Exploring fault rocks at the nanoscale

This paper aims to demonstrate the potential role of micro/nanoscale investigations in the study of fault rocks, given that a multiscale and multidisciplinary approach linking structural geology, petrology and mineralogy from the outcrop to the unit-cell scale is essential to the comprehensive characterization of geological materials. To explore fault rocks at the sub-micrometer scale, a fundamental contribution is provided by the Transmission Electron Microscope (TEM), which offers a real-time combination of high-resolution images, diffraction patterns, and chemical data for extremely small volumes, providing accurate mineralogical and nanostructural determinations.This paper focuses on a few selected examples, that are particularly appropriate for TEM investigation, in particular: 1) grain-size determinations on ultrafine-grained fault rocks; 2) detection and characterization of poorly crystalline minerals (e.g., clays) and amorphous phases within fault rocks; 3) identification of deformation-induced mineral reactions occurring within fault zones (e.g., dolomite decarbonation and serpentine dehydration); and 4) observations of recurrent deformation nanotextures in phyllosilicates. TEM investigation can provide an unexpected amount of data, much of which cannot be obtained by conventional techniques, and it can therefore significantly contribute to an understanding of the physico-chemical conditions for faulting and fault mechanics.     

Evaluation of Lateral Interpretation Criteria for Drilled Shaft Capacity in Gravels

Representative interpretation criteria are examined in detail to evaluate the lateral response of drilled shaft foundations in gravels. A database of field lateral load tests is used for the analysis. The representative criteria are subdivided into absolute displacement, displacement as a function of shaft diameter, rotation limit, mathematical model, and graphical construction method. Comparison of these criteria shows that the initial elastic region ends at approximately 3–5 mm, 0.50 %B, and 0.08° rotation, which represent the serviceability limit state. The final region begins at about 25 mm, 2.5 %B, and 0.33° rotation, which represent the ultimate limit state. The graphical construction methods, Q_L and Q_S&W, are located within the transition region of the curve. Among these criteria, the displacement limits, Q_L, and Q_S&W methods demonstrate more reliable results. The typical load–displacement curves for lateral capacity in gravels are developed for engineering practical use. Further, recommendations for the use of these interpretation criteria are also given.     

Life cycle phenology, secondary production, and trophic guilds of caddisfly species in a lake-outlet stream of Patagonia

Lake-outlets are transitional areas recognized as highly productive ecosystems in terms of density and biomass of aquatic insects. Life cycle, secondary production, trophic guilds and environmental constraints of caddisfly assemblages were investigated on a natural lake-outlet stream (Nant y Fall) in Patagonia, Argentina. We investigated the site monthly from May 2007 to April 2008 by recording environmental data and sampling caddis larvae using a Surber sampler at riffle areas (n = 36). Mastigoptila longicornuta, Smicridea annulicornis, Smicridea frequens, Brachysetodes quadrifidus and Parasericostoma ovale displayed well synchronized univoltine life cycles, while Neoatopsyche brevispina, Neopsilochorema tricarinatum, showed an asynchronous development pattern, although most of them had an extended recruitment, similar to those reported for non lake-outlet streams in the area. Annual secondary production per species varied from 8.22 (B. quadrifidus) to 3568.83 mg m⁻² y⁻¹ (P. ovale), with overall caddisfly production amounting to 4.8 g m⁻² y⁻¹. Shredder/collector-filterer ratio was 3.3/1 suggesting that the system was detrital based. Redundancy analysis indicated that seasonally dynamic variables such as discharge, benthic particulate organic matter and temperature were the main predictors of seasonal caddisfly assemblage variation. We propose that the variety of food resources and the significant spatial heterogeneity at lake-outlet streams contribute to sustain a rich caddisfly community.     

The Puesto Piris Formation: Evidence of basin-development in the North Patagonian Massif during crustal extension associated with Gondwana breakup

The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.     

A continuum representation of fracture networks. Part II: application to the Äspö Hard Rock laboratory

A method to represent fracture networks in a continuum model is evaluated by an application to the Äspö Hard Rock Laboratory (HRL). The basic approach of the method is to first generate a fracture network, based on data from field measurements and then represent the network as grid cell conductivities, using a staggered grid arrangement. It is argued that the resulting conductivity fields capture the correlation and anisotropy structures, as well as the mean conductivity, of the rock in a realistic way. The main objective is to evaluate if the suggested method can be used in an application to a real site. The objective is formulated in three questions: ‘Can the method utilize available field data?’, ‘Can the generated fields be calibrated and conditioned?’ and ‘Are realistic distributions of pressure, flow and density obtained?’. From the application to the Äspö HRL, it is concluded that the hydraulic conductivity fields, generated by the suggested method, can utilize field data and be calibrated. It is also demonstrated that realistic distributions of pressure, flow and density can be simulated.     

Effects of supplemental viscous damping on inelastic seismic response of asymmetric systems

This paper investigates the effects of supplemental viscous damping on the seismic response of one‐storey, asymmetric‐plan systems responding in the inelastic range of behaviour. It was found that addition of the supplemental damping reduces not only deformation demand but also ductility and hysteretic energy dissipation demands on lateral load resisting elements during earthquake loading. However, the level of reduction strongly depends on the plan‐wise distribution of supplemental damping. Nearly optimal reduction in demands on the outermost flexible‐side element, an element generally considered to be the most critical element, was realized when damping was distributed unevenly in the system plan such that the damping eccentricity was equal in magnitude but opposite in algebraic sign to the structural eccentricity of the system. These results are similar to those noted previously for linear elastic systems, indicating that supplemental damping is also effective for systems expected to respond in the inelastic range. Copyright © 2001 John Wiley & Sons, Ltd.     

Hydrodynamic modelling of mesoscale eddies in the Black Sea

A three dimensional structure of mesoscale circulation in the Black Sea is simulated using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System. A number of sensitivity tests reveal the response of the model to changes in the horizontal resolution, time steps, and diffusion coefficients. Three numerical grids are examined with x-fine (3.2 km), fine (6.7 km) and coarse (25 km) resolution. It is found that the coarse grid significantly overestimates the energy of the currents and is not adequate even for the study of basin-scale circulation. The x-fine grid, on the other hand, does not give significant advantages compared to the fine grid, and the latter is used for the bulk of simulations. The most adequate parameters are chosen from the sensitivity study and used to model both the basin-scale circulation and day-to-day variability of mesoscale currents for the months of May and June of 2000. The model is forced with actual wind data every 6 h and monthly climatic data for evaporation, precipitation, heat fluxes and river run-off. The results of the fine grid model are compared favourably against the satellite imagery. The model adequately reproduces the general circulation and many mesoscale features including cyclonic and anticyclonic eddies, jets and filaments in different parts of the Black Sea. The model gives a realistic geographical distribution and parameters of mesoscale currents, such as size, shape and evolution of the eddies.     

Institutional change and natural resource use in coastal Vietnam

Vietnam is currently undergoing a rapid economic and social transition involving the dismantling of the co-operative system and the official embracing of a market economy. The paper uses an institutional approach to examine adaptation to such changes in two coastal communes in mangrove forest areas. Having provided the historical and policy context of reforms which have taken place in Vietnam in the area of resource management, the paper goes on to discuss changes currently taking place in access to resources. The complexity of property rights regimes are then examined in the light of such changes, with particular focus on the effects of privatisation and the increased effects of integration with external markets. Using livelihood diversification as a key concept for understanding local adaptation to such changes, the paper concludes with discussion of the socially differentiated impacts of the process and the implications for future livelihoods. This revised version was published online in July 2006 with corrections to the Cover Date.