Upper crustal velocity structure of the southwestern Canadian Cordillera from explosion recordings on the WCTN earthquake seismic net

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dc.contributor.authorFallows, Stephen Johnen_US
dc.date.accessioned2024-08-13T22:16:32Z
dc.date.available2024-08-13T22:16:32Z
dc.date.copyright1994en_US
dc.date.issued1994
dc.degree.departmentSchool of Earth and Ocean Sciences
dc.degree.levelMaster of Science M.Sc.en
dc.description.abstractThe Western Canadian Telemetered Network (WCTN) in southwestern B.C recorded explosion shots from Lithoprobe's Southern Cordillera Refraction Experiment (SCoRE) in 1989 and 1990 and from the USGS Pacific Northwest refraction survey in 1991. Of the 24 shots which produced detectable arrivals at the 18 WCTN stations 14 shots and 14 stations were selected as the utilizable data set. The geographical distribution of the shots and receiver stations enables a large three dimensional area to be sampled. Most receivers show good P wave arrivals and S waves are recorded at many sites. Only ray paths considered to be in the top 10 km of the crust were used, and so all velocity estimates made were for the upper crust. The data sets were modelled using two methods: an in-line refraction least squares method and a tomographic inversion procedure. Seismograms from combinations of shots and receivers were separated from the main data set to leave only those which sample along a two dimensional profile. Along five profiles estimates of P wave velocity, S wave velocity and Poisson's ratio were made. P wave velocities were found to be highest over southern Vancouver Island (6.55 km/s), while S waves were highest over the southernmost Coast Belt and Georgia Strait (3.75 km/s). Poisson's ratio along the five profiles is homogenous except for an increase in the profile on the south of Vancouver Island. The travel time tomographic inversion data were also modelled using a procedure. The real earth was represented as a near surface velocity layer of uniform thickness over a refracting velocity grid. The results obtained were in overall agreement with the two dimensional profiles, and previous refraction surveys conducted in the region. High values of Poisson's ratio over Vancouver Island (0.27-0.28) may be related to (a) high mafic content represented by the volcanics of Wrangellia, or (b) fluids moving up through the continental crust released by the subducting Juan de Fuca Plate. Both the Georgia Strait and mainland have lower Poisson's ratios than Vancouver Island. The northern region of the Coast Belt has especially low values (0.20-0.24} which may be related to high quartz content in the crust.en
dc.format.extent122 pages
dc.identifier.urihttps://hdl.handle.net/1828/17732
dc.rightsAvailable to the World Wide Weben_US
dc.titleUpper crustal velocity structure of the southwestern Canadian Cordillera from explosion recordings on the WCTN earthquake seismic neten_US
dc.typeThesisen_US

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