M. Schmidt1, H. Dragert1,2, A. Lambert1, N. Courtier1, L. Wolynec1,2, Y. Lu1, W. Sundholm3, B. Schofield1
During 2002 the Western Canada Deformation Array (WCDA) was enhanced by two new sites on southern Vancouver Island, (PTAL and BAMF), bringing to a total of 15 stations currently in the array. WCDA network operations enhancements currently underway include a complete audit of all site meta-data and the re-RINEXÕing of all WCDA data. The complete WCDA data set from 1991 will be made available on the new FTP server (wcda.pgc.nrcan.gc.ca) in the near future. Near term enhancements to the data management system include a RAID level 5 system for all GPS (WCDA and campaign) data as well as levelling and other geodetic data sets, meta data and site information files. A RAID level 1 FTP server external to the PGC firewall is planned for FY 2003-04.
Data analysis has expanded in scope to include data from permanent GPS reference stations operated by the Province of British Columbia and recently relocated onto geodetic quality, stable antenna piers. The primary WCDA analysis using the Bernese software currently encompasses approximately 30 sites from Canada and from the U.S. (PANGA consortium). A re-analysis of the continuous GPS data from the WCDA, PANGA and BC arrays from 1994 to 2002, has yielded an indication of seven aseismic slip events in the northern Cascadia Subduction Zone (CSZ). The surface displacement detected at each continuous GPS site is similar in amplitude, direction, and duration from epoch to epoch. This consistency suggests that the location of the slip is centered beneath southern Vancouver Is. (BC) and the eastern Olympic Plateau (WA).
During the summer of 2002 a combined GPS, Absolute Gravity and precise levelling campaign took place across Vancouver Island in order to improve the resolution of vertical deformation across the island. This was the first time all three methods were used simultaneously on this transect. Precise levelling and relative gravity transects have been run in the past and Absolute Gravity measurements are routinely carried out at the permanent GPS sites Ucluelet (UCLU) on the west coast and Nanoose (NANO) on the east coast of the island. The results from the recent re-analyses of 6.5 years of continuous GPS data (1995 to 2002) and four years of quarterly Absolute Gravity data (1997Ð2001) indicate almost no tilting between UCLU and NANO. Preliminary indications from the comparison of past levelling campaigns with the 2002 survey similarly indicate minimal net cross-island tilting over the past 10 years.
contact: schmidt@pgc.nrcan.gc.ca
1 Geological Survey of Canada, NRCan
2 School of Earth and Ocean Sciences, University of Victoria
3 Geodetic Survey Division, Geomatics Canada, NRCan