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Aug 22,2010 - Yikes! Lots of Cascadia is lighting up with tremor today. The main ETS patch is now straddling the Straits (Honn's TAMS system using only Canadian data has been reporting tremor being seen on southern Vancouver Island stations for a few days). The patch of tremor just south of Olympia continues. There is a new patch just south of Portland and a burble in southern Oregon. What the heck is going on? Time will tell.
Aug 24, 2010 - The main ETS tremor is now on southern Vancouver Island but with a persistent patch continuing just south of Olympia. However, the total number of tremor locations by the wech-o-meter is down quite a bit compared to the past week or so. The AofA team has switched with John and Steve returning to Seattle and Ken and Heidi talking over doing the servicing. Reviewing the course of the tremor associated with this ETS it seems to be following very closely the previous two ETS. At this rate it will be over in about 7-10 days.
Aug 25, 2010 - Most of the tremor is now north and west of the AoA experiment and thus we are starting to talk about when to pull the plug on the Texans (which take daily diaper changes). To help we have produced a set of comparative tremor plot maps for the most recent 4 ETS broken down by weeks. The last column is for the current ETS and will be updated with another week in a few days. Anyone care to guess when we can figure this puppy is too far away to be seen by Texans?
Aug 30, 2009 - Today was the last day for regular servicing of the Texans. However, since a big rain is forecast for tomorrow we decided to let them all go one extra day and not start the pull out until Wednesday. They all should have batteries to keep clocks going until at least Thur even if they stop recording on Wednesday morning. Tremor continues on Vancouver Island; with most of it quite a bit north-west of Victoria. However there was a small burst yesterday evening near Sooke on the south coast that might be recordable on the AofA.
if the Yellowstone hotspot is indeed fed by a plume from the deep mantle, as these results seem to indicate, when it first ascended towards the surface it would have intersected with the subducting slab, and what we are seeing in the tomography is the aftermath of that interaction. Effectively, the upwelling plume burnt through the subducted plate beneath Oregon on its way to the surface, heating it up enough that it lost its rigidity and was assimilated into the asthenosphere, leaving isolated fragments further down dip that were no longer connected to the plate at the surface. Tectonic changes at the Cascadia subduction boundary around 19 million years ago, notably a large reduction in the rate of plate convergence, could be linked to this splintering of the subducted plate, and the reduction in slab pull that would have resulted. After overcoming this barrier to its upward passage, the plume head then reached the surface 2 million years later, causing the eruption of the Columbia River Basalts.