This thesis applies three-dimensional (3-D) non-linear seismic tomography to image crustal/upper mantle structure of S.W. British Columbia and N.W. Washington. Two tomographic inversions are carried out including high-resolution imaging of upper crustal structure using controlled source data, and deeper imaging by simultaneous inversion of controlled source and earthquake data.
Non-linear first arrival travel-time tomography is applied to controlled source data from the Seismic Hazards Investigation of Puget Sound (SHIPS) experiment conducted in 1998. Nearly 175,000 first arrival travel-times are inverted to obtain a minimum structure upper crustal velocity model to a depth of 12 km with a cubical cell size of 1 km. Results from checker-board tests for this velocity model indicate a lateral resolution of 20 km and above. The main geological and structural features in the study area are well defined by this velocity model. The structural outline of the sedimentary basins in the Straits of Georgia and Juan de Fuca are distinctly mapped. The Crescent Terrane is mapped beneath southern Vancouver Island with velocities up to 7 km/s that correlate well with the presence of gabbro in the subsurface. The northwest-southeast structural trend observed in the Strait of Georgia correlates with the observed seismicity. Shallow seismicity observed at the southern tip of Vancouver Island correlates with the location of the Leech River Fault.
An earthquake tomography algorithm was developed for joint estimation of hypocentral and velocity parameters, and tested on a synthetic data set. Using this algorithm, tomographic inversion was performed simultaneously on earthquake and controlled source data from southwestern British Columbia and northwestern Washington. Approximately 15,000 first arrivals from 1,400 earthquakes and 40,000 first arrivals from the SHIPS experiment were simultaneously inverted for hypocentral parameters and velocity structure. Model resolution studies indicate a lateral resolution of 30 km and above.
Upper-crustal earthquakes close to southern Vancouver Island correlate with the velocity contrasts associated with the Leech River, Southern Whidbey Island, and Darrington-Devils Mountain faults. Three mafic to ultramafic high velocity units are identified at approximately 25 km depth beneath the Crescent Terrane and above the subducting Juan de Fuca crust. The continental crust and subducting Juan de Fuca crust and mantle are well mapped. The transition zone to continental mantle occurs at 35 km depth beneath the eastern Strait of Georgia. The slab seismicity beneath the Strait of Georgia at depths >65 km lies below a low velocity zone mapped in the mantle wedge at depths of about 45–55 km. This low velocity zone may be indicative of the presence of fluids released during the phase change from basalt/gabbro to eclogite in the subducting slab. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/10185 |
| Date | 25 October 2018 |
| Creators | Ramachandran, Kumar |
| Contributors | Dosso, Stanley Edward |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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