earthquake swarm off west coast of Vancouver Island

In the past couple of weeks, there has been an increase in the level of activity in the offshore region of Vancouver Island. While earthquakes occur daily in this setting, occasionally the number of events dramatically increases, often including earthquakes of magnitude 4 or 5. Three such earthquakes have occurred in recent days: a M5.6 on February 4th, plus a M4.1 on St.Valentine’s Day and a M4.7 today. When such a cluster of many earthquakes occurs within a confined geographical area and a short period of time (usually over the course of a few weeks), these are generally refered to as earthquake swarms.

The following map is by no means comprehensive as it takes time to locate such a large number of events, but several have been located, including all those of magnitude greater than 4.

Last month of earthquakes in the offshore region of Vancouver Island. Note that many earthquakes are still to be located and added to this map, as time permits.

Earthquake swarms happen in this region fairly regularly, although with no clear temporal pattern. While they are not a pre-cursor to a megathrust earthquake, they serve as a good reminder that this region is under constant tectonic stress and a large earthquake can occur at any moment, without warning.