3 Abstract Gravimetry is an enormously expanding geophysical exploration method during the last decade. Unfortunately the gravity inversion ambiguity problem introduces the necessity to constrain gravity model parameters by other independent data. Overview of gravity data processing and interpretation is presented. All stages of the project lifecycle are discussed with emphasis to the methodological aspects and new challenges introduced by common use of modern digital zero-length spring gravimeters. Special attention is drawn on approaches used in the presented case histories projects. Description of the interpretation stage of the project concentrates on constraining of gravity model parameters with a complex of geophysical and geological data in order to reduce ambiguity of the inversion process in gravimetry. In addition, approaches used for delineation of tectonic structures, an important aspect of the interpretation stage, are described. Three case histories examples are presented to demonstrate methodological aspects of the interpretation of gravity data. They are focused on environmental problems and tectonic structure assessment. The first project represents an attempt to use micro-gravity for determination of internal structure of an undocumented sealed landfill. The second project demonstrates...

No description available.

No description available.

Direct-current resistivity prospecting methods have been used but rarely in the past in physical investigations of icecaps and glaciers. However these methods have the advantage of using light-weight and inexpensive equipment that is simple to operate. As part of the geophysical program of the Arctic Institute of North America's Devon Island Expedition, resistivity measurements were made in the accumulation and ablation zones of an ice-cap and on an adjoining glacier during the summers of 1961 and 1962. Depths of ice ranging from 50 to 750 meters were measured on the Sverdrup Glacier. Depth soundings on the ice-cap were not very successful owing primarily to insufficient power. However, some indication of the depth and composition of the firn was obtained. Ice resistivities were for the most part in the range from 4.10⁴ to 10⁵ ohm-meters, as compared with values of several megohm-meters found for temperate glaciers in lower latitudes. Variations of ice resistivities as a function of other physical properties were investigated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The magnetotelluric method, which depends upon the determination of impedance values over a wide frequency range (0.001-1 cps) from a pair of orthogonal electric and magnetic field components, has been used in the past by several investigators to determine the resistivity of the crust and upper mantle. Because of the diversity of the results obtained by the magnetotelluric method it was felt necessary to examine the method critically in order to obtain useful and unambiguous results. To carry this out an investigation was made of the magnetotelluric field recorded simultaneously at six stations in central Alberta during August 1961. The investigation is divided into five main sections; the recording of the magnetotelluric field, the analysis of the field records by various methods, the evaluation of the validity of the different assumptions made in the magnetotelluric method, the determination of subsurface resistivities, and the investigation of inhomogeneous and anisotropic bodies. Continuous recordings of Ey, Hx and Hz were made during August 1961 for two weeks at six stations, each approximately 100 km apart and oriented in a north-south direction (113.5° W longitude). In addition two extra components Ex, Hy were recorded at the central station, Beiseker. Estimates of the wave impedance Ey/Hx were obtained by inspection of quasi-sinusoidal events on the records from Meanook and Cardston. Using Cagniard's method an estimate of the subsurface resistivity ρ was made at Meanook. No estimate could be made at Cardston because of the large scatter of points in the plot of Ey/Hx against period T, Subsurface inhomogeneities near Cardston are believed to be the main cause of this scattering. At Beiseker, power spectra of selected lengths of records were computed and from them the ratios Ey/Hx and Ex/Hy were obtained in order to estimate subsurface resistivities. In addition a method for interpreting anisotropic bodies has been suggested and used at Beiseker to explain the differences which exist between the ratios EV/HL and Ex/Hy. A comparison between the various methods suggested by different investigators to interpret magnetotelluric data has been made and it has been shown with the help of theoretical models that these methods have no advantage over the curve matching method suggested by Cagniard. Moreover, it has been shown that such methods may give ambiguous results if applied to the interpretation of high frequency ( > 0.005 cps) magnetotelluric data. In order to judge the validity of the basic assumption of Cagniard's method, viz. that the horizontal gradients of the field vectors are negligible compared to vertical gradients, power spectra of corresponding lengths of records, used for the estimation of the resistivities, were computed at all six stations for the components Hx and Hz. Micro-pulsation activity which exhibited high coherence of Hx at all six stations yielded the least scatter in the ρ vs T plot as was expected. By carefully selecting data on the basis of this and other coherence criteria it is believed that a reliable indication has been obtained of a marked decrease in the resistivity in the upper part of the Earth's mantle. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

No description available.

No description available.

No description available.

No description available.