Will part of Vancouver Island "break off and sink," or "split in two at Alberni Inlet?" No. In a big earthquake the seafloor offshore from Vancouver Island will be uplifted and the area along the coast will sink, but at worst that sinking will only be a few meters.
Dr. Gerard Fryer
Hawaii Inst. of Geophysics & Planetology
University of Hawaii, Honolulu, HI 96822
https://www.soest.ha.../vancouver.html