Geotechnical assessment of the bearing capacity of coal mine floors

Summary This investigation concerns 3 longwall faces having variable strata and mining conditions, but supported by 202 tonnes hydraulic 6-leg chocks. Bearing capacity tests along the faces were conducted to evaluate the factors influencing floor deformation and failure. The effect of size, shape and perimeter of the base plates, thickness of the floor layer, time and moisture on the ultimate bearing capacity of the floor was measured and discussed. Application of this work is the prediction of stability and support performance of face ends, as well as the design of support systems and ground control on production faces.     

The Nootka Fault Zone — a new plate boundary off western Canada

Summary. Relative motion across a boundary between the main Juan de Fuca plate and its northern extension, the Explorer plate, had earlier been suggested from sea-floor magnetic anomaly analysis and from earthquakes recorded on the western Canada land seismic network. The location of the boundary, called the Nootka fault zone, and the motion across it have been examined through seismic reflection profiles, accurate location of earthquakes with an array of ocean bottom seismometers and through analysis of magnetic, gravity and bathymetric data. The fault zone extends from a ridge-fault—fault triple point at the northern end of the Juan de Fuca ridge to a fault—trench—trench triple junction at the margin off north-central Vancouver Island. The active portion of the fault zone is about 20 km wide, and has produced extensive disturbance in the 0.5 to 1 km of overlying sediments. Magnetic anomaly analysis suggests present left-lateral strike slip motion of about 3 cm/yr, with convergence at the margin being more rapid to the south than to the north of the fault zone. Because of rapidly changing spreading parameters on the Explorer and Juan de Fuca ridges over the past 5 Myr the Nootka fault zone has had a very complex history.     

Improved Resolution of Ambient Flow through Fractured Rock with Temperature Logs

In contaminant hydrogeology, investigations at fractured rock sites are typically undertaken to improve understanding of the fracture networks and associated groundwater flow that govern past and/or future contaminant transport. Conventional hydrogeologic, geophysical, and hydrophysical techniques used to develop a conceptual model are often implemented in open boreholes under conditions of cross-connected flow. A new approach using high-resolution temperature (±0.001°C) profiles measured within static water columns of boreholes sealed using continuous, water-inflated, flexible liners (FLUTe™) identifies hydraulically active fractures under ambient (natural) groundwater flow conditions. The value of this approach is assessed by comparisons of temperature profiles from holes (100 to 200 m deep) with and without liners at four contaminated sites with distinctly different hydrogeologic conditions. The results from the lined holes consistently show many more hydraulically active fractures than the open-hole profiles, in which the influence of vertical flow through the borehole between a few fractures masks important intermediary flow zones. Temperature measurements in temporarily sealed boreholes not only improve the sensitivity and accuracy of identifying hydraulically active fractures under ambient conditions but also offer new insights regarding previously unresolvable flow distributions in fractured rock systems, while leaving the borehole available for other forms of testing and monitoring device installation.     

Precipitation — elevation relationships over Sri Lanka

Summary The change of rainfall totals with height has been the subject of much investigation in many parts of the world. The rates of increase or decrease vary with the climatic regime experienced. This study of Sri Lankan rainfall shows that the relationship between height and mean annual rainfall is complex. Examples of increases and decreases of rainfall with height are found. The climatic regime of the area is important in controlling the level of maximum rainfall.With 7 Figures     

Correlation of longitudinal currents with Alfvén wave generation in the solar atmosphere

Current instability of Alfvén waves in coronal loops is considered. Such a mechanism of Alfvén wave generation is shown to be very efficient, and it can give rise to low-frequency perturbations even in the case of very weak currents, thus fostering the reconnection of magnetic fields and development of a flare. The low-frequency turbulence which arises in the process can be favorable to the heating and acceleration of particles.     

2-D or 3-D interpretation of conductivity anomalies: example of the Rhine-Graben conductivity anomaly

Summary. Evidence of a conductivity anomaly in the Rhine-Graben was first given about 15 years ago and consequently led to the definition of various models of induction in the region for periods ranging from a few minutes to a few hours. These models reflect two antagonistic ways of explaining the observed anomalous variations of the magnetic field: direct induction in a two-dimensional (2-D) structure or static distortion of telluric currents by the resistive crystalline Vosges (France) and Schwarzwalde (Germany) massifs. We discuss the two approaches using a simple formalism. In particular, we show that the self-induction related to the anomalous currents flowing in the Rhine-Graben is negligible for periods larger than 1000 s, and that, even though the static distortion of telluric currents does account for the observed anomaly, 2-D models can explain some of its features. We also show how the channelled currents are induced in the large sedimentary basins surrounding the area under study.
An experimental verification of this result is given.     

The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye

Summary. A palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of Skye, Scotland, by the Sound of Sleat.
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here.     

Palaeomagnetism of the teschenitic rocks (Lower Cretaceous) in the Outer Western Carpathians of Poland: constraints for tectonic rotations in the Silesian unit

Results of palaeomagnetic investigations of the Lower Cretaceous teschenitic rocks in the Silesian unit of the Outer Western Carpathians in Poland bring evidence for pre-folding magnetization of these rocks. The mixed-polarity component reveals inclinations, between 56° and 69°, which might be either of Cretaceous or Tertiary age. Apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary, although a Neogene or earlier remagnetization cannot be totally excluded since inclination-only test between localities gives 'syn-folding' results. Higher palaeoinclinations (66°–69°) correlate with a younger variety of teschenitic rocks dated for 122–120 Ma, while lower inclinations (56°–60°) with an older variety (138–133 Ma). This would support relatively high palaeolatitudes for the southern margin of the Eurasian plate in the late part of the Early Cretaceous and relatively quick northward drift of the plate in this epoch, together with the Silesian basin at its southern margin. Declinations are similar to the Cretaceous–Tertiary palaeodeclinations of stable Europe in the eastern part of the studied area but rotated ca. 14°–70° counter-clockwise in the western part. This indicates, together with older results from Czech and Slovakian sectors of the Silesian unit, a change in the rotation pattern from counter-clockwise to clockwise at the meridian of 19°E. The rotations took place before the final collision of the Outer Carpathians nappe stack with the European foreland.