Present-day motions of the Juan de Fuca plate from seafloor geodetic
measurements

by Dave Chadwell
MPL SIO
University of California, San Diego

2:30-3:30pm
Friday April 4, 2003
Refreshments served at 2:15pm
Munk Conference Room
Cecil and Ida M. Green Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
http://mahi.ucsd.edu/seminar/

Abstract

The Juan de Fuca (JdF) plate has no islands on which conventional GPS,
VLBI (Very Long Baseline Interferometry) or SLR (Satellite Laser
Ranging) observation stations can be operated.  Seafloor geodetic
techniques have been developed and applied at four sites on the JdF
plate to determine current motions in terms of measurements comparable
to those of the adjacent Pacific and North American plates. In general,
the data suggest that seafloor spreading along the southern Juan de Fuca
Ridge occurs episodically and the plates are currently locked across the
axial valley and out to at least 25 km east of the south Cleft segment.
These results contrast with observations of continuous motion along the
Cascadia subduction zone observed to be nearly perpendicular to strike of
the thrust fault in the northern JdF plate offshore Vancouver Island and
with significant trench parallel components at a site 150 km offshore
Newport, Oregon.  Techniques, their repeatability and implications of
the results will be discussed.