Monday, July 19, 2010

Odd PNW Earthquake

Via OregonLive, I learned there was a minor earthquake this morning (17:15 UTC, 10:15 AM local) off of Vancouver Island. At magnitude 5.1, I doubt many people even noticed it, and I'm sure there was no damage. The article mentions that no tsunami was expected. It's interesting to note the location though; the zig-zag line from north to south is the Juan de Fuca spreading ridge, and the smoother line swinging to the SSE is the Cascadia subduction zone. The line extending to the NNW is the Queen Charlotte transform fault, making the point south of the comma-shaped Queen Charlotte Islands a triple junction. The epicenter was off the ridge axis, and away from the subduction zone. I'm not finding a beach-ball quake solution for this event, but I'd guess it was along a NW-SE transform fault. There are several possibilities, but that seems most likely to me. The USGS information is here.

In looking for information on this, the wikipage on the QC transform told me that in 1949, there was a magnitude 8.1 quake along that fault. Whoa. I knew the fault was there, and I knew it was active, but I had no idea it had produced such a large quake in modern times. There have been quite a number of smaller quakes as well, in the 5 to 7.4 range.

No comments: