Implication des salariés dans la vie de l'entreprise : lorsque le droit pose les fondements d'une nouvelle gouvernance

Attendue, débattue, décriée … l’impulsion française de ces dernières années tendant à faire du salarié un acteur à part entière de l’entreprise interpelle. En effet, le microcosme de la firme s’en trouve bouleversé et l’évidence d’une réalité sociale condamnée à évoluer pose la nécessité de rechercher un nouvel équilibre. Reste à disséquer les implications de cette tendance récente, à en comprendre les fondements et à en mesurer les enjeux. Le dispositif juridique français est animé d’une préoccupation qui ne cesse de prendre de l’ampleur depuis la fin des années 2000 : faire du salarié un partenaire impliqué dans la vie de l’entreprise. L’étude de cette perception innovante d’une gouvernance axée sur la collaboration des salariés ne peut être menée sans appréhender les travaux de l’OCDE qui, dans ses Principes de gouvernement d’entreprise, fournit une grille d’analyse complète. En conséquence, le droit s’inscrit en droite ligne des nombreux écrits d’autres disciplines prônant une implication croissante des employés. Toutefois, l’accélération de la prise en compte des salariés dont témoignent les textes récemment adoptés en France rend complexe la synthèse de ce phénomène.Waited, discussed, and slandered … The French impulse of these last years tending to make of the employee a separate actor of the company calls. Indeed, the microcosm of the firm is upset there and the evidence of a social reality condemned to evolve puts the necessity of looking for a new balance. Remain to dissect the implications of this recent tendency, to understand foundations and to measure the stakes. The French legal device is stimulated by a concern which does not stop being growing since the end of 2000s : make of the employee a partner involved in the life of the company. The study of this innovative perception of a governance centred on the collaboration of the employees cannot be led without studying the works of the OECD which, in its Principles of corporate governance, supplies a complete analysis. As a consequence, the law joins numerous papers of the other disciplines lauding an increasing implication of the employees. However, the acceleration of the consideration of the employees of which show texts recently adopted in France makes complex the synthesis of this phenomenon

The effects of planetary and stellar parameters on brittle lithospheric thickness

P.K.B. acknowledges support from North Carolina State University. Funding for S.M. was provided by NERC standard grant NE/PO12167/1 and UK Space Agency Aurora grant ST/T001763/1. M.J.H. thanks the Institut Universitaire de France (IUF) for support.The thickness of the brittle lithosphere—the outer portion of a planetary body that fails via fracturing—plays a key role in the geological processes of that body. The properties of both a planet and its host star can influence that thickness, and the potential range of those properties exceeds what we see in the Solar System. To understand how planetary and stellar parameters influence brittle lithospheric thickness generally, we modeled a comprehensive suite of combinations of planetary mass, surface and mantle temperature, heat flux, and strain rate. Surface temperature is the dominant factor governing the thickness of the brittle layer: smaller and older planets generally have thick brittle lithospheres, akin to those of Mercury and Mars, whereas larger, younger planets have thinner brittle lithospheres that may be comparable to the Venus lowlands. But certain combinations of these parameters yield worlds with exceedingly thin brittle layers. We predict that such bodies have little elevated topography and limited volatile cycling and weathering, which can be tested by future telescopic observations of known extrasolar planets.Publisher PDFPeer reviewe

The influence of roughness on experimental fault mechanical behavior and associated microseismicity

Fault surfaces are rough at all scales, and this significantly affects fault-slip behavior. However, roughness is only occasionally considered experimentally and then often in experiments imposing a low-slip velocity, corresponding to the initiation stage of the earthquake cycle. Here, the effect of roughness on earthquake nucleation up to runaway slip is investigated through a series of dry load-stepping biaxial experiments performed on bare rock surfaces with a variety of roughnesses. These laboratory faults reached slip velocities of at least 100 mm/s. Acoustic emissions were located during deformation on bare rock surfaces in a biaxial apparatus during load-stepping experiments for the first time. Smooth surfaces showed more frequent slip instabilities accompanied by slip bursts and larger stress drops than rough faults. Smooth surfaces reached higher slip velocities and were less inclined to display velocity-strengthening behavior. The recorded and localized acoustic emissions were characterized by a greater proportion of large-magnitude events, and therefore likely a higher Gutenberg-Richter bGR-value, for smoother samples, while the cumulative seismic moment was similar for all roughnesses. These experiments shed light on how local microscopic heterogeneity associated with surface topography can influence the macroscopic stability of frictional interfaces and the associated microseismicity. They further provide a laboratory demonstration of roughness' ability to induce stress barriers, which can halt rupture, a phenomenon previously shown numerically

