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looking for clear explanation of the earthquake



Say, I bet there are people on this list who are qualified to explain this.
Or maybe could tell me where to go to get an actual clear logical
explanation.  There are specialists in Southeast Asian plate tectonics at UT
Austin but they are on vacation and I can't reach them.

First of all, what are teh Burma and Sunda plates - besides part of the
Eurasian Plate?

Is the Burma "microplate" actually just a zone of loose rock and faults?
It appears to constitute the entire region immediately east of the java/
sunda trench, which is the point where the Australian and Indian plates
(which of those plates is actually there and whether they are two plates is
clearly a matter of controversy) slides under the Eurasian plate.   Why is
the Burma plate or microplate called a plate at all?    Logically it is a
fault zone, probably uplifted above the trench.

On one of the faults in the area I found evidence that some rock tries to
move out of the way, along the fault zone.   Is the Burma plate an area of
crust that is behaving in this way?    That would logically account for
NEIS's insistence that the India and Australia plates move northward as well
as eastward with respect to it ( though it would require that the Burma
plate in fact be moving south) - and that there are slip/ slide faults along
the boundary.

WHAT exactly is the Sunda plate, and why is it called a separate plate?
The Sunda plate is part of the Eurasian plate and not usually depicted as a
separate plate.   In fact before last night I could find next to nothing
about it in Google, except that two countries sit on it.    I have been
unable to find a map that shows the entire Sunda plate, but it appears to
constitute Burma, Thailand, and Vietnam, and the Indonesian islands to the
north and east of the java trench/ island arc formed where the Australian
and Indian plates meet the Eurasian Plate.    On the western border, it
meets with the Pacific plate, and its rigidity relative to plates around it
purportedly causes trouble for Bali and another nation that sits on its
boundaries.

I didn't find anything that says it moves differently with respect to the
rest of the Eurasian plate or something - which is the rationale for
thinking there is an Indian plate separate from the Australian plate.    I
found a whole article showing that those two paltes move differently with
respect to each other though thye have a poorly defined border and noone can
decide where it is.

Speaking of noone knowing where the boundary is between the India and
Australia plates, where is it?   Before yesterday, the eastern border of teh
India plate was I think the mid-ocean Ninety-east ridge.    Now suddenly the
India and Australian plates have an east-west boundary that ends at the java
/ sunda trench off of northern Sumatra, near where the quake occurred - and
that helped cause the earthquake.

Now the part I REALLY don't understand.   NEIS's explanation of how the
quake happened - which I found more or less paraphrased elsewhere.    The
India and Australia plates move northeast with respect to the Eurasia plate
and subducts underneath it where the plates meet.   Logical so far.    Where
this takes place there are thrust faults.   Also logical.   It more or less
requires that parts of the Eurasia plate are thrust upward at the boundary.
That in fact created the entire island arc.

Now for not logical.    According to NEIS, the India and Australian plates
also move northeast with respect to the "Burma microplate", which makes
slip/ slide faults like the San Andreas fault in California, where two
plates glide sort of smoothly past each other.   Occasionally they hang up,
and when the rock breaks there is a quake.  Then the two plates continue
their seperate northward and southward journeys.   Quakes in California do
not result in land near the fault thrusting upward.

According to NEIS, as paraphrased in various places with no other detailed
explanation of the quake available, this quake resulted from a rock breaking
loose along a SLIP/ SLIDE fault, between the India/ Australia and Burma /
Eurasia plates.    When that happened, a nine- mile wide strip along the
entire near boundary of the Burma/ Eurasian plate, abruptly SLIPPED, and
THRUST a hundred feet UPWARD.    That just doesn't sound like something a
slip/slide fault could do.

How is this even possible?   Is what really happened that the Australia/
India plate got stuck while sliding UNDER the Burma plate, and when it broke
free the edge of the Burma plate abruptly thrust upward?     That would be
far more logical.

By the way, is there ANY justification for thinking that New Zealand sits on
its own plate?  Two plates meet and twist in a bizarre way there - hard to
see how there could be a separate plate, nor how there would be just ONE
separate plate, logic says there would have to be two;  but maybe it's a
Burma microplate sort of thing?

By the way, the best single article I have seen on the quake by far is at
http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake, and there are
links to the main media web sites on the quake, which is more than google
news has managed to do.

Yours,
Dora Smith
Austin, Texas
villandra@austin.rr.com