Download The Dynamic Planet Revealed - Frankfurt Institute for Advanced

The natural world can be dramatic, dynamic and dangerous place.
Every year television picturures and newspapers report scene of devastation,
droughts, cyclons, landslides, earthquakes and volcanic eruptions. The Asian tsunami,
with around 250,000 deaths and Haiti earthqake with 230,000 life losses, long-term
damage to developing economies, brought home to the worldworld the realities of
danger.
We live in times of increasing vulnarability to extreme hazards.
1
A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot
magma, ash and gases to escape from below the surface. Volcanic eruptions may be
potentially very dangerous, only c. 20% of the world‘s volcanoes with potential for
explosive eruption have records that extend back over 10,000 years.
2
An earthquake (also known as a quake, tremor, temblor or seismic activity) is the
result of a sudden release of energy in the Earth's crust and upper mantle that
creates seismic waves.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes
displacing the ground.
Haiti's worst quake in two centuries hit south of the capital Port-au-Prince on
Tuesday, wrecking the presidential palace, UN HQ and other buildings.
3
Tsunami or tidal wave is a series of water waves (called a tsunami wave train)
caused by the displacement of a large volume of a body of water, such as an ocean or
a large lake.
4
The location of almost all earthquakes and the motion that causes them are
consistent with the concept of plate tectonics (Isacks, Oliver
& Sykes 1968) . In particular, studies of relative motion across the transverse faults
connecting segments of the oceanic-ridge system confirm the relative
motion of the adjacent plates (Wilson 1965, Sykes 1967) .
The mean energy associated with seismic activity is estimated to be 3.3 X 10 10 J/sec
(Gutenberg 1956) and with volcanism
7. 4 X 1010 J/sec (Holmes 1965) .
Heat flux =4.3x1013 J/sec
5
Continental drift has long been a subject for speculation and controversy. Since the
earliest maps were available, the striking
match between South America and Africa has been noted (Carey 1955, Bullard et aI
1965) , and many scientists inferred that these continents were once connected.
Wegener (1924) and Du Toit (1927) have provided much of the qualitative evidence
favoring continental drift. In addition to the shape, the match between South
America and Africa is expressed both in the type and age of rocks on opposite sides
and in the continuity of mountain ranges, ancient fault zones, and mineral deposits
(Miller 1965, Westo1l 1965, Hurley et al 1967, Halpern 1968) . Wegener (1924)
supposed that continents moved across the floor of the oceans and that the motion
was driven by gravitational forces.
6
Wegener hypothesized that there was an original, gigantic supercontinent 200 million
years ago, which he named Pangaea, meaning "All-earth". Pangaea was a
supercontinent consisting of all of Earth's land masses. It existed from the Permian
through Jurassic periods. It began breaking up during the late Triassic period 130 My
ago.
Pangaea started to break up into two smaller supercontinents, called Laurasia and
Gondwanaland, during the late Triassic. It formed the continents Gondwanaland and
Laurasia, separated by the Tethys Sea. By the end of the Cretaceous period (65 My
ago), the continents were separating into land masses that look like our modern-day
continents.
Fossils of Mesosaurus (one of the first marine reptiles, even older than the dinosaurs)
were found in both South America and South Africa. These finds, plus the study of
sedimentation and the fossil plant Glossopteris in these southern continents led
Alexander duToit, a South African scientist, to bolster the idea of the past existence of
a supercontinent in the southern hemisphere, Eduard Suess's Gondwanaland. This
lent further support to A. Wegener's Continental Drift Theory.
7
Sea-floor spreading. - With improved mapping of the ocean floor it was found that a
mountain range, the mid-Atlantic ridge, symmetrically divides the Atlantic ocean. This
ridge is part of a world-wide ocean-ridge system. The crests of the ridges have
considerable shallow seismic activity and volcanism. Ridges also display extensional
features that suggest that the crust is moving away on both sides. These and other
considerations led to the hypothesis of sea-floor spreading (Hess 1962, 1965, Dietz
1961) : the concept that the whole sea floor is moving laterally away from each side
of a ridge and that new sea floor is continuously created at the ridge crest by the
injection of magmas from the mantle. Thus the sea floor on one side of an ocean
ridge may be viewed as a great conveyor belt, with continuous movement away from
the ridge.
8
Paleomagnetism. - Today continental drift is generalIy accepted as a geological fact
(Bullard 1964, Takeuchi et al 1967) . This is due to quantitative evidence that has
accumulated in the last 20 years. The first such evidence for relative movement
between continents came from paleomagnetism. When an igneous rock forms by the
crystallization of a hot silicous liquid (magma), if the rock contains a few percent of a
ferromagnetic compound such as magnetite, the rock acquires a strong remanent
magnetism on cooling through the Curie point (Blackett 1956, N agata 1961, Collinson
et al 1967) related in orientation, polarity, and intensity to the earth's ambient
magnetic field. The orientation of the remanent magnetic vector is a function of the
magnetic latitude at which the cooling occurred, and the position of the magnetic
pole can be obtained as a function of time. In addition, systematic measurements
made in relatively undisturbed rock sequences show that the earth's magnetic field
has in the past been subject to periodic reversals on the scale of 100000-1000000
years (Cox et al 1964, 1968, Dalrymple et al 1967) .
Through analysis of palaeomagnetic data, it is now known that the Earth's magnetic
field has reversed its orientation tens of thousands of times during the history of the
Earth since its formation. With the increasingly accurate Global Polarity Timescale
(GPTS) it has become apparent that the rate at which reversals occur has varied
considerably throughout the past. During some periods of geologic time (e.g.
Cretaceous Long Normal), the Earth's magnetic field is observed to maintain a single
orientation for tens of millions of years. Other events seem to have occurred very
rapidly, with two reversals in a span of 50,000 years. The last reversal was the
Brunhes–Matuyama reversal approximately 780,000 years ago.
9
Plate tectonics.
A natural consequence of the creation and destruction of ocean floor at ocean ridges
and trenches is the concept of p late tectonics ( Morgan 1968) . The earth's surface is
considered to be composed of a number of rigid surface plates that move with
respect to each other. Each plate is bounded by some or all of three kinds of
boundaries: ocean ridges where plates are created, ocean trenches where plates are
destroyed, and great faults where lateral motion between plates occurs.
10
Current pattern of major plates.
To summarize, the plate tectonic model provides a mechanism by which:
(1) continents can move across the surface of the globe
(2) patterns of volcanism can change and shift across the globe as plates and their
boundaries evolve and move
(3) new oceans may grow and different sedimentary basins evolve
(4) oceans and sedimentary basins close and are deformed to produce mountains
11
1. Constructive plate margins create more land. As the plates split apart and magma
rises up from beneath and creates mid-ocean ridges. The Mid-Atlantic Ridge being
the most famous. Rift valleys are also features of constructive plate margins.
2. Destructive plate margins, however, destroy the land. As one plate sinks beneath
the other the disappearing land is turned into magma, features include subduction
zones and deep sea trenches.
3. Collision plate margins don’t destroy or create land. They collide and move
together, this causes earthquakes and volcanoes.
12
Earth is unique in many ways from the other silicate-metal planets in the solar
system. In addition to oceans and an atmosphere that contains oxygen, Earth is the
only planet that exhibits plate tectonics. Plate tectonics appears to be the result of
convective cooling of the mantle, although the gravitational pull of subducted slabs
probably drives plate motions. Plate tectonics includes sites of plate formation at
ocean ridges and sites of recycling into the mantle, which today is at subduction
zones. Although geodynamic models support coherent plates throughout Earth
history, just when and how plates became negatively buoyant is not yet clear. This is
partly due to our uncertainty about the early thermal history of the mantle. Was the
mantle hotter than at present, as generally assumed, or was it the same temperature
(or even lower) due to enhanced rates of convective cooling during the early
Archean?
13
So it is not clear whether plate tectonics could have been present in the hotter Earth.
We might need to look for alternative models. Here I will discuss a few.
1) Sleep assumed only one type of tectonics (plate tectonics) that can have different
modes. In the past, the Earth was too hot to form rigid plates, instead everything was
molten  magma ocean. Magma oceans are very effective in cooling the Earth until
plates occur. Especially in the early Earth, plate tectonics may have been not effective
enough to cool the Earth with all its radioactive heating, and Earth started heating in
the mode. After enough heating, we form a magma ocean again. This loop continues
until radioactivity is decreased and plate tectonics becomes efficient enough. This is
the stage we are in now. After more cooling, plates (and especially MORS) will be too
stiff and plate tectonics will stop, and will form a stagnant lid (like on Venus and
Mars).
14
The onset of thermal convection to be a spectacular example of far-from-equilibrium selforganization Convection is simply the movement of heat along with material. Consider a
viscous fluid with a temperature gradient ΔT across a distance d from top to bottom . If it is
conducting heat only and there is no heat production, then the temperature profile is linear.
For convection to work, material has to move fast enough that the heat in the moving
material isn’t lost by conduction faster than the material is moving. So let us have a body, let
us approximate this as a sphere of radius l, moving upward with speed v. Our body needs to
move faster than heat travels conductively, so d/v > l2/κ (from above), where we’ve let the
body traverse the full width of our conducting layer d. The body will only continue to move
upward if it is buoyant. The buoyancy forces are due to it being somewhat less dense than its
surroundings, for in rising quickly the body has not lost (much) heat and so is warmer than its
surroundings. This buoyancy force/unit mass (i.e., acceleration from buoyancy) is g∙δρ/ρ,
where δρ is the change in density from rising up the distance d. If we use the coefficient of
thermal expansion, , we get the force/unit mass is g∙α∙δT. Balanced against this is the viscous
drag keeping the material from rising up. Our body has velocity v and dimensions on order of
l, so we might expect a velocity gradient around its sides in the order of v/l (which has units of
strain rate, time-1). Recall that the shear stress in a Newtonian fluid is the dynamic viscosity η
times the velocity gradient, here v/l. Our body has a surface with size on the order of l2, so
the total force is η∙v∙l. The force per unit mass is the force divided by the product of the
density and the volume, and the volume is proportional to l3, so the resistive force is
r∙l²/(h∙v).
15
The eigenvalue solution for the critical Rayleigh number also yields the wavelength of
the critical disturbance. Both the value of the critical Rayleigh number Ra and the
wavelength depend upon the boundary conditions applied at the upper and lower
boundaries of the fluid layer. Alternative boundary conditions are free surface (zero
shear) and fixed surface (zero velocity) .
16
The onset of convection in a fluid cooled from above is a simple fluid dynamical
problem, with profound applications for the dynamics of the Earth’s mantle. Because
of the strong temperature dependency of mantle rheology, most of temperature
variations in mantle convection are confined in a cold and stiff boundary layer
(lithosphere), the dynamics of which dominates the global energetics of mantle
convection. The thickness of the boundary layer is one of essential controlling
parameters in such energetics. Thicker lithosphere requires greater energy to be
dissipated for its deformation at subduction zones. The growth of the boundary layer
is limited by its intrinsic convective instability, which is characterized by the onset of
convection [Korenaga and Jordan, 2002].
17
Certainly the stability calculation for a fluid layer heated from below with constant
fluid properties is only approximately valid for the Earth's mantle. It is of interest to
examine the stability of a fluid layer heated from within since the heating of the
mantle is caused by distributed radioactive heat sources.
18
With vigorous convection, the temperature structure of the convecting fluid becomes nearly
isothermal. The geotherm in a convecting medium is termed the adiabat and averages only
about
0.4°C/km in the mantle. The adiabat is a limit: it is the temperature structure that would exist
if
material rose and fell without losing or gaining heat through conduction. It is derived from
the
fact that Earth materials heat up as they are compressed as the pressure does work by
decreasing
the volume of the rock. This is usually addressed thermodynamically, as the entropy of a
body
of rock moving up or down is assumed to stay constant. In this case, the entropy per unit
mass
ds is given by
ds = C/T*dT −α/ρ*dP = 0
As the convecting fluid approached an adiabatic gradient, one might ask how this can work
when the Earth’s surface is a
little above 0°C and the core mantle boundary is somewhere in the neighborhood of about
4000°C, as suggested from the observations of a molten outer core. The 0.4°/km mean
adiabatic
gradient would only produce no more than 1200° difference across the mantle.
19
Ascending convection.-Ascending convection is associated with oceanic ridges (Hess 1962,
Girdler 1965, Orowan 1965, 1966) . As mantle material rises beneath the ridge, it undergoes
a nearly adiabatic pressure reduction and partial mel ting occurs. There is strong evidence
that the upper mantle is of a broadly peridotite composition and that basalt represents a lowmelting fraction derived from it (Yoder & Tilley 1962, Oxburgh 1 964, Green & Ringwood
1967) . Engel et al (1965) and Kay et al ( 1970) have found that olivine tholeiite basalt of
extremely uniform composition is the most abundant volcanic rock of the ocean ridges. Its
abundance, uniformity of composition, and occurrence in the deep oceans all suggest that it
is a relatively u nmodified first-melting fraction of the mantle (but see O' Hara 1968) .
Consistent with mantle convection, it is concluded that the oceanic crust is predominantly
basalt that has been produced by partial melting of the upper mantle in the vicinity of
oceanic ridges (Oxburgh & Turcotte 1968a, Cann 1968, Wyllie 1971) . The crust is created by
volcanism in the vicinity of oceanic ridges and is then convected away by sea-floor spreading.
I t has been shown by Oxburgh & Turcotte (1969) that considerable heat is lost directly to the
sea water by volcanic activity in the vicinity of ridges.
Descending convection.-Descending convection is associated with oceanic trenches (Hess
1962, Orowan 1967b) . The oceanic surface plate appears to bend and to descend into the
mantle at trenches. This is equivalent to the transition of a cold thermal boundary layer into a
cold descending plume in the boundary-layer theory for thermal convection. On the basis of
the boundary layer model, one would expect that these regions would have below average
surface heat flow. However, it is observed that behind oceanic trenches there is a great deal
of volcanism, and the measured values of the surf ace heat fl ux are high (Vacquier et al
1966, Sclater & Menard 1967) . This volcanism and the high surface heat flux are attributed
to frictional heating on the slip zone between the descending oceanic plate and the
stationary mantle above (Oxburgh & Turcotte 1968b, 1970, Turcotte & Oxburgh 1968,
McKenzie & Sclater 1968) .
20
So it is not clear whether plate tectonics could have been present in the hotter Earth.
We might need to look for alternative models. Here I will discuss a few.
1) Sleep assumed only one type of tectonics (plate tectonics) that can have different
modes. In the past, the Earth was too hot to form rigid plates, instead everything
was molten  magma ocean. Magma oceans are very effective in cooling the
Earth until plates occur. Especially in the early Earth, plate tectonics may have
been not effective enough to cool the Earth with all its radioactive heating, and
Earth started heating in the mode. After enough heating, we form a magma
ocean again. This loop continues until radioactivity is decreased and plate
tectonics becomes efficient enough. This is the stage we are in now. After more
cooling, plates (and especially MORS) will be too stiff and plate tectonics will stop,
and will form a stagnant lid (like on Venus and Mars).
2. Earth was hotter in past, because it looses more heat (surface heat flow) than it
produces (radioactivity): according geological observations: 50-300 K in Archean. This
has several implications for plate tectonic mechanism:
-material weaker, rule-of-thumb: every 100K hotter makes mantle material 10x
weaker  guess relative weakness in past. Effect on mantle vigor & strength slabs?
- Hotter Earth gave more melting  more crust  gravitational stable oceanic plates
 subduction?
21
The flow is divided in to cellular, two-dimensional rolls; alternate rolls rotate in the
clockwise and counterclockwise directions. The
entire flow field is highly viscous. On the hot and cold boundaries thin thermal
boundary layers form. When the two hot boundary layers from adjacent cells meet,
they separate from the boundary and form a thermal plume, which rises to the upper
surface. When the hot plume impinges on the upper cold boundary, a stagnationpoint thermal boundary layer forms. As the flow splits and continues along the cool
upper surface, the stagnation-point boundary layer becomes the cold thermal
boundary layer on the upper surface. When two cold boundary layers from adjacent
cells meet, they form a cold descending plume. The buoyancy forces on the
ascending and descending plumes drive the flow. The core of each cell is a nearly
isothermal, viscous rotational flow. One of the most important consequences of the
boundary-layer theory with regard to the mantle is the presence of the cold thermal
boundary layer adjacent to the upper surface. Within the cold boundary layer the
mantle rock becomes rigid and forms a plate-like structure both riding on the
convection cell and forming part of it. These are the plates of plate tectonics. The
thicknesses of the surface plates are not related to the thickness of the crust (which is
a compositional layer) but is the thickness of the thermal boundary layer [Troubitzyn,
2010].
22
Schematic representation of the shape of the boundary between layers in the heat
convection for the cases of chemical and phase
jumps in density.
Convection through a univariant transformation. Curve a in the phase equlibrium. AB
is adiabatic path in the phase 1, d id the thickness of the transition zone.
Orange line represents undidturbed density distribution
23
Curves a and b represent the beginning and the end of the transformation for a given
composition. The mineral composition of the mantle is complicated. In a simplistic
case it can be represented as a two component mineral (forsterite and fayalite). The
phase transtion pressure and temperature depends on the overall composition or
Mg-Fe ratio in minerals. Instead of a localised Pressure-temperature phase transition
in a two component minerals there is a range of pressures and temperatures at which
the phase transition occurs.
24
Depth distribution of the mantle temperature: (a) along the submerging cold
lithospheric plates, (b) the mean geotherm in the
mantle, (c) along the ascending flows, (d) the solidus temperature, and (e) the liquidus
temperature.
25
Diagram of the mineral content in the mantle and the most important phase
transitions. The upper mantle consists mainly of
olivine, ortho and clinopyroxene and garnet. The upper part of transition zone
contains wadsleyite, garnet, and clinopyroxene. The
lower part of transition zone consists mostly of ringwoodite and garnet. The lower
mantle contains perovskite, magnesiowustite, calcium perovskite and corundum. The
phase transition at a depth of 660 km is sharp, with a width of several kilometers, and
at a depth of 410 km it is about 10km wide. The phase transitions at depths 520 km,
685 km and 2650 km are spread and have the widths of the order of several tens
kilometers. The phase transition at a depth of 1500 km has a width of several
hundreds kilometers.
26
Volumetric mineral content of a model peridotite mantle (MgO/MgO+
FeO = 0.88) along a 1400°C adiabat from experimental studies of Akaogi & Akimoto
(1979), Irifune et al (1986), Irifune (1987), Ito & Takahashi (1987), Irifune & Ringwood
(1987), Akaogi et al (1987), and Takahashi & Ito (1987). alfa = (Mg,Fe)2Si04 olivine,
beta = (Mg,Fe),Si04 beta-phase, gamma = (Mg,Fe)2Si04 gamma-phase, Gt = (Mg,Fe,CahAl2Si30'2 garnet,
Cpx = (Mg,Fe,Ca).(AI,Si)40 12 clinopyroxene, Majorite = garnet-pyroxene (Mg,Fe,Ca)3
AI2Si30'2-(Mg,Fe,Ca).(AI,Si)40'2 solid solution, Ca-Pv = CaSi03 perovskite, Mg-Pv =
(Mg,Fe,Ca)(AI,Si)O, perovskite, Mg-Wü = (Mg,Fe)O magnesiowiistite (elements shown
in italics are minor constituents). Horizontal segments between alfa and beta, beta and gamma, and gamma and
Mg-Pv+Mg-Wii denote the approximate kilometer widths of corresponding divariant
phase loops where botn low pressure and high pressure phases coexist.
alfa, beta, and gamma are shown
as a constant 60 volume percent for simplicity. Variations in Fe-Mg partitioning between
(Mg,Fe)2Si04 polymorphs and majorite could cause the volume for (Mg,Fe)2Si04 to be
either slightly less than or greater than 60 volume percent at different depths. Possible minor
mantle constituents such as a post-spinel Al20rrich phase or SiO,-stishovite have been
omitted.
Analysis of seismic waves travel time allow the measurement of the the variation of density within the Earth.
Several jump in density can be observed among which are the 400 and 670 km depth discontinuities.
The experimental study of the phase diagram of olivine shows the existence of several phase transitions and a
decomposition of this mineral around 24 GPa.
The correspondance between these observations confirms the hypothesis of an upper mantle mainly composed
of olivine. Moreover, we can determine the temperature at the discontinuities from the phase diagram. The
decomposition of olivine at 670 km depth characterizes the transition between the upper and lower mantle.
27
Phase p–T diagrams for olivine and garnet, according to the data presented in the
work [Bina and Liu, 1995]:
(a) forsterite (olivine without iron),
(b) mantle olivine (with 10% content of iron),
(c) nonolivine components of pyrolite (pyroxene–garnet);
(d) α, β and γ are the phase of olivine, (the initial olivine (Ol), wadsleyite (Wd), and
ringwoodite (Rv));
(Pv) perovskite, (Mw) magnesiowustite, (Px) pyroxene, (Gt) garnet, (Il) ilmenite. The
zones of the spread phase transitions are designated by gray color.
Dotted lines are (1) the geotherm of subduction zones, (2) the mean geotherm and
(3) the geotherm of hot ascending mantle flows.
28
The schematic arrangement of d levels is displayed in Fig.
Since the magnitude of the trigonal distortion of octahedra is low, the designations of the cubic
representations t2g(=a1g+e g pi ) and eg(=eg sigma ) are frequently used. The electron configuration
d5 of iron ions can be realized in a low-spin or a high-spin state shown schematically in Fig. Which of
the two spin states is realized in iron ions depends on the relationship between the magnitudes of the
parameters of splitting of the sublevels t2g and eg
by the octahedral crystalline field Δoct and on the exchange Hund interaction J. Neglecting the trigonal
splitting Δtrig (this quantity is approximately
0.2 eV, whereas Δoct= 2–4 eV), it can be found from the ionic model that upon the transition from a
high-spin to a low-spin state the energy of the electronic system changes by a value 6J– 2Δoct caused
by the transition of two electrons from the onto sublevels (see Fig. ). Thus, for the realization of the
low-spin state it is required that a condition Δoct> 3J be fulfilled. The exchange Hund parameter J is a
characteristic of an ion and remains constant even under pressure, whereas the splitting by the
crystalline field can substantially change because of a decrease in the interatomic distance and, as
consequence, because of the strengthening of the hybridization of O 2p–Fe 3d orbitals under pressure.
The spin state of iron ions in Fe 2O3 can be different, depending on the applied pressure. Under the
standard conditions, the exchange interaction is superior to the crystalline field (6 J> 2Δoct) and a
high-spin state is realized, which is confirmed by the high values of the magnetic moments of the iron
ions M= 4.6–4.8μB[12]. At high pressures, the exchange interaction is inferior to the crystalline field
(6J< 2Δoct) and a low spin state is realized in iron ions, which is also predicted by numerous
experimental data.
However, a much greater effect is the increasing overlap and subsequent hybridization of the oxygen
2p states with the metal 3d states[3]. This change in single particle energy levels favors the pairing of
the d electrons in the lower energy d orbitals, resulting in a reduced magnetic moment.
The other explanation for the spin collapse is that as the pressure is increased, the band energy
sacrificed to break symmetry and form a magnetic state eventually becomes larger than the energy to
be gained by the magnetic interaction.
29
It is now known that the iron present in minerals of the lower mantle of the Earth
undergoes a pressure-induced transition with pairing of the spins of its 3d electrons.
In the standard mineralogical model, the lower mantle (the region between 670 and
2900 km below the surface) consists mainly of magnesium-rich (Mg,Fe)SiO3
perovskite, magnesium-rich magnesiowüstite, and CaSiO3 perovskite in a mass ratio
64:31:5, plus minor phases.
Quantifying the effect of the spin-pairing transition on the elastic properties of the
two major minerals of the lower mantle is one of the most fascinating research fronts
of deep-Earth geophysics because variations of density (ρ) and of elastic moduli
(incompressibility K and rigidity μ) control the speed of seismic waves and play a
crucial role in the interpretation of seismological data.
Using synchrotron x-ray diffraction at Beamline 12.2.2 of the ALS and Beamlines 13IDD (GSECARS) and 16ID-B (HPCAT) at the Advanced Photon Source (APS), the
researchers determined the pressure dependence of density of magnesiowüstite with
compositions (Mg0.80, Fe0.20) O and (Mg0.83,Fe0.17)O compressed in a diamond-anvil
cell to pressures found in the lower mantle (24 to 135 GPa).
30
An observed high-spin to low-spin transition of iron in magnesiowüstite results in an
abnormal compressional behaviour between the high-spin and the low-spin states.
The high-pressure, low-spin state exhibits a much higher bulk modulus and bulk
sound velocity than the low-pressure, high-spin state; the bulk modulus jumps by 35
per cent and bulk sound velocity increases by 15 per cent across the transition in
(Mg0.83,Fe0.17)O.
31
The dominant effect of bouyancy caused by the spin transition is comparable to a
strong exothermic phase change, similar to a discrete phase change. However, the
nature of Fe2+ spin transition generated boyancy over a broader pressure range for
upwellings then for downwellings. Spin-forcing depends strongly on temperature
contrasts, predicting increase plume velocities and heat transfer, and marginally
reduced temperatures above CMB.
32
Possible Earthquake precusors fall into broad categories:
1. Hydrological or hydrogeochemical changes (in well or stream level or in the chemistry of
groundwater)
2. Electromagnetic signals (anomolous electrical currents or ultra-low-frequency magnetic
signals (eathquake lights) VAN
3. Changes in the physical properties of the Earth‘s crust, changes in Vp/Vs
4. Changes in the patterns of samll or moderate earthquakes (clustering statistics)
5. Anomolous warping of the crust
6. Anomolous release of gas or heat along a fault
(1) Line of sight velocity of the Earth’s surface from a stack of radar interferograms
spanning a time interval between 1992 and 2000. The velocity map is draped on top of
shaded
topography. LOS velocities toward the satellite are assumed to be positive. White arrow
shows the radar look direction. Black wavy lines denote Quaternary faults (SJF - San Jacinto
fault, CCF - Coyote Creek fault, SHF - Superstition Hills fault). Red dashed line shows a
hypothesised location of an active southern branch of the San Jacinto fault. Black box
outlines a profile from which the InSAR and GPS data are extracted for a comparison and
modeling (Figure 2). Color symbols denote positions of the GPS and EDM sites within the
profile. Data from these sites are provided by the Southern California Earthquake Center
(SCEC) and Southern California Integrated GPS Network (SCIGN).
33
In the last fifteen years the differential interferometric SAR, Synthetic Aperture Radar,
(DInSAR) techniques have demonstrated their
potential as land deformation measurement tools. In the last few years their
capability has been considerably improved by using large
stacks of SAR images acquired over the same area, instead of the classical two images
used in the standard configurations. With
these advances the DInSAR techniques are becoming more and more quantitative
geodetic tools for deformation monitoring, rather
than simple qualitative tools. The goal of the paper is to review the state-of-the-art of
the spaceborne DInSAR-based land
deformation monitoring. The airborne DInSAR is not considered in this work. The
paper begins with a concise description of some
basic DInSAR concepts, followed by a brief discussion of some important DInSAR
applications. Then the state-of-the-art of
DInSAR is analysed, by discussing few important technical issues, by addressing the
issues of data and software availability, and by
describing some relevant DInSAR results.
34
Losses from great natural disasters (far exceeding 100 deaths or US$ 100 m in losses),
1950–2005. Figures are adjusted for inflation.
World Map of Natural Hazards. Earthquake hazard is shown in yellow–brownish
colours and has been classified into five grades according to the minimum intensity
(Modified Mercalli scale) to be reached or exceeded once in 475 years. Darkest colour
means highest hazard. The hazard of tropical windstorms is presented in green
colours, again darkest colour corresponds to highest hazard. Classification is
according to the five degree Saffir–Simpson scale. Green arrows represent the main
cyclone tracks. Other hazards shown are extratropical storms (grey shading) and
active volcanoes (small black symbols).
35
Trends in number of reported disasters. Much of the increase in the number of
hazardous events reported is probably due to significant improvements in
information access and also to population growth, but the number of floods and
cyclones reported is still rising compared to earthquakes. Is global warming affecting
the frequency of natural hazards?
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Boxing 2004 Day Asian Tsunami became a „mile stone“ in the natural disaster
insurance policy world wide.
Natural disaster insurance plays a key role in this context, but also private parties and
governments have to share a part of the risk. A main responsibility of governments is
to formulate regulations for building construction and land use. The insurance sector
and the state have to act together in order to create incentives for building and
business owners to take loss prevention measures. A further challenge for the
insurance sector is to transfer a portion of the risk to the capital markets, and to
serve better the needs of the poor. Catastrophe bonds and microinsurance are the
answer to such challenges.
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The Munich Re risk model MRHazard. Data on hazard, exposed values and
vulnerability are combined probabilistically. This results in an event set which serves
as the basis for calculating insurance rates and probable maximum losses.
MRHazard—example for a PML (or loss exceedance) curve. The PML curve is the
graphical representation of the event set produced by MRHazard. It shows the losses
to be expected as a function of annual occurrence probability or its inverse, that is
the recurrence period (in years). The curve in the graph is an example for a sample
portfolio in Japan and tells that a loss of about 2.3% (or higher) of exposed values all
over the country would have to be expected once in 100 years, and a loss of 6.5%
once in 1000 years.
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Some places are more prone to disaster than others. But that does it take to turn a
cyclone into a disaster in one place and just a climatic event somewhere else? The
main reasons are obvious enough. Economically deprived people living in shacks are
more likely to suffer from any calamity. Rich countries may have more to lose
financially, but they also have more resources for anticipating hazards. There are
many ways of determining vulnerability, apart from economic factors: previous
environmental damage leaving barren land, nearby industrial sites aggravating a
hazard's potential, poor social organisation and transparency, shortage of key
resources, etc. Whatever you focus on, developing countries seem - predictably - to
be the most frequent and most vulnerable victims of disasters.
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