Over at Deep-Sea News, they’re talking about the recent earthquake in the Tonga Kingdom and comparing it to the 2006 earthquake in the same region, and they’ve got a nice visualization of the earlier event.
Next is the cross section of the velocity waves (P-waves) that show crustal density. The arc of blue is the seafloor of the Pacific Plate subducting beneath the Australian Plate. The yellow and red color is the less dense rock (due to heating by friction at the plate boundary), which is directly under the Tongan Ridge (and probably portion of the Kermedec Ridge to the south).
The last layer is the points where past seismic activity has occurred. Each cube represents an earthquake, with the large diamond the big one on May 6th, 2006. Note also how deep these earthquakes occur and how they follow the subduction trench.
