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



Because this explanation by David Marjanovich looks very similar to an
abstract of a paper by J. Curray, and I had e-mailed J. Curray earlier
today, I phoned J. Curray - who has been busy all day answering questions
like mine.

Here is the abstract of J. Curray's paper;

Tectonics and History of the Andaman Sea Region
J R Curray (Scripps Institution of Oceanography, La Jolla, CA 92093-
0220; ph. 858-534-3299; fax 858-534-0784; e-mail: jcurray@ucsd.edu)

The Andaman Sea is an active backarc basin lying above and behind
the Sunda subduction zone where convergence between the overriding
southeast Asian plate and the subducting Australian plate is highly
oblique. The effect of the oblique convergence has been formation of a
sliver plate between the subduction zone and a right lateral fault
system, which has evolved since the Oligocene into the Sumatra Fault
System, the Sagaing Fault in Myanmar, and the obliquely-opening
Andaman Sea at the bend in the once-continuous strike slip fault.

The middle Eocene hard continent-continent collision of India and Asia
started clockwise rotation and bending of the northern and western
Sunda Arc. Sliver faulting started in the Oligocene on the West
Andaman Fault extending through the outer arc ridge offshore from
Sumatra, through the present region of the Andaman Sea into the
Sagaing fault. In late Oligocene, ca 32 Ma, the Mergui Basin started
opening at the intersection with the Klong Marui and Ranong faults by
extension of continental and/or volcanic arc crust. In early Miocene, ca
23 Ma, backarc spreading started forming the sea floor which later
became Alcock and Sewell Rises. From middle Miocene, ca 16 Ma,
these contiguous features were separated from the foot of the
continental slope by NW-SE spreading, and the motion of the southern
part of the West Andaman Fault was taken up by the Mentawai Fault in
the forearc basin off Sumatra. At about 3-4 Ma, the present plate edge
was formed, Alcock and Sewell were separated by formation of the
central Andaman Basin, and the faulting started moving from the
Mentawai Fault to the Sumatra Fault System bisecting Sumatra.

Prof. Curray said that the Burma microplate IS the sliver plate - which runs
all the way from northern Burma southward through Sumatra.    He said the
maps on the NEIS web page have the northern and southern boundaries wrong.
A piece of it broke loose in the quake.

He said he didn't want to send me this paper and a similar one cited in
Hall's 1997 papers, because it is out of date.   He has an up to date paper
on it in print, which should come out in the Journal of Asian Earth
Sciences, hopefully in a month or two.   He said he asked them if they could
possibly expedite it in view of current events.  He's sending me a copy of
the abstract - but the paper itself is too large.   (and my computer hangs
up on big pdf graphics.)

As to the rest of my questions, Prof. Curray said that the Indian and Burma
plate are moving relative to each other, at a very oblique angle.   He said
most of the action connected with this quake has been thrust faulting but
there may have been some slip/ strike fault activity along the faults in the
Andaman Sea.

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.
>