There have been relatively few investigations into the attenuation properties of unconsolidated sediments using marine surface seismic data. Several methods of measuring attenuation were assessed for reliability in a noise-free case and with the addition of noise using a set of synthetically absorbed and dispersed wavelets. Wavelet modelling proved to be superior to the other techniques, followed by spectrum modelling and the spectral ratios method. Complex trace analysis using the analytical signal proved to be unreliable for non-sinusoidal wavelets, whilst the risetime method was found to be very susceptible to noise for practical purposes. Numerical modelling was carried out to assess the spectral effects of layering on a propagating pulse. The thin layer / peg-leg phenomenon has varying filtering effects on the propagating pulse. In particular, layers which are less than the "tuning thickness" of the propagating pulse have a low-pass effect. The quality factor, Q, was measured in two case studies. In the first, the mean Q was determined from wavelet and spectrum modelling and found to be 60 for fine sands and 47 for coarse sands in the 1 kHz to 3 kHz frequency band. In the second, Q was determined as 59 for poorly sorted sandy diamicts in the 100 Hz to 240 Hz frequency band. The close fit between synthesised spectra and wavelets and observed data showed that a constant- Q mechanism would account for the spectral changes between the seabed and the deeper target reflection events in the two case studies. The spectra of the target reflection events in both case studies were lacking in low frequencies which is likely to be due to low-pass filtering from composite reflection events due to thin bed layering. For practical purposes, the determination of Q from a mean normalised seismic trace yielded the same result as measuring a mean Q from individual traces. In a third case study, the seabed multiple was compared to the seabed reflection using wavelet and spectrum modelling. A lack of low frequencies in the seabed multiple showed that the seabed can act as a low-pass filter to an incident pulse. As the numerical methods rely on the seabed as having a white reflection and transmission response, the low-pass effect will result in erroneous estimates of the quality factor, Q.

The intrinsic high accuracy of modern HF direction finders cannot be realized in practice due to the perturbations and tilts which exist in the ionosphere. Particular attention is given in this dissertation to the effect of Travelling Ionospheric Disturbances (TIDs) since their occurrence is difficult to predict and the magnitude of the induced bearing error extremely variable. TID activity is quantified by monitoring simultaneously the bearings of a number of transmitters whose locations and frequencies are well known. This information is then employed to determine the expected bearing error on a target transmission reflected in the same area of the ionosphere. The major limitations of this correction scheme are investigated. The large-scale temporal and spatial variations of the quiet ionosphere (Systematic Ionospheric Tilts, SITs) produce bearing errors of similar magnitude to those due to TIDs. Rapid calculation of these errors for various path geometries and ionospheric conditions is possible by raytracing through 3-D ionospheric models. The limitations of a correction scheme which employs a 3-D model based on ionospheric predictions are examined. Variance is a particularly useful statistic in assessing the 'reliability' of bearings made on a particular HF circuit. A scheme is proposed in which the bearings of a network of reference transmitters are monitored continuously allowing a variance to be assigned to any target transmission, even if it is only present for a very short time. These variance values are of considerable value in practical DF applications. Whenever possible the experimental observations are related to the underlying physical processes in the ionosphere which generate these DF errors.

As part of the 1989 BABEL project, Durham University recorded large quantities of high resolution wide-angle data from six deep seismic lines shot in the Gulf of Bothnia. Fifteen analogue and three digital seismic recording stations were used, located in Sweden around the Sea of Bothnia. The wide-angle data is of very high quality due to the low noise and good transmission of seismic energy through the cratonic crust of the Baltic Shield. BABEL line 6 is a 240 km long, north-south profile in the western half of the Sea of Bothnia that runs almost parallel to several deep seismic refraction profiles previously acquired in Sweden and Finland. A crustal model has been developed for this line from P- and S-wave wide-angle data recorded at five of the online recording stations and from the normal-incidence data. This model has been generated by raytracing methods using a modified version of the BEAMS? gaussian beam package. Wide-angle arrivals are interpreted as diving rays and wide-angle reflections and as 'diffraction-type' arrivals from offsets on reflecting boundaries. The wide-angle reflections appear to correspond to the boundaries between high and low reflectivity zones in the normal-incidence data. The 'diffraction-type' arrivals appear to be related to surface features such as the Ljusnan tectonic zone and the Aranda rift. There is no evidence for a Moho trench similar to those seen on neighbouring profiles. Several high velocity layers are required in the model. These may be the related to the numerous post-orogenic intrusions that have occurred in the Svecofennian region of the Baltic Shield. Traditional approaches to modelling wide-angle data assume that the crust consists of a series of extensive, quasi-horizontal, layers. There are several problems with this approach. In particular it does not explain the patchy reflectivity seen in the normal-incidence data or the rapid variation in amplitude seen along wide-angle arrivals in high resolution data sets. Apparently continuous wide-angle arrivals may be generated from a series of short length reflectors. These show an amplitude variation similar to that seen in the experimental data. This suggests that wide-angle arrivals may arise from the assemblages of reflectors that are often imaged on normal-incidence data.

Fourier transformed amplitudes of the compressional waves recorded between 9° and 91° (about 1000 to 10,000 km) epicentral distance from Gnome, Shoal, Haymaker,and Bilby underground nuclear explosions have been compared with Fourier transformed amplitudes of P waves measured at distances between 9.0 and 1 3. 0 km from the explosions. Using a formula of the type A= ε AoF(ξ)e - πfr/QV apparent Qs have been computed for frequency ranges of 0.5 to 1.0 cps and 0.7 to 1.0 cps at the various epicentral distances. The geometrical spreading factor F(ξ) and interface loss parameter ε drop out of the computations when assumed to be frequency independent in the narrow frequency pass-bands considered. The computed apparent Q values indicate that the mantle is inhomogeneous with respect to the absorption of seismic energy. Relatively low Q (high absorption) regions are centered around 25°, 42° and 74° and high Q (low absorption) regions are centered around 20°, 31°, 71°, and 78° epicentral distances. These are superimposed on a gradually increasing Q with epicentral distance trend. The average apparent Q value for the upper mantle is found to be 286 ± 38. The highest Q value of this study occurs between 78° and 80° epicentral distance where it is greater than 3000. The high and low Q values obtained in this investigation are of the same order of magnitude as those reported by other investigators from body wave studies and the general variation of the absorption properties with depth agrees reasonably well with those obtained from surface wave studies. The depth of great increase in electrical conductivity and the observed maximum depth of earthquake foci both agree roughly with a region of large increase in Q in the upper mantle. A relatively high absorption zone is found to occur below this depth. / Graduation date: 1967

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Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1967. / Typescript.

Thesis (Ph. D.)--State University of New York at Binghamton, Geological Sciences & Environmental Studies Department, 2007. / Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 126-127). Also available via the Internet.