Hey Dave,

Thanks for your explanation and response.

I believe I understood the fundamental and distinguishable concepts between
subduction quakes and transform ones but wasn't certain why megaquakes can
happen along these subduction boundaries if theoretically, there's enough
heat there to keep the material "plasticy" and less brittle than the more
shallower strike slip zones.




-----Original Message-----
From: psnlist-request@.............. [mailto:psnlist-request@...............
On Behalf Of Dave Nelson
Sent: Tuesday, March 15, 2011 4:02 AM
To: psnlist@..............
Subject: Re: Subduction zone quakes...

Hi Kareem,
                  ohhh gosh, where do I start  :)    Oh... Maj 
M7.5+  events are NOT restricted
to subduction zones  :)  Think of the big ones in SW Missouri, New Madrid,
1811-1812; Lisbon, Portugal 1755, M8.7  some of the large  M7.9 or so
ruptures of the San Andreas fault.

ok some differences (and others can chime in with ones I forget about)......

1) The focal mechanism are very different to strike-slip faults  have a look
at the brief explanation on my www page...
http://www.sydneystormcity.com/fomec.htm
It is a direct result of these types of motions that give rise to tsunamis
that wouldnt be created by a strike slip motion on the seafloor.

2) The quakes can be VERY deep. It is relatively rare for strike slip events
to be deeper than ~ 50km. Whereas subduction events can be as deep as 650km.
Have a look through the USGS records for events in the Kermadec to Fiji
region, north of New Zealand ( and even under the North Island of NZ)
    The reasons for the causes of the really deep subduction events is quite
amazing.....
In regions as mentioned in previous paragraph, the seafloor is subducting so
fast in that region, it gets very deep before its core becomes "plastic" and
starts to melt all the way through.  That is the core can still be cold have
brittle failure whilst the outer layers of the
  subducting slab is virtually molten.  Plate motion rates are in excess of
8cm / year as they are off the east coast of Japan.

ok there's a little morsel for you to chew on for a start  :)

cheers
Dave
Sydney



At 11:48 AM 15/03/2011, you wrote:
>Aside from the large magnitude (i.e. M8.0+) What's the difference 
>between these subduction zone events and events along a transform plate
boundary?
>Kareem
>Elk Grove, California

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