The Derbyshire Dome is thought to have been a stable uplifted area since at least Lower Carboniferous times. This project is principally concerned with four 30km seismic refraction lines which crossed the limestone outcrop of Derbyshire and N. Staffordshire in order to investigate the Dome's upper crustal structure, using quarry blasts as seismic sources. A time-term analysis of refracted arrival data defined basement structure more complicated than implied by the surface geology. The interpretation of these data was complicated by high (5.6-5.8km/s) velocity refractions from dolomitic horizons within the limestone sequence; the mean overburden velocity was determined to be about 5.2 km/s. The Dome could be divided into two pre-Carboniferous geological units separated approximately by the line of the NNW trending Bonsall Fault. To the north a broadly domal refractor of velocity 5.5-5.55km/s was mapped, and thought to correlate with both the shallow pre-Carboniferous volcanics encountered by the Woo Dale borehole and"the Ordovician shales encountered by the Eyam borehole below 1.8km of limestone. This refractor accordingly deepens beneath the Carboniferous sedimentary basins flanking the Dome. To the south of the Bonsall Fault zone, the Carboniferous was found to be underlain by a refractor of velocity 5.63-5.7km/s, thought to be of Precambrian material similar to the rocks of Charnwood Forest, Leicestershire, some 40km south. By analysing later arrivals, this refractor has been mapped to the north of the Bonsall Fault at a depth of 2.5-3.5km. The shallower Lower Palaeozoic refractor is thought to be no more than 500m thick, and underlain by lower velocity, possibly Cambrian, material. This interpretation is consistent with the Bouguer anomaly map of the region, and sheds light on the structural control of Carboniferous sedimentation. The basement fault dividing the two pre-Carboniferous units is thought to have been active during the Dinantian as the northern unit tilted eastwards.

No description available.

A seismic explosion program has been carried out in the Vancouver Island-Strait of Georgia area of Western Canada. The program included a relatively-intensive survey in the Strait of Georgia between Campbell River and the south end of Texada Island, as well as a number of longer range refraction lines extending from Kelsey Bay along the coast as far south as northern California, and east through the mountains to a distance of 700 km. Gravity readings were obtained at intervals of about ten km. along the east coast of Vancouver Island as well as for a number of east-west traverses. Readings were also obtained for a few locations on the British Columbia mainland. Except for a marked positive trend in the Victoria area, the regional value of the Bouguer anomaly for the Vancouver Island area is nearly zero. The average structure for the area, derived from the seismic refraction observations consists of a layer of volcanic and granitic strata less than five km. in thickness, and an intermediate layer with a constant velocity for compressional waves of 6.66 km/sec, 46 km. thick. A velocity of about 7.7 km/sec. for the mantle has been observed along unreversed refraction lines, both along the coast and east through the mountains. Interpretation of the refraction observations has been based mainly on first arrival phases. The observed regional gravity anomaly is compatible with the crustal model obtained from the seismic results. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Recent developments in cone penetration testing have resulted in the addition of both pore pressure measurements and seismometers. The seismometers allow shear wave velocity testing to be performed at designated intervals. Both of these additions were researched to improve their application and interpretation. The significant factors effecting the pore pressure generated during cone penetration tests are discussed. The importance of various factors is especially dependent upon permeability, strength, and stiffness. For all sands tested, pore pressures lower than static were recorded behind the tip and higher than static were recorded on the face of the cone. It is believed that the large compressive stresses on the cone face result in positive pore pressures. As the cone tip passes a soil element unloading and continued shearing generate pore pressures lower than static in all sands. The sign of this pore pressure (higher or lower than static) was therefore considered primarily a function of the test equipment. Pore pressure response and the rate of dissipation of excess pore pressures were found useful in distinguishing fine granular soils and explaining soil stratigraphy. In cohesive soils the details of pore pressure measurement were found to be important only in stiff soils. Pore pressures at all measurement locations were found to increase with soil strength in soft to firm clays but may be negative of static in very stiff clays. Pore pressures behind the cone tip were often negative of static in stiff clays. Measurement techniques were refined to improve the accuracy of downhole shear wave velocity measurements. Comparisons of downhole and crosshole measurements were made at three well documented sites validating the technique. At several sites it was found useful to consider the Gmax values determined from shear wave velocity and density to distinguish soil type. Gmax to cone resistance ratios were shown to vary systematically with cone resistance values in sands. A wide range in Gmax to cone resistance was observed in clays. The dependence of both cone penetration resistance and Gmax to increased stress level or overburden stress is discussed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The crustal thickness and P velocities in the Port Arthur, Ontario region of the Canadian Shield have been previously determined by seismic refraction techniques during the Lake Superior Experiment and Project Early Rise. In this study, the P phases of eleven teleseismic earthquakes recorded near Port Arthur have been studied by computing azimuths, angles of incidence, and spectral ratios to ascertain some crustal properties and compare these values with the refraction results. A P velocity at the surface of 6.1 ± .8 km/sec and a crustal thickness of 40 ± 5 km determined from the earthquakes are similar to but less precise than the refraction estimates of 6.3 km/sec and 38 km respectively. Transverse motions generated by the earthquake signal passing through the crust were observed and contributed to the uncertainty. / 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

