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Thesis (Ph. D.)--University of Cambridge, 1971. / Chapter 4 consists of a reprint, "A method for calculating the output pressure waveform from an airgun", Geophysical journal of the Royal Astronomical Society, v. 21, 1970, inserted between leaves 47 and [48]. Bibliography: last three leaves of text.

An 80 km seismic refraction line was recorded on an array of three ocean bottom seismometers located 5 km west of the northern tip of Explorer ridge and parallel to Revere-Dellwood fracture zone on the Pacific plate. One reversed and two split-spread profiles have been obtained. The combined use of rotated SV component and polarization filtered record sections enabled identification and timing of the refracted S-wave on most sections. The travel time - distance relation for both P and S waves is interpreted in the intercept time (tau) and ray parameter domain using the technique introduced by Bessonova et al. (1974). This enables application of tau inversion to give extremal bounds for velocity-depth curves. A linearized inversion technique is applied to give the smoothest velocity-depth profiles consistent with the travel time data. Amplitude analysis using disk ray theory synthetic seismograms further refine the P-wave velocity-depth models. The final P- and S-wave velocity-depth profiles show a general increase of velocity with depth and no distinct structural discontinuities. A normal oceanic crustal thickness of approximately 6.5 km and an anomalously low Pn velocity of 7.3 km sec⁻¹ are interpreted. The existence of an abnormally thick crust (8-10 km}., on the opposite side of the ridge in Explorer plate, determined in other studies, contrasts markedly with the results of this research. Such a contrast lends support to the proposal that the complex structure and thick crust are the result of compressive interaction between the young, small Explorer plate and the older, larger North America plate. Values of Poisson's ratio in the range of 0.25 to 0.32 are determined for the crustal material but better resolution of the velocity-depth profiles is required before a meaningful geological interpretation can be made. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The seismic signal generated by the underground nuclear explosion, Long Shot, has been compared with seismic signals of earthquake origin and found to be similar on a regional scale. Negative Long Shot magnitude residuals are associated with areas of recent tectonic activity as are late arrivals, while positive Long Shot magnitude residuals and early arrivals have been found to be associated with tectonically stable regions. These trends are coincident with those indicated by data from other seismic events. The more detailed comparison of Long Shot and earthquake magnitude residuals at Penticton and Port St. James indicates that the Long Shot residuals also reflect the location of the source. At these stations, earthquakes with distances and azimuths comparable to Long Shot exhibit magnitude residuals that are most similar to those of Long Shot. The magnitude residuals at the University of British Columbia exhibit the same dependence on source parameters although a direct comparison with Long Shot could not be made. An examination of earthquake travel time residuals at Penticton and Fort St. James also indicates the same dependence on source location. Long Shot surface waves indicate an average unified magnitude of 5.1 at Canadian stations as compared with an average unified magnitude of 6.0 from body waves at the same stations. The comparison of the power spectra of Long Shot and earthquakes at Leduc and Victoria indicates relatively more energy at high frequencies from Long Shot than from earthquakes. This variation in spectral decrement is interpreted as an effect of the different source mechanisms. The spectrum of Long Shot at Rocky Mt. House appeared to be anomalous as it had a significantly larger spectral decrement than at the other stations and was indistinguishable from the spectra of earthquakes recorded at Rocky Mt. House. The trend of the power spectra also appear to be partially determined by the crustal and upper mantle structure in the vicinity of the station. The effect of the source parameters and travel path is also indicated by a tendency for the spectral decrement to increase with increased distance to source and with increased depth. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Negative feedback can be applied to an electromagnetic seismometer through the coil terminals using a Maxwell impedance bridge to bypass the coil impedance. The application of feedback by this method obviates the need for a second transducer, and permits direct calibration of the feedback seismometer. Feedback of a simulated ground acceleration proportional to the acceleration of the suspended mass effectively increases the mass, lengthening the natural period of the seismometer. Displacement feedback effectively stiffens the spring, decreasing the resonant period, while the seismometer damping can be increased with velocity feedback. Experimentally determined sensitivity curves obtained with a Willmore Mk.I. seismometer demonstrate the capabilities of negative feedback in altering the response of the seismometer. A resonant period of 17 sec. corresponding to an equivalent suspended mass of 1230 kg. is readily obtained. A discussion of instrument noise in the feedback seismometer is included. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (doctoral)--Rijksuniversiteit te Utrecht, 1954. / "Stellingen" ([2] p.) inserted. Includes bibliographical references (p. 43).

Thesis (Ph.D.)--Victoria University of Wellington, 2008. / Includes bibliographical references.

Thesis (doctoral)--Rijksuniversiteit te Utrecht, 1954. / "Stellingen" ([2] p.) inserted. Includes bibliographical references (p. 43).

Graduation date: 1994

No description available.