The CQU Regional Seismic Network and applications to underground mining in Central Queensland,Australia

Digital seismograms continuously recorded from 1988 to 1992 by two stations of the RESNOM seismic network in northern Baja California, Mexico, were used to search for probable shear-wave anisotropic characteristics in the region of the Cerro Prieto fault. Shear-wave splitting was identified in many of the three-component records analyzed. We measured the polarization direction of the leadingS wave inside theS-wave window as well as the delay times between fast and slow phases on those records displaying shear-wave splitting. For station CPX, which is nearest the Imperial Valley region to the north, the preferred polarization direction found in this study (azimuth 180°±10°) coincides with the direction of the regional maximum compressive stress determined for the region. This polarization direction can be interpreted in terms of the “Extensive Dilatancy Anisotropy” model as the effect of vertical parallel aligned cracks. The preferred polarization direction measured at LMX, however, gives an azimuth of 45°±5°. Thus, it appears that faults and fractures aligned oblique to the main tectonic trend have a greater influence on the anisotropic characteristics of the crust south of Cerro Prieto volcano than that of the regional stress field. Time delays between slow and fastS waves observed at CPX appear constant from 1988 to 1992 while delays measured at LMX for the same interval indicate a small increase with time which cannot be attributed to azimuthal variations of paths.     

Iowa catalog of solar X-ray flux (2–12 Å)

The absolute X-ray flux from the whole disc of the sun in the wave length range 2 to 12 Å has been observed for a prolonged period by University of Iowa equipment on the earth-orbiting satellite Explorer 33 and the moon-orbiting satellite Explorer 35, both of the Goddard Space Flight Center of the National Aeronautics and Space Administration. The observations are continuing at the date of writing (July 1969). A comprehensive catalog of the flux F (2–12 Å) is being produced. The observational technique and the scheme of reducing data are described herein. Sample tabulations and plots are given. A catalog of tabular and graphical data with a time resolution of either 81.8 or 163.6 sec has been completed for the following periods: From Explorer 33: 2 July 1966 to 27 July 1967 From Explorer 35: 26 July 1967 to 18 September 1968 These blocks of data have been delivered to the National Space Science Data Center National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland 20771, U.S.A. and made available through that agency to interested workers in solar and ionospheric physics. Further blocks of data will be made available as they are completed. An abridged summary of principal flares is published in the monthly Solar-Geophysical Data of the U.S. Department of Commerce, Environmental Science Services Administration.     

Overview of the geography of the Monte Desert biome (Argentina)

The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.     

A Critical Re-Examination of the Factors Influencing Determination of Organic Matter in Soils

Geotechnical and Geological Engineering - Organic matter is an undesirable constituent of the soil. Soils containing organic matter are associated with significant secondary compression and...     

Spinel–cordierite symplectites replacing andalusite: evidence for melt-assisted diapirism in the Bushveld Complex, South Africa

Spinel–cordierite symplectites partially replacing andalusite occur in metapelitic rocks within the cores of several country rock diapirs that have ascended into the upper levels of layered mafic/ultramafic rocks in the Bushveld Complex. We investigate the petrogenesis of these symplectites in one of these diapirs, the Phepane dome. Petrographic evidence indicates that at conditions immediately below the solidus the rocks were characterized by a cordierite‐, biotite‐ and K‐feldspar‐rich matrix and 5–10 mm long andalusite porphyroblasts surrounded by biotite‐rich fringes. Phase relations in the MnNCKFMASHT model system constrain the near‐solidus prograde path to around 3 kbar and imply that andalusite persisted metastably into the sillimanite + melt field, where the fringing relationship between biotite and andalusite provided spatially restricted equilibrium domains with silica‐deficient effective bulk compositions that focused suprasolidus reaction. MnNCKFMASHT pseudosections that model these compositional domains suggest that volatile phase‐absent melting reactions consuming andalusite and biotite initially produced a moat of cordierite surrounding andalusite; reaction progressed until all quartz was consumed. Spinel is predicted to grow with cordierite at around 720 °C. Formation of the aluminous solid products was strongly controlled by the receding edge of andalusite grains, with symplectites forming at the andalusite‐cordierite moat interface. Decompression due to melt‐assisted diapiric rise of the floor rocks into the overlying mafic/ultramafic rocks occurred close to the thermal peak. Re‐crossing of the solidus at P = 1.5–2 kbar, T > 700 °C resulted in preservation of the symplectites. Two features of the silica‐deficient domains inhibited resorption of spinel. First, the cordierite moat armoured the symplectites from reaction with crystallizing melt in the outer part of the pseudomorphs. Second, an up‐T step in the solidus at low‐P, which may be in excess of 100 °C higher than the quartz‐saturated solidus, resulted in high‐T crystallization of melt on decompression. Even in metapelitic rocks where melt is retained, preservation of spinel is favoured by decompression.     

