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Wednesday, July 6, 2011

Kermadec Quake

29.312°S, 176.204°W
(Note decimal degrees; see lat/long article for information about conversion. How many degrees is this from your school?)

Orange, yellow, and green are closer to surface;
blue and violet are deeper than 150km
see map page for more details and views
Thanks to our local paper, the Brockton Enterprise, for letting us know about the magnitude 7.8 earthquake that struck the very remote Kermadec Islands earlier today (although it was already "tomorrow" where the quake occurred, just a few degrees east of the International Date Line. (The Globe and Mail provides just a few more details.)

The remote outpost of New Zealand houses only a weather station (currently 67 degrees F with a light breeze) and a hostel for visiting scientists. It is almost 1,000 kilometers south of Tonga, the nearest "major" island and almost 1,200 kilometers northeast of Auckland. The earthquake is remote even from these islands, with Raoul Island, the nearest, over 100 kilometers away. (See EarthView blog posts about another remote New Zealand island, Tokelau.)

The quake occurred 44 kilometers below the surface, which leads the USGS tentatively to conclude that is is located in a normal fault within the downward-moving Pacific plate.

The map at right is among several interesting depictions of seismic activity in this remote area. It indicates that the area is seismically quite active, with thousands of mostly small events over the past twenty years. Although the depth of each event can vary according to many factors, in subduction zones of this kind, the tendency -- well-illustrated here -- is for shallow events to cluster near the fault line, with depth increasing with distance away from the advancing plate (in this case, westward as the denser Pacific Plate advances under the Australian Plate).

As with any major quake in a marine environment, tsunamis are a possibility, and in this case it appears that a 2.2-foot wave was the highest generated by the event.

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