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Rupture et instabilités : sismicité et mouvements de terrain

Abstract : We analyze the rupture associated with two natural phenomena, earthquakes and landslides. In the first part, we study a simple stochastic model of seismicity, based on the two best-established empirical laws for earthquakes, the power law decay of seismicity after an earthquake and the power law distribution of earthquake energies. This model assumes that each earthquake can trigger aftershocks, with a rate increasing with its magnitude. The seismicity rate is in this model the result of the whole cascade of direct and secondary aftershocks. We analyze the space-time organization of the seismic activity in the different sub- and super-critical regimes of the model. We show that this simple model can reproduce many properties of real seismicity, such as the variability of the aftershocks decay law, the acceleration of the seismic activity before large earthquakes, the diffusion of aftershocks, the migration of foreshocks, and the modification of the magnitude distribution before large earthquakes. We find that this model provides a good predictability for a fraction of earthquakes that are triggered by a previous large event. We demonstrate the essential role played by the cascades of earthquake triggering at all scales in controlling the seismic activity. The second part is devoted to the analysis of landslides. A study of several catalogs of rock falls shows that the distribution of rockfall volumes follows a power-law distribution, arising either from the scale invariant heterogeneity of the rock-mass, or from the dynamics of a self-organized critical system. We propose that the precursory acceleration of the displacement before some catastrophic landslides can be reproduced using a slider block model with a rate-and-state dependent friction law. Application of this model to two landslide slip histories suggests that we can distinguish an acceleration of the sliding velocity in the stable regime from an unstable acceleration leading to a catastrophic collapse.
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https://tel.archives-ouvertes.fr/tel-00010935
Contributor : Agnes Helmstetter <>
Submitted on : Friday, November 11, 2005 - 5:50:45 PM
Last modification on : Thursday, November 26, 2020 - 3:52:11 PM
Long-term archiving on: : Friday, April 2, 2010 - 11:03:34 PM

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  • HAL Id : tel-00010935, version 1

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Agnès Helmstetter. Rupture et instabilités : sismicité et mouvements de terrain. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00010935⟩

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