Deep Earthquakes Get A Little Less Mysterious
Deep earthquakes occur where the oceanic lithosphere, driven by tectonics, plunges under continental plates - examples are off the coasts of the western United States, Russia and Japan.
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“Geologist [I'm Climate Change]”
Since: Mar 07
#1 Sep 25, 2013
Was able to see deep earthquakes on the map on the NEIC before they scrapped the historic seismicity option as a result of one or other executive decision @ about the same time as the sequester came through.
Via the now defunct data image map the deep quakes were visible in descending contours in areas where a previous relatively large megathrust quake & plate lurch had happened in relatively recent history or prehistory.
Classic volume change earthquakes in a relatively cold descending slab shrinking under pressure were visible at decreasing frequency down to 400Km or so. Above 400Km depth the rate of deep quakes increased reaching a peak at about 550Km and tailing off through the 600-700Km contour.
This charming little paper appears to deal with the quakes at the 400-700Km contour depth caused by olivine phase transition & involves not just the plate crust area but also the upper mantle of the descending slab where olivine is stable so the contour spread of deep quakes thickens considerably.
This is particularly obvious in the shallow descending plate contour @ the Tonga arc @ Fiji. The area beneath Fiji itself is actually being uplifted by the Fiji plateau mantle plume and some deep quakes there are a result of rigid slab deformation caused by folding due to uplift & upwelling.
Would like to see a return of the "historic seismicity" option on the NEIC website, as it was a very handy tool.
Have a nice day: Ag
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