Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.Eng. Sc.) -- University of Adelaide, 1983. / Bibliography: leaves 91-94

Thesis (Ph. D. in Geophysics)--University of California, Berkeley, June 1977. / "January 1977." Includes bibliographical references.

No description available.

Seismicity occurs mainly around plate boundaries, but there are rare occurrences of large magnitude earthquakes with a plate. When and why these events occur is not well understood but they are capable of producing significant damage to these regions. Where these earthquakes occur, are known as intraplate seismic zones. In the American Midwest there are two seismically active intraplate seismic zones, the New Madrid and Wabash Valley seismic zones. Each of these zones is capable of producing large magnitude earthquakes though it has proven somewhat difficult to study intraplate seismicity because the reoccurrence intervals for intraplate events are much longer than interplate earthquakes, requiring a much longer timescale for study. One approach to avoid the longer timescale of observation is to focus on studying smaller events, which occur more often. However, these events will have their own disadvantages with less optimal signal-to-noise ratios which does not allow events to be located by the minimum three seismometers needed to triangulate the events epicenter. A potential solution to remedy this difficulty is to use methods using one-station events that go beyond the conventional ways of locating earthquakes and possibly improve locating microseismic events that normally go unnoticed. A small seismograph array was set up around Cedar Lake, in Makanda, Illinois. This location is situated southwest of the Wabash Valley seismic zone and north of the New Madrid seismic zone but is typically viewed as aseismic. The conventional method was used for finding events by triangulation on three months data from January 1, 2011 to March 31, 2011. Through triangulation there 14 events located in January, 10 in February, and 74 in March. In addition to triangulated events, event probabilities for one-station also applied events and located a few of these events via azimuth by utilizing three component seismometers. As a result the area closest to Cedar Lake exhibited a measurable amount of activity that was not detected through triangulation. Along the Pomona Fault there were numerous azimuth events located and a few triangulated events. A linear trend of events, both azimuth and triangulated, were depicted to possibly be an unknown fault in the areas that trend NW-SE through the north portion of Cedar Lake. The comparison of rainfall and seismicity suggest the possibility of a seasonal component in background seismicity. Through our study, utilizing the one-station events to locate areas of probability for events, and locating through azimuth, methods are able to improve upon when examining microseismicity in an intraplate setting.

No description available.

No description available.

Local, regional and teleseismic earthquakes recorded at seismic stations in northern Kenya have been analysed to determine the seismicity in this region and the crustal and upper mantle structure beneath an array on the north-eastern flank of the Kenya dome. A total of 389 microearthquakes, occurring during the period 17th Jan. to 26th Aug., 1981, have been located using a simple half space velocity model. The seismic activity is mainly confined to the Kenya rift and a zone approximately 150km to the east of the main rift. The northward extent of the activity suggests that the active section of the rift continues beneath Lake Turkana. Apparent velocities of local and regional earthquakes recorded at the Ngurunit array have been interpreted in terms of crustal velocity structure. A two layered crustal velocity model has been derived. The velocity of the upper crustal layer is considered to increase linearly with depth, according to the function V = 5.8 + 0.0245z. The velocity of the lower crustal layer is 6.5 0.2 km/s and the intermediate crustal boundary is placed at 24km. The variation of apparent velocity with azimuth of Moho arrivals suggests an eastwardly dipping Moho of 7 beneath the array. The depth of the Moho directly beneath the array is derived to be 46km and the velocity of sub-Moho material is 8.3 0.2 km/s. Delay times and slowness measurements of teleseismic P wave arrivals indicate the presence of anomalously low P wave velocity material in the upper mantle. Three-dimensional ray tracing modeling suggests a thickening of the anomalous body to the north and east of the array, such that the top surface of the body reaches to within 60-80km of the ground surface. The thickening may be associated with rift structures beneath Lake Turkana and Quaternary volcanic activity observed on the eastern flank of the Kenya dome.

Vancouver Island, located in southwestern coastal British Columbia, overlies the northern portion of the Cascadia Subduction Zone. This region is characterized by extensive seismicity which includes M ∼ 7 crustal earthquakes and less frequent M ∼ 9 megathrust events. Crustal deformation measurements have been carried out in this region since 1978 using various geodetic field techniques: levelling, tide gauge studies, precise gravity, laser ranging, and most recently, GPS. Earlier survey data provided key constraints to elastic slip-dislocation models for estimating the size and location of the rupture area for the next subduction-thrust earthquake. Recent estimates of crustal motions within the North Cascadia Margin based on both campaign GPS network surveys and up to 6.5 years of data from continuous GPS sites are consistent with the strain accumulation expected from a locked subduction fault. The deformation vectors are in the direction of plate convergence within the uncertainty of plate motion models. The observed strain rate across Vancouver Island is, however, smaller (by approximately a factor of 1.5) than the dislocation model prediction, suggesting the presence of visco-elastic effects. Crustal deformation measurements for central Vancouver Island fail to resolve motions that could be associated with the occurrence of large crustal earthquakes, and also suggest that the extent of the seismogenic subduction thrust zone north of the Nootka Fault Zone is extremely limited. / Graduate

A seismic refraction profile was undertaken to investigate the source of an aeromagnetic anomaly located above the Widmerpool Gulf, East Midlands. Ten shots were fired into 51 stations at c. 1.5km spacing in a 70km profile during 41 days recording. The refraction data were processed using standard techniques to improve the data quality. A new filtering technique, known as Correlated Adaptive Noise Cancellation was tested on synthetic data and successfully applied to controlled source and quarry blast data. Study of strong motion data reveals that the previous method of site calibration is invalid. A new calibration technique, known as the Scaled Amplitude method is presented to provide safer charge size estimation. Raytrace modelling of the refraction data and two dimensional gravity interpretation confirms the presence of the Widmerpool Gulf but no support is found for the postulated intrusion. Two dimensional magnetic interpretation revealed that the aeromagnetic anomaly could be modelled with a Carboniferous igneous source. A Lower Palaeozoic refractor with a velocity of 6.0 km/s is identified at a maximum depth of c. 2.85km beneath the Widmerpool Gulf. Carboniferous and post-Carboniferous sediments within the gulf have velocities between 2.6-5.5 km/s with a strong vertical gradient. At the gulf margins, a refractor with a constant velocity of 5.2 km/s is identified as Dinantian limestone. A low velocity layer of proposed unaltered Lower Palaeozoics is identified beneath the limestone at the eastern edge of the Derbyshire Dome. The existence and areal extent of this layer are also determined from seismic reflection data. Image analysis of potential field data, presents a model identifying 3 structural provinces, the Midlands Microcraton, the Welsh and English Caledonides and a central region of complex linears. This model is used to explain the distribution of basement rocks determined from seismic and gravity profiles.