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Science Forum Index » Geology Forum » marine seismic alternatives?
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| Angelo Campanella |
 Posted: Wed Dec 10, 2003 5:50 pm |
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David Dalton wrote:
Quote: Well, in this case you are trying to measure what's in
the solid rock under the ocean layer, and that doesn't
move around, so it shouldn't be a problem, unlike
long path ocean acoustics. The density and velocity
variations between rock layers can be much greater than
the time-variant small variations in the ocean layer.
I suspect that the marine animal damage from geological exploration
would be caused by charges set off near or on the bottom. Such charges
will deliver a tremendous wallop to the water that would affect animals
for miles around.
In that case, it makes sense to me to set a mechanical shaker on the
bottom, or on a firm pedestal driven into the bottom, to deliver the
continuous MLSA signal.
Angelo Campanella |
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| David Dalton |
| Posted: Wed Dec 10, 2003 8:51 pm |
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Angelo Campanella wrote:
Quote: David Dalton wrote:
Well, in this case you are trying to measure what's in
the solid rock under the ocean layer, and that doesn't
move around, so it shouldn't be a problem, unlike
long path ocean acoustics. The density and velocity
variations between rock layers can be much greater than
the time-variant small variations in the ocean layer.
I suspect that the marine animal damage from geological exploration
would be caused by charges set off near or on the bottom. Such charges
will deliver a tremendous wallop to the water that would affect animals
for miles around.
Well, in the early days of marine seismic exploration I think
they used dynamite blasts just above the water but have
switched to an array of airguns (injecting extremely high
pressure bubbles) with slightly varying signatures such
that they constructively interfere to give a combined
wavelet similar to that of a dynamite blast. So, no,
it is done at or near surface but there still is a
pretty intense blast to the water.
Quote: In that case, it makes sense to me to set a mechanical shaker on the
bottom, or on a firm pedestal driven into the bottom, to deliver the
continuous MLSA signal.
But in seismic work while it is possible to get some results
from a single source with an array of receivers around it,
in general the source is moved around as well to improve
coverage even further. Now perhaps a fast crawling bottom
MLSA source can be developed (but the bottom is sometimes
a bit irregular), though the advantage would be that the
coupling would be directly with the sea floor and thus the
loss from the reflection coefficient between sea and sea floor
would not occur. But the surface or near surface Vibroseis-like
or MLSA source, though it would have that reflection coefficient
problem, which airguns also have, might be cheaper in the
near term but again may take a couple of years to develop a
prototype and a few years beyond that to phase in so for now at least
there should be scheduling of airgun use to minimize interaction
with marine organism migration patterns.
Good night,
David |
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| John Sharry |
| Posted: Wed Dec 10, 2003 11:23 pm |
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There is something called a marine vibrator. Its manufacted by IVI of Tulsa.
Works very similar to land vibrators. Best used in shallow water ecologically
sensitive areas. Can build up signal by remaining on station whereas airgun
must be constantly moving. |
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| Daryl Krupa |
| Posted: Wed Dec 10, 2003 11:53 pm |
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David Dalton <dalton@nfld.com> wrote in message news:<br8498$42i$2@coranto.ucs.mun.ca>...
<snip>
Quote: Hmmm, I have Jon Lien's e-mail address from a
few years ago somewhere (Michael Rochester gave
it to me) and if it is still the same may
e-mail him in the new year with all of my
past whale-related ideas and any new ones
that I think of while compiling them. He
heads a local group that rescues a lot of
whales from fishing gear, here in Newfoundland.
David:
Ah, you're at Memorial.
Have you happened to meet Hiscott or Aksu?
Daryl Krupa |
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| David Dalton |
| Posted: Thu Dec 11, 2003 3:32 pm |
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Daryl Krupa wrote:
Quote: Ah, you're at Memorial.
Yeah, I put my off-campus e-mail in the header even when
posting from campus though so that more SPAM goes there
and also so I deal with newsgroup related e-mail just on
Saturdays off-campus.
Quote: Have you happened to meet Hiscott or Aksu?
I know the name Hiscott and have seen him around (but not
at the beer mixers, I think) but haven't met him. I know
Aksu fairly well since he is the graduate chair. However
I know geophysicists Slawinski, Rochester, Wright, Hurich,
Hall, Leitch, Miller, Quinlan, and Hodych better since
they are all in my corridor, and Hiscott and Aksu are
up two floors. And I guess the best known geologist
here is Hank Williams who is retired but still has a
professor emeritus office and I see him around a good bit;
but haven't heard him play fiddle yet. But there's
an end-of-exam clean-out-the-fridge Murray Club (UBC has
Dawson, we have Murray) mixer this coming Wednesday, right  .
Anyway it is a good Earth Sciences department and anyone
interested in coming for a grad degree I guess could
look at http://www.esd.mun.ca or ask me for info
on the department and the city if you like. Other
departments are listed on http://www.mun.ca .
David |
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| David Dalton |
| Posted: Mon Dec 15, 2003 3:02 pm |
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Anyway I have to pull off almost all newsgroups including these
for a while except perhaps for Saturdays.
My Ph.D. candidacy exam will probably be rescheduled for late January
and I need to get a proposal draft in this week and last night wasted
quite a few hours on newsgroups. But I will still reply to e-mail
to the address in the header on Saturdays.
Bye for a while,
David
http://www.nfld.com/~dalton |
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| CAP |
| Posted: Tue Dec 16, 2003 1:22 am |
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"Peter Larsen" <SPAMSHIELD_plarsen@mail.tele.dk> wrote in message
news:3FD11324.753926B2@mail.tele.dk...
Quote: David Dalton wrote:
Now as long ago as ten years ago there were some protests in BC
on the effect or marine seismic airguns on marine life, and now
there is a fair bit more in Nova Scotia.
About time. The planets oceans are full of life that uses audio for
orientation and navigation. Simple common sense should dictate that we
try to avoid making unnecessary noise in the sea. Hearing damage is
considered as being one possible explanation of the beached cetacean
problem.
I think we should look into using something other than sound for
charting the seas, the current scientific noise pollution is as
defendable as "scientific whaling" (presumeably done to verify that the
cooking time for whale meat is unchanged!).
David (geophysicist but more applied math than practical)
Kind regards
Peter Larsen
During the 60's, Conoco were experimenting with marine vibrator as an energy
source. I have worked with some of the data they collected in Malaysia and
it is quite good. You might want to contact ConocoPhillips to see if they
have published anything in that regard. |
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