Pyrite-organic matter relationships: Currant Bush Limestone,Georgina Basin,Australia

The relationship between the TOC (total organic carbon) and S (pyritic sulphur) contents of some organic-rich (TOC 3–14%) silty limestones and calcareous siltstones from the Cambrian Currant Bush Limestone of the Georgina Basin, Australia, is similar to that of euxinic sediments, but could also indicate deposition in a non-saline environment. However, such conditions are not easily reconciled with the shallow equatorial epeiric sea in which the formation is considered to have been deposited. The relationship can alternatively be explained by the relatively low Fe content of the sediment being the main limiting factor in pyrite generation, coupled with a slightly increased degree of pyritization with increased TOC. The relationship between the TOC and S contents of organic-poor (TOC 0.2–2.4%) samples from the same formation is similar to that of normal marine sediments, but the Fe content is probably also the major controlling factor on pyrite generation. These interpretations demonstrate that in using TOC and S contents to aid in reconstruction of depositional environments, it is important to check whether Fe content could have been the limiting factor in the formation of pyrite, even in sediments with only moderate carbonate contents.     

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils.

Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (similar to 27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals.     

Which households are most distant from health centers in rural China? Evidence from a GIS network analysis

In this paper we have two objectives—one empirical; one methodological. Although China’s leaders are beginning to pay attention to health care in rural China, there are still concerns about access to health services. To examine this issue, we use measures of travel distances to health services to examine the nature of coverage in Shaanxi Province, our case study. The mean distance by road to the nearest health center is still more than 6 km. When we use thresholds for access of 5 and 10 km we find that more than 40 (15) percent of the rural population lives outside of these 5 (10) kilometer service areas for health centers. The nature of the access differs by geographical region and demographic composition of the household. The methodological contribution of our paper originates from a key feature of our analysis in which we use Geographic Information System (GIS) network analysis methods to measure traveling distance along the road network. We compare these measures to straight-line distance measures. Road distances (produced by network analysis) produce measures (using means) that are nearly twice as great as straight-line distances. Moreover, the errors in the measures (that is, the difference between road distances and straight-line distances) are not random. Therefore, traditional econometric methods of ameliorating the effects of measurement errors, such as instrument variables regression, will not produce consistent results when used with straight-line distances.     

Spatial plans and urban development trajectory in Kumasi,Ghana

This research uses empirical data to explore the link between spatial plans and ‘actual development’ occurring in Kumasi, Ghana. The research found that urban development is determined by both spatial plans and spontaneous informal development patterns (i.e. self-organisation). However, self-organisation is more widespread compared to spatially planned neighbourhoods. This phenomenon was expressed in a context of uncertainty created by weak institutional planning system which promote and reinforce haphazard development disregarding urban planning requirements. These findings provide a perspective on urban development that differs from that occurring in cities of developed countries, where planning institutions in consultation with urban residents determine the patterns of urban development. Unfortunately in Kumasi, self-organisation is not viewed as important in mainstream planning system. The paper concludes that more needs to be done in terms of understanding self-organisation processes, and the way they could be integrated into mainstream planning process to respond more fully to the urban development challenges in Kumasi.