Download Structure of the Earth

The Earth’s Structure from Travel Times
Spherically
Spherically symmetric
symmetric structure:
structure: PREM
PREM
-- Crustal
Crustal Structure
Structure
-- Upper
Upper Mantle
Mantle structure
structure
Phase
Phase transitions
transitions
Anisotropy
Anisotropy
-- Lower
Lower Mantle
Mantle Structure
Structure
D”
D”
-- Structure
Structure of
of the
the Outer
Outer and
and Inner
Inner Core
Core
3-D
3-D Structure
Structure of
of the
the Mantle
Mantle from
from Seismic
Seismic Tomography
Tomography
-- Upper
Upper mantle
mantle
-- Mid
Mid mantle
mantle
-- Lower
Lower Mantle
Mantle
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Spherically Symmetric Structure
Parameters
Parameters which
which can
can be
be determined
determined for
for aa reference
reference model
model
--P-wave
P-wavevelocity
velocity
--S-wave
S-wavevelocity
velocity
--Density
Density
--Attenuation
Attenuation(Q)
(Q)
--Anisotropic
Anisotropicparameters
parameters
--Bulk
Bulkmodulus
modulusKKss
--rigidity
rigidityµµ
−−pressure
pressure
--gravity
gravity
Seismology and the Earth’s Deep Interior
The Earth’s Structure
PREM: velocities and density
PREM:
PREM: Preliminary
Preliminary Reference
Reference Earth
Earth Model
Model (Dziewonski
(Dziewonski and
and Anderson,
Anderson, 1981)
1981)
Seismology and the Earth’s Deep Interior
The Earth’s Structure
PREM: Attenuation
PREM:
PREM: Preliminary
Preliminary Reference
Reference Earth
Earth Model
Model (Dziewonski
(Dziewonski and
and Anderson,
Anderson, 1981)
1981)
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Earth’s Regions and Fractional Mass
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Crust: Travel Times
Continental
Continental crust
crust (a)
(a)
and
and oceanic
oceanic crust
crust (b)
(b)
with
with corresponding
corresponding
travel-time
travel-time curves
curves
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Crust: Minerals and Velocities
Average
Average crustal
crustal
abundance,
abundance,
density
density and
and
seismic
velocities
seismic velocities
of
of major
major crustal
crustal
minerals.
minerals.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Crust: Crustal Types
SS shields,
shields, CC Caledonian
Caledonian provinces,
provinces, VV Variscan
Variscan provinces,
provinces, RR rifts,
rifts, OO orogens
orogens
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Crust: Refraction Studies
Refraction
Refraction profiles
profiles
across
North
across North America,
America,
(reduction
velocity
(reduction velocity
6km/s)
6km/s) all
all the
the
determination
determination of
of lateral
lateral
velocity
velocity variations:
variations:
PmP
PmP Moho
Moho reflection
reflection
Pn
Pn Moho
Moho refraction
refraction
Pg
Pg direct
direct crustal
crustal wave
wave
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s crust: Crustal Types
Reflection
Reflection data
data often
often
show
a
highly
reflective
show a highly reflective
lower
lower crust.This
crust.This may
may
indicate
indicate fine
fine layering
layering or
or
lamination,
lamination, some
some
transition
transition from
from crust
crust to
to
upper
mantle.
upper mantle.
TWT
TWT two-way
two-way traveltimes
traveltimes
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s crust: Crustal Types
Recently
Recently compiled
compiled world-wide
world-wide crustal
crustal thickness
thickness (km)
(km) indicates
indicates cratonic
cratonic areas
areas and
and
mountain
mountain ranges
ranges with
with active
active tectonics.
tectonics. These
These data
data are
are important
important to
to correct
correct
travel
travel times
times regionally,
regionally, i.e.
i.e. calculate
calculate the
the contribution
contribution of
of crustal
crustal thickness
thickness to
to aa
teleseismic
teleseismic travel-time
travel-time perturbation.
perturbation.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s crust: Crustal Types
Left:
Left: Crust
Crust P-velocity
P-velocity profiles
profiles for
for young
young (<20
(<20 million
million year)
year) oceanic
oceanic basin
basin
structures.
structures. Right:
Right: Crustal
Crustal PP and
and SS velocities
velocities for
for oceanic
oceanic regions
regions older
older than
than 20
20
million
million years.
years.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Upper Mantle: Athenosphere
The
The high-velocity
high-velocity lid
lid
above
the
low
velocity
above the low velocity
zone
zone (asthenosphere)
(asthenosphere) isis
called
called the
the lithosphere.
lithosphere.
The
The upper-mantle
upper-mantle velocity
velocity structure
structure leads
leads to
to
complex
complex ray
ray paths.
paths.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Upper Mantle: Phase transitions
Upper
Upper mantle
mantle
discontinuities
discontinuities (e.g.
(e.g.
410km)
are
caused
410km) are caused by
by
phase
transitions
(left:
phase transitions (left:
low
low pressure
pressure olivine,
olivine,
right:
right: high
high pressure
pressure ββspinel)
spinel)
Various
Various upper
upper mantle
mantle
seismic
models
seismic models and
and
experimental
experimental results
results
for
for minerals
minerals and
and
mineral
mineral assemblages.
assemblages.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Upper Mantle: Discontinuities
Various
Various reflections
reflections
from
upper
from upper mantle
mantle
discontinuities
discontinuities are
are
being
being used
used to
to
investigate
investigate the
the
structural
structural details
details of
of
the
transition
zones
the transition zones
(e.g.
