Triggering of Seismicity Remote from Active Mining Excavations

Summary. Observations of seismicity and ground control problems in the Sudbury mining camp have shown that late-stage (young) sub-vertical strike-slip faults are sensitive to small mining-induced stress changes. The strength-limited nature of stress measurements made in the region indicates that these structures are in a state of marginal stability. Numerical continuum models are developed to analyze the behavior of such structures. In the models, shear strain localizations (faults) evolve such that there is close interaction between the fault system, stresses, and boundary deformation. Fault slip activity in these systems is naturally sporadic and reproduces the commonly observed Gutenberg-Richter magnitude frequency relation. It is shown that a relatively minor disturbance to such a system can trigger significant seismicity remote from the source of the disturbance, a behavior which cannot be explained by conventional numerical stress analysis methodologies. The initially uniform orientation of the stress field in these systems evolves with increasing disorder, which explains much of the scatter commonly observed in data sets of stress measurements. Based on these results, implications for stress measurement programs and numerical stability analysis of faults in mines are discussed.     

Stress field analysis at the El Teniente Mine: evidence for N–S compression in the modern Andes

There is a large database of triaxial stress measurements at the El Teniente Mine, Central Chile, but the complex geology, severe topography, and proximity of all measurements to extensive mining excavations made interpretation of the stress field difficult. The measurements were analyzed using three-dimensional numerical stress analysis and decomposition of the stress field into gravitational and tectonic components. By removing gravitational stresses plus local effects from the tectonic component of the stress field a calculation of the far-field tectonic stress tensor is made. It is shown that variations in the tectonic component of stress are related to shear zones cutting through the mine. The far-field major principal component of the tectonic stress field was found to be oriented approximately N–S. This is consistent with the most recent direction of local shortening based on kinematic analysis of faults, but is perpendicular to the direction of regional crustal shortening. There appears to be a limiting envelope to the magnitude of the stress field implying that the shear zones are in a state of limiting equilibrium with regional tectonic driving forces.     

Strengthen the Environmental Sense of Local Community with PRA and MIGIS

Foundation item: The Project entitled "A Feasibility Study to Strengthen Participatory Planning Capacity by MIGIS" supported by Asian Development Assistance Facility (ADAF), Ministry of Foreign Affairs and Trade. New ZealandAlthough the govenunent has paid great attenhon to the environmental improvement by means of policyand inVestment the environmental condihon is aill getting worse in C~ The current environmentalsitUation is chalacterized by serious POlluhoft expanded land degra…     

The cycling and fate of terrestrially-derived sediments and nutrients in the coastal zone of the Great Barrier Reef shelf

The coastal zone of the Great Barrier Reef shelf, with an area of 30,000 km(2) and a water volume of 300 km(3), receives an average annual input of sediment on the order of 14-28 Mty(-1)--an estimated two- to fourfold increase since European settlement. There is considerable concern about the impact and ultimate fate of terrestrially-derived nutrients entering the Great Barrier Reef World Heritage Area (GBRWHA). Analysis of current data suggests that microbial communities in coastal waters and in unconsolidated sediments metabolise nutrients equivalent to the entire dissolved and particulate nutrient load debouched from land. River-derived nutrients account for 40-80% of the carbon, 13-30% of the nitrogen, and 2-5% of the phosphorus necessary to support the observed rates of benthic and pelagic mineralisation in Princess Charlotte Bay in the far north, and in Rockingham Bay and Missionary Bay in the central section, of the GBRWHA. Nearly all nitrogen is ultimately returned to the atmosphere via denitrification. There is little net burial of nutrients in subtidal sediments. These budget estimates are based on a sparse data set, but it is clear that marine sources of nutrients (N-fixation by pelagic and benthic cyanobacteria) must be important, but the magnitude of these sources is poorly known and likely to be highly variable in space and time. Data from sediment trap deployments suggest that, despite significant re-suspension, sedimentation fluxes are sufficient to balance benthic mineralisation rates. Most organic material deposited to the benthos appears to be flocculent or colloidal aggregates, perhaps formed via microbial mediation and exudation of extra-cellular material. The geophysical dynamics of the coastal boundary layer plays an important role in concentrating biological and biogeochemical activity within a shallow, narrow coastal zone. Mangroves and tidal flats are small in area, but trap, transform, and store a disproportionate amount of sediment and organic matter within the GBRWHA. The highly efficient use of terrestrially-derived nutrients by benthic and pelagic microbes in the coastal zone helps to explain why coral reefs on the middle and outer shelf have remained relatively unscathed despite a significant increase in sediment delivery.     

Mystery of Callisto: Is It Undifferentiated?

The Galileo-determined moment-of-inertia factor for Callisto of 0.406 ± 0.039 (1σ) is consistent with only a small amount of ice–rock differentiation (<10%), because the moment-of-inertia for a totally undifferentiated Callisto is 0.38 (not 0.40). The apparently high value for the moment-of-inertia may include nonhydrostatic contributions originating in Callisto's lithosphere. The anhydrous rock/(rock + water–ice) mass ratio for Callisto is ≈0.45, close to the theoretically predicted value of ≈0.40.     

Zooplankton In An Australian Tropical Estuary

The composition of the zooplankton community in a macrotidal (8 m tidal range), tropical estuarine system (Darwin Harbour, Australia; 12^o28′ S, 130^o50′ E) was studied over a 2 year period with the goal of describing biodiversity and determining the environmental factors that have the greatest impact on community structure. Most (82–84%) of the >73 μm plankton was composed of copepod nauplii and copepodites, and plankton samples taken with larger, coarser meshed (150 and 350 μm) nets did not contain significant numbers of larger (non-copepod) organisms. In all, 32 copepod species were recorded, with small euryhaline marine copepod species such as Parvocalanus crassirostris, Bestiolina similis and Oithona aruensis dominating the zooplankton. Plankton abundances ranged between 30,000 and 110,000 m⁻³, and there were significant year (2003 > 2004), season (wet > dry) and site differences (inner harbour sites > outer harbour sites), but negligible diurnal differences. Multivariate analyses identified three sample groups: (1) middle and outer harbour sites, (2) inner harbour and river sites and (3) the river site during the wet seasons. Middle and outer harbour stations were characterised by a diverse mixture of coastal copepods, whereas inner harbour and river sites were dominated by P. crassirostris and O. aruensis. During the wet season, there was a distinct copepod community within the Blackmore River, dominated by Acartia sinjiensis, Oithona nishidai and Pseudodiaptomus spp. Environmental variables (nutrients and chlorophyll a) were correlated with salinity, which had the strongest influence on community structure. There was a significant drop in species richness from harbour to river sites. Small copepods of the families Paracalanidae and Oithonidae dominate tide-dominated Australian tropical estuaries, whereas copepods belonging to the family Centropagidae (such as Gladioferens spp.) appear to be characteristic of wave-dominated estuaries in southern Australia.     

Plasma, plumes and rings: Saturn system dynamics as recorded in global color patterns on its midsize icy satellites

New global maps of the five inner midsize icy saturnian satellites, Mimas, Enceladus, Tethys, Dione, and Rhea, have been constructed in three colors (UV, Green and near-IR) at resolutions of 1 km/pixel. The maps reveal prominent global patterns common to several of these satellites but also three major color features unique to specific satellites or satellite subgroups. The most common features among the group are first-order global asymmetries in color properties. This pattern, expressed on Tethys, Dione and Rhea, takes the form of a ∼1.4-1.8 times enhancement in redness (expressed as IR/UV ratio) of the surface at the center of the trailing hemisphere of motion, and a similar though significantly weaker IR/UV enhancement at the center of the leading hemisphere. The peak in redness on the trailing hemisphere also corresponds to a known decrease in albedo. These double hemispheric asymmetries are attributable to plasma and E-ring grain bombardment on the trailing and leading hemispheres, respectively, for the outer three satellites Tethys, Dione and Rhea, whereas as E-ring bombardment may be focused on the trailing hemisphere of Mimas due to its orbital location interior to Enceladus. The maps also reveal three major deviations from these basic global patterns. We observe the previously known dark bluish leading hemisphere equatorial band on Tethys but have also discovered a similar band on Mimas. Similar in shape, both features match the surface patterns expected for irradiation of the surface by incident MeV electrons that drift in a direction opposite to the plasma flow. The global asymmetry on Enceladus is offset ∼40° to the west compared to the other satellites. We do not consider Enceladus in detail here, but the global distribution of bluish material can be shown to match the deposition pattern predicted for plume fallback onto the surface (Kempf, S., Beckmann, U., Schmidt, S. [2010]. Icarus 206, 446-457. doi:10.1016/j.icarus.2009.09.016). E-ring deposition on Enceladus thus appears to mask or prevent the formation of the lenses and hemispheric asymmetries we see on the other satellites. Finally, we observe a chain of discrete bluish splotches along the equator of Rhea. Unlike the equatorial bands of Tethys and Mimas, these splotches form a very narrow great circle ?10-km wide (north-to-south) and appear to be related to surface disruption, exposing fresh, bluish ice on older crater rims. This feature is unique to Rhea and may have formed by impact onto its surface of orbiting material.     

On estimating contributions of basin ejecta to regolith deposits at lunar sites

Abstract— We have developed a quantitative model for predicting characteristics of ejecta deposits that result from basin‐sized cratering events. This model is based on impact crater scaling equations (Housen, Schmitt, and Holsapple 1983; Holsapple 1993) and the concept of ballistic sedimentation (Oberbeck 1975), and takes into account the size distribution of the individual fragments ejected from the primary crater. Using the model, we can estimate, for an area centered at the chosen location of interest, the average distribution of thicknesses of basin ejecta deposits within the area and the fraction of primary ejecta contained within the deposits. Model estimates of ejecta deposit thicknesses are calibrated using those of the Orientale Basin (Moore, Hodges, and Scott 1974) and of the Ries Basin (Hörz, Ostertag, and Rainey 1983). Observed densities of secondary craters surrounding the Imbrium and Orientale Basins are much lower than the modeled densities. Similarly, crater counts for part of the northern half of the Copernicus secondary cratering field are much lower than the model predicts, and variation in crater densities with distance from Copernicus is less than expected. These results suggest that mutual obliteration erases essentially all secondary craters associated with the debris surge that arises from the impacting primary fragments during ballistic sedimentation; if so, a process other than ballistic sedimentation is needed to produce observable secondary craters. Regardless, our ejecta deposit model can be useful for suggesting provenances of sampled lunar materials, providing information complementary to photogeological and remote sensing interpretations, and as a tool for planning rover traverses (e.g., Haskin et al. 1995, 2002).