A magnitude 4.0 earthquake struck the west side of Vancouver Island on Thursday, making it the second time in a week that tremors have rocked the West Coast. The U.S. Geological survey calls the quake relatively mild, and more likely to be an aftershock of the 6.3 magnitude quake that hit B.C.’s coast on Sept. 9 – the most powerful tremor to hit the area since the Nov. 2, 2004, when a magnitude 6.6 quake occurred.