In March of 1987, the Geologic Survey of Canada conducted a major seismic refraction experiment in the Mackenzie Delta-Southern Beaufort Sea-Northern Yukon area. This study involves the analysis of a portion of the resulting data set. A 2D velocity profile through the Richardson Mountains of the northern Yukon has been constructed using raytracing to model the travel-times and amplitudes. The line is approximately 320 km long, running from a shotpointon the Eagle Plains in the south to one 50 km offshore in Mackenzie Bay to the north, with an average receiver spacing of 3.5 km. An additional shotpoint is located at Shingle Point, on the shore of Mackenzie Bay. A series of four sedimentary basins separated by major structural highs produces a complex basement structure. Two distinct upper crustal layers were modelled, a 5.95 km/s layer overlying a 6.3 km/s layer, as well as a lower crustal layer with a velocity of 7.25 km/s. Crustal velocity gradients are low (≤ 0.005 s⁻¹). The 6.3 km/s layer pinches out beneath the Beaufort-Mackenzie Basin in the north, accompanied by a thinning of the lower crust from a thickness of 20 km in the south to less than 10 km beneath MB. This results in the crust as a whole thinning from a thickness of 50 km under the Richardson Mountains to only 40 km under the Beaufort-Mackenzie Basin. The velocity of the upper mantle is 7.95 km/s. The modelling of shear wave arrivals indicate Poisson's ratios of 0.23 ±0.02 in the upper crust and 0.25 + 0.02 in the lower crust. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

published_or_final_version / Earth Sciences / Master / Master of Science

Thesis (Ph.D.(Exploration Geophysics))--University of Pretoria, 2007. / Abstract in English. Includes bibliographical references (leaves 72-76).

Thesis (M.Sc.)--Memorial University of Newfoundland, 1995. / Typescript. Computer disk contains: Appendix A, Fortran programs. Bibliography: leaves 134-137. Also available online.

This study sets out to evaluate the use of geophysical methods for delineating buried stream channels, which can act as zones of preferential flow within a less hydraulically conductive aquifer. This information is important for gaining an understanding of flow dynamics of alluvial systems. The most reliable method of delineating the dimensions of aquifers is by drilling, which is an expensive proposition and is best preceded by a preliminary geophysical study to help define target zones for a drilling program. The study area is located adjacent to the Coerney River in the Sundays River Valley. Geologically it consists of approximately 5 metres of alluvial fines, covering 3 metres of coarse cobbles and boulders, all underlain by alternating siltstone and sandstone beds of indeterminate thickness. Throughout the area the water is very shallow at approximately 2 metres depth and the groundwater tends to be very saline. An air photo study revealed an old oxbow channel that had been covered over by subsequent agricultural land use. The geophysical methods available for the study were portable seismic refraction, electrical resistivity and electromagnetics. Preliminary field tests clearly showed that seismics did not produce valid results. The methods of electrical resistivity and electromagnetics produced good data and were subjected to further assessment. A grid was surveyed over the study area and both geophysical methods were applied at regularly spaced stations. Soil samples were taken over the same survey grid and analyzed for electrical conductivity in a soils laboratory. The results were compared to the geophysical data in an attempt to quantify the relationship between geophysical response and soil salinity. The data from the electromagnetic survey showed areas of low electrical conductivity which was a possible indication of zones of preferential groundwater flow. A transect of boreholes was drilled over selected electrical conductivity lows and successfully intersected the buried stream channel. A comparison of the borehole logs with the layered earth models from the Vertical Electrical Soundings indicated that the electrical resistivity method was not responding to the features of the buried stream channel and the cobblestone layer. This proved the electromagnetic method to be more valuable for this particular study

