reply to post by skitzspiricy
This is a reply I gave to another member, so maybe it will help.
The Banda Aceh area of the 2004 event had a subsequent 8.5 and whilst the seismicity from the event may go on for some time, I don't expect anything
major there in the immediate future. This arc however extends over thousands of kilometres so just because one area is done for the present does not
mean it all is.
When the original 9.1 went off the geologists did say that the more Northerly part still had stress, and I would imagine that this latest area was the
one they were meaning, but maybe not.
The strike/slip event recently was very different to the mega-thrust of 2004 and of course in a different plate area being the opposite side of a
If this was relating to the (almost) North/ South junction then there still exists potential for a mega-thrust on the other side ( the side of the
recent ones )
The is some interesting information in this article
Looking at this again I used to be uncertain now I am not so sure
so apologies to BO if this seems to be a change.
A pattern seems to be emerging and I don't really know how best to explain it.
Is it my imagination or is there a definite 'line' where I have drawn the white lines? (The X could be interpreted as a straight line perhaps with
quakes falling either side)
Thinking out loud here, and looking for some input from the experts (John), if this was as is said a strike/slip rupture then would that not run in a
line with the convergent oceanic boundary? I drew this to illustrate where I would have thought the quakes would lie. The angle of this is purely
illustrative and may be closer to a transform joint)
Problems of terminology here in that a 'convergent' boundary can be a subduction sone or a 'collision' boundary but I have to assume that since in
Google Earth they are labelled separately then the main arc is the convergent subduction boundary and the south west pointing element is the
convergent collision boundary.
Now have a read of this learned paper Neotectonics of the Sumatran
. This paper is mainly concerned with the fault running down the spine of Sumatra but is relevant and has many good illustrations.
From that document I have extracted this map of the faults contained therein.
In order that you can see the position of the current earthquakes I have attempted an overlay of the Google Earth mapping onto this image above.
(Unfortunately curved earth images and flat earth images are difficult to match precisely but I have attempted to get the registration as close as I
These, whilst close to a convergent boundary on GE, do not seem to match the learned document at all! You can see the feint line of the GE boundary
and the positions of the 9.1 and 8.5
I am not sure if this is wild uneducated speculation or not but it seems to me that the lines (as drawn by me) if 'real' may in fact be indicating a
slab pull by the subducting area, but if that was the case why would the two bigger quakes be strike slip?
There is a possible alternative alignment that does not seem as 'neat', but the Mother Earth is not prone to being neat just to suit us!
This alternate alignment then fits in with the slip movement indicated for the Ninetyeast Ridge as indicated but leaves the other possible alignment
still sitting in an area unmarked for faults, but is above and therefore could be an extension to the fault immediately south.
The GE oceanic transform boundary not being shown in the paper does make this a little confusing.