THE QUEEN CHARLOTTE FAULT, BRITISH COLUMBA: SURFICIAL ANATOMY OF AN ACTIVE TRANSFORM FAULT

The Queen Charlotte Fault Zone (QCFZ) off western Canada is the northern equivalent to the San Andreas Fault Zone, the Pacific – North American plate boundary. Geomorphologic expression and surface processes associated with the QCFZ system have been revealed in unprecedented detail by recent seabed mapping surveys. Convergence of the Pacific and North American plates along northern British Columbia is well known, but how the QCFZ accommodates this convergence is still a subject of controversy. The multibeam sonar bathymetry data reveals, for the first time, evidence of a fault valley with small depressions on the upper slope, offshore central Haida Gwaii (Queen Charlotte Islands). The depressions form where strike-slip right-steps offsets have realigned the fault due to oblique convergence. Core stratigraphy and radiocarbon dating of sediments within the fault valley and small depressions suggest that these features are recent in origin. In addition, the continued development of the fault valley and dislocation of submarine canyons controls sediment migration from the continental shelf through to the lower slope. Subsequent to the October 2012 magnitude 7.7 earthquake a single repeat multibeam sonar bathymetric line along the axis of the primary fault suggests horizontal movement of less than 5 m and vertical movement southeast of the epicenter. These recent seafloor changes will be confirmed by a marine survey in 2015.