Prediction of faulting from the theories of elasticity and plasticity: what are the limits?

Elasticity, rigid-plasticity and elasto-plasticity are the simplest constitutive models used to describe the initiation and evolution of faulting. However, in practice, the limits of their application are not always clear. In this paper, we test the behaviour of these different models using as examples tectonic problems of indentation of a die, compression with basal shear, bending of a plate and normal faulting around a dike. By comparing the results of these tests, we formulate some guidelines that may be useful for the selection of an appropriate constitutive model of faulting. The theory of elasticity reasonably predicts the initiation of the fault pattern but gives erroneous results for large strains. The theory of rigid-plasticity is more appropriate for large deformations, where the geometry of faults can be found by the method of characteristics. This method works well for zones of failure that are not severely constrained by elastic material outside e.g. when faults are connected to the free-surface, a viscous substratum or a zone of weakness. Non-associated elasto-plasticity is the most complete theory among those considered in this paper. It describes the evolution of faults from the initiation of localized deformations to the formation of a complicated fault network

Comment on “Stability of the Earth with respect to the spin axis for the last 130 million years” by J.A. Tarduno and A.Y. Smirnov [Earth Planet. Sci. Lett. 184 (2001) 549–553]

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Le quartier bas d'Ambrussum : essai de relecture d'une carte de prospection géophysique

This paper in an attempt to analyse the errors and reading difficulties which often arise during the interpretation of geophysical survey maps. Grey shadowing as well as data treatment, (destriping and median filtering) can be used not only for legibility improvement but for correction of some erroneous measurements. The efficiency of these methods is discussed in the case of an already published electrical survey realised on the site of Ambrussum. The archaeological interpretation is accordingly revised.On tente d'analyser les causes d'erreurs et de difficultés de lecture que présentent souvent les cartes de prospection géophysique. La représentation en tons de gris et les traitements des données (délignage et filtrage par la médiane) sont autant de procédés qui, non seulement améliorent la lisibilité, mais corrigent certains défauts des mesures. L'efficacité de ces procédés est discutée à partir d'un cas déjà publié de prospection électrique réalisé sur le site d'Ambrussum. L'interprétation archéologique est révisée en conséquence.Hesse A., Daignieres Marc, Fiches Jean-Luc, Tabbagh J. Le quartier bas d'Ambrussum : essai de relecture d'une carte de prospection géophysique. In: Revue d'Archéométrie, n°16, 1992. pp. 5-12

Present-day strain distribution across the Minab-Zendan-Palami fault system from dense GPS transects

International audienceP>The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr-1 of relative motion in N10 degrees E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr-1 in N10 degrees direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27 degrees N reveal a much narrower shear zone (similar to 10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a 'stacking' and a 'persistant-scatterers' approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic 'block model' inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle