Open Collections

Structure of the Cascadia subduction zone off Vancouver Island : new evidence from seismic refraction data

University of British Columbia

The Cascadia subduction zone forms the present convergent margin between the North American plate and the oceanic Gorda, Juan de Fuca and Explorer plates from approximately 40°N to 50°N. This thesis examines a subset of the offshore-onshore seismic refraction/wide-angle reflection data recorded during the RECAP'89 (Reflectionrefraction Experiment: Cascadia Accretionary Prism). RECAP'89 was a "piggyback" experiment in which The University of British Columbia deployed four continuous recording seismographs at eight land sites on the west coast of Vancouver Island to record airgun shots fired during an offshore multichannel reflection survey acquired by the Geological Survey of Canada. An iterative combination of two-dimensional travel time inversion and amplitude forward modelling was used to interpret crust and upper mantle P-wave velocity structure. With the aid of interpretation of corresponding reflection data, velocity structures were developed for Line 89-02/03 and 89-09 in Cascadia subduction zone. The principal tectonic elements for which velocity structures are determined are (i) the Pacific Rim with an average velocity of 5.0-6.2 km/s, and Crescent terranes with an average velocity of 4.5-6.4 km/s, which He along the coast against and beneath Wrangellia, (ii) the Accreted Wedge with an average velocity of 4.1-5.0 km/s below Tofino Basin, (iii) the subducting Juan de Fuca plate with an average velocity of 6.1-7.0 km/s. The new velocity models are consistent with the gravity field constraints. The final velocity model of Line 89-02/03 indicates a possible position for the updip limit of the seismic rupture zone for a potential great thrust earthquake in the area. This new improved velocity structure would also help to determine more accurate earthquake locations for the region.

Thesis/Dissertation

application/pdf

2009-04-29

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.

http://hdl.handle.net/2429/7688

Geophysics

University of British Columbia

UBCV

DSpace