The Queen Charlotte Fault

Abstract

The Queen Charlotte Fault (QCF) is a transform fault that separates the Pacific plate and the North American plate. It is often referred to as the right lateral strike-slip equivalent to the San Andreas fault zone. The QCF formed off the west coast of the islands of Haida Gwaii upon the termination of margin subduction in the Eocene. To the south of the QCF is the Cascadia Subduction Zone (CSZ) where the Pacific plate is subducted below the North American plate. A complex plate triple junction between the QCF and the CSZ demonstrates slow margin convergence at the Winona basin and short spreading centers known as the Tuzo Wilson and Dellwood Knolls. To the north the QCF transitions into the Fairweather fault extending from the coast of Alaska into the continent. Along the continental margin of Haida Gwaii, the Pacific plate and North American plate motion was strike slip from the Eocene to approximately 6 Ma with a period of extensional volcanism and subsidence in the Queen Charlotte basin. At 6 Ma, a change in the Pacific-America relative plate motion resulted in 15-20° oblique convergence and caused the subduction-type underthrusting of the Pacific plate beneath Haida Gwaii. This underthrusting resulted in an offshore flexural bulge, downbowing of the oceanic lithosphere at the margin, and the uplift and erosion of the west coast of Haida Gwaii which exposed mid-Tertiary rocks. Evidence to support subduction-type underthrusting includes: an offshore forebulge, the Queen Charlotte trench, the Queen Charlotte terrace accretionary sedimentary prism and GPS vectors and small earthquake mechanisms that indicate oblique convergence. This type of underthrusting is known to cause earthquakes, such as the magnitude 7.8 earthquake off the coast of Haida Gwaii in 2012. It is important to understand complex fault systems and their structure to ensure safety in hazardous places.

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