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| Science Forum Index » Geology - Earthquakes Forum » Risk Of Huge Pacific Ocean Tsunami On West Coast Of... |
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| Gigilo Joe... |
 Posted: Sat Jul 25, 2009 9:56 am |
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Of course the Magnitude is only a reference to the amount of energy
released. A 9.0 at a depth of 175 km would let you know it is there,
but the uplift would be minimal. Raise the depth to 35km and you can
have major uplift. Up to and exceeding 20 meters. The Tsunami will be
in direct relation to the amount of uplift. The general rule is the
mag. must be greater than 8.0 and the depth must be less than 25km. to
get the maximum uplift. The length of the rift must exceed 4km to have
a significant wave that does not diminish it's energy over the fan
within 3,000km. There are a lot of variables and when they all come
together, it is like the "Perfect Storm". It can be devastating.
On Thu, 23 Jul 2009 20:37:29 -0700, "Mike Williams"
<miklwlms at (no spam) charter.net> wrote:
[quote:598e395a23]"David Oberman" <doberman at (no spam) socal.rr.com> wrote in message
news:8qph65d54ltvm6jrjri28hb342c70ah0l6 at (no spam) 4ax.com...
Skywise <into at (no spam) oblivion.nothing.com> wrote:
A question comes to mind now. Just what could be the theoretical
maximum magnitude for an Aleutian quake? Could it be bigger than
the 9.4/9.5 Chilean quake?
Is it a simple case of rupture length, or can other factors ... uh,
factor in?
Say one subduction zone fault ruptures a given length & creates an
M9.0. Can another fault rupture a length two-thirds that length &
still generate an M9.5 -- if, say, the displacement is big enough?
You seem to have two of the factors, Dave - almost. Rather than rupture
length it should be total area of the fault whereon slip took place, and
displacement is probably a good enough term; though I think seismologists
would say "average amount of slip" on that surface. The third factor, for
moment magnitude at least, is rock rigidity.
So - I dunno what the theoretical maximum might be that for an Aleutian
quake. But I shouldn't think it could match the Chilean one. The rupture
length for Chile was huge, close to a thousand miles. I don't think the
Aleutians could match that distance. Both the proposed Aleutian quake and
the Chile quake are subduction quakes. So, barring the Aleutians slipping
over a much greater area (L. X W.), and having much greater rock strength, I
don't think the Aleutians could beat the Chile quake in magnitude. But to
answer your question, Dave, I think that yes - in your scenario that second
quake _could_ have a larger magnitude.
I seem to recall reading somewhere that the maximum plausible earthquake due
to tectonic forces (i.e. not including meteor or comet impacts) for the
Earth would be below M10.
Maybe a professional could help us out here . . .
In the history of art, late works are catastrophes.
-- Adorno
The same could be said of war and wildland firefighting, with a slightly
different definition of "late works".
Mike Williams
Arroyo Grande, CA
[/quote:598e395a23] |
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| Mike Williams... |
| Posted: Wed Jul 29, 2009 7:31 am |
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Guest
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"Gigilo Joe" <PartyBot at (no spam) school.tv> wrote in message
news:kaam65l11eglnb4qgb30v07sh2mduh1173 at (no spam) 4ax.com...
[quote:2a7f574bed]Of course the Magnitude is only a reference to the amount of energy
released. A 9.0 at a depth of 175 km would let you know it is there,
but the uplift would be minimal. Raise the depth to 35km and you can
have major uplift. Up to and exceeding 20 meters. The Tsunami will be
in direct relation to the amount of uplift. The general rule is the
mag. must be greater than 8.0 and the depth must be less than 25km. to
get the maximum uplift. The length of the rift must exceed 4km to have
a significant wave that does not diminish it's energy over the fan
within 3,000km. There are a lot of variables and when they all come
together, it is like the "Perfect Storm". It can be devastating.
On Thu, 23 Jul 2009 20:37:29 -0700, "Mike Williams"
miklwlms at (no spam) charter.net> wrote:
[/quote:2a7f574bed]
[snip]
Thanks for bringing up an important point I missed; hypocenter depth is, as
you say, a vital component in determining whether or not, or how large, a
tsunami will result. But I do take issue with you regarding your statement
that "The Tsunami will be in direct relation to the amount of uplift." I
don't believe that is mathematically nor literally correct. A doubling of
uplift would probably not produce a doubling of tsunami height. And, even if
it did, since there are other factors involved, you would have needed to add
"all other factors being equal."
My recollection is that there are particular characteristics of the rupture
and the resulting seismic wavetrains that are important elements in
determining whether a quake is tsunamigenic.
Mike Williams
Arroyo Grande, Ca U.S. |
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| Belba Grubb... |
| Posted: Mon Aug 24, 2009 8:49 am |
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