[meteorite-list] Peruvian bolide message rehash, ALL

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 3 Mar 2007 02:41:32 -0600
Message-ID: <0ab701c75d6f$bf7c5ce0$32ea8c46_at_ATARIENGINE>

Hi,

    Randall, the impact calculator you are using is
an excellent tool, but it has real limitations. The
authors say in their disclaimer that it breaks down
and becomes "unreliable" for very small or very
large impacts, and the event you are talking about
is, by their standards, very small.

    I've played with it a lot and read the .pdf file
documentation on their assumptions -- it is very
poor at modeling seismic responses (among other
defects). You can't trust it for that. It has problems
(see the example given a few paragraphs down).

    As an example of how hard it is to untangle an
"event," I offer one I witnessed. One afternoon,
in my little downstate Illinois store, I heard a
tremendous boom from outside. Going out, I
discovered that everyone in town had heard it.
The Fire Chief had called the Propane Company
to make sure one of their big tanks hadn't exploded.
Within a few hours, it was on St. Louis, MO,
radio stations. The "explosion" had been heard
from points 85 miles apart. The "epicenter" had
been about 30 miles from me. Seismographs 30
miles away had registered a 3.2 event. Airports were
queried, as well as the (then) MacDonnell-Douglas
works, and an Air National Guard station. No, they
had no supersonic flights going on. Suspicion in
the public mind began to center on an industrial
facility that had had such incidents in the past and
tried to conceal them, but they issued vigorous denials.

    I naturally thought: Meteorite!! But there were no
reports of a flash in the sky, a trail, the sighting of a
fireball, or any other indication of meteoric origin
for the boom. Four days later, a sheepish pilot, who
had been testing a new military jet, came forward
and admitted to accidentally taking his craft supersonic
at high altitude: "I just nosed her over a little and boom!
she went super..." Boom indeed.

    That's all it took to create a boom heard for 40+
miles in every direction, that registered well on a local
seismograph. At 30 miles away, where I was running
an antique store filled with glass, the entire building
filled with the sound of glass tinkling on glass, eerily
and all at once. Just one plane, not even a big plane
(I think it was an F-18E).

    About six weeks before the Moss meteorite fireball
in Norway, there was a much bigger Norwegian fireball,
seen over 400 miles, that left 3.7 to 3.8 seismic traces,
and thunderously detonated. We all thought it might be
a good one for meteorites, but none was ever found.
The original estimate was that it was an "Hiroshima
bomb" sized explosion. When those seismic traces
were finally evaluated by an expert, they were produced
by an equivalent to the explosion of 300 tons of TNT.
(We would have all missed that but Darren Garrison
found it.) The famous Park Forest meteorite event
was even less energetic. The astronomer who made
that Hiroshima estimate apologized; he said he got
"carried away." It's easy to get "carried away."

    Another coincidence is that the witnesses to that
first Norwegian fireball saw it "hit a mountain." And,
soon, there was discovered a cup-shaped crater on
the side of an appropriately placed mountain! Another
long story, but the result was that the mountainside
"crater" was a land-slip (and it turned out to be in
the wrong place by many miles). You too seem to
have a mountainside "crater." Telling whether it's an
impact feature or a landslip requires a geological expert,
but the odds are in favor of a landslip, particularly
since the question of seismic events is involved;
it's seismic active spot, Peru.

    It was in trying to model that Norwegian event with
that on-line calculator that you're using that I discovered
some real weaknesses in the way it works...
    "I very quickly detected some very odd behavior
on its part. Taking a specific run of the model which
had produced a good blast (airburst) with seismic
effects and plenty of noise, I altered one parameter
by the smallest unit amount: I changed the angle of
entry from 45 degrees to 44 degrees. Obviously,
such a small change should only produce a very
slight change IN THE REAL WORLD, but in the
model -- all the blast, seismicity, and sound
vanished from the results!" Bad Javascript math?

