Distribution of the Pacific/North America motion in the Queen Charlotte Islands-S. Alaska plate boundary zone

Abstract

We present GPS data that constrain the distribution of the relative Pacific/North America motion across the Queen Charlotte Islands-Alaska Panhandle margin (NW North America). Velocities from a network of 22 campaign and permanent sites indicate that the Pacific/North America transpressive motion is mostly accommodated along the locked Queen Charlotte-Fairweather Fault. A significant portion (6 7 mm/yr) of the relative plate motion is taken up by distributed dextral shear across a ∼200 km wide region of the margin. Two models have been proposed to describe how the Pacific/North America convergence is accommodated off the Queen Charlotte Islands: Internal shortening vs. underthrusting of the Pacific plate. Although the GPS data cannot discriminate between the models, they provide strong constraints on the convergence distribution. The significant non-transient motion of GPS sites along the central British Columbia-southern Alaska margin has implications for seismic hazard and tectonic evolution models of the Canadian Cordillera.