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K.Chanard, P. Rebischung, L. Fleitout, L. Métivier, X. Collilieux & Z. Altamimi
IGS WORKSHOP 2017 | PARIS
Reconciling GRACE derived loading deformation with GNSS station position time series
MST2, Nepal
Site positions at continuous GNSS station LHAZ, Tibet
North
East
Vertical
2 IGS WORKSHOP 2017 | PARIS
Irregularities (ex: equipment replacement)(Co-seismic)
• Tectonics • Post-glacial rebound
Quasi-linear displacements
+~2cm/yr
~2cm/yr
~2mm/yr
Site positions at continuous GNSS station LHAZ, Tibet
North
East
Vertical
Measurement discontinuities
2 IGS WORKSHOP 2017 | PARIS
• Tectonics • Post-glacial rebound
Quasi-linear displacements
+
Site positions at continuous GNSS station LHAZ, Tibet
ITRF2008
North
East
Vertical• Seasonal loading (continental hydrology,
atmospheric and non-tidal oceanic loads)• (Postseismic deformation)• (Transient deformation)
NON-LINEAR DEFORMATION IN TIME
+
~ 5mm
~ 10mm
Irregularities (ex: equipment replacement)(Co-seismic)
Measurement discontinuities
2 IGS WORKSHOP 2017 | PARIS
IGS WORKSHOP 2017 | PARIS
Physical Explanation
3
Surface load Horizontal Vertical
Seasonal displacements
Loading Season Unloading Season
Physical Model 1. Hypothesis: Rheological model for Earth
2. Convolve seasonal load with Green functions associated to Earth model
Modeling Seasonal Deformation
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
0 100 200 300 400 500 600 700 800 mm
Datasets - Degree-1 - Earth rheology
GRACE — Seasonal Equivalent Water Height 2002-2012
: Water height variations between Summer and Winter (CNES/GRGS)�h
Continental water, oceanic and atmospheric massLong term trends and earthquake contributions removed
IGS WORKSHOP 2017 | PARIS 4
http://grgs.obs-mip.fr/grace/
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
0 100 200 300 400 500 600 700 800 mm
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
Datasets - Degree-1 - Earth rheology
GNSS - IGS REPRO 2 RESIDUALS
: Water height variations between Summer and Winter (CNES/GRGS)�h
IGS WORKSHOP 2017 | PARIS 5
1078 GNSS sites globally distributed Time series corrected for co- and postseismic contributions
(http://acc.igs.org/reprocess2.html)
LHAZGOLD
Numbers of models: difficulty to predict horizontal components
(Fu et al., 2013)
Vertical
GRACE derived model
GPSdata
1cm
Horizontal
GPS dataGRACE derived model
5mm
(Van Dam et al., 2001 ; Davis et al. 2004)
Empirical estimates overlooking spatio-temporal complexity of seasonal signals
(Fu et al., 2013)
IGS WORKSHOP 2017 | PARIS 6
Loading models VS GNSS observations
Global seasonal signals in GNSS time series are related to satellite derived hydrology
Elastic spherical and layered Earth model
(PREM)
Seasonal loading (GRACE)
+ GNSS observations
1. Predict seasonal horizontal and vertical displacements
OUTLINE
IGS WORKSHOP 2017 | PARIS 7
GRACE-derived model VS GNSS:Degree-1 deformation and reference frame issue
CM
CF
CM
CF
Season 1
Season 2
CN
CN
CM
CF
CM
CF
Season 1
Season 2
CN
CN
Degree-1 loading induces:
- Geocenter Motion (translation CM-CF)- Deformation field of the Earth surface
GRACE does not capture degree-1 spherical harmonics loads, contrary to GNSS
To insure comparison, degree-1 contributions are added using coefficients from Swenson et al. (2008)
IGS WORKSHOP 2017 | PARIS 8
Datasets - Degree-1 - Earth rheology
Datasets - Degree-1 - Earth rheology
IGS WORKSHOP 2017 | PARIS 9
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
LHAZ
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson
Elastic (PREM) & Seasonal Load (GRACE + Deg1-Swenson)
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
GOLD
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson
Datasets - Degree-1 - Earth rheology
IGS WORKSHOP 2017 | PARIS 10
Elastic (PREM) & Seasonal Load (GRACE + Deg1-Swenson)
Datasets - Degree-1 - Earth rheology
IGS WORKSHOP 2017 | PARIS 11
East − PREM/Deg1−Swenson
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)North − PREM/Deg1−Swenson
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
Vertical − PREM/Deg1−Swenson
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
WRMS Obs. - Elastic & GRACE + Deg1-Swenson
EAST
NORTH
VERTICAL
WRMS reduction (%)North: 536 sites (mean 1.2% )East: 506 sites (mean 4.1%)Vert.: 864 sites (mean 32%)
GRACE-derived model VS GNSS:Degree-1 deformation and reference frame issue
CM
CF
CM
CF
Season 1
Season 2
CN
CN
CM
CF
CM
CF
Season 1
Season 2
CN
CN
To insure comparison, degree-1 contributions are added using coefficients from Swenson et al. (2008)
IGS WORKSHOP 2017 | PARIS 12
Datasets - Degree-1 - Earth rheology
derived from comparing GNSS-GRACE derived model with no degree-1
Deformation field
,
Linear combination of:- 1 Translation on horizontal components- 1 Translation on the vertical component
Degree-1
(prevents the deg-1 horizontal deformation to be biasedby unmodelled vertical signals (thermal expansion, etc.))
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
LHAZ
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson PREM/Deg1-estimated
IGS WORKSHOP 2017 | PARIS 13
Datasets - Degree-1 - Earth rheology
Elastic (PREM) & Seasonal Load (GRACE + Deg1-Estimated)
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
GOLD
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson PREM/Deg1-estimated
IGS WORKSHOP 2017 | PARIS 14
Datasets - Degree-1 - Earth rheology
Elastic (PREM) & Seasonal Load (GRACE + Deg1-Estimated)
Vertical − PREM/Deg1−estimated
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
East − PREM/Deg1−estimated
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
North − PREM/Deg1−estimated
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
Datasets - Degree-1 - Earth rheology
IGS WORKSHOP 2017 | PARIS 15
WRMS Obs. - Elastic & GRACE + Deg1-EstimatedEAST
NORTH
VERTICAL
WRMS reduction (%)North: 1048 sites (mean 43% )East: 1010 sites (mean 31%)Vert.: 902 sites (mean 34%)
Derived Geocenter motion compatible with other techniques (annual amplitude: Tx=2.3mm,Ty=2.6mm,Tz=4.5mm)
2. Use seasonal deformation to infer Earth rheological properties
OUTLINE
Rheology of the Earth at an annual time scale?
Seasonal loading (GRACE)
+ GNSS Observations
IGS WORKSHOP 2017 | PARIS 16
Viscoelasticity in the asthenosphere (70-270km)?
Surface displacements & Seismic cycleEa
st d
ispl
acem
ent n
orm
aliz
ed b
y co
seis
mic
Time since earthquake (yr) (Trubienko et al., 2014)
Earthquake
Postseimic deformation
East
dis
plac
emen
t nor
mal
ized
by
