Surface fault rupture poses a serious threat to infrastructure in many seismically active regions, but knowledge about the factors which control the likelihood of surface displacement is limited. Current probabilistic frameworks rely only on fault mechanism and moment magnitude to predict the probability of rupture to the ground surface. However, recent work has shown that there may be other parameters which also deserve consideration. For example, statistical analyses have demonstrated that variation in near surface material stiffness may significantly affect the probability of surface rupture over reverse faults. In addition, numerical investigations indicate that the rupture history of native soil deposits also greatly influences the nature of rupture propagation. Given that evidence exists which suggests multiple variables are at work, this study aimed to improve our understanding of which are most critical for predicting surface fault rupture hazard. We sought to generate physical evidence concerning the impact of near surface soil stiffness, soil type, and rupture history on fault rupture propagation. A 3 meter long by 1 meter wide fault box apparatus was constructed to simulate idealized reverse fault rupture oriented at 45° beneath 60cm of soil. Relatively large dimensions were chosen so that shear wave velocity measurements could be taken directly without interference from the walls of the apparatus. Experiments were conducted on loose sand, dense sand, stiff clay, and soft clay. The same sand was used for both the dense and loose sand experiments and is identified as Monterey #2/16. The clay was a scale model mixture of San Francisco Bay Mud and consisted of kaolinite, bentonite, class C fly ash, and water. Separate batches of clay were mixed with differing final water contents for the stiff and soft clay experiments. In each case, the fault box was filled to 60 cm and rupture was driven to the surface in two phases. The first phase represented an undisturbed native soil deposit with no existing shear band. The second simulated repeat rupture along a pre-existing shear band. The results indicate that increasing material stiffness promotes rupture propagation in both sand and clay. When disturbed soil is re-ruptured, surface rupture occurred much more readily in all materials. Overall, the presence of a pre-existing shear band was shown to have the greatest impact on the likelihood of surface rupture, though both material stiffness and type were also found to have a strong influence as well. The fault box experiments support the findings from previous work as well as shed new light on which parameters are most critical for accurate surface rupture predictions.

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Times New Roman'} A methodology is presented for evaluating the potential surface fault displacement on reverse faults in a probabilistic manner. This methodology follows the procedures put forth for Probabilistic Fault Displacement Hazard Analysis (PFDHA). Empirical probability distributions that are central to performing a PFDHA are derived from field investigations of reverse faulting events. Statistical analyses are used to test previously assumed properties of scale invariance with respect to magnitude for normalized displacement. It is found that normalized displacement is statistically invariant with respect to magnitude and focal mechanism, allowing for the combination of a large number of events into a single dataset for regression purposes. An empirical relationship is developed using this single dataset to be used as a fault displacement prediction equation. A PFDHA is conducted on the Los Osos fault zone in central California and a hazard curve for fault displacement is produced. A full sensitivity analysis is done using this fault as a reference, to test for the sources of variability in the PFDHA methodology. The influence of the major primary variables is quantified to provide a future direction for PFDHA.

Analogue modelling of strike-slip faulting provides insight into the development and behaviour of surface ruptures with accumulated slip, with relevance for understanding how information recorded in paleoseismic trenches relates to the earthquake behaviour of active faults. Patterns of surface deformation were investigated in analogue experiments using cohesive and non-cohesive granular materials above planar strike-slip basement faults. Surface deformation during the experiments was monitored by 3D PIV (particle image velocimetry) and 2D time lapse photography. Analysis focused on fault zone morphology and development, as well as the relationship of the models to surface deformation observed at the Greendale Fault that resulted from the 2010 Darfield earthquake. Complex rupture patterns with similar characteristics to the Greendale Fault (e.g. en echelon fractures, Riedel shears, pop-up structures, etc.) can be generated by a simple fault plane of uniform dip, slip, and frictional properties. The specific structures and the style of their development are determined by the properties of the overburden and the nature of the material surface. The width of the zone of distributed deformation correlates closely with sediment thickness, while the width of discrete fracturing is controlled by the material properties as well as the thickness of the overburden. The overall deformation zone width increases with the growth of initial, oblique fractures and subsequently narrows with time as strain localizes onto discrete fractures parallel to the underlying basement fault. Mapping the evolution of fracture patterns with progressive strain reveals that Riedel shears, striking at 90-120° (underlying fault strike = 90°) are more frequently reactivated during multiple earthquake cycles, and are thus most likely to provide reliable paleoseismic records. This will help identify suitable locations for paleoseismic trenches and interpret trench records on the Greendale Fault and other active, strike-slip faults in analogous geologic settings. These results also highlight the tendency of trenching studies on faults of this type to underestimate the number and displacement of previous ruptures, which potentially leads to an underestimate of the magnitude potential and recurrence interval of paleoearthquakes.

La fissuration intergranulaire par corrosion sous contrainte affecte depuis plusieurs décennies certaines pièces en alliage 600 (NC15FE) des réacteurs nucléaires à eau sous pression, telles que les tubes de générateur de vapeur et les manchettes d'adaptateur pour couvercle de cuve, exposées pendant plusieurs dizaines de milliers d'heures au milieu primaire (eau pure désaérée, additionnée d'hydrogène, de bore et de lithium entre 290 et 325°C). L'objectif de l'étude est une meilleure compréhension des mécanismes responsables de la fissuration, en particulier des interactions entre les sollicitations mécaniques locales et les effets d'environnement liés à la présence d'un milieu oxydant. Des essais de propagation de fissure sur éprouvettes CT ont été réalisés en fatigue continue et en fatigue fluage. L'analyse des résultats a porté sur les sollicitations mécaniques locales (calcul par éléments finis), les modes d'oxydation (expertises par microscopie électronique en transmission) et les interactions entre l'environnement et le comportement mécanique du matériau (essais sur produit mince). La propagation de fissure intergranulaire à 550°C sous différentes pressions partielles d'oxygène a été reliée à un endommagement de fluage. La formation d'oxydes riches en nickel et/ou en fer accélère le fluage dislocation à proximité de la surface. Elle étend alors le domaine de rupture intergranulaire vers les vitesses de déformation locales plus élevées imposées en fatigue continue. Des résultats analogues ont été obtenus à 400°C. Les essais en présence d'eau désaérée (vapeur à 400°C, milieu primaire à 320°C) ont également conduit à une propagation de fissure intergranulaire et à la formation d'oxydes riches en nickel. Les faciès de rupture sont identiques à ceux obtenus en corrosion sous contrainte. Une activation locale du fluage dislocation par les réactions d'oxydation est également envisagée pour rendre compte des résultats expérimentaux.