Janex Gaël. Écoute sismique et acoustique du mouvement de terrain de Séchilienne (massif de Belledonne). In: Collection EDYTEM. Cahiers de géographie, numéro 19, 2017. Monitoring en milieux naturels. Retours d’expériences en terrains difficiles. pp. 271-278

Ruptures et instabilités (sismicité et mouvements gravitaires)

GRENOBLE1-BU Sciences (384212103) / SudocRENNES-Géosciences (352382209) / SudocSudocFranceF