Officials say an earthquake has jolted the sea floor off British Columbia, the latest in a series of tremors on the coast this week. The US Geological Survey says Thursday's quake had a magnitude of 6.1 and struck 156 kilometers west of Port Hardy, off the north coast of Vancouver Island. There were two quakes on Wednesday in the same area, both with magnitudes of around 5. There have been 18 quakes in the region this week. Seismologists say this is not unusual because the tremors are occurring in what's called a active region, and they are too far offshore to be felt on land and too small to generate a tsunami.