A practical and versatile feedback seismograph station has been constructed. Using feedback techniques developed by R.D. Meldrum, the relative low frequency response and the damping ratio of a Willmore Mk. I seismometer have been significantly increased for use in a broadband, low frequency bandpass seismograph station. Within limits imposed by a very high ambient ground noise level at the University of British Columbia site, circuit noise and instrument amplifier characteristics, it is possible to vary the damping ratio and resonant period through modification of the feedback loop transfer function. The seismograph has been continuously operating since November 1965 and has recorded over 40 local tremors and distant earthquakes from as far away as the mid Indian Ocean. It has shown that it is a useful demonstration and research instrument. A pilot analysis of the Long Shot nuclear explosion data received by the Canadian seismic stations indicates a consistent compressional first arrival as expected from an impulsive explosion source. Significant travel time discrepancies are observed in the commencement of the P arrival which arrived up to 6 seconds early at all stations with the largest residuals at the most distant sites. A comparison earthquake in the Rat Islands area indicates a similar bias trend. The P arrival amplitudes appear to be anomalously low in the central B.C. area and high in eastern Canada. The effect is also evident in the unified magnitude determinations which are based on these amplitudes. The causes of the variations of magnitudes and the anomalously low amplitudes have not been explained. The average magnitude and standard deviation for all Canadian stations is shown to be 6.01 ±0.40 which agrees well with the world-wide average determination of 5.99 ± 0.52. Spectral investigations demonstrate that there are both common and individual characteristics among the ground amplitude spectra of the different stations. These characteristics have not been correlated to the explosion source mechanism or to geological structure although some causative suggestions have been made. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Previous seismic studies of crustal structure using short-period P coda recorded in the vicinity of Leduc, central Alberta have indicated that serious discrepancies between the experimental observations and those based on a horizontally layered model of the crust exist in both the time and frequency domains. This 'Standard' crustal model is based on well log data for the sedimentary section, and on seismic refraction work in southern Alberta for the lower layers. The principal discrepancy lies in the large amplitude radial motion on the experimental seismograms which lags vertical arrivals by approximately two seconds. It is concluded that this radial motion, which is absent from synthetic seismograms generated using the 'Standard' crustal model, represents the generation of large-amplitude shear waves within the crust. This large radial motion is manifested in the frequency domain by experimental vertical-radial spectral ratios which are considerably lower than those computed using the 'Standard' crustal model. Using vertical-radial spectral ratios-and synthetic seismograms, a modified crustal model has been derived which gives much better agreement between experimental and theoretical results. This model involves the insertion of a layer several kilometers thick having large velocity contrast with respect to the surrounding media at the base of the Precam-brian basement (12 km deep). The new crustal model is discussed in the light of widespread evidence for a low velocity zone in the upper crust in continental regions. Several important discrepancies between experimental and synthetic seismograms remain unresolved: among these are the small onset amplitude and the character of the delayed motion of the radial component. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

archives@tulane.edu / The crustal state-of-stress is influenced by crustal heterogeneity and anisotropy, regional tectonics, gravitational loading of topographic relief, and subsurface magma pressure. The local stress field dictates the location and orientation of magmatic intrusions and faulting, which are important to understand tectonic processes and to inform hazard studies. I analyze earthquakes and their corresponding source mechanisms, complemented by analytical and numerical stress modeling, to interpret state-of-stress in rifting and magmatic regions. I investigate how brittle deformation is accommodated in early-stage rifting of cratonic lithosphere via seismic moment tensors in regions that are considered magma-rich and magma-poor. I also study the caldera stress change associated with an eruption. My research can contribute to our understanding of the controlling mechanisms in an extensional regime and in volcanic regions, and contribute to earthquake and volcanic hazard assessment in magmatic and rift zones in Africa, and worldwide. / 1 / Sarah Jaye Oliva

The recent geomorphologic history of the Apalachicola River can be related to local changes in sea level and the sediment output of the river. These changes can be observed in seismic data and boreholes collected in the bay. This project employed seismic, borehole and geochronologic data in order to map and better understand the paleogeography of the Apalachicola River and Bay region. These maps include; the seabed, the top of a mid-Holocene stratigraphic unit, the top of the Pleistocene, the top of the uppermost Mio-Pliocene unit, which includes a karst surface. In addition, Holocene-aged fluvial paleo-channels and paleo-deltas were identified in the subsurface and their paleogeographic relationships were mapped. The uppermost Mio-Pliocene aged sedimentary unit was described by Schnable (1966) on the basis of borehole data, as primarily sandy and clayey limestones, known as the Choctawhatchee Formation (Schnable, 1966). Huddlestun (1976) later described the same unit as the Intracoastal Formation, due to its location in the Intracoastal Waterway. Schmidt (1984) described the Intracoastal Formation as an easily recognizable stratigraphic unit composed of sandy, highly microfossliferous calcarenitic limestone. The thickness and dip of the Intracoastal Formation varies widely over the Apalachicola River region, due to the influence of the regions's largest subsurface structure, the Apalachicola Embayment (Schmidt, 1984). The embayment dates back to the early Tertiary and is the result of regional tectonic forces. The embayment is located between the Chatahoochee Anticline to the west and the Ocala Platform to the east (Rupert, 1997). The northern end of the Apalachicola Embayment narrows and extends into the Gulf Trough in southern Georgia (Rupert, 1997). It widens and deepens as it extends into the modern Gulf of Mexico (Rupert, 1997). The southernmost extent of the embayment is not well established due to the lack of offshore well data (Schmidt, 1984). The early to mid-Holocene paleo-deltaic features beneath the modern estuary migrated from west to east over the last approximately 7000 years. The specific subsurface features were identified and located by use of both seismic data and vibrocore logs. The depth of the features observed in the seismic data was calibrated based on bridge borehole transects collected from the Eastpoint to Apalachicola and the Apalachicola to St George Island bridge-causeways. The Apalachicola River's paleo-discharge was determined by using the Manning equation to calculate the maximum discharge of the river, based on the channel geometry and regional gradient. Several paleochannel profiles were found and measured. The calculated paleo-discharge was 86,000 cfs. This discharge was based on the entire cross-section of the river and therefore represents a bank-full or maximum discharge. The modern and paleo-streamflow were found to be comparable. The calculated paleo-discharge value falls within the range of the average annual peak discharge of the modern Apalachicola over the last 30 years. A possible explanation comes from Holocene climate data extracted from the palynology of long cores from regional lakes. Data from two lakes indicates that climate in the region has changed little in the past 6,000 years and perhaps for as much as 8,000 years. The paleofluvial history of the region's largest river, the Apalachicola, appears to corroborate that finding. / A Thesis Submitted to the Department of Geological Sciences in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Fall semester, 2008. / November 24, 2008. / Geomorphology, Apalachicola Bay, Florida, Seismic, Discharge, Delta, Karst / Includes bibliographical references. / Joseph F. Donoghue, Professor Directing Thesis; Lynn Dudley, Committee Member; Bill Hu, Committee Member.