In recent years there have been significant advances in the acquisition and processing of crosshole seismic reflection data, and the method has been shown to be a high resolution imaging technique. However, the fidelity of the final images produced by this technique needs to be considered carefully to avoid incorrect interpretation. This thesis concerns the imaging capability of crosshole surveys, as well as advances made in processing techniques for application to crosshole seismic reflection surveys. In a migrated seismic section, a meaningful image is only obtained if a range of dips around the local structural dip is sampled at each image point. For crosshole seismic reflection surveys, the distribution of dips sampled at an image point is controlled principally by the survey geometry, including source and receiver array lengths and their element spacings. By considering the dips sampled, the imaging capability of crosshole reflection surveying is discussed, with suggestions as to how to ensure optimal imaging of the target zone. To overcome problems encountered in applying standard processing procedures, two new processing techniques are presented which enhance the imaging potential of crosshole reflection seismics. Generalised Berryhill migration has been developed as a full generalised Kirchhoff migration to include the near-field term, with the aim of improving image accuracy close to the source and receiver arrays. 3-D f-k-k filtering is an improved method of wavefield separation for crosshole seismic data. Finally, the results of processing three types of dataset are presented. One is from a site in the Groningen gas field, another was acquired through a model interrogated at ultrasonic frequencies in a water tank, and the third type was acquired using coal exploration boreholes in Yorkshire. The results demonstrate the imaging capability of the crosshole reflection method, and the success of the two new processing schemes.

A network of four independently-recording seismic stations was operated by the University of Durham in South-Central Afar during 1973 and 1974. Each station consisted of a three-component set of seismometers, whose signals were recorded on to magnetic tape. This study concerns local earthquakes recorded from February to September, 1974.250 earthquakes were located from relative arrival times of P and S phases using an optimized, laterally homogeneous, 4-layer structural model. Upper crustal P-wave velocities are found to be 4.4±0.2 km s(^-1) (0 to 4.5 km depth) and 6.2± 0.1 km s(^-1) (4.5 to 11 km). Deeper structure is poorly constrained. Anomalous upper mantle exists, with low seismic velocity (Vp about 7.4 km s(^-1)) and raised Poisson's ratio (0.31). S(_n) is transmitted, 8.0 km s(^-1) upper mantle cannot exist above about 43 km depth. Earthquake focal depths within Afar do not exceed 5 km. Epicentres correlate well with Recent axial volcanism. Spatial epicentral patterns reflect intense regional NW-SE extensional faulting. One line of epicentres shows the NNE-SSW trend of the Main Ethiopian rift. Focal mechanisms are very poorly constrained, but are consistent with NW-SE strike-slip or normal faulting, or with NE-SW dextral transcurrent faulting. Signal duration magnitude and Richter local magnitude scales are defined for Afar, Frequency-magnitude b-coefficient values are 0.87+0.05, The three-component records are polarization filtered, a technique previously applied only to teleseisms. The performance of the filters is discussed. Azimuths and apparent angles of incidence of events are determined from their first arrivals at a single recording station. Hypocentres are then obtained by ray tracing. Earthquake frequency spectra are computed through the fast Fourier transform. The spectra are dominated by the effects of the superficial crust below the receivers. Crustal transfer ratios are discussed. Increased attenuation is demonstrated below the Tendaho graben. Seismic source parameters are calculated using BRUNE's (1970) method. All results are consistent with diffuse NE-SW crustal extension. It is concluded that well-defined spreading axes do not yet exist.

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.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 26, 2007) Includes bibliographical references (p. 139-146).

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). "March 2008." Includes bibliographical references (leaves 129-138). Also available via the World Wide Web.

Thesis (M. S.)--Michigan State University. Dept. of Geological Sciences, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references (p. 116-120). Also issued in print.

Thesis (Ph. D.)--California Institute of Technology, 1964. / Includes bibliographical references (leaves 69-70).

Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 150-161).