| Topic: |
Science > Philosophy |
| User: |
"Sir Frederick" |
| Date: |
11 Oct 2004 01:01:34 AM |
| Object: |
On the Great Lisbon Earthquake |
EARTH SCIENCE: ON THE GREAT LISBON EARTHQUAKE
ScienceWeek http://scienceweek.com
The following points are made by Marc-Andre Gutscher (Science
2004 305:1247):
1) On 1 November 1755, as worshipers in Portugal and southwestern
Spain were gathered for mass on All Saint's Day, a tremendous
earthquake struck, toppling many churches and killing
approximately 60,000 people (1,2). Many churchgoers were killed,
sparking a lively debate among philosophers about divine justice.
Recent studies have shed light on what caused the earthquake and
what the seismic future of the region may be.
2) The Great Lisbon earthquake had an estimated magnitude (M)
8.7. It triggered a 5- to 10-m-high tsunami and caused many
casualties in Europe and northwestern Morocco (2). In this
region, the African plate pushes toward the northwest against
southern Iberia at a rate of 4 mm/year. But the plate boundary
off southern Iberia is not well defined (3), and the source of
the Great Lisbon earthquake has remained elusive (2). Indeed, it
has been difficult to find a simple plate-tectonic model that
explains all geological observations in the region (4,5).
3) During the past 15 million years, crustal thinning and
extension have produced a deep marine basin in the West Alboran
Sea (western Mediterranean), while shortening and thrusting
continued in the horseshoe-shaped Betic and Rif mountain
belts(4,5). A popular model concluded that this region was a
prime example of "delamination" (breaking off of a deep mantle
root following continental collision) (4). However, new data
increasingly support eastward subduction beneath the Straits of
Gibraltar(5). Tomographic cross sections of the Earth show cold,
dense material -- a slab of oceanic lithosphere -- descending
from the surface to depths of nearly 700 km. The chemistry of 15-
to 5-million-year-old volcanoes in the Alboran Sea shows that
they were formed in an arc setting (like that of arcuate island
chains in the West Pacific landward of the subduction zone).
4) Overall, the movement of tectonic blocks in the southern
Iberia region is best explained by a model of slab retreat (roll-
back) during subduction, causing extension in the region behind
the subduction zone (5). The southeastern limit of deformation in
this back-arc region appears to be a major north-east trending
strike-slip fault across the West Alboran Sea. This fault emerges
on land in northeast Morocco, right where the Al Hoceima
earthquake (M = 6.3) struck on 24 February 2004, causing nearly
600 deaths.
5) One big question remains. Is the subduction system still
active, and does it pose a seismic risk? New evidence supports
continued activity. Numerous active mud volcanoes have been
identified and sampled in the Gulf of Cadiz. These features
indicate ongoing dewatering processes, which are widespread in
accretionary wedges (compressed sediment piles formed at
subduction zones, like piles of dirt in front of a bulldozer).
Marine seismic data indicate active folding and thrusting of the
youngest sediments (which are a few thousand years old) at the
outermost edge of this accretionary wedge. Marine heat flow data
are also indicative of active subduction.
References (abridged):
1. J. M. Martinez-Solares, A. Lopez, J. Mezcua, Tectonophysics
53, 301 (1979)
2. M. A. Baptista et al., J. Geodyn. 25, 159 (1998)
3. I. Jimenez-Munt, M. Fernandez, M. Torne, P. Bird, Earth
Planet. Sci. Lett. 192, 175 (2001)
4. J. P. Platt, R. L. M. Vissers, Geology 17, 540 (1989)
5. L. Lonergan, N. White, Tectonics 16, 504 (1997)
Science http://www.sciencemag.org
--------------------------------
Related Material:
GEOPHYSICS: FAULTS, EARTHQUAKES, AND PLATE MOTION
The following points are made by Craig H. Jones (Science 2003
300:1105):
1) In early 1983, geologists confidently held that the main
seismic hazard in California came from faults exposed at the
surface: faults like the San Andreas that accommodate the Pacific
plate sliding past the North American plate. But later that year,
they were in for a surprise. The 1983 earthquake in Coalinga,
California, was the first in a spate of earthquakes that showed
considerable hazard from faults that were not slipping parallel
to Pacific-North American plate motion.
2) Slip on these other faults, which in short order produced the
Whittier Narrows, Northridge, and Loma Prieta earthquakes,
shortens California nearly perpendicular to the big San Andreas
fault. A more complicated case exists in Alaska, where large
strike-slip ("sliding-past") faults exist inland of and east from
the subduction zone that was responsible for the magnitude (M) =
9.2 "Good Friday" 1964 earthquake. One such fault, the Denali
Fault, produced the M = 7.9 earthquake on 3 November 2002.
3) It is now clear that adjacent parallel faults slip in
different directions at many plate boundaries where the two
plates both move toward one another and slide past one another.
Termed "slip partitioning", it is the tendency for deformation to
divide the motion between two (or more) faults, with one
accommodating the horizontal motion and the other the convergent
motion.
Science http://www.sciencemag.org
--------------------------------
Notes by ScienceWeek:
Seismic studies indicate the interior of the Earth consists of
three parts: a metallic core, a dense rocky mantle, and a thin
low-density crust. The central part of the core is solid, but the
outer part of the core is evidently liquid. The mantle, the layer
of dense rock and metal oxides between the molten part of the
core and the surface, has plastic properties (i.e., it is a solid
capable of flow under pressure).
The term "lithosphere" refers to the outer layer of the Earth,
comprising the crust and upper mantle, and extending to a depth
of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer, the system producing two forms of deformation,
namely, brittle fracture in the upper layer (accompanied by
earthquakes), and aseismic (without earthquakes) ductile flow in
the lower layer. The current consensus is that this view is
generally correct but imprecise, since the accumulated evidence
is now interpreted to indicate that frictional events along fault
lines, rather than new fractures, are the causes of earthquakes.
Plate tectonics is the current consensus theory that the Earth's
lithosphere is broken into fairly rigid plates, seven major
plates and many smaller plates, and that convection within the
underlying less rigid "asthenosphere" causes the plates (and the
associated continents and crust) to move relative to each other,
the movement manifested in continental drift and sea-floor
spreading. "Continental drift" is the slow movement of the
Earth's land masses, a shifting across the underlying molten
material.
"Sea-floor spreading is the process whereby sea floor is
continuously created as the crustal plates move apart and
continuously destroyed where the plates push against each other.
A "strike-slip fault" is a movement parallel to the fault plane,
and the San Andreas fault of California is of this type.
In this context, the term "subduction" refers to the process of
underthrusting of the edge of a tectonic plate into the mantle
underlying an adjacent plate.
--------------------------------
Related Material:
GEOPHYSICS: EARTHQUAKES AND TECTONIC FAULT DYNAMICS
The following points are made by Chris Marone (Nature 2004
427:405):
1) For several decades now, geophysicists have been trying to
understand why the energy budget for tectonic faulting does not
seem to add up. The problem is that faults appear to be more
slippery -- less constrained by friction -- than has been
predicted by laboratory and theoretical work. The measurements of
rock friction described by Di Toro and colleagues(1), may put
things on firmer ground. They demonstrate that friction of
quartz-rich rock is indeed high at low slip rates, consistent
with previous studies, but that under certain conditions it drops
dramatically as slip velocity approaches a few millimeters per
second.
2) Conventional wisdom is that missing expenses are the cause of
the imbalance in the faulting budget. On the income side of this
budget are the driving forces of plate tectonics and the elastic
energy stored in Earth's crust. Laboratory measurements of fault-
zone friction indicate that the frictional stress during faulting
near Earth's surface should be of the order of 50 to 100
megapascals. This implies that substantial frictional heat is
produced during faulting, because the other main energy expenses
-- radiation of seismic waves, and the creation of surface area
from the production and comminution of "wear material" -- are
thought to account for only a small fraction of energy
dissipation. The problem is that the expected frictional heat is
missing(2,3).
3) To study the strength of frictional contact between rock
surfaces, Di Toro et al(1) used an apparatus that applies rotary
shear to the samples. The apparatus allows only comparatively
small unidirectional movement, so the authors sheared samples
back and forth to achieve the large net displacements that occur
at earthquake faults. As in previous experiments in geophysical
rock mechanics, they sheared samples under the high stresses
expected to apply at tectonic faults.
4) Consistent with existing data, Di Toro et al(1) found that the
coefficient of friction was 0.6-0.7 at low sliding velocities (up
to 1 mm/s). However, their experiments show that the coefficient
for novaculite -- a rock composed of silicon dioxide (quartz) --
decreases dramatically to values as low as 0.2 when the shearing
velocity exceeds 1 to 10 mm/s. This effect is transient. On
returning to lower sliding velocity, the coefficient of friction
returns to high values. Identical experiments on samples of
granite did not show the same reduced friction (or "weakening")
at high speed. So the authors suggest that the weakening
mechanism is related to the formation of a thin layer of silica
gel, which acts as grease between the surfaces.(4,5)
References (abridged):
1. Di Toro, G., Goldsby, D. L. & Tullis, T. E. Nature 427, 436
439 (2004)
2. Saffer, D. M., Bekins, B. A. & Hickman, S. J. Geophys. Res.
108, doi:10.1029/2002JB001849 (2003)
3. Scholz, C. H. Geology 28, 163 166 (2000)
4. Spray, J. G. J. Geophys. Res. 98, 8053 8068 (1993)
5. Mair, K. & Marone, C. J. Geophys. Res. 104, 28899 28914 (1999)
Nature http://www.nature.com/nature
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcneill@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
*************************
Mathematicians my flatter themselves that they possess new ideas
which mere human language is as yet unable to express. Let them
make the effort to express these ideas in appropriate words
without the aid of symbols, and if they succeed they will not
only lay us laymen under a lasting obligation, but, we venture to
say, they will find themselves very much enlightened during the
process, and will even be doubtful whether the ideas as expressed
in symbols had ever quite found their way out of the equations
into their minds.
-- James Clerk Maxwell (mathematical physicist) (1831-1879)
:-))))Snort!)
*************************
.
|
|
| User: "Immortalist" |
|
| Title: Re: On the Great Lisbon Earthquake |
11 Oct 2004 01:38:33 AM |
|
|
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:416A21BE.CEF93B2A@fuzzysys.com...
EARTH SCIENCE: ON THE GREAT LISBON EARTHQUAKE
ScienceWeek http://scienceweek.com
The following points are made by Marc-Andre Gutscher (Science
2004 305:1247):
1) On 1 November 1755, as worshipers in Portugal and southwestern
Spain were gathered for mass on All Saint's Day, a tremendous
earthquake struck, toppling many churches and killing
approximately 60,000 people (1,2). Many churchgoers were killed,
sparking a lively debate among philosophers about divine justice.
Recent studies have shed light on what caused the earthquake and
what the seismic future of the region may be.
2) The Great Lisbon earthquake had an estimated magnitude (M)
8.7. It triggered a 5- to 10-m-high tsunami and caused many
casualties in Europe and northwestern Morocco (2). In this
region, the African plate pushes toward the northwest against
southern Iberia at a rate of 4 mm/year. But the plate boundary
off southern Iberia is not well defined (3), and the source of
the Great Lisbon earthquake has remained elusive (2). Indeed, it
has been difficult to find a simple plate-tectonic model that
explains all geological observations in the region (4,5).
3) During the past 15 million years, crustal thinning and
extension have produced a deep marine basin in the West Alboran
Sea (western Mediterranean), while shortening and thrusting
continued in the horseshoe-shaped Betic and Rif mountain
belts(4,5). A popular model concluded that this region was a
prime example of "delamination" (breaking off of a deep mantle
root following continental collision) (4). However, new data
increasingly support eastward subduction beneath the Straits of
Gibraltar(5). Tomographic cross sections of the Earth show cold,
dense material -- a slab of oceanic lithosphere -- descending
from the surface to depths of nearly 700 km. The chemistry of 15-
to 5-million-year-old volcanoes in the Alboran Sea shows that
they were formed in an arc setting (like that of arcuate island
chains in the West Pacific landward of the subduction zone).
4) Overall, the movement of tectonic blocks in the southern
Iberia region is best explained by a model of slab retreat (roll-
back) during subduction, causing extension in the region behind
the subduction zone (5). The southeastern limit of deformation in
this back-arc region appears to be a major north-east trending
strike-slip fault across the West Alboran Sea. This fault emerges
on land in northeast Morocco, right where the Al Hoceima
earthquake (M = 6.3) struck on 24 February 2004, causing nearly
600 deaths.
5) One big question remains. Is the subduction system still
active, and does it pose a seismic risk? New evidence supports
continued activity. Numerous active mud volcanoes have been
identified and sampled in the Gulf of Cadiz. These features
indicate ongoing dewatering processes, which are widespread in
accretionary wedges (compressed sediment piles formed at
subduction zones, like piles of dirt in front of a bulldozer).
Marine seismic data indicate active folding and thrusting of the
youngest sediments (which are a few thousand years old) at the
outermost edge of this accretionary wedge. Marine heat flow data
are also indicative of active subduction.
Things get strange, if I remember right, when new oceans begin to form. Like how
Baja California is the origin of a new ocean which will become separate in a few
million years. The place in Africa where they are finding all the hominid fossils
is also one of these places where a new ocean is further along in its creation.
About Spain I don't know if it is in the strike/slip stage like most of
California is. That is where in a million year LA will be next to Anchorage
Alaska. The sea floor has stopped going under in California bust is still going
under up North in Washington. Once the Baja peninsula gets out a couple hundred
mile the might be enough life in the center of the sea floor and the weight near
the edges to rigger sea floor spreading. Well it has to start from something like
Baja but further advanced then the Rift valley in Africa. Interesting though if
anyone knows if there is anything going on like the Baja over in Europe.
http://images.google.com/images?q=baja%20california
http://images.google.com/images?q=rift+valley
http://images.google.com/images?q=sea+floor+spreading
References (abridged):
1. J. M. Martinez-Solares, A. Lopez, J. Mezcua, Tectonophysics
53, 301 (1979)
2. M. A. Baptista et al., J. Geodyn. 25, 159 (1998)
3. I. Jimenez-Munt, M. Fernandez, M. Torne, P. Bird, Earth
Planet. Sci. Lett. 192, 175 (2001)
4. J. P. Platt, R. L. M. Vissers, Geology 17, 540 (1989)
5. L. Lonergan, N. White, Tectonics 16, 504 (1997)
Science http://www.sciencemag.org
--------------------------------
Related Material:
GEOPHYSICS: FAULTS, EARTHQUAKES, AND PLATE MOTION
The following points are made by Craig H. Jones (Science 2003
300:1105):
1) In early 1983, geologists confidently held that the main
seismic hazard in California came from faults exposed at the
surface: faults like the San Andreas that accommodate the Pacific
plate sliding past the North American plate. But later that year,
they were in for a surprise. The 1983 earthquake in Coalinga,
California, was the first in a spate of earthquakes that showed
considerable hazard from faults that were not slipping parallel
to Pacific-North American plate motion.
2) Slip on these other faults, which in short order produced the
Whittier Narrows, Northridge, and Loma Prieta earthquakes,
shortens California nearly perpendicular to the big San Andreas
fault. A more complicated case exists in Alaska, where large
strike-slip ("sliding-past") faults exist inland of and east from
the subduction zone that was responsible for the magnitude (M) =
9.2 "Good Friday" 1964 earthquake. One such fault, the Denali
Fault, produced the M = 7.9 earthquake on 3 November 2002.
3) It is now clear that adjacent parallel faults slip in
different directions at many plate boundaries where the two
plates both move toward one another and slide past one another.
Termed "slip partitioning", it is the tendency for deformation to
divide the motion between two (or more) faults, with one
accommodating the horizontal motion and the other the convergent
motion.
Science http://www.sciencemag.org
--------------------------------
Notes by ScienceWeek:
Seismic studies indicate the interior of the Earth consists of
three parts: a metallic core, a dense rocky mantle, and a thin
low-density crust. The central part of the core is solid, but the
outer part of the core is evidently liquid. The mantle, the layer
of dense rock and metal oxides between the molten part of the
core and the surface, has plastic properties (i.e., it is a solid
capable of flow under pressure).
The term "lithosphere" refers to the outer layer of the Earth,
comprising the crust and upper mantle, and extending to a depth
of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer, the system producing two forms of deformation,
namely, brittle fracture in the upper layer (accompanied by
earthquakes), and aseismic (without earthquakes) ductile flow in
the lower layer. The current consensus is that this view is
generally correct but imprecise, since the accumulated evidence
is now interpreted to indicate that frictional events along fault
lines, rather than new fractures, are the causes of earthquakes.
Plate tectonics is the current consensus theory that the Earth's
lithosphere is broken into fairly rigid plates, seven major
plates and many smaller plates, and that convection within the
underlying less rigid "asthenosphere" causes the plates (and the
associated continents and crust) to move relative to each other,
the movement manifested in continental drift and sea-floor
spreading. "Continental drift" is the slow movement of the
Earth's land masses, a shifting across the underlying molten
material.
"Sea-floor spreading is the process whereby sea floor is
continuously created as the crustal plates move apart and
continuously destroyed where the plates push against each other.
A "strike-slip fault" is a movement parallel to the fault plane,
and the San Andreas fault of California is of this type.
In this context, the term "subduction" refers to the process of
underthrusting of the edge of a tectonic plate into the mantle
underlying an adjacent plate.
--------------------------------
Related Material:
GEOPHYSICS: EARTHQUAKES AND TECTONIC FAULT DYNAMICS
The following points are made by Chris Marone (Nature 2004
427:405):
1) For several decades now, geophysicists have been trying to
understand why the energy budget for tectonic faulting does not
seem to add up. The problem is that faults appear to be more
slippery -- less constrained by friction -- than has been
predicted by laboratory and theoretical work. The measurements of
rock friction described by Di Toro and colleagues(1), may put
things on firmer ground. They demonstrate that friction of
quartz-rich rock is indeed high at low slip rates, consistent
with previous studies, but that under certain conditions it drops
dramatically as slip velocity approaches a few millimeters per
second.
2) Conventional wisdom is that missing expenses are the cause of
the imbalance in the faulting budget. On the income side of this
budget are the driving forces of plate tectonics and the elastic
energy stored in Earth's crust. Laboratory measurements of fault-
zone friction indicate that the frictional stress during faulting
near Earth's surface should be of the order of 50 to 100
megapascals. This implies that substantial frictional heat is
produced during faulting, because the other main energy expenses
-- radiation of seismic waves, and the creation of surface area
from the production and comminution of "wear material" -- are
thought to account for only a small fraction of energy
dissipation. The problem is that the expected frictional heat is
missing(2,3).
3) To study the strength of frictional contact between rock
surfaces, Di Toro et al(1) used an apparatus that applies rotary
shear to the samples. The apparatus allows only comparatively
small unidirectional movement, so the authors sheared samples
back and forth to achieve the large net displacements that occur
at earthquake faults. As in previous experiments in geophysical
rock mechanics, they sheared samples under the high stresses
expected to apply at tectonic faults.
4) Consistent with existing data, Di Toro et al(1) found that the
coefficient of friction was 0.6-0.7 at low sliding velocities (up
to 1 mm/s). However, their experiments show that the coefficient
for novaculite -- a rock composed of silicon dioxide (quartz) --
decreases dramatically to values as low as 0.2 when the shearing
velocity exceeds 1 to 10 mm/s. This effect is transient. On
returning to lower sliding velocity, the coefficient of friction
returns to high values. Identical experiments on samples of
granite did not show the same reduced friction (or "weakening")
at high speed. So the authors suggest that the weakening
mechanism is related to the formation of a thin layer of silica
gel, which acts as grease between the surfaces.(4,5)
References (abridged):
1. Di Toro, G., Goldsby, D. L. & Tullis, T. E. Nature 427, 436
439 (2004)
2. Saffer, D. M., Bekins, B. A. & Hickman, S. J. Geophys. Res.
108, doi:10.1029/2002JB001849 (2003)
3. Scholz, C. H. Geology 28, 163 166 (2000)
4. Spray, J. G. J. Geophys. Res. 98, 8053 8068 (1993)
5. Mair, K. & Marone, C. J. Geophys. Res. 104, 28899 28914 (1999)
Nature http://www.nature.com/nature
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcneill@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
*************************
Mathematicians my flatter themselves that they possess new ideas
which mere human language is as yet unable to express. Let them
make the effort to express these ideas in appropriate words
without the aid of symbols, and if they succeed they will not
only lay us laymen under a lasting obligation, but, we venture to
say, they will find themselves very much enlightened during the
process, and will even be doubtful whether the ideas as expressed
in symbols had ever quite found their way out of the equations
into their minds.
-- James Clerk Maxwell (mathematical physicist) (1831-1879)
:-))))Snort!)
*************************
.
|
|
|
| User: "Immortalist" |
|
| Title: Re: On the Great Lisbon Earthquake (best possible world) |
11 Oct 2004 01:55:49 AM |
|
|
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:E8udnaebKvBht_fcRVn-oA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:416A21BE.CEF93B2A@fuzzysys.com...
EARTH SCIENCE: ON THE GREAT LISBON EARTHQUAKE
ScienceWeek http://scienceweek.com
The following points are made by Marc-Andre Gutscher (Science
2004 305:1247):
1) On 1 November 1755, as worshipers in Portugal and southwestern
Spain were gathered for mass on All Saint's Day, a tremendous
earthquake struck, toppling many churches and killing
approximately 60,000 people (1,2). Many churchgoers were killed,
sparking a lively debate among philosophers about divine justice.
Recent studies have shed light on what caused the earthquake and
what the seismic future of the region may be.
2) The Great Lisbon earthquake had an estimated magnitude (M)
8.7. It triggered a 5- to 10-m-high tsunami and caused many
casualties in Europe and northwestern Morocco (2). In this
region, the African plate pushes toward the northwest against
southern Iberia at a rate of 4 mm/year. But the plate boundary
off southern Iberia is not well defined (3), and the source of
the Great Lisbon earthquake has remained elusive (2). Indeed, it
has been difficult to find a simple plate-tectonic model that
explains all geological observations in the region (4,5).
Hope this isn't off topic but a philosopher was greatly moved by this quake.
Voltaire used that Earthquake as a prop in his major contribution to philosophy
and asked about what is the best possible world;
One of the most difficult issues confronting believers is the problem of
evil in the world. How can a person possibly believe in a good, wise and
powerful God in the face of human suffering. An answer sometimes given is
that of all possible worlds, this one, a world where humans have free will,
is the best possible world.
The French philosopher Voltaire revolted against this approach. In 1755 an
earthquake struck the city of Lisbon. It was All Saints Day when it struck,
meaning that the churches were full. In just six minutes 15,000 people were
killed and another 15,000 severely wounded. Voltaire could not accept that
this was somehow the outworking of the plans of a good God. In Poem on the
Disaster of Lisbon he asks why it is if God is free, just and good we suffer
under his rule.
Later he wrote a satirical novel titled Candide. It tells the story of a
young man Candide, and his teacher, Dr Pangloss. Whatever disaster befalls
them Dr Pangloss glibly asserts that "this is the best of all possible
worlds." They are shipwrecked near Lisbon just as the earthquake strikes.
Candide is almost killed and Pangloss ends up hanged by the Inquisition.
This forces Candide to question. "Candide" writes Voltaire, "terrified,
speechless, bleeding, palpitating, said to himself: 'If this is the best of
all possible worlds, what can the rest be?'"
http://groups.google.com/groups?selm=vpql40t6sjqbd3%40corp.supernews.com
--------------------------------------
....Persecution and disillusionment had worn down his faith in life; and his
experiences at Berlin and Frankfort had taken the edge from his hope. But both
faith and hope suffered most when, in November, 1755, came the news of the awful
earthquake at Lisbon, in which 30,000 people had been killed. The quake had come
on All Saints' Day; the churches had been crowded with worshippers; and death,
finding its enemies in close formation, had reaped a rich harvest. Voltaire was
shocked into seriousness and raged when he heard that the French clergy were
explaining the disaster as a punishment for the sins of the people of Lisbon. He
broke forth in a passionate poem in which he gave vigorous expression to the old
dilemma: Either God can prevent evil and he will not; or he wishes to prevent it
and he cannot. He was not satisfied with Spinoza's answer that good and evil are
human terms, inapplicable to the universe, and that our tragedies are trivial
things in the perspective of eternity.
I am a puny part of the great whole.
Yes; but all animals condemned to live,
All sentient things, born by the same stern law,
Suffer like me, and like me also die.
The vulture fastens on his timid prey,
And stabs with bloody beak the quivering limbs:
All's well, it seems, for it. But in a while
An eagle tears the vulture into shreds;
The eagle is transfixed by shafts of man;
The man, prone in the dust of battlefields,
Mingling his blood with dying fellow men,
Becomes in turn the food of ravenous birds.
Thus the whole world in every member groans,
All born for torment and for mutual death.
And o'er this ghastly chaos you would say
The ills of each make up the good of all!
What blessedness! And as, with quaking voice,
Mortal and pitiful ye cry, "All's well,"
The universe belies you, and your heart
Refutes a hundred times your mind's conceit. . . .
What is the verdict of the vastest mind?
Silence: the book of fate is closed to us.
Man is a stranger to his own research;
He knows not whence he comes, nor whither goes.
Tormented atoms in a bed of mud,
Devoured by death, a mockery of fate;
But thinking atoms, whose far-seeing eyes,
Guided by thoughts, have measured the faint stars.
Our being mingles with the infinite;
Ourselves we never see, or come to know.
This world, this theatre of pride and wrong,
Swarms with sick fools who talk of happiness. . . .
Once did I sing, in less lugubrious tone,
The sunny ways of pleasure's general rule;
The times have changed, and, taught by growing aget
And sharing of the frailty of mankind,
Seeking a light amid the deepening gloom,
I can but suffer, and will not repine.
A few months later the Seven Years' War broke out; Voltaire looked upon it as
madness and suicide, the devastation of Europe to settle whether England or
France should win "a few acres of snow" in Canada. On the top of this came a
public reply, by Jean Jacques Rousseau, to the poem on Lisbon. Man himself was to
be blamed for the disaster, said Rousseau; if we lived out in the fields, and not
in the towns, we should not be killed on so large a scale; if we lived under the
sky, and not in houses, houses would not fall upon us. Voltaire was amazed at the
popularity won by this profound theodicy; and angry that his name should be
dragged into the dust by such a Quixote, he turned upon Rousseau "that most
terrible of all the intellectual weapons ever wielded by man, the mockery of
Voltaire." In three days, in 1751, he wrote Candide.
Never was pessimism so gaily argued; never was man made to laugh so heartily
while learning that this is a world of woe. And seldom has a story been told with
such simple and hidden art; it is pure narrative and dialogue; no descriptions
pad it out; and the action is riotously rapid. "In Voltaire's fingers," said
Anatole France, "the pen runs and laughs." It is perhaps the finest short story
in all literature.
Candide, as his name indicates, is a simple and honest lad, son of the great
Baron of Thunder-Ten-Trockh of Westphalia, and pupil of the learned Pangloss.
Pangloss was professor of metaphysicotheologicocosmonigology. . . . "It is
demonstrable," said he, "that all is necessarily for the best end. Observe that
the nose has been formed to bear spectacles . . . legs were visibly designed for
stockings . . . stones were designed to construct casdes . . . pigs were made so
that we might have pork all the year round. Consequently, they who assert that
all is well have said a foolish thing; they should have said all is for the
best."
While Pangloss is discoursing, the castle is attacked by the Bulgarian army, and
Candide is captured and turned into a soldier.
He was made to wheel about to the right and to the left, to draw his rammer; to
return his rammer, to present, to fire, to march. . . . He resolved,, one fine
day in spring, to go for a walk, marching straight before him, bejleving that it
was a privilege of the human as well as the animal species to make use of their
legs as they pleased. He had advanced two leagues when he was overtaken by four
heroes six feet tall, who bound him and carried him to a dungeon. He was asked
which he would like the best, to be whipped six and diirty times through all the
regiment, or to receive at once two balls of lead in his brain. He vainly said
that human will is free, and that he chose neither the one nor the other. He was
forced to make a choice; he determined, in virtue of that gift of God called
liberty, to run the gauntlet six-and-thirty times. He bore this twice.
Candide escapes, takes passage to Lisbon, and on board ship meets Professor
Pangloss, who tells how the Baron and Baroness were murdered and the castle
destroyed. "All this," he concludes, "was indispensable; for private misfortune
makes the general good, so that the more private misfortunes there are, the
greater is the general good." They arrive in Lisbon just in time to be caught in
the earthquake. After it is over they tell each other their adventures and
sufferings; whereupon an old servant assures them that their misfortunes are as
nothing compared with her own. "A hundred times I was on the point of killing
myself, but I loved life. This ridiculous foible is perhaps one of our most fatal
characteristics; for is there anything more absurd than to wish to carry
continually a burden which one can always throw down?" Or, as another character
expresses it, "All things considered, the life of a gondolier is preferable to
that of a doge; but I believe the difference is so trifling that it is not worth
the trouble of examining."
Candide, fleeing from the Inquisition, goes to Paraguay; "there the Jesuit
Fathers possess all, and the people nothing; it is a masterpiece of reason and
justice." In a Dutch colony he comes upon a negro with one hand, one leg, and a
rag for clothing. "When we work at the sugar canes," the slave explains, "and the
mill snatches hold of a finger, they cut off a hand; and when we try to run away,
they cut off a leg. . . . This is the price at which you eat sugar in Europe."
Candide finds much loose gold in the unexplored interior; he returns to the coast
and hires a vessel to take him to France; but the skipper sails off with the gold
and leaves Candide philosophizing on the wharf. With what little remains to him,
Candide purchases a passage on a ship bound for Bordeaux; and on board strikes up
a conversation with an old sage, Martin.
"Do you believe," said Candide, "that men have always massacred one another as
they do today, that they have always been liars, cheats, traitors, ingrates,
brigands, idiots, thieves, scoundrels, gluttons, drunkards, misers, envious,
ambitious, bloody-minded, calumniators, debauchees, fanatics, hypocrites and
fools?"
"Do you believe," said Martin, "that hawks have always eaten pigeons when they
have found them?"
"Without doubt," said Candide.
"Well, then," said Martin, "if hawks have always had the same character, why
should you imagine that men have changed theirs?"
"Oh!" said Candide, "there is a vast deal of difference, for free will-"
And reasoning thus they arrived at Bordeaux.
We cannot follow Candide through the rest of his adventures, which form a
rollicking commentary on the difficulties of medieval theology and Leibnitzian
optimism. After suffering a variety of evils among a variety of men, Candide
settles down as a farmer in Turkey; and the story ends with a final dialogue
between master and pupil:
Pangloss sometimes said to Candide:
"There is a concatenation of events in this best of all possible worlds: for if
you had not been kicked out of a magnificent castle; ... if you had not been put
into the Inquisition; if you had not walked over America; ... if you had not lost
all your gold; . . . you would not be here eating preserved citrons and
pistachio-nuts."
"All that is very well," answered Candide; "but let us cultivate our garden."
The Story of Philosophy
The Lives and Opinions of the Great Philosophers of the Western World
by WILL DURANT
http://www.amazon.com/exec/obidos/tg/detail/-/0671739166/
.
|
|
|
|
| User: "Welsh Taxidermist" |
|
| Title: Re: On the Great Lisbon Earthquake |
11 Oct 2004 02:03:53 AM |
|
|
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:E8udnaebKvBht_fcRVn-oA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:416A21BE.CEF93B2A@fuzzysys.com...
EARTH SCIENCE: ON THE GREAT LISBON EARTHQUAKE
ScienceWeek http://scienceweek.com
The following points are made by Marc-Andre Gutscher (Science
2004 305:1247):
1) On 1 November 1755, as worshipers in Portugal and southwestern
Spain were gathered for mass on All Saint's Day, a tremendous
earthquake struck, toppling many churches and killing
approximately 60,000 people (1,2). Many churchgoers were killed,
sparking a lively debate among philosophers about divine justice.
Recent studies have shed light on what caused the earthquake and
what the seismic future of the region may be.
2) The Great Lisbon earthquake had an estimated magnitude (M)
8.7. It triggered a 5- to 10-m-high tsunami and caused many
casualties in Europe and northwestern Morocco (2). In this
region, the African plate pushes toward the northwest against
southern Iberia at a rate of 4 mm/year. But the plate boundary
off southern Iberia is not well defined (3), and the source of
the Great Lisbon earthquake has remained elusive (2). Indeed, it
has been difficult to find a simple plate-tectonic model that
explains all geological observations in the region (4,5).
3) During the past 15 million years, crustal thinning and
extension have produced a deep marine basin in the West Alboran
Sea (western Mediterranean), while shortening and thrusting
continued in the horseshoe-shaped Betic and Rif mountain
belts(4,5). A popular model concluded that this region was a
prime example of "delamination" (breaking off of a deep mantle
root following continental collision) (4). However, new data
increasingly support eastward subduction beneath the Straits of
Gibraltar(5). Tomographic cross sections of the Earth show cold,
dense material -- a slab of oceanic lithosphere -- descending
from the surface to depths of nearly 700 km. The chemistry of 15-
to 5-million-year-old volcanoes in the Alboran Sea shows that
they were formed in an arc setting (like that of arcuate island
chains in the West Pacific landward of the subduction zone).
4) Overall, the movement of tectonic blocks in the southern
Iberia region is best explained by a model of slab retreat (roll-
back) during subduction, causing extension in the region behind
the subduction zone (5). The southeastern limit of deformation in
this back-arc region appears to be a major north-east trending
strike-slip fault across the West Alboran Sea. This fault emerges
on land in northeast Morocco, right where the Al Hoceima
earthquake (M = 6.3) struck on 24 February 2004, causing nearly
600 deaths.
5) One big question remains. Is the subduction system still
active, and does it pose a seismic risk? New evidence supports
continued activity. Numerous active mud volcanoes have been
identified and sampled in the Gulf of Cadiz. These features
indicate ongoing dewatering processes, which are widespread in
accretionary wedges (compressed sediment piles formed at
subduction zones, like piles of dirt in front of a bulldozer).
Marine seismic data indicate active folding and thrusting of the
youngest sediments (which are a few thousand years old) at the
outermost edge of this accretionary wedge. Marine heat flow data
are also indicative of active subduction.
Things get strange, if I remember right, when new oceans begin to
form.Likehow
Baja California is the origin of a new ocean which will become separate in
a few
million years. The place in Africa where they are finding all the hominid
fossils
is also one of these places where a new ocean is further along in its
creation.
About Spain I don't know if it is in the strike/slip stage like most of
California is. That is where in a million year LA will be next to
Anchorage
Alaska. The sea floor has stopped going under in California bust is still
going
under up North in Washington. Once the Baja peninsula gets out a couple
hundred
mile the might be enough life in the center of the sea floor and the
weight near
the edges to rigger sea floor spreading. Well it has to start from
something like
Baja but further advanced then the Rift valley in Africa. Interesting
though if
anyone knows if there is anything going on like the Baja over in Europe.
http://images.google.com/images?q=baja%20california
http://images.google.com/images?q=rift+valley
http://images.google.com/images?q=sea+floor+spreading
References (abridged):
1. J. M. Martinez-Solares, A. Lopez, J. Mezcua, Tectonophysics
53, 301 (1979)
2. M. A. Baptista et al., J. Geodyn. 25, 159 (1998)
3. I. Jimenez-Munt, M. Fernandez, M. Torne, P. Bird, Earth
Planet. Sci. Lett. 192, 175 (2001)
4. J. P. Platt, R. L. M. Vissers, Geology 17, 540 (1989)
5. L. Lonergan, N. White, Tectonics 16, 504 (1997)
Science http://www.sciencemag.org
--------------------------------
Related Material:
GEOPHYSICS: FAULTS, EARTHQUAKES, AND PLATE MOTION
The following points are made by Craig H. Jones (Science 2003
300:1105):
1) In early 1983, geologists confidently held that the main
seismic hazard in California came from faults exposed at the
surface: faults like the San Andreas that accommodate the Pacific
plate sliding past the North American plate. But later that year,
they were in for a surprise. The 1983 earthquake in Coalinga,
California, was the first in a spate of earthquakes that showed
considerable hazard from faults that were not slipping parallel
to Pacific-North American plate motion.
2) Slip on these other faults, which in short order produced the
Whittier Narrows, Northridge, and Loma Prieta earthquakes,
shortens California nearly perpendicular to the big San Andreas
fault. A more complicated case exists in Alaska, where large
strike-slip ("sliding-past") faults exist inland of and east from
the subduction zone that was responsible for the magnitude (M) =
9.2 "Good Friday" 1964 earthquake. One such fault, the Denali
Fault, produced the M = 7.9 earthquake on 3 November 2002.
3) It is now clear that adjacent parallel faults slip in
different directions at many plate boundaries where the two
plates both move toward one another and slide past one another.
Termed "slip partitioning", it is the tendency for deformation to
divide the motion between two (or more) faults, with one
accommodating the horizontal motion and the other the convergent
motion.
Science http://www.sciencemag.org
--------------------------------
Notes by ScienceWeek:
Seismic studies indicate the interior of the Earth consists of
three parts: a metallic core, a dense rocky mantle, and a thin
low-density crust. The central part of the core is solid, but the
outer part of the core is evidently liquid. The mantle, the layer
of dense rock and metal oxides between the molten part of the
core and the surface, has plastic properties (i.e., it is a solid
capable of flow under pressure).
The term "lithosphere" refers to the outer layer of the Earth,
comprising the crust and upper mantle, and extending to a depth
of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer, the system producing two forms of deformation,
namely, brittle fracture in the upper layer (accompanied by
earthquakes), and aseismic (without earthquakes) ductile flow in
the lower layer. The current consensus is that this view is
generally correct but imprecise, since the accumulated evidence
is now interpreted to indicate that frictional events along fault
lines, rather than new fractures, are the causes of earthquakes.
Plate tectonics is the current consensus theory that the Earth's
lithosphere is broken into fairly rigid plates, seven major
plates and many smaller plates, and that convection within the
underlying less rigid "asthenosphere" causes the plates (and the
associated continents and crust) to move relative to each other,
the movement manifested in continental drift and sea-floor
spreading. "Continental drift" is the slow movement of the
Earth's land masses, a shifting across the underlying molten
material.
"Sea-floor spreading is the process whereby sea floor is
continuously created as the crustal plates move apart and
continuously destroyed where the plates push against each other.
A "strike-slip fault" is a movement parallel to the fault plane,
and the San Andreas fault of California is of this type.
In this context, the term "subduction" refers to the process of
underthrusting of the edge of a tectonic plate into the mantle
underlying an adjacent plate.
--------------------------------
Related Material:
GEOPHYSICS: EARTHQUAKES AND TECTONIC FAULT DYNAMICS
The following points are made by Chris Marone (Nature 2004
427:405):
1) For several decades now, geophysicists have been trying to
understand why the energy budget for tectonic faulting does not
seem to add up. The problem is that faults appear to be more
slippery -- less constrained by friction -- than has been
predicted by laboratory and theoretical work. The measurements of
rock friction described by Di Toro and colleagues(1), may put
things on firmer ground. They demonstrate that friction of
quartz-rich rock is indeed high at low slip rates, consistent
with previous studies, but that under certain conditions it drops
dramatically as slip velocity approaches a few millimeters per
second.
2) Conventional wisdom is that missing expenses are the cause of
the imbalance in the faulting budget. On the income side of this
budget are the driving forces of plate tectonics and the elastic
energy stored in Earth's crust. Laboratory measurements of fault-
zone friction indicate that the frictional stress during faulting
near Earth's surface should be of the order of 50 to 100
megapascals. This implies that substantial frictional heat is
produced during faulting, because the other main energy expenses
-- radiation of seismic waves, and the creation of surface area
from the production and comminution of "wear material" -- are
thought to account for only a small fraction of energy
dissipation. The problem is that the expected frictional heat is
missing(2,3).
3) To study the strength of frictional contact between rock
surfaces, Di Toro et al(1) used an apparatus that applies rotary
shear to the samples. The apparatus allows only comparatively
small unidirectional movement, so the authors sheared samples
back and forth to achieve the large net displacements that occur
at earthquake faults. As in previous experiments in geophysical
rock mechanics, they sheared samples under the high stresses
expected to apply at tectonic faults.
4) Consistent with existing data, Di Toro et al(1) found that the
coefficient of friction was 0.6-0.7 at low sliding velocities (up
to 1 mm/s). However, their experiments show that the coefficient
for novaculite -- a rock composed of silicon dioxide (quartz) --
decreases dramatically to values as low as 0.2 when the shearing
velocity exceeds 1 to 10 mm/s. This effect is transient. On
returning to lower sliding velocity, the coefficient of friction
returns to high values. Identical experiments on samples of
granite did not show the same reduced friction (or "weakening")
at high speed. So the authors suggest that the weakening
mechanism is related to the formation of a thin layer of silica
gel, which acts as grease between the surfaces.(4,5)
References (abridged):
1. Di Toro, G., Goldsby, D. L. & Tullis, T. E. Nature 427, 436
439 (2004)
2. Saffer, D. M., Bekins, B. A. & Hickman, S. J. Geophys. Res.
108, doi:10.1029/2002JB001849 (2003)
3. Scholz, C. H. Geology 28, 163 166 (2000)
4. Spray, J. G. J. Geophys. Res. 98, 8053 8068 (1993)
5. Mair, K. & Marone, C. J. Geophys. Res. 104, 28899 28914 (1999)
Nature http://www.nature.com/nature
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcneill@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
*************************
Mathematicians my flatter themselves that they possess new ideas
which mere human language is as yet unable to express. Let them
make the effort to express these ideas in appropriate words
without the aid of symbols, and if they succeed they will not
only lay us laymen under a lasting obligation, but, we venture to
say, they will find themselves very much enlightened during the
process, and will even be doubtful whether the ideas as expressed
in symbols had ever quite found their way out of the equations
into their minds.
-- James Clerk Maxwell (mathematical physicist) (1831-1879)
:-))))Snort!)
*************************
The problem is caused in a large part by the plates shifting
across unlubricated surfaces, causing excess friction. It is
well known that the enormous amount of crude oil taken
from the earth has caused an earthwide oil shortage beneath
the surface. What the earth needs is a gigantic oily enema, with
the syringe inserted in the oval office. This will help to
relieve the binding problems and smooth out earthquakes.
.
|
|
|
| User: "Immortalist" |
|
| Title: Re: On the Great Lisbon Earthquake |
11 Oct 2004 01:09:35 PM |
|
|
"Welsh Taxidermist" <lemon@limey.uk> wrote in message
news:l4Gdne6TrqLBrffcRVn-pg@comcast.com...
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:E8udnaebKvBht_fcRVn-oA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:416A21BE.CEF93B2A@fuzzysys.com...
EARTH SCIENCE: ON THE GREAT LISBON EARTHQUAKE
ScienceWeek http://scienceweek.com
The following points are made by Marc-Andre Gutscher (Science
2004 305:1247):
1) On 1 November 1755, as worshipers in Portugal and southwestern
Spain were gathered for mass on All Saint's Day, a tremendous
earthquake struck, toppling many churches and killing
approximately 60,000 people (1,2). Many churchgoers were killed,
sparking a lively debate among philosophers about divine justice.
Recent studies have shed light on what caused the earthquake and
what the seismic future of the region may be.
2) The Great Lisbon earthquake had an estimated magnitude (M)
8.7. It triggered a 5- to 10-m-high tsunami and caused many
casualties in Europe and northwestern Morocco (2). In this
region, the African plate pushes toward the northwest against
southern Iberia at a rate of 4 mm/year. But the plate boundary
off southern Iberia is not well defined (3), and the source of
the Great Lisbon earthquake has remained elusive (2). Indeed, it
has been difficult to find a simple plate-tectonic model that
explains all geological observations in the region (4,5).
3) During the past 15 million years, crustal thinning and
extension have produced a deep marine basin in the West Alboran
Sea (western Mediterranean), while shortening and thrusting
continued in the horseshoe-shaped Betic and Rif mountain
belts(4,5). A popular model concluded that this region was a
prime example of "delamination" (breaking off of a deep mantle
root following continental collision) (4). However, new data
increasingly support eastward subduction beneath the Straits of
Gibraltar(5). Tomographic cross sections of the Earth show cold,
dense material -- a slab of oceanic lithosphere -- descending
from the surface to depths of nearly 700 km. The chemistry of 15-
to 5-million-year-old volcanoes in the Alboran Sea shows that
they were formed in an arc setting (like that of arcuate island
chains in the West Pacific landward of the subduction zone).
4) Overall, the movement of tectonic blocks in the southern
Iberia region is best explained by a model of slab retreat (roll-
back) during subduction, causing extension in the region behind
the subduction zone (5). The southeastern limit of deformation in
this back-arc region appears to be a major north-east trending
strike-slip fault across the West Alboran Sea. This fault emerges
on land in northeast Morocco, right where the Al Hoceima
earthquake (M = 6.3) struck on 24 February 2004, causing nearly
600 deaths.
5) One big question remains. Is the subduction system still
active, and does it pose a seismic risk? New evidence supports
continued activity. Numerous active mud volcanoes have been
identified and sampled in the Gulf of Cadiz. These features
indicate ongoing dewatering processes, which are widespread in
accretionary wedges (compressed sediment piles formed at
subduction zones, like piles of dirt in front of a bulldozer).
Marine seismic data indicate active folding and thrusting of the
youngest sediments (which are a few thousand years old) at the
outermost edge of this accretionary wedge. Marine heat flow data
are also indicative of active subduction.
Things get strange, if I remember right, when new oceans begin to
form.Likehow
Baja California is the origin of a new ocean which will become separate in
a few
million years. The place in Africa where they are finding all the hominid
fossils
is also one of these places where a new ocean is further along in its
creation.
About Spain I don't know if it is in the strike/slip stage like most of
California is. That is where in a million year LA will be next to
Anchorage
Alaska. The sea floor has stopped going under in California bust is still
going
under up North in Washington. Once the Baja peninsula gets out a couple
hundred
mile the might be enough life in the center of the sea floor and the
weight near
the edges to rigger sea floor spreading. Well it has to start from
something like
Baja but further advanced then the Rift valley in Africa. Interesting
though if
anyone knows if there is anything going on like the Baja over in Europe.
http://images.google.com/images?q=baja%20california
http://images.google.com/images?q=rift+valley
http://images.google.com/images?q=sea+floor+spreading
References (abridged):
1. J. M. Martinez-Solares, A. Lopez, J. Mezcua, Tectonophysics
53, 301 (1979)
2. M. A. Baptista et al., J. Geodyn. 25, 159 (1998)
3. I. Jimenez-Munt, M. Fernandez, M. Torne, P. Bird, Earth
Planet. Sci. Lett. 192, 175 (2001)
4. J. P. Platt, R. L. M. Vissers, Geology 17, 540 (1989)
5. L. Lonergan, N. White, Tectonics 16, 504 (1997)
Science http://www.sciencemag.org
--------------------------------
Related Material:
GEOPHYSICS: FAULTS, EARTHQUAKES, AND PLATE MOTION
The following points are made by Craig H. Jones (Science 2003
300:1105):
1) In early 1983, geologists confidently held that the main
seismic hazard in California came from faults exposed at the
surface: faults like the San Andreas that accommodate the Pacific
plate sliding past the North American plate. But later that year,
they were in for a surprise. The 1983 earthquake in Coalinga,
California, was the first in a spate of earthquakes that showed
considerable hazard from faults that were not slipping parallel
to Pacific-North American plate motion.
