Geophysical imaging methods provide solutions to a wide range of environmental and engineering problems: protection of soil and groundwater from contamination; disposal of chemical and nuclear waste; geotechnical site testing; landslide and ground subsidence hazard detection; location of archaeological artefacts. This book comprehensively describes the theory, data acquisition and interpretation of all of the principal techniques of geophysical surveying: gravity, magnetic, seismic, self-potential, resistivity, induced polarization, electromagnetic, ground-probing radar, radioactivity, geothermal, and geophysical borehole logging. A final chapter is devoted to inversion theory and tomography. Each chapter is supported by a large number of richly illustrated case histories. This book will prove to be a valuable course-book for advanced undergraduates and postgraduates in environmental and applied geophysics, a supplementary course-book for students of geology, engineering geophysics, civil and mining engineering, and a reference work for professional earth scientists, engineers and town planners.

Paleomagnetic investigations have been carried out on about 250 oriented block samples collected from Early Tertiary lava flows representing an altitude span of about 1200 m on the Disko Island and 600 m on the Nûgssuaq Peninsula of West Greenland. The results reveal a record of two polarity transitions on the Disko Island and the existence of normal (N) and reverse (R) groups of lava flows on the Nûgssuaq Peninsula. A tentative correlation of the lava sequences from the two areas, on the basis of polarity of magnetization, has been suggested. Subject to the assumption of relatively uniform extrusion rates in northern Disko, a correlation of the comparatively thick sequence of reverse (R) polarity flows with the relatively long reverse epoch between the anomaly no. 25 (ca. 63 m.y.) and anomaly no. 24 (ca. 60.5 m.y.B.P.), has been attempted and an age estimate of the lava flows has been obtained.The Early Tertiary paleomagnetic pole for Greenland, computed from stable remanent magnetic directions of the Disko lavas is located at 67.5 °N and 165 °W. This pole position and the one for contemporaneous lava flows on the Baffin Island of Canada have been used in testing the models proposed by various workers for a paleogeographic reconstruction of Greenland and Canada, involving a closure of the Baffin Bay – Labrador Sea. The results of this paleomagnetic test suggest the existence of an ocean basin in the area, prior to the eruption of Early Tertiary lava sequences on Baffin Island and West Greenland, and also that this ocean basin had a much wider extent in Pre-Tertiary times.A model for the evolution of Baffin Bay – Labrador Sea has been suggested in the light of available geological/geophysical information about the region. It involves the opening of this sea in the Mesozoic and its partial closure during the Cenozoic as a consequence of the drift of Greenland in the northwesterly direction.

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Samples from the Nexg Sandstone of the Lower Cambrian-Precambrian boundary in South Bomholm reveal a stable NRM with a direction after magnetic cleaning of D = 226", I = -30" (ag5 = 1 1 So). This NRM appears to originate in the detrital hematite grains rather than in the red cement of the sandstone. The stable NRM is likely to be of primary origin and reflects a Lower Cambrian pole at 104" W, 38" N (dp = 7", dm = 1 lo). Apparent discrepancies between the Bornholm pole and the few other published Early Cambrian/Late Precambrian poles from the Baltic Shield are consistent with the suggestion of large polar movements in those times.

Demagnetization factors have so far been introduced and calculated only for bodies bounded by a second degree surface. For taking into account the demagnetization effect of a body of some other shape, such as a rectangular prism, the normal practice hitherto has been to approximate it by an ellipsoid of known demagnetization factor. As shown later, the demagnetization factors so obtained are, in general, subject to considerable errors excepting for some particular dimensional ratios.