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Title: Studies of crustal shear waves and Poisson's ratio
Author: Assumpcao, Marcelo Sousa de
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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A large deep crustal and upper mantle seismic refraction experiment was carried out in 1974 with the cooperation of many British and German institutions - the Lithospheric Seismic Profile in Britain (LISPS), along a distance of 1000 Km from north of Scotland to south of England. The experiment has produced valuable detailed information about the deep crust and upper mantle structure in Britain. The present work is an interpretation of the shear waves recorded in the northern part of the LISPB profile (mainly Scotland), complementing the information derived from the compressional waves. The ratio of compressional to shear wave velocities in various parts of the crust of Northern Britain was determined by a method using the observed travel time ratio of shear to compressional waves (ts/tp). The resulting Poisson's ratios in northern Britain are close to the conventional value of 0.25 (equivalent to a velocity ratio of Vp/Vs = T) except in the Southern Uplands upper crustal and Midland Valley mid crustal layers (about 0.23). The pre-Caledonian basement of Lewisian granulites thought to continue beneath the Highlands down to the Southern Upland Fault shows different Poisson's ratios under the Midland Valley and under the Northern Highlands which might be interpreted as significant differences in mineral composition. The Poisson's ratio structure was used to help analyse a PS reflection from the Moho (P converted to S). The high apparent velocity of this phase was interpreted as due to a localized dip in the Moho discontinuity which is in agreement with Pn time-term data for the area. The Poisson's ratio structure was also used for accurate determination of epicentres of an earthquake swarm in the Kintail area of NE Scotland. The S wave arrival times of these earthquakes are in general agreement with the LISPB results showing that the Poisson's ratio determined in the LISPB profile north of the Highland Boundary Fault are representative of the rest of the Highlands.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available