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.     

Land use/cover classification using enhanced IRS-1A LISS 1 data — A case study of Calcutta Metropolitan District,India — 1989

The land use/cover in any urban area is dynamic in nature. Maps of existing land use/covers have to be updated periodically to monitor changes. To speed up mapping and decision making, remotely sensed satellite data have been advocated. This study used the IRS-1A LISS 1 satellite data for delineation of selected urban features in Calcutta Metropolitan District. Due to lack of ground information, some known features have been used as reference categories to classify the study area.The satellite data was transformed through a principal components analysis and two new bands of data were created and combined with the original four band data. Both supervised and unsupervised methods were used for spectral signature collection. Thirty-six classes derived from Isodata clustering, after comparing with the selected known features, these were grouped to form five generalized land use/cover categories. The spatial distribution of these land use/cover categories have been explained in this study.     

The structure and sequence of geological events in the Basement Complex of the Ibadan area,Western Nigeria

The Basement Complex in Western Nigeria in general, and in the Ibadan area in particular, is composed primarily of a banded gneiss in which hornblende-biotite rich bands alternate with quartz-oligoclase rich bands. The banded gneiss, which originated as part of a sedimentary sequence, contains large lenses of granite gneiss and thin intercolated layers of quartzite and amphibolite.Two distinct major structural events can be clearly identified in the early geological history of the Ibadan area. Detailed field studies suggest that the formation of the Ibadan Granite Gneiss, which had yielded an Eburnean Rb-Sr isochron age, was associated with the later of these events. Five phases of dyke or vein formation, two of which pre-date the formation of the Granite Gneiss, have also been identified giving an overall sequence of geological events the first of which may correspond to the beginning of the Liberian orogeny, around 3000 m.y. ago, and the last of which reflects the waning of the Pan-African thermo-tectonic event about 500 m.y. ago.     

Granite diapirism in the Rum Jungle area,Northern Australia

Early studies in the Rum Jungle area suggested an intrusive relationship between the Rum Jungle and Waterhouse “Granites”, and the overlying sediments. It was later shown that the granitic “intrusions” were Archaean basement complexes onto which Lower Proterozoic sediments had been deposited. Polyphase folding was postulated as being responsible for doming of the basement and cover rocks.This paper proposes to show that the domed structures in the Rum Jungle area, and the emplacement of Middle Proterozoic granites in the Pine Creek Geosyncline were related, and caused by diapiric intrusion of granites, in a solid state, into basement complexes and cover rocks.Structural and metamorphic evidence in support of diapiric intrusion in the Rum Jungle area includes: pebble deformation within steeply dipping beds of quartz conglomerate; disappearance of polyphase fold structures away from the basement complexes; bending of folded country-rock strata into concordance with the complex—sediment contact; and metamorphic and metasomatic alteration of sediments in contact with the basement complexes. Gravity data show mass deficiencies in the Archaean complexes which possibly coincide with young granite diapirs.     

A derivation of the equations for transport of liquid and heat in three dimensions in a fractured porous medium

Governing equations can be derived for transient, three-dimensional transport of heat and mass in compressible, liquid saturated fractured porous media. Recently developed mathematical techniques can be used which relate local space averages of derivatives of medium properties to the derivatives of those averages. Using these techniques, well established thermomechanical transport equations which apply at microscopic points may be transformed into equations in macroscopic variables; i.e. in variables which pertain to the scale of observation. In the absence of chemical reactions, transfer between source entities and the medium may be taken care of in a consistent, physically realistic way, such that macroscopic source terms arise naturally in the course of the macroscopization procedures.     

Sorted stripes orientated by wind action: Some observations from sub-antarctic marion island

Sorted stripes found on the volcanic scoria and glacial deposits of sub-Antarctic Marion Island indicate a distinct preferred orientation. Despite uniformity of slope and material, the stripes are predominantly aligned parallel to the wind. It is suggested that melting of needle ice by the early morning sun is of only limited importance in the sub-Antarctic owing to the almost continual overcast conditions. The effect of the wind is so great that in exposed situations stripes are formed on horizontal surfaces.     

An analytic stress model applied to the Snake River Plain (Northern Basin and Range province U.S.A.)

The complex representation of plane stress is used for an analytic model to describe the stress regime of the Snake River Plain (SRP) region of the western United States. The area is modeled as an infinite elastic sheet cut along a circular arc with tension applied at infinity. Modeling results include the following: (1) south of the Snake River Plain, the principal direction of tension rotates from the direction of the applied stress to a direction sub-parallel to the cut, consistent with the orientation of normal faulting and nodal planes given by fault plane solutions; (2) north of the Snake River Plain, calculated stress directions are consistent with the variable nature of faulting in that region; (3) a decrease in magnitude of predicted stresses is observed within the Snake River Plain consistent with relatively low levels of seismicity on the Plain.     

A thought on heat flow and tidal drag as possible driving forces of plate tectonics

The amount of useful work that can be extracted from the Earth's heat flow is examined from a thermodynamic standpoint.