Thesis (Ph.D.) - Carleton University, 2002. / Includes bibliographical references (pt. 8, p. 1-7). Also available in electronic format on the Internet.

Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 122-127). Also available in electronic format on the Internet.

Thesis (M. Phil.)--University of Hong Kong, 1992.

The implications of the acceleration data recorded during the September 19, 1985 Mexican earthquake for seismic design in Canada are investigated by determining if the deep deposits of the Fraser Delta could cause large amplification of earthquake motions. The conditions for amplification of low level incoming ground motions at deep sites are identified; in particular, the critical role of variation in shear modulus with shear strain. The current procedure for determining site specific ground motions is evaluated and major sources of uncertainty in the results identified. Criteria for selecting representative input motions for site response studies are recommended based on analyses of Mexico City sites. A comparative study of sites in the Fraser Delta area of British Columbia showed that offshore subduction earthquakes should be considered when developing design spectra for deep sites in the Delta. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The structure of seismic discontinuities at depths of about 410 km and 660 km provides important constraints on mantle convection as the associated mineral phase transformations in the transition zone are sensitive to thermal perturbations. Teleseismic P-to-S receiver functions have been widely used to map the depths of the two discontinuities. In this study, we investigate the resolution of receiver functions in imaging topographic variations of the 410-km and 660-km discontinuities based on wave propagation simulations using a Spectral Element Method (SEM). We investigate finite-frequency effects of direct P waves as well as P-to-S converted waves by varying the length scale of discontinuity topography in the transition zone. We show that wavefront healing effects are significant in broadband receiver functions. For example, at a period of 10 to 20 seconds, the arrivaltime anomaly in P-to-S converted waves is about 50% of what predicted by ray theory when the topography length scale is in the order of 400 km. The observed arrival anomaly further reduces to 10-20% when the topography length scale reduces to about 200 km. We calculate 2-D boundary sensitivity kernels for direct P waves as well as receiver functions based on surface wave mode summation and confirm that finite frequency-effects can be properly accounted for. Three-dimensional wavespeed structure beneath seismic stations can also introduce significant artifacts in transition zone discontinuity topography if time corrections are not applied, and, the effects are dependent on frequency. / Master of Science

On August 31, 1886 a large scale earthquake occurred in Summerville, S.C. causing severe damage in the coastal city of Charleston. Although intensive geological and geophysical studies have been conducted in the area, uncertainty remains about the details of the event. Recently evidence from seismic reflection profiles have shed light on the tectonic environment of the area. The epicentral area of the 1886 event lies within the South Georgia Rift, a Mesozoic rift terrane. Previous studies have revealed clues to the geologic structure and evolution of this feature. SEISDATA4 is the largest seismic reflection profile recorded in the area. By re-processing the line, information about the tectonic structure of the area was revealed. The early Mesozoic extensional basin that hosted the 1886 earthquake and is host to the modern seismicity recorded in the area, extends several kilometers to the south and west of Charleston, along SEISDATA4. Cenozoic and Mesozoic faults were resolved within the basin and along its northwestern boundary that is distinguished by a strong gradient in the magnetic field. However, the question as to which fault was responsible for the rupture of 1886 still remains. The refraction analysis provides better resolution of the lithology in Lower Mesozoic section. The termination of the strong reflection at the base of the Atlantic Coastal Plain occurs in a section of the profile that shows major disruption of the underlying reflections, and suggests that the termination of a lower Mesozoic basalt flow responsible for the reflection may be related to tectonic deformation. / Master of Science