    There are not a lot of experts in this sort of thing
but a fair number of them are on this List. Rob is
one, as is Marco Langobroeck, and Chris Peterson.
When I was being misled by that on-line calculator
about this first (pre-Moss) Norway event, Chris
gave me this example of an "ordinary" fireball:

    "Well, there are models and there are models (and
there is reality). That model may have many useful elements,
but consider one actual example. I have a very well
characterized event over southwest Colorado from
2002. The meteoroid fragmented at a height of 36 km
and dissipated 1e10 joules, or about 2.4 tons TNT.
The estimated entry mass was 95 kg. This event was
recorded barometrically at three stations, the farthest
being 720 km away. Witnesses reported sounds up
to 64 km from the terminal explosion. The fireball
lit up entire valleys bright enough to stimulate full
color vision (the absolute visual magnitude was -17).
The explosion produced a signal on a seismometer
325 km away. This event may have produced up
to 2 kg of meteorites, but nothing has been recovered.
This was an impressive fireball, but such meteors
happen several times every day over the Earth."

    That's worth repeating: such meteors happen
several times every day over the Earth.

    Another List quote from Chris Peterson (both
are from June 13, 2006): "Seismic events are routine
with moderate and large fireballs... Even sonic booms
from airplanes are recorded on seismometers. The
effect of a large mass of air on the ground is
significant. On the other hand, I'm not aware of any
actual impacts producing measurable seismic signals."
    In other words, airbursts are likely to produce
seismic signals, but the making of a small crater is
not.

    Also, proving a crater-like feature to actually BE
a crater and proving that stones that you found actually
ARE meteorites are not necessarily logically connected.
You can have a crater without meteorites and meteorites
without a crater; proof of one does not prove the other.
Since a prospective meteorite is an actual bird-in-the-hand
and you say you have such stones, I would think the
logical thing would be to investigate the stones you have.

    I'm pretty sure you're the provider of the pictures of the
stones (similar to the stones on the venusmeteorite.com site)
that appear on Randy Korotev's Meteorwrong site. He
suggested that you get some thin sections cut and examined
by a petrologist. The expense wouldn't be outrageous and
I would guess you'd find some willing talent with experience
of meteorite thin sections right here in the List. Did you ever
do that?


Sterling K. Webb
----------------------------------------------------------------------
----- Original Message -----
From: "Matson, Robert" <ROBERT.D.MATSON at saic.com>
To: <Meteorite-list at meteoritecentral.com>
Sent: Friday, March 02, 2007 4:56 PM
Subject: [meteorite-list] Peruvian bolide message rehash, #2


Hi All,

Here was my reply to the first message from yesterday:

- - - -
Sent: 3/1/2007 11:15am PST

Hi Randall,

> Do you really believe that a dust-devil the size of a F3* tornado,
> eyewitnesses to a streak leaving a trail, and a 4.0 earthquake event
> just happened to occur simultaneously at exactly 12:00 is just a
> coincidence? Isn't that stretching Occam's Razor just a tweak?

I'm not saying all three pieces of "evidence" are unrelated; I'm saying
that all THREE cannot be due to the fall/impact of a meteorite.

> It give a rough approximation to the expected effects of a large
> mass impacting the earth's surface. I tried adjusting the variables
> to approximate a 4.0 seismo.

> The results are at the lower levels of impact. This program indicated
> that there probably would not have been impactites created but would
> have produced small cratering. It also indicates that meteorites would
> have a much higher velocity than you stated. You indicated a couple
> of hundred meters per second. The actual velocity I believe would
> be closer to 15 kilometers/sec.

Pardon my saying so, but you are obviously well out of your area of
expertise. There is absolutely NO WAY a meteoroid with cosmic velocity
hit the earth in Peru without the entire world knowing about it. Do you
have any idea how large an object has to be in order to retain much of
its cosmic velocity and impact the ground at even 5 km/sec, let alone
15 km/sec? As I wrote earlier, you wouldn't be talking about a puny
1 kiloton event. The shock wave would have killed your witnesses.

The seismometers could have measured only three things: an earthquake,
a manmade explosion (less likely if the 4.0 reading is to be believed),
or
the terminal explosion of a bolide. As I wrote earlier, all you need to
do
is look at the timing of the shock waves at the geographically dispersed
seismic stations. In 30 seconds I could tell you just from inspection
whether the network detected an atmospheric (acoustic) event, or a
seismic event. You claim you have this data, so why speculate about
farfetched scenarios? --Rob
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Received on Sat 03 Mar 2007 03:41:32 AM PST