2) Slip on these other faults, which in short order produced the
Whittier Narrows, Northridge, and Loma Prieta earthquakes,
shortens California nearly perpendicular to the big San Andreas
fault. A more complicated case exists in Alaska, where large
strike-slip ("sliding-past") faults exist inland of and east from
the subduction zone that was responsible for the magnitude (M) =
9.2 "Good Friday" 1964 earthquake. One such fault, the Denali
Fault, produced the M = 7.9 earthquake on 3 November 2002.
3) It is now clear that adjacent parallel faults slip in
different directions at many plate boundaries where the two
plates both move toward one another and slide past one another.
Termed "slip partitioning", it is the tendency for deformation to
divide the motion between two (or more) faults, with one
accommodating the horizontal motion and the other the convergent
motion.
Science http://www.sciencemag.org
--------------------------------
Notes by ScienceWeek:
Seismic studies indicate the interior of the Earth consists of
three parts: a metallic core, a dense rocky mantle, and a thin
low-density crust. The central part of the core is solid, but the
outer part of the core is evidently liquid. The mantle, the layer
of dense rock and metal oxides between the molten part of the
core and the surface, has plastic properties (i.e., it is a solid
capable of flow under pressure).
The term "lithosphere" refers to the outer layer of the Earth,
comprising the crust and upper mantle, and extending to a depth
of 50 to 70 kilometers. The traditional view of tectonics
(changes in the structure of the Earth's crust) is that the
lithosphere consists of a strong brittle layer overlying a weak
ductile layer, the system producing two forms of deformation,
namely, brittle fracture in the upper layer (accompanied by
earthquakes), and aseismic (without earthquakes) ductile flow in
the lower layer. The current consensus is that this view is
generally correct but imprecise, since the accumulated evidence
is now interpreted to indicate that frictional events along fault
lines, rather than new fractures, are the causes of earthquakes.
Plate tectonics is the current consensus theory that the Earth's
lithosphere is broken into fairly rigid plates, seven major
plates and many smaller plates, and that convection within the
underlying less rigid "asthenosphere" causes the plates (and the
associated continents and crust) to move relative to each other,
the movement manifested in continental drift and sea-floor
spreading. "Continental drift" is the slow movement of the
Earth's land masses, a shifting across the underlying molten
material.
"Sea-floor spreading is the process whereby sea floor is
continuously created as the crustal plates move apart and
continuously destroyed where the plates push against each other.
A "strike-slip fault" is a movement parallel to the fault plane,
and the San Andreas fault of California is of this type.
In this context, the term "subduction" refers to the process of
underthrusting of the edge of a tectonic plate into the mantle
underlying an adjacent plate.
--------------------------------
Related Material:
GEOPHYSICS: EARTHQUAKES AND TECTONIC FAULT DYNAMICS
The following points are made by Chris Marone (Nature 2004
427:405):
1) For several decades now, geophysicists have been trying to
understand why the energy budget for tectonic faulting does not
seem to add up. The problem is that faults appear to be more
slippery -- less constrained by friction -- than has been
predicted by laboratory and theoretical work. The measurements of
rock friction described by Di Toro and colleagues(1), may put
things on firmer ground. They demonstrate that friction of
quartz-rich rock is indeed high at low slip rates, consistent
with previous studies, but that under certain conditions it drops
dramatically as slip velocity approaches a few millimeters per
second.
2) Conventional wisdom is that missing expenses are the cause of
the imbalance in the faulting budget. On the income side of this
budget are the driving forces of plate tectonics and the elastic
energy stored in Earth's crust. Laboratory measurements of fault-
zone friction indicate that the frictional stress during faulting
near Earth's surface should be of the order of 50 to 100
megapascals. This implies that substantial frictional heat is
produced during faulting, because the other main energy expenses
-- radiation of seismic waves, and the creation of surface area
from the production and comminution of "wear material" -- are
thought to account for only a small fraction of energy
dissipation. The problem is that the expected frictional heat is
missing(2,3).
3) To study the strength of frictional contact between rock
surfaces, Di Toro et al(1) used an apparatus that applies rotary
shear to the samples. The apparatus allows only comparatively
small unidirectional movement, so the authors sheared samples
back and forth to achieve the large net displacements that occur
at earthquake faults. As in previous experiments in geophysical
rock mechanics, they sheared samples under the high stresses
expected to apply at tectonic faults.
4) Consistent with existing data, Di Toro et al(1) found that the
coefficient of friction was 0.6-0.7 at low sliding velocities (up
to 1 mm/s). However, their experiments show that the coefficient
for novaculite -- a rock composed of silicon dioxide (quartz) --
decreases dramatically to values as low as 0.2 when the shearing
velocity exceeds 1 to 10 mm/s. This effect is transient. On
returning to lower sliding velocity, the coefficient of friction
returns to high values. Identical experiments on samples of
granite did not show the same reduced friction (or "weakening")
at high speed. So the authors suggest that the weakening
mechanism is related to the formation of a thin layer of silica
gel, which acts as grease between the surfaces.(4,5)
References (abridged):
1. Di Toro, G., Goldsby, D. L. & Tullis, T. E. Nature 427, 436
439 (2004)
2. Saffer, D. M., Bekins, B. A. & Hickman, S. J. Geophys. Res.
108, doi:10.1029/2002JB001849 (2003)
3. Scholz, C. H. Geology 28, 163 166 (2000)
4. Spray, J. G. J. Geophys. Res. 98, 8053 8068 (1993)
5. Mair, K. & Marone, C. J. Geophys. Res. 104, 28899 28914 (1999)
Nature http://www.nature.com/nature
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcneill@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
*************************
Mathematicians my flatter themselves that they possess new ideas
which mere human language is as yet unable to express. Let them
make the effort to express these ideas in appropriate words
without the aid of symbols, and if they succeed they will not
only lay us laymen under a lasting obligation, but, we venture to
say, they will find themselves very much enlightened during the
process, and will even be doubtful whether the ideas as expressed
in symbols had ever quite found their way out of the equations
into their minds.
-- James Clerk Maxwell (mathematical physicist) (1831-1879)
:-))))Snort!)
*************************
The problem is caused in a large part by the plates shifting
across unlubricated surfaces, causing excess friction. It is
well known that the enormous amount of crude oil taken
from the earth has caused an earthwide oil shortage beneath
the surface. What the earth needs is a gigantic oily enema, with
the syringe inserted in the oval office. This will help to
relieve the binding problems and smooth out earthquakes.
Now there's some greased up logerc!
All oil comes from dead dinosaurs and ancient tropical forests. Continental
materials (rock) are lighter than ocean crust materials (rock) and kinda (float)
and drift.
http://images.google.com/images?q=pangea
.
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