(e.g. vertical
vertical
gradients,
gradients, thickness
thickness of
of
transition
transition zone,
zone,
topography
topography of
of
discontinuities,
discontinuities, etc.)
etc.)
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Upper Mantle: Phase transitions
The
The location
location of
of seismic
seismic
source
source within
within high
high
velocity
velocity anomalies
anomalies
indicates
indicates downgoing
downgoing
slab
structures.
slab structures. Where
Where
do
earthquakes
seem
do earthquakes seem to
to
happen
happen preferentially?
preferentially?
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Upper Mantle: Subduction Zones
Shear
Shear wave
wave splitting
splitting of
of
the
the SKS
SKS phase
phase
indicates
indicates seismic
seismic
anisotropy
anisotropy inin the
the upper
upper
mantle.
The
alignment
mantle. The alignment
of
of the
the anisotropic
anisotropic
symmetry
symmetry system
system isis
thought
thought to
to be
be
correlated
with
correlated with
tectonic
tectonic plate
plate motion.
motion.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Lower Mantle: D”
The
The mid-mantle
mid-mantle shows
shows little
little lateral
lateral heterogeneity.
heterogeneity. The
The lowermost
lowermost mantle
mantle (D”)
(D”)
hast
strong
(possibly
>10%)
lateral
velocity
perturbations.
The
may
originate
hast strong (possibly >10%) lateral velocity perturbations. The may originate inin
aa thermal
thermal boundary
boundary layer
layer or
or from
from subducted
subducted lithosphere.
lithosphere.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Lower Mantle: Diffracted Waves
The
The lowermost
lowermost mantle
mantle structure
structure can
can be
be
studies
studies using
using waves
waves diffracted
diffracted at
at the
the
core-mantle
core-mantle boundary.
boundary.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Core
The
The Earth’s
Earth’s inner
inner
core
shows
core shows
considerable
considerable
anisotropy.
anisotropy. TimeTimedependent
dependent
differential
differential travel
travel
times
have
led
times have led to
to
the
the speculation
speculation
that
that the
the Earth’s
Earth’s
inner
inner core
core isis
rotating
rotating faster
faster
than
the
than the mantle.
mantle.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Core: Multiples
Multiple
Multiple reflection
reflection
ray
paths
ray paths PK
PKnnPP inin
the
the outer
outer core
core
and
recording
and recording of
of
PK
PK44PP from
from an
an
underground
underground
nuclear
nuclear explosion.
explosion.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Upper mantle: 3-D structure
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Mid-mantle: 3-D structure
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Lower Mantle: 3-D structure
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Global Cut: 3-D structure
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Geodynamic Modelling: Subduction Zones
Perturbation
Perturbation of
of seismic
seismic velocity
velocity and
and density
density for
for aa subducting
subducting plate
plate
obtained
from
numerical
convection
modelling
including
phase
obtained from numerical convection modelling including phase
transitions.
transitions.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Geodynamic Modelling: Subduction Zones
Snapshots
Snapshots through
through subducting
subducting slab
slab model
model and
and the
the wavefield
wavefield
perturbation
due
to
the
slab.
The
background
model
perturbation due to the slab. The background model isis PREM.
PREM.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
Geodynamic Modelling: Plumes
High-resolution
High-resolution numerical
numerical study
study of
of plumes
plumes and
and the
the effects
effects of
of the
the
mantle
viscosity
structure.
mantle viscosity structure.
Seismology and the Earth’s Deep Interior
The Earth’s Structure
The Earth’s Structure: Summary
The
The Earth’s
Earth’s seismic
seismic velocity
velocity structure
structure can
can be
be determined
determined from
from
inverting
seismic
travel
times
(e.g.
using
the
Wiechertinverting seismic travel times (e.g. using the WiechertHerglotz
Herglotz technique
technique for
for spherically
spherically symmetric
symmetric media).
media).
The
The Earth’s
Earth’s radial
radial structure
structure is
is dominated
dominated by
by the
the core-mantle
core-mantle
boundary,
boundary, the
the inner-core
inner-core boundary,
boundary, the
the upper-mantle
upper-mantle
discontinuities
(410km
and
670km)
and
the
discontinuities (410km and 670km) and the crust-mantle
crust-mantle
transition
transition (Moho).
(Moho).
The
The 3-D
3-D structure
structure of
of the
the Earth’s
Earth’s interior
interior can
can be
be determined
determined
by
by inverting
inverting the
the travel-time
travel-time perturbations
perturbations with
with respect
respect to
to aa
spherically
spherically symmetric
symmetric velocity
velocity model
model (e.g.
(e.g. PREM).
PREM). The
The
positive
positive and
and negative
negative velocity
velocity perturbations
perturbations are
are thought
thought to
to
represent
represent cold
cold (dense)
(dense) or
or hot
hot (buoyant)
(buoyant) regions,
regions, respectively.
respectively.
There
There is
is remarkable
remarkable correlation
correlation between
between fast
fast regions
regions and
and
subductin
subductin zones
zones as
as well
well as
as slow
slow regions
regions with
with hot-spot
hot-spot (plume)
(plume)
activity.
activity.
Seismology and the Earth’s Deep Interior
The Earth’s Structure