The continental margins off Vancouver Island and the Queen Charlotte Islands have been studied extensively in projects by SEOS researchers. Program objectives are to determine crustal structure at the transition between oceanic and continental plates, and to understand the history and dynamics of the interaction between the two plates. Information on margin structure and dynamics provides important constraints for understanding earthquakes in the region.  Researchers include Spence, Hyndman, Rogers, Dragert, Wang , of the Pacific Geoscience Centre.

Upcoming projects

• Georgia Basin 3D seismic project : Spring 2002
  • examine structure near 1995 earthquake swarm (max magnitude ~5.0), where possible northward-dipping fault was identified from seismicity
  • seismic equipment
    • small airgun array, ?200-300 cu. in. total capacity
    • 1200 m multichannel streamer (COAMS)
    • onland recording with 20-30 Reftek seismographs
  • collect closely-spaced seismic lines over proposed fault, image detailed 3D structure from reflection seismic, form 3D velocity model from tomographic inversion
    
    
• CASSIS – Collaborative Cascadia Seismic Experiment : proposed for summer 2003 (?)
  • proposed major international collaborative experiment with Japanese
  • active source program to study (a) structure and character of subduction decollement (b) velocity structure of downgoing slab, accretionary wedge and continental plate
    • one Canadian and two Japanese seismic vessels, for reflection and refraction
    • ~100 ocean bottom seismometers
    • ~100 Reftek seismographs on Vancouver Island/mainland plus ~10 drillhole explosive shots
  • seismicity program (~3 month deployment of 10-15 broadband seismometers in both onshore and offshore regions) to examine low-level seismicity, intraplate stress, and correlation with plate structure
    
    
    

Current and recent projects

• GEOIDE : Earthquake Hazards and Space Geodetic Techniques
  • participate in GPS expansion of the Western Canada Deformation Array and in campaign-style deployment of GPS receivers
  • determine velocity field giving strain deformation near continental margin
  • deploy fixed point reflectors in Fraser Valley for InSAR interferometric radar
  • integrate with seismicity to provide constraints on earthquake risk
    
    
• SHIPS : Seismic Hazards Investigations in Puget Sound (Ramachandran 2001)
  • crustal structure of Cascadia subduction zone and overriding continental plate, including active faults and sediment basins that may control wave propagation and amplify ground motion.
  • marine multichannel sesimic in Puget Sound, Georgia Strait, Juan de Fuca Strait
  • wide-angle recording on onshore and seafloor seismometers
  • tomographic inversion of earthquakes and controlled-source data, for simultaneous determination of velocities and hypocentres
    
    
• Detailed structure of the Vancouver Island accretionary margin (Yuan et al. 1994)
  • multichannel semblance analyses: zone of reduced velocities found landward of deformation front interpreted as undercompacted sediments which are buried faster and can respond by dewatering
  • provides constraints on finite element modelling of fluid flow in the accretionary wedge
    
    
• Geodynamics
  • Thermal modelling : determine seismogenic zone on subduction interface for great thrust earthquakes
  • Cascadia, Alaska, Chile margins (Oleskevitch et al. 1999)
  • central America trench off Mexico (Currie et al. 2002)
  • Ecuador/Colombia margin (Collot et al. 2002)
  • Cascadia deformation studies : determination of vertical uplift and horizontal compressional motions to determine state of stress and potential earthquake risk, using precise GPS positions from the Western Canada Deformation Array (Mazzotti et al. 2002)
  • northern Canadian Cordillera (Flueck, Ph.D. project)
    • elastic thickness from coherence analysis of gravity and topography
    • analysis of n. Cordillera thermal regime and relation with lithospheric strength
    • current deformation from GPS analysis, relation with seismicity
      
      
  • crustal structure of Cascadia subduction zone and overriding continental plate, including active faults and sediment basins that may control wave propogation and amplify ground motion.
  • marine multichannel sesimic in Puget Sound, Georgia Strait, Juan de Fuca Strait
  • wide-angle recording on onshore and seafloor seismoneters
    
    

Selected publications

• Brocher, T.M., T. Parsons, R.E. Blakely, N.I. Christensen, M.A. Fisher, R.E. Wells, and the SHIPS Working Group (12 authors incl. G.D. Spence), 2001. Three-dimensional geometry of crustal faults, basins, and uplifts in Puget Lowland, Washington: Results from SHIPS, the 1998 seismic hazards investigation in Puget Sound, J. Geophys. Res., 106, 13541-13564.
  
  
• Collot, J-Y, P. Charvis and the SISTEUR Scientific Party (27 authors including G.D. Spence), Exploring the Ecuador-Colombia active margin and inter-plate seismogenic zone, EOS submitted Oct 2001 (9 pages + 4 figures).
  
  
• Currie, C.A., R.D. Hyndman, K. Wang, and V. Kostoglodov, 2002. The seismogenic zone of Mexican thrust earthquakes, J. Geophys. Res., submitted Aug 2001.
  
  
• Flück, P., R. D. Hyndman, K. Wang, 3-D Dislocation Model for Great Earthquakes of the Cascadia Subduction Zone, Journal of Geophysical Research, 102, 20'539-20'550, 1997.
  
  
• Hyndman, R.D., Spence, G.D., Yuan, T. and Davis, E.E. 1993. Regional geophysics and structural framework of the Vancouver Island margin accretionary prism, ODP Init. Repts, Cascadia Margin Volume 146, 399-419.
  
  
• Hyndman, R.D. and K. Wang. 1995. Current deformation and thermal constraints on the zone of potential great earthquakes on the Cascadia subduction thrust, Journal of Geophysical Research, 100: 22133-22154.
  
  
• Oleskevitch, D.A., R.D. Hyndman, and K. Wang, 1999. The updip and downdip limits to great subduction earthquakes: thermal and structural models of Cascadia, south Alaska, S..W. Japan, and Chile, J. Geophys. Res., 104, 14965-14991.
  
  
• Ramachandran, K. 2001. Velocity of s.w. British Columbia and n.w. Washington from 3-D non-linear seismic tomography, Ph.D. thesis, U. of Victoria.
  
  
• Spence, G.D. and Asudeh, I. 1993. Seismic velocity structure of the Queen Charlotte Basin beneath Hecate Strait, Can. J. Earth Sci., 30, 787-805.
  
  
• Yuan, T., Spence, G.D. and Hyndman, R.D. 1994. Seismic velocities and inferred porosities in the accretionary wedge sediments at the Cascadia margin, J. Geophys. Res. 99, 2653-2670.