THE DEVILS MOUNTAIN FAULT ZONE: AN ACTIVE FAULT AND FOLD BELT OF THE PACIFIC NORTHWEST OF NORTH AMERICA

The Devil’s Mountain Fault Zone (DMFZ) extends east to west from Washington State to just south of Victoria, British Columbia in the northern Strait of Juan de Fuca of Canada and the USA. Recently collected geophysical data were used to map this fault zone in detail, which show the main trace fault, and associated primary and secondary (conjugate) strands and extensive NE-SW oriented folding that occur within a 6 km wide deformation zone. The fault zone has been active in the Holocene as seen in the offset and disrupted upper Quaternary strata, seafloor displacement, and deformation within sediment cores taken close to the surface exposure of the faults. Data suggests that the present DMFZ and the re-activated Leech River Fault may be the same fault system. Based on the length and previously estimated slip rates of the fault zone in Washington State, the DMFZ appears to have the potential of producing a strong earthquake, perhaps as large as magnitude 7.5 or greater within 2 km of the city of Victoria.