[meteorite-list] falls per year

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From: Kelly Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:38 2004
Message-ID: <3AAC3E24.6AB4FE5_at_bhil.com>

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Hi, Jeff, Phil, and List,

 Sorry to be so long replying on this topic (it's that pesky day job).

Jeff Grossman wrote:

> Over the last 20 years of the 20th century, 10 falls were recovered there
> [Japan]: Aomori, Tomiya, Kokubunji, Tahara, Mihonoseki, Senboku, Neagari,
> Tsukuba, Kobe, and Sayama.

 Kobe and Sayama are too new enough to be in the Catalogue, but of the eight
remaining, Senboku is a century-old stone that had been held by a family until
finally identified as a meteorite, so it is not of that 20-year period.

 Of the remaining seven from 1980 through 1996:

 Aomori (one stone of 320 gm) punctured a zinc (galvanized) roof.

 Kokubunji (one stone of 10 kg + 1 kg of fragments) damaged tile rooves and
paved roadways.

 Tahara (one stone of 5 kg) hit a ship, damaging the steel deck. (It is only
by luck that 1 kg of fragments were recovered, as the crew swept the meteoric
debris into the sea.)

 Mihonoseki (one stone of 6.38 kg) got a roof, perforated a two-story house
and its floor, and was found underneath the house.

 Neagari (one stone of 420 gm) was the world's sixth verified with stone
recovered hit on a car (4 US, 1 UK, 1 Japan).

 Tsukuba (23 stones totaling 800 gm) also got a roof and penetrated it.

 Tomiya (two stones totaling 27.5 gm) It is only noted that they fell in a
village in the Tomiya prefecture, but I think they must have done something to
get noticed! (Like hit a roof?)

 I would submit that the target cross section for these 6-7 falls is not the
294,000 km^2 of the main islands, but the much smaller area of human
constructions (rooves, roads, ships, cars), which I would estimate as totaling
less than 20,000 km^2 (<1/15 of total area).

 The sample is a little small for this, but with three stones in the 1 kg to
10 kg range, one would expect ten stones in the 100 gm to 1 kg range (instead
of three) and 32 stones in the 10 gm to 100 gm range (instead of one), or about
40 stones in the 10 gram to 10,000 gram range.

 As I understand it, Phil Bland has scaled his samples in a similar manner
to account for the declining recovery rates as the stones get smaller (although
the falls he studied cover a much longer time period, of course).

> We get 870 falls/year on earth, which we can take as a lower limit on the
> true value.

 So, if the 870 falls per year (world) figure was scaled up by the power law
in this way, it would be 5800 (which is almost exactly what Nininger's 1940
figure scales up to).

 And if it were to be considered that only the human infrastructure area of
Japan was the target area of these six stones, the fall rate figure would have
to be enlarged by a multiplier of 15, to 87,000 per year! Which, oddly enough,
puts it right in the middle of the range I derived by sampling only meteorites
that hit persons (worldwide) and autos (USA only), infrastructure impacts just
like these six.

 So, again, I see an essential similarity here. Of course, Jeff, if you
object to what I did with your sample, you might say, well, something else.

 I think it's not the high population density of Japan that accounts for the
high reported incidence of falls, but rather the intensive level of care for
human infrastructure in that ancient high-utilization landscape (all those
Japanese rooves!) and the social structure of obligation (giri) -- somebody has
to responsible for everything! -- so, if a roof is damaged, you'd better have
the stone to prove it.

 Actually, there are reasons (apart from the above) why the area of Japan
might be considered a candidate to be under-represented in falls. A substantial
amount of Japan is devoted to year-round rice cultivation, which means that
those areas are shallowly flooded much of time. I can't imagine a poorer
environment for small meteorites to get noticed in than that. Plop! Gone. The
cultivated ricefield area of Japan greatly exceeds the housing area of Japan.
How many rice field finds or falls are there?

 The Catalogue shows 38 meteorites for Japan for 1897 through 1996. Only 5
are finds (a farmer digging out tree roots, a road crew digging ditches). Most
of the 33 falls are detonating fireballs, but there is also the case of 1.6
gram stone that broke a window, 8 roof and car impactors, and 2 witnessed
ricefield splashdowns, which are the only ricefield cases. One of the ricefield
falls was the classic "it just plopped down at the feet of the witnesses." In
the other, the stone "was seen to fall."

 Two of the 38 are simply described as doubtful and another handful have
very scanty data and poor provenance. Among the 38 are 5 falls of irons in that
100-year period. Since the world-wide rate for irons is 3.2% of all falls, that
implies that there should have been 145 falls of stones in the same period (at
an identical reporting rate, which I believe to be very poor).

Jeff Grossman wrote:

> This calculation assumes that the Japanese are 100% efficient at recovering
> all falls in the country, which is not likely. Adding another fudge factor
> for this which I'll conservatively place at 0.3 (30% efficiency), we get an
> adjusted figure of 2900 falls/year on earth.

 Ultimately, the recovery rate for falls (and finds, too) depends on the
acuity of the human observers. Looking at the statistics for Japan, I would
have to rate the Japanese very low in acuity. Finds worldwide outnumber falls
by 70% (excluding Antarctic finds); in Japan, finds are a fraction of falls. I
propose that whenever finds are less than 63% of the total recoveries for a
time period a condition of find deficiency exists. Only one Japanese find is a
stone; the other four are the more easily noticed irons. All the recovered
falls were obtrusive, even obnoxious; they all did something to get noticed.
They range from very loud detonating fireballs, through behaviors like smashing
roof tiles, penetrating houses, shattering windows, up to killing a Honda
(Neagari).

> To get the number up to 10,000-50,000 per year would require an efficiency
> in Japan, India, and N. Europe of 2-10%. 2% seems implausible to me for
> Japan, but perhaps it's possible. The 10% seems more possible.

 Actually, the Japanese performance in noticing meteorites reminds me of the
ancient American mule joke. (Man buys a mule on assurance it was well broken-in
and obedient. He takes the mule home, harnesses it up. Nothing he does will
make the mule stir, much less pull. He complains to the seller, who returns
with him to his farm. Again, nothing the buyer does will make the mule stir a
hoof. The seller picks up a heavy baulk of timber and smashes the mule a
devastating blow right between the eyes, then quietly says, "Giddiup." The mule
plods forward. The seller turns to the buyer and explains, "You gotta git his
attention first.") I would place the Japanese in this category for acuity.

 If I were giving vocational counseling to meteoroids whose ambition was to
find a place in the Meteorite Hall of Fame (the Catalogue), I would advise
them, "Humans are inobservant, slow, and dull-witted. If you want them to
notice you, hit one of them! If not one of them, then one of their vehicles.
Failing that, strike one of their nests."

 And, yes, I guess I am suggesting a overall reporting and recovery rate of
about 1% or less (the 1/2% to 2% range), although I hadn't tried to calculate
it in those terms up to now. Not a criticism of the Japanese, I put humans
generally in that "need to get their attention" category. Humans are just lousy
observers. This is both a subjective judgment on my part and the result of a
considerable psychological consensus on witness studies, perceptual accuracy,
and so forth.

 Carl Sagan quoted a poll, taken in the U.S. in 1989, which contained the
question, "Have you ever seen the Moon in the day-time?" Despite the fact that
the average human life span is nearly 1,000 lunations long and that probably no
sighted human has failed to see the Moon in day-time, 83% answered, "No, of
course not, the Moon is only up at night." The observer's conceptualization
(however erroneous) overrules their perception (however accurate).

 So, if the average observer can fail to place a 3,000,000 meter celestial
object in the correct context, how well can they be trusted to perform in the
recognition and recovery of a 3 centimeter object?

 For contrast, the state I am writing from, Illinois (USA), has an area
almost exactly half of the Japanese main islands (146,000 km^2 vs. 294,000
km^2). The Catalogue shows eight recoveries from Illinois (1927 to present):
Benld, Bloomington, Havana, Marengo, South Dixon, Tilden, Toulon, and Woodbine.
We can eliminate South Dixon, a pseudometeorite, and Havana, an archeological
find.

 Of the remaining six, three are falls:

 Benld, a single stone H5 of 1.8 kg, is the first car smasher (1938) ever
recorded.

 Bloomington, a 68 gram LL6, hit a porch (in a university town with a good
geology department). It fell in the summer of 1938, but was not examined and
identified until after the news of the Benld stone whacking a car was heard. If
it had not been for the Benld stone, the Bloomington stone never would have
been reported.

 Tilden was a detonating fireball that dropped 3 stones totaling 75 kg in
1927.

 The three finds were in farm fields: two stones (Marengo and Toulon) in
fieldside ditches. Fieldside is where stones found in the field are tossed so
they won't damage a plowshare. Woodbine, a 50 kilogram silicated iron, was
"found" while plowing. I'd imagine that a 50 kg iron would be pretty noticeable
if you hit it with a plow (time to replace another share).

