Vancouver Island, located in southwestern coastal British Columbia, overlies the northern portion of the Cascadia Subduction Zone. This region is characterized by extensive seismicity which includes M ∼ 7 crustal earthquakes and less frequent M ∼ 9 megathrust events. Crustal deformation measurements have been carried out in this region since 1978 using various geodetic field techniques: levelling, tide gauge studies, precise gravity, laser ranging, and most recently, GPS. Earlier survey data provided key constraints to elastic slip-dislocation models for estimating the size and location of the rupture area for the next subduction-thrust earthquake. Recent estimates of crustal motions within the North Cascadia Margin based on both campaign GPS network surveys and up to 6.5 years of data from continuous GPS sites are consistent with the strain accumulation expected from a locked subduction fault. The deformation vectors are in the direction of plate convergence within the uncertainty of plate motion models. The observed strain rate across Vancouver Island is, however, smaller (by approximately a factor of 1.5) than the dislocation model prediction, suggesting the presence of visco-elastic effects. Crustal deformation measurements for central Vancouver Island fail to resolve motions that could be associated with the occurrence of large crustal earthquakes, and also suggest that the extent of the seismogenic subduction thrust zone north of the Nootka Fault Zone is extremely limited. / Graduate

This work takes a look at some of the literature on calcretes and especially the problem of geochemical exploration in calcrete terrains. The conclusion that will be reached is that exploration in calcrete terrains is not futile and that provided the explorationist is aware of the types of calcrete and their genetic implications calcrete can be used as a sampling medium and anomalies can be detected through calcrete (p.1.) / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

Anomalous element distributions within the regolith result from chemical adjustments of the earth's surface to prevailing climatic conditions. Because of the lack of moisture in the arid environment, chemical equilibrium related to paleoclimates is largely maintained. Mechanical or clastic dispersion dominates arid weathering and hence the exploration approach is largely dictated by the degree of preservation of the paleoregolith. Arid environment geochemists thus have to contend with surface materials ranging from laterite and calcrete in areas where the imprint of aridity is minimal, to more conventional sample media such as bedrock, stream sediment and lithic soils in actively dissecting areas. Extraction techniques are designed specifically to isolate clastic dispersion trains. Thick mantles of aeolian and water-borne overburden characterise desert lowlands and are a challenge to the exploration geochemist. Techniques showing the most promise in these areas include groundwater geochemistry, vapour geochemistry, surface microlayer geochemistry, geobotany and biogeochemistry which attempt to isolate gaseous and weak hydromorphic, ore-related trace-element dispersions. Termite mound sampling yields convincing results and appears to be an under-utilised geochemical approach. / KMBT_363 / Adobe Acrobat 9.53 Paper Capture Plug-in

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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

Ocean bottom magnetometer data from a site on the Pacific plate above 3 my old lithosphere are inverted for electrical conductivity as a function of depth. Magnetotelluric impedances are calculated by the vertical gradient method using the fields at the OBM in conjuction with those measured at the Victoria Geomagnetic Observatory. The approximations involved are examined. Winnowing criteria are proposed which isolate those impedances compatible with all the model and source field assumptions. These then define the best possible data set. A number of inversion algorithms are applied to the data and a wide range of acceptable conductivity profiles are constructed. All profiles exhibit a uniform, relatively high conductivity of about 0.2 S/m from the surface down to a depth of 100 km. Exact and approximate bounds on the conductance are calculated in an effort to quantify the non-uniqueness of the diverse conductivity models. Profiles with a minimum of structure are used to calculate the partial melting and temperature variations beneath the 3 my old site. All results are compared with three other magnetotelluric analyses above 1, 30 and 72 my old lithosphere. The 3 my old datum is discordant and does not fit the trends interpreted from the other three studies. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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