Slo-Mo PNW Earthquake

I've been reading about these critters for some years, and I find them confusing.

So-called "tremor-and-slip" events have occurred about every 15 months since they were first detected in 2002. The latest was found early Sunday north of Olympia and west of Tacoma, and is expected to travel north under the peninsula toward Vancouver Island. UW scientists say it can't be felt at the surface, but over the course of several weeks can release as much energy as a magnitude 6 earthquake.

I doubt I'm alone in that. The amount of seismic energy released is surprising to me: I would have guessed it was in the range of four to five, much smaller by a factor of 30 to 1000.

Comments like this, "Vidale said better understanding the changing slow-slip patterns may provide clues in advance of the next Cascadia mega-quake," should always be regarded carefully. Yes, it may, but on the other hand, it may not. In either case, without supporting information, theoretical framework and evidence, the alert reader should assume there's no reason to believe that X is likely to lead to Y. It's simply a possibility.

One other thing I should point out: The energy released in this quake is tiny compared to the amount anticipated in a major Cascadia subduction quake, typically discussed as a magnitude 9 (+/-). The difference between the former and the latter is a factor of 32,000, so this event is not dissipating any significant fraction of the region's latent seismic energy.

Interesting article overall; I'm left curious as to the apparent periodicity of these events, and why they're apparently restricted to the northern end of the subduction zone.