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+--- Thread: M7.8-7.9 quakes in SW Pacific (/showthread.php?tid=640)
M7.8-7.9 quakes in SW Pacific - Island Chris - 12-18-2016
It could be a coincidence, but in November there was the M7.8 quake in New Zealand, yesterday a M7.9 east of New Ireland island New Guinea, and a couple weeks ago a M7.8 in Solomon Islands. All have Pacific plate on east or NE side (although there are some microplates in the region).
Chris
RE: M7.8-7.9 quakes in SW Pacific - Duffy - 12-18-2016
Chris;
I don't have the quake experience that most members have here, but from a novice point of view, some of these events seem unprecedented, particularly the New Zealand quakes. Is my assumption correct, or is this the norm over a forecast period for a given seismic region.
Duffy
RE: M7.8-7.9 quakes in SW Pacific - marc / berkeley - 12-19-2016
Hi Chris!
It's very interesting to look at the moment tensors, on one side it's a primarily thrust type events, on the otherside of the plate, it is normal type events!
In someways classic textbook. It's almost impressive.
--M
RE: M7.8-7.9 quakes in SW Pacific - Island Chris - 12-20-2016
Hi Duffy,
While there are a lot of M7+ quakes each year (15 or 20?), there are only 1 or 2 (or is it one every 2 years?) M8 quakes in the world. I think having 3 M7.8 quakes in a region is higher than the long term occurrence rate by quite a bit. But this is statistics of small numbers (3), so it does not mean a whole lot. The New Zealand quake is not unprecedented on its size: it has a subduction zone and a transform fault; New Zealand is a plate boundary. But it breaking numerous individual faults is interesting, and the right-lateral slip is as much as 12 m, which is huge, and the vertical motions locally are quite large.
Chris
RE: M7.8-7.9 quakes in SW Pacific - Island Chris - 12-20-2016
Marc,
Yes, I saw the M7 normal quake...was that central America? But it came a few days after a similar size normal quake in the subduction zone offshore Honshu, in the rupture area of the 2011 M9 quake. I recall I sent an email to earth scientist Leonardo "Nano" Seeber and others, and Nano thought it was interesting that this was not a stretching quake in the slab, but instead was above the slab (maybe above the megathrust?).
The thrust quakes in SW and the normal one in Central America (?) are not cause and effect: the plates don't change velocity on this time scale. It is not how quakes work. The plates are always moving the same way, but the faults are locked, and they flex and eventually rupture.
Chris
RE: M7.8-7.9 quakes in SW Pacific - Duffy - 12-21-2016
Thanks for the info Chris ... much appreciated.
Duffy