A technique has been developed to estimate the directions of principal stresses from focal mechanism solutions, under the assumption that the stress is homogeneous throughout the seismic zone. That method is called the Multiple Solution per Earthquake Technique (MSET), and utilizes each member of multiple focal mechanism solution set as a possible solution. The MSET is useful when applied to small data sets, and differs from existing techniques in that (1) the use of multiple focal mechanisms for individual earthquakes allows for a range in the possible orientation of the fault geometry, while preserving fit to the original polarity and amplitude ratio data, and (2) the differences between the observed and theoretical fault slip is used as a weighting scheme for the results of the tensor estimation. Other methods, which rotate the single observed focal mechanism solution from its original configuration to estimate misfit, do not take into consideration the fit of that final solution to the original input data but assume that a minimization of errors between the theoretical stress model and the focal mechanism solution indicates a reasonable fit. For large data sets that assumption is likely to be met. The MSET was applied to a set of 32 earthquakes to estimate the principal stress orientations for seismically active zones in the Southeastern United States, using focal mechanism solution sets derived by the program FOCMEC. Eight events were studied for the Giles County Seismic Zone, 13 for the Central Virginia Seismic Zone, and 11 for the Eastern Tennessee Seismic Zone. After testing against approximately 25000 theoretical solutions, an average of sixteen focal mechanism solutions fit the input polarity and (SV/P)₂ amplitude ratio data for each earthquake. The P-axes of the multiple focal mechanism solutions were averaged to determine a provisional single P-axis direction for each earthquake. P-axes for the Giles County and Eastern Tennessee Seismic Zones trended generally NE-SW, while those of the Central Virginia Zone varied with depth, with the P-axes of events above approximately 8 km trending NE-SW, and those below trending NW-SE. Application of the MSET resulted in consistent principal stress orientations for the Giles County and Eastern Tennessee Zones, with the horizontal component of the maximum compressive stress direction (σ₁) trending about N40°E and N50°E, respectively. Results for the Central Virginia Zone also suggested differently oriented stress regimes above and below a depth of 8 km. The direction of the σ₁ axis above that boundary was N70°E, while below it was east-west, with a shallow plunge to the west. While those results were not as pronounced as suggested initially by the P-axis data alone, the hypothesis of two stress tensors produced better MSET results than for a single stress tensor for the combined data set. The technique developed for this study produces comparable results to other methods when applied to identical data sets. Estimation of error is based on subjective criteria, and includes the lit of the original seismic polarity and amplitude ratio data with the focal mechanism solutions. The error associated with each step in the process (e.g. distribution and reliability of the polarity and ratio data, calculation of focal mechanism solutions and estimation for the stress field) is very difficult to parameterize, and thus, no formal statistical analyses were undertaken. After the estimate of the homogeneous stress field was made for each zone, a single best focal mechanism solution for each earthquake could be objectively chosen by constraining the slip associated with each mechanism to be aligned with the resolved stress derived from the principal stress directions. In that manner, focal mechanism solutions could be identified which fit the sparse input polarity and amplitude ratio data, but which were not compatible with the calculated stresses. Also, in that same procedure, the fault plane was chosen from the set of two nodal planes for each focal mechanism solution by examination of the theoretical slip on each of those planes. The faults within the Giles County Seismic Zone matched the direction found in previous seismic reflection surveys, with an average strike of N25°E. In the Eastern Tennessee Seismic Zone, faulting also occurred on planes oriented predominantly NE-SW. For the five shallow Central Virginia events, faults trended NW-SE, while for the deeper events there was no consistent trend. A comparison was made between the P-axis and σ₁ axis derived for each earthquake. Although in 81% of the cases σ₁ was within 35° of at least one P-axis of the focal mechanism solution set, no further empirical relationship was found. The MSET has proven itself useful in two ways when applied to sparse data sets. First of all, the primary seismic data (polarities and amplitude ratios) are not overlooked when deriving the orientation of a stress tensor associated with local faulting. Secondly, the MSET is an objective method for defining the best fitting solution among a family of focal mechanism solutions by requiring compatibility with the regional stresses. In the future, after integration with a program such as FOCMEC, regional stress tensors may be derived by the MSET which incorporate reasonable statistical parameters based on the fit of that primary data. / Ph. D.

No description available.

This thesis concerns the application of seismic interferometry to surface waves. Seismic interferometry is the process by which the wavefield between two recording locations is estimated, resulting in new recordings at one location as if a source had been placed at the other. Thus, in surface-wave interferometry, surface waves propagating between two receiver locations are estimated as if one receiver had recorded the response due to a source of surface-wave energy at the other receiver. In global and engineering seismology new surface-wave responses can allow for imaging of the subsurface, and in exploration seismology it has been proposed that these new surface-wave responses can allow for the prediction and removal of socalled ground-roll (surface waves that are treated as noise). This thesis presents a detailed analysis of surface-wave interferometry: using a combination of modelling studies, real-data studies, and theoretical analyses the processes involved in the application of interferometry to complex (both multi-mode and scattered) surface waves are revealed. These analyses identify why surface waves are often dominant in the application of interferometry, where errors may be introduced in the application of surface-wave interferometry, and how interferometry may be processed in such a way as to minimise those (and other) errors. This allows for the proposal of new data-processing strategies in the application of seismic interferometry to surface waves, potentially resulting in improved surface-wave estimates. Much of the work in this thesis focuses on the use of seismic interferometry to predict and subtract surface waves in land-seismic exploration surveys. Using insights from the presented analyses it is shown that seismic surface waves can be successfully predicted and removed from land-seismic data using an interferometric approach. However, the work in this thesis is not only limited to applications in exploration seismology. In addition to the ground-roll removal method, improved estimates of higher-mode and scattered surfaces waves may allow for more advanced imaging algorithms to be used in conjunction with seismic interferometry. Also, as a consequence of the analysis presented a Generalized Optical Theorem for Surface Waves is derived. This highlights a link between seismic interferometry and the optical theorem and may allow for further application of optical theorems in seismology.

This thesis investigates the origin of large-scale sandstone intrusions.  A new approach combining seismic, well data, core and outcrop observations with numerical modelling has been undertaken. Two possible end members of saucer-shaped, seismic-scale sandstone intrusions from the North Sea were identified on the basis of seismic data and core observation.  Diagnostic criteria were proposed to differentiate between fully and only partially injected sand bodies.  Outcrop and core data presented in this thesis provide a direct example and analogue for seismic and sub-seismic scale sandstone intrusions, highlighting the brittle nature of the host rock deformation at all levels within the examined intrusion complexes.  On this basis, the rheological behaviour of the host strata at the time of sand injection is inferred to be elastic with brittle fracturing.  This outcome is used as an input condition for Finite Difference and Finite Element modelling that aim to test hypotheses describing triggering mechanisms and estimate their regional extent, depth and overpressures present during sand injection.  The results of numerical modelling indicate that formation of the North Sea sandstone intrusions could potentially be triggered by catastrophic event(s) such as a meteorite impact or earthquakes, leading to sand liquefaction and remobilization.  It has also been shown that depths at which sand injection can take place reach 1 km.  Only supra-lithostatic pressures generate bodies composed of lower, bedding concordant part of intruded or depositional origin feeding inclined dykes at its marginal parts resembling those observed today on seismic data from the North Sea and in outcrops.