 As in Japan, the falls were noticed because they were obtrusive. The
correlation of recovery rates of finds with cultural practices is fairly clear.
Obviously, if the Japanese grew corn instead of rice, they'd find more
meteorites in the fields! I would also expect that, with the present
change-over to "no-till" agriculture in Illinois, the number of field-found
stones would decline somewhat (although farmers still toss stones to the field
edge).

 Scaling for area, time period, and population density, it turns out that
Japan only recovers one-third of the meteorites per capita per unit area as
Illinois does. This result surprises me. I would not have rated my
co-regionists that highly. Sorry, neighbors. This disparity suggests that
looking at areas like northern India for high recovery rates may be misleading.
(India has 115 falls but only 8 finds, a clear find deficiency, suggesting that
only those meteorites that attract attention are recovered, while the USA has
132 falls and 1082 finds.)

 Although I have not crunched the numbers for every location on the planet,
I would bet that the state of Kansas (USA) has the highest recovery rate per
capita per unit area per time for the entire planet. (I exclude Antarctica,
Libya, Algeria, areas of recent concentrated searches by non-locals.) Kansas
had 8 recoveries in the 1920's, 20 in the 1930's, 23 in the 1940's, and 18 in
the 1950's, all finds, in a state with less than 2 million people! In the same
40 years, there were only two falls, a recovery ratio of finds to falls of 35
to 1! This remarkable rate of recovery may well be due primarily to the
influence on that state of one person: H. H. Nininger.

 This would suggest that cultural and educational factors play perhaps the
most significant role in a high recovery rate. To improve the recovery rate, we
should increase public awareness, educate as many people as possible in what to
notice, and make a reporting network more accessible.

Sterling K. Webb

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<tt>Hi, Jeff, Phil, and List,</tt>
<tt>    Sorry to be so long replying on this topic (it's
that pesky day job).</tt>
Jeff Grossman wrote:
<blockquote TYPE=CITE>Over the last 20 years of the 20th century, 10 falls
were recovered there [Japan]: Aomori, Tomiya, Kokubunji, Tahara, Mihonoseki,
Senboku, Neagari, Tsukuba, Kobe, and Sayama.</blockquote>
<tt>    Kobe and Sayama are too new enough to be in the
Catalogue, but of the eight remaining, Senboku is a century-old stone that
had been held by a family until finally identified as a meteorite, so it
is not of that 20-year period.</tt>
<tt>    Of the remaining seven from 1980 through 1996:</tt>
<tt>    Aomori (one stone of 320 gm) punctured a zinc
(galvanized) roof.</tt>
<tt>    Kokubunji (one stone of 10 kg + 1 kg of fragments)
damaged tile rooves and paved roadways.</tt>
<tt>    Tahara (one stone of 5 kg) hit a ship, damaging
the steel deck. (It is only by luck that 1 kg of fragments were recovered,
as the crew swept the meteoric debris into the sea.)</tt>
<tt>    Mihonoseki (one stone of 6.38 kg) got a roof,
perforated a two-story house and its floor, and was found underneath the
house.</tt>
<tt>    Neagari (one stone of 420 gm) was the world's
sixth verified with stone recovered hit on a car (4 US, 1 UK, 1 Japan).</tt>
<tt>    Tsukuba (23 stones totaling 800 gm) also got
a roof and penetrated it.</tt>
<tt>    Tomiya (two stones totaling 27.5 gm) It is only
noted that they fell in a village in the Tomiya prefecture, but I think
they must have done something to get noticed! (Like hit a roof?)</tt>
<tt>    I would submit that the target cross section
for these 6-7 falls is not the 294,000 km^2 of the main islands, but the
much smaller area of human constructions (rooves, roads, ships, cars),
which I would estimate as totaling less than 20,000 km^2 (<1/15 of total
area).</tt>
<tt>    The sample is a little small for this, but with
three stones in the 1 kg to 10 kg range, one would expect ten stones in
the 100 gm to 1 kg range (instead of three) and 32 stones in the 10 gm
to 100 gm range (instead of one), or about 40 stones in the 10 gram to
10,000 gram range.</tt>
<tt>    As I understand it, Phil Bland has scaled his
samples in a similar manner to account for the declining recovery rates
as the stones get smaller (although the falls he studied cover a much longer
time period, of course).</tt>
<blockquote TYPE=CITE>We get 870 falls/year on earth, which we can take
as a lower limit on the true value.</blockquote>
<tt>    So, if the 870 falls per year (world) figure was
scaled up by the power law in this way, it would be 5800 (which is almost
exactly what Nininger's 1940 figure scales up to).</tt>
<tt>    And if it were to be considered that only the
human infrastructure area of Japan was the target area of these six stones,
the fall rate figure would have to be enlarged by a multiplier of 15, to
87,000 per year! Which, oddly enough, puts it right in the middle of the
range I derived by sampling only meteorites that hit persons (worldwide)
and autos (USA only), infrastructure impacts just like these six.</tt>
<tt>    So, again, I see an essential similarity here.
Of course, Jeff, if you object to what I did with your sample, you might
say, well, something else.</tt>
<tt>    I think it's not the high population density
of Japan that accounts for the high reported incidence of falls, but rather
the intensive level of care for human infrastructure in that ancient high-utilization
landscape (all those Japanese rooves!) and the social structure of obligation
(giri) -- somebody has to responsible for everything! -- so, if a roof
is damaged, you'd better have the stone to prove it.</tt>
<tt>    Actually, there are reasons (apart from the above)
why the area of Japan might be considered a candidate to be under-represented
in falls. A substantial amount of Japan is devoted to year-round rice cultivation,
which means that those areas are shallowly flooded much of time. I can't
imagine a poorer environment for small meteorites to get noticed in than
that. Plop! Gone. The cultivated ricefield area of Japan greatly exceeds
the housing area of Japan. How many rice field finds or falls are there?</tt>
<tt>    The Catalogue shows 38 meteorites for Japan for
1897 through 1996. Only 5 are finds (a farmer digging out tree roots, a
road crew digging ditches). Most of the 33 falls are detonating fireballs,
but there is also the case of 1.6 gram stone that broke a window, 8 roof
and car impactors, and 2 witnessed ricefield splashdowns, which are the
only ricefield cases. One of the ricefield falls was the classic "it just
plopped down at the feet of the witnesses." In the other, the stone "was
seen to fall."</tt>
<tt>    Two of the 38 are simply described as doubtful
and another handful have very scanty data and poor provenance. Among the
38 are 5 falls of irons in that 100-year period. Since the world-wide rate
for irons is 3.2% of all falls, that implies that there should have been
145 falls of stones in the same period (at an identical reporting rate,
which I believe to be very poor).</tt>
Jeff Grossman wrote:
<blockquote TYPE=CITE>This calculation
assumes that the Japanese are 100% efficient at recovering all falls in
the country, which is not likely.  Adding another fudge factor for
this which I'll conservatively place at 0.3 (30% efficiency), we get an
adjusted figure of 2900 falls/year on earth.</blockquote>
<tt>    Ultimately, the recovery rate for falls (and finds,
too) depends on the acuity of the human observers. Looking at the statistics
for Japan, I would have to rate the Japanese very low in acuity. Finds
worldwide outnumber falls by 70% (excluding Antarctic finds); in Japan,
finds are a fraction of falls. I propose that whenever finds are less than
63% of the total recoveries for a time period a condition of find deficiency
exists. Only one Japanese find is a stone; the other four are the more
easily noticed irons. All the recovered falls were obtrusive, even obnoxious;
they all did something to get noticed. They range from very loud detonating
fireballs, through behaviors like smashing roof tiles, penetrating houses,
shattering windows, up to killing a Honda (Neagari).</tt>
<blockquote TYPE=CITE> To get the number up to 10,000-50,000 per year
would require an efficiency in Japan, India, and N. Europe of 2-10%. 2%
seems implausible to me for Japan, but perhaps it's possible.  The
10% seems more possible.</blockquote>
<tt>    Actually, the Japanese performance in noticing meteorites
reminds me of the ancient American mule joke. (Man buys a mule on assurance
it was well broken-in and obedient. He takes the mule home, harnesses it
up. Nothing he does will make the mule stir, much less pull. He complains
to the seller, who returns with him to his farm. Again, nothing the buyer
does will make the mule stir a hoof. The seller picks up a heavy baulk
of timber and smashes the mule a devastating blow right between the eyes,
then quietly says, "Giddiup." The mule plods forward. The seller turns
to the buyer and explains, "You gotta git his attention first.") I would
place the Japanese in this category for acuity.</tt>
<tt>    If I were giving vocational counseling to meteoroids
whose ambition was to find a place in the Meteorite Hall of Fame (the Catalogue),
I would advise them, "Humans are inobservant, slow, and dull-witted. If
you want them to notice you, hit one of them! If not one of them, then
one of their vehicles. Failing that, strike one of their nests."</tt>
<tt>    And, yes, I guess I am suggesting a overall reporting
and recovery rate of about 1% or less (the 1/2% to 2% range), although
I hadn't tried to calculate it in those terms up to now. Not a criticism
of the Japanese, I put humans generally in that "need to get their attention"
category. Humans are just lousy observers. This is both a subjective judgment
on my part and the result of a considerable psychological consensus on
witness studies, perceptual accuracy, and so forth.</tt>
<tt>    Carl Sagan quoted a poll, taken in the U.S. in
1989, which contained the question, "Have you ever seen the Moon in the
day-time?" Despite the fact that the average human life span is nearly
1,000 lunations long and that probably no sighted human has failed to see
the Moon in day-time, 83% answered, "No, of course not, the Moon is only
up at night." The observer's conceptualization (however erroneous) overrules
their perception (however accurate).</tt>
<tt>    So, if the average observer can fail to place
a 3,000,000 meter celestial object in the correct context, how well can
they be trusted to perform in the recognition and recovery of a 3 centimeter
object?</tt>
<tt>    For contrast, the state I am writing from, Illinois
(USA), has an area almost exactly half of the Japanese main islands (146,000
km^2 vs. 294,000 km^2). The Catalogue shows eight recoveries from Illinois
(1927 to present): Benld, Bloomington, Havana, Marengo, South Dixon, Tilden,
Toulon, and Woodbine. We can eliminate South Dixon, a pseudometeorite,
and Havana, an archeological find.</tt>
<tt>    Of the remaining six, three are falls:</tt>
<tt>    Benld, a single stone H5 of 1.8 kg, is the first
car smasher (1938) ever recorded.</tt>
<tt>    Bloomington, a 68 gram LL6, hit a porch (in a
university town with a good geology department). It fell in the summer
of 1938, but was not examined and identified until after the news of the
Benld stone whacking a car was heard. If it had not been for the Benld
stone, the Bloomington stone never would have been reported.</tt>
<tt>    Tilden was a detonating fireball that dropped
3 stones totaling 75 kg in 1927.</tt>
<tt>    The three finds were in farm fields: two stones
(Marengo and Toulon) in fieldside ditches. Fieldside is where stones found
in the field are tossed so they won't damage a plowshare. Woodbine, a 50
kilogram silicated iron, was "found" while plowing. I'd imagine that a
50 kg iron would be pretty noticeable if you hit it with a plow (time to
replace another share).</tt>
<tt>    As in Japan, the falls were noticed because they
were obtrusive. The correlation of recovery rates of finds with cultural
practices is fairly clear. Obviously, if the Japanese grew corn instead
of rice, they'd find more meteorites in the fields! I would also expect
that, with the present change-over to "no-till" agriculture in Illinois,
the number of field-found stones would decline somewhat (although farmers
still toss stones to the field edge).</tt>
<tt>    Scaling for area, time period, and population
density, it turns out that Japan only recovers one-third of the meteorites
per capita per unit area as Illinois does. This result surprises me. I
would not have rated my co-regionists that highly. Sorry, neighbors. This
disparity suggests that looking at areas like northern India for high recovery
rates may be misleading. (India has 115 falls but only 8 finds, a clear
find deficiency, suggesting that only those meteorites that attract attention
are recovered, while the USA has 132 falls and 1082 finds.)</tt>
<tt>    Although I have not crunched the numbers for
every location on the planet, I would bet that the state of Kansas (USA)
has the highest recovery rate per capita per unit area per time for the
entire planet. (I exclude Antarctica, Libya, Algeria, areas of recent concentrated
searches by non-locals.) Kansas had 8 recoveries in the 1920's, 20 in the
1930's, 23 in the 1940's, and 18 in the 1950's, all finds, in a state with
less than 2 million people! In the same 40 years, there were only two falls,
a recovery ratio of finds to falls of 35 to 1! This remarkable rate of
recovery may well be due primarily to the influence on that state of one
person: H. H. Nininger.</tt>
<tt>    This would suggest that cultural and educational
factors play perhaps the most significant role in a high recovery rate.
To improve the recovery rate, we should increase public awareness, educate
as many people as possible in what to notice, and make a reporting network
more accessible.</tt>
  
<tt>Sterling K. Webb</tt>
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Received on Sun 11 Mar 2001 10:10:29 PM PST

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