On the scale dependence in the dynamics of frictional rupture: constant fracture energy versus size-dependent breakdown work

Potential energy stored during the inter-seismic period by tectonic loading around faults is released during earthquakes as radiated energy, heat and fracture energy. The latter is of first importance since it controls the nucleation, propagation and arrest of the seismic rupture. On one side, fracture energy estimated for natural earthquakes (breakdown work) shows a clear slip-dependence. On the other side, recent experimental studies highlighted that, fracture energy is a material property limited by an upper bound value corresponding to the fracture energy of the intact material independently of the size of the event. To reconcile these contradictory observations, we performed stick-slip experiments in a bi-axial shear configuration. We analyzed the fault weakening during frictional rupture by accessing to the near-fault stress-slip curve through strain gauge array. We first estimated fracture energy by comparing the measured strain with the theoretical predictions from Linear Elastic Fracture Mechanics and a Cohesive Zone Model. By comparing these values to the breakdown work obtained from the integration of the stress-slip curve, we show that, at the scale of our experiments, fault weakening is divided into two stages; the first one consistent with the estimated fracture energy, and a long-tailed weakening corresponding to a larger energy not localized at the rupture tip, increasing with slip. Through numerical simulations, we demonstrate that only the first weakening stage controls the rupture initiation and that the breakdown work induced by the long-tailed weakening can enhance slip during rupture propagation and allow the rupture to overcome stress heterogeneity along the fault. We conclude that the origin of the seismological estimates of breakdown work could be related to the energy dissipated in the long-tailed weakening rather than to the one dissipated near the tip

On the scale dependence in the dynamics of frictional rupture: Constant fracture energy versus size-dependent breakdown work

Potential energy stored during the inter-seismic period by tectonic loading around faults is released during earthquakes as radiated energy, frictional dissipation and fracture energy. The latter is of first importance since it is expected to control the nucleation, the propagation and the arrest of the seismic rupture. On one side, the seismological fracture energy estimated for natural earthquakes (commonly called breakdown work) ranges between 1 J/m2 and tens of MJ/m2 for the largest events, and shows a clear slip dependence. On the other side, recent experimental studies highlighted that, concerning rupture experiments, fracture energy is a material property (energy required to break the fault interface) independently of the size of the event, i.e. of the seismic slip. To reconcile these contradictory observations and definitions, we performed stick-slip experiments, as analog for earthquakes, in a bi-axial shear configuration. We estimated fracture energy through both Linear Elastic Fracture Mechanics (LEFM) and a Cohesive Zone Model (CZM) and through the integration of the near-fault stress-slip evolution. We show that, at the scale of our experiments, fault weakening is divided into a near-tip weakening, corresponding to an energy of few J/m2, consistent with the one estimated through LEFM and CZM, and a long-tailed weakening corresponding to a larger energy not localized at the rupture tip, increasing with slip. Through numerical simulations, we demonstrate that only near-tip weakening controls the rupture initiation and that long-tailed weakening can enhance slip during rupture propagation and allow the rupture to overcome stress heterogeneity along the fault. We conclude that the origin of the seismological estimates of breakdown work could be related to the energy dissipated in the long-tailed weakening rather than to the one dissipated near the tip

Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids

The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2 fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2 storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2 fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2 mixtures

HighSTEPS. A high strain temperature pèressure and speed apparatus to study earthquake mechanics

We present a state of-the-art biaxial apparatus able to study both earthquake rupture nucleation and propagation at conditions typical of the seismogenic crust. The HighSTEPS, High Strain TEmperature Pressure Speed, apparatus simulates fault deformation in a wide range of slip velocities, i.e., from 10-5m/s to 0.25 m/s. Within this velocity range, it is possible to study, the rate-and-state friction, the fault dynamic weakening, and healing under unique boundary conditions, i.e., normal stress up to 100 MPa, confining pressure up to 100 MPa, pore fluid pressure up to 100 MPa and temperature up to 120 °C. The apparatus consists of a hydraulic system integrated with four linear motors. The hydraulic system allows for the application of normal stress, confining pressure and pore fluid pressure. The main peculiarity of this apparatus is the system of four linear motors that are mounted in series in order to apply shearing velocities up to 0.25 m/s, accelerations up to 10 m/s2 and shear stresses up to 200 MPa. Moreover, both experiments in sliding velocity control or shear stress control on the experimental faults are possible. Preliminary experiments on carbonate and silicate bearing rocks are coherent with the previous literature. The investigation of fault friction under a wide range of velocities, normal stresses, confining pressures and pore fluid pressures will provide insights into the mechanics of earthquakes and reduce the gap between natural and laboratory observations

Effect of glass on the frictional behavior of basalts at seismic slip rates

We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB