Following the very interesting discussion on this list regarding the
possible causes of the Indian Ocean Tsunami, those list members who
didn't hear the news bulletins in the UK this morning may be
interested to know that the type of sea bed survey suggested during
the discussion has in fact taken place, and that images are to be
released shortly. Those interested can find more information at:
http://news.bbc.co.uk/1/hi/sci/tech/4247409.stm
and
http://www.soc.soton.ac.uk/soc_home2.php?pagetype=news3&idx=219
Unfortunately there is no indication as to whether or not this
research programme was inspired by the comments made here!
Chris Elders
>My point exactly! There are huge debris flows in the subsurface and
>there have been dire predicitions of tsunami's resulting from a
>flank of the canari's and the hawaiin Islands colapsing. But
>there's not been such an event since the 50's and our views and
>technology have changed and grown significantly since then. So if
>one could demonstrate that there was OR was not an associated
>catastrophic debris flow offshore Indonesia then this would be of
>some consequence. Furthermore the there was a apparently a tsunami
>on the west coast of Sumatra as well as the east coast. Seems that
>the epicenter was on the east coast, but so there should be no
>rupture on the west coast, but there could be significan debris
>flows from such an earthquake on all coast.
>
>Finally: I could go do my own homework but it's easier to post the
>question here: What was the hypocenter or depth of the initiation of
>the earthquake below the epicenter? Displacement theory suggest
>that if the fault's initial rupture was as at 10,000 meters below
>the sea, the magnitude of the surface rupture may not be great
>enough initiate such a tsunami.
>Josh
>
>
>
>
>-----Original Message-----
>From: Tectonics & structural geology discussion list on behalf of
>Christopher Morley
>Sent: Thu 1/20/2005 10:12 PM
>To: [log in to unmask]
>Cc:
>Subject: Re: Earthquake
>
>The notion of giant slides triggered by an earthquake
>as a cause of the tsunami is interesting, - the
>modelling associated with landslides associated with
>volcanic islands is well known. However the scale of
>debris flows on continental margins may not be so well
>known to many structural geologists, so I thought I
>would chip in here with the following: - I have been
>recently mapping some 3D seismic data deepwater
>offshore Brunei, and there is one debris flow at the
>seafloor today - (so it is well imaged), that is about
>120 km long, and 50-80 km wide, and in places tens of
>metres thick. It is very easily identified from less
>disturbed parts of the seafloor by the very irregular
>rugged surface topography caused by entrained blocks.
>Compared with say 10 m vertical displacement of the
>seafloor along a 100 km surface fault, the volume of
>material in the debris flow capable of displacing
>water is much greater. However one problem with this
>particular debris flow is understanding whether it was
>a single catastrophic event or an amalgamation of
>events, and mixed fast and slow creep processes.
>Chris
--
___________________________
Dr. Chris Elders,
Course Director, M.Sc. in Basin Evolution and Dynamics
Department of Geology,
Royal Holloway,
University of London,
Egham,
Surrey TW20 0EX
Tel: 01784-443627
Fax: 01784-471780
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