The geographical distribution of the sense of the first motion of P waves (and to a very limited extent, S waves) has been studied by seismologists to provide information on the focal mechanism of earthquakes. In this thesis we investigate the inverse problem; knowing the type and form of displacement at the focus at the focal instant, we study the azimuthal distribution of the sense of first P and S motion, using model seismic technique. The source of elastic energy is a thermally induced tensile fracture in a glass plate. Two types of fractures have been studied: Initial (Bilaterally propagating) Fractures and Extended (Unilaterally propagating) Fractures. The azimuthal distribution of the P and S wave amplitudes is indicated. The experiments reported in this thesis constitute a partial test of a recent theory by Knopoff and Gilbert (1960) on first motions from seismic sources. The type of fracture studied corresponds to Case 3 of Knopoff and Gilbert. Our results show significant discrepancies with the theory. The sense of the measured first S motion is opposite to that predicted by the theory, for both Initial and Extended Fractures.
The ratios Pө /P₉₀ and Sө/Pө differ in magnitude from the theory in many azimuths. It is suggested that the discrepancies are possibly due to the neglect in the theory of non-linear elastic effects near the tip of the fracture. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/38872 |
| Date | January 1962 |
| Creators | Mansinha, Lalatendu |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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