A new interpretive slow-varying (long-wavelength) static estimation method is introduced to remove the effects of static anomalies caused by lateral variations in near-surface velocity. The application becomes critical where the wavelength of the variation of statics is larger than the maximum offset between source and receiver (spreadlength) used during data acquisition. The method used in this study utilizes the reflection and refraction arrival times from the shallowest reflector or refractor to determine the statics variations. The study include reprocessing of 12 seismic reflection data sets from the Savannah River Site area, near Aiken, South Carolina. The same data sets were also used to extract the refracted arrivals by the refraction stack processing. Application of the estimated slow-varying statics enhanced the S/N ratio, lateral continuity, and coherency for deep as well as shallow data and allowed to better determine the geometry of faults in the Coastal Plain sediments, which penetrate from the basement. Interpretation of the enhanced seismic reflection and generated seismic refraction sections helped to constrain the depth of upward penetration of the faults imaged in the seismic data. Refraction stack sections were used to obtain better definition of the delineation of the upward penetration of the faults at shallower depths. Despite the smoothing effect that is incorporated in the refraction stacks due to long refracted paths they exhibit clear-cut termination and offset on some of the lines in spatial zones where the Pen Branch fault can be projected in the shallow sediments. The seismic data indicate that the Coastal Plain sediments dip and thicken toward the southeast in the area. The basement top provides a high acoustic impedence contrast, and has a regional dip towards the southeast. The Pen Branch fault is one of the longest faults in the area, that acts as a basin bounding fault separating the Paleozoic crystalline basement from the Triassic basin fill. Other faults such as the Steel Creek and A TT A have also been discerned by the seismic data in the area. Small antithetic faults appear to join the Pen Branch and the A TT A fault. The offset of the Pen Branch fault (15 ms; 32 m) is relatively higher then the offsets observed for the ATTA (11.5 ms; 24.5 m) and Steel Creek (13 ms; 27.5 m) faults. The delineation of the upward depth of penetration of the Pen Branch fault is imaged best on lines 28 and 2EXP where the reflections at 0.18 to 0.2 s exhibit termination with amplitude changes, thereby suggesting the presence of the fault at that level. The offset associated with the A TT A fault can be traced up to 0.16 son line 27. The expression associated with the Steel Creek fault does not seem to go above 0.2 s. On the basis of the result from the interpretation of line 27, the upward depth of penetration of the A TT A fault in the Coastal Plain sediments reaches to a higher level then that of the Pen Branch fault. On the basis of the reflection and refraction data it is interpreted that the reactivation of the Pen Branch and the A TT A fault is as young as the age of the shallow reflector at 200 ms (top of Cretaceous?). / Master of Science

The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study.

SP, resistivity/IP and seismic refraction responses of the Woodlawn Orebody and Mt.Bulga Deposit are examined and compared. Both exhibit similar responses produced mainly by uneconomic and disseminated sulphide mineralization and host rock features, demonstrating that the magnitude and character of electrical and seismic responses are not reliable indicators of size and economic sulphide content of volcanogenic sulphide ores. SP, soil geochemistry and electrogeochemistry are found to be the most effective exploration methods followed by resistivity/IP and seismic refraction. The large SP responses over both ore zones are simulated using new methods which allowed the width and depth of oxidation to be computed. Conventional and compensation array resistivity responses best define the deposits. Computer simulation shows that dipole- dipole and Unipole arrays are most useful. First order IP responses are large and similar, but the ore zones are not easily distinguished from polarizable host rocks. Second order responses, at Woodlawn, better define these lithologies and cross-plots of EM coupling removed first order parameters prove useful. The supergene and gossan zones are defined as sources of electrical anomalies and correlate with interpreted SP sources. Seismic velocities of fresh Woodlawn ore samples indicate only small contrasts with host rocks. Refraction travel-time data are highly complex but host rocks are clearly distinguished by their seismic velocities. Both deposits appear as low velocity zones at the general bedrock level which are shallower and narrower than the electrical sources associated with the ore zones. Extensive model simulation shows that the Reciprocal interpretation method is most useful when compared to other time- term methods for refraction interpretation but has some limitations. Computer simulation shows the significance of non- critical refractions, diffractions and laterally hidden zones which define the lateral resolution of the refraction method. The results of this study and the interpretative techniques developed will assist the exploration for similar and deeper massive volcanogenic orebodies in comparable geological environments.

Graduation date: 1988

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Jeofizik Mühendisliği Anabilim Dalı, 2008. / Kaynakça var.