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Re: More questions on the Burma microplate (allegedly where the quake occurred)



OK, I'm looking at the first of them.

By the way, the text on that page and its associated more details page have
gotten clearer - it no longer claims any slip/ strike fault movement
happened, nor that the quake occurred along a slip/ strike zone.    It
states that slip/ strike faults up to several hundred km from the thrust
fault line (eg the trench) take up the north-west motion of the oblique
angle of convergence.    Then it says that this quake involved only thrust
faulting, and if some of the aftershocks have involved compensatory motion
on the slip/ strike faults it doesn't say so.    It mentions the aftershocks
and gives no details about them.

In the 1833 Andaman Sea Quake, aftershocks along the West Andaman Fault
compensated for the thrust fault along the trench.

This map that I'm looking at appears to show that the eastern boundary of
the burma plate is the "back arc" island arc.   I didn't notice that because
it's too strange.  The explanations I have for that ridge of islands and
uplift and volcanic mountains is uplift from the thrust fault, caused by the
subduction of the Indian plate underneath it, and volcanic activity, caused
by the melting of the sinking Indian crust and the formation of magma
pockets.   I understand that every subduction fault has such a ridge of
uplifted and volcanic mountains.   I also understand that this is teh
eastern end of the subduction fault zone.

So the Burma plate is basically the fault zone?   Maybe with an extraaneous
Gondwanan rock or two in it?    LOL!    No wonder noone calls it a plate
unless they're talking to the public or the media.

But why is the Burma plate depicted as stopping at northern Sumatra?  The
ridge continues on down Sumatra and Java - and so does the plate spreading.
According to that dissertation by Kerry Sieh's student.   The plate
spreading doesn't stop just south of where this quake occurred.

Kerry Sieh says that the movement of this Burma quake caused the entire
island of Sumatra - or maybe the northern end of it?   to possibly move
westward.   How would that happen without visible faults opening up on the
island - and if the edge of the plate is the central mountain range, could
the WHOLE island have moved?

Yours,
Dora Smith
Austin, Texas
villandra@austin.rr.com
----- Original Message -----
From: "David Marjanovic" <david.marjanovic@gmx.at>
To: "DML" <dinosaur@usc.edu>
Sent: Monday, January 03, 2005 4:03 PM
Subject: Re: More questions on the Burma microplate (allegedly where the
quake occurred)


> > What about its eastern boundary?
>
> A midocean ridge in the Andaman Sea. Back-arc spreading.
>
> Just yesterday four maps of the region were posted on this list. One has
> disappeared from the page
> http://earthquake.usgs.gov/eqinthenews/2004/usslav/, but the other 3 are
> still there. Scroll down a little.
>