Sunday, October 28, 2012
BC aftershocks look interesting
This big earthquake - M7.7 did not produce much seismic ground motion (PGV), or much tsunami action. I am quite amazed that the aftershocks are way out of the zone where the descending slab rubs against the continent. That means high stresses within the slab and very little actual displacement downward. It will all come out if they have strong ground motion sensors on the island, but I detect something weird here. Remember Vancouver, if the whole thing doesn't unzipper in 2 days, you can breathe a sigh of relief that Halloween won't be spoiled. :)
Update: An M6.3 aftershock in the exposed slab! Fascinating, but no action bleeding south, so everybody should be happy.
Update2: Oblique strike-slip with some thrust. That's why we have shallow aftershocks in the upper ocean crust. Displacement of 5m, but the strike-slip makes for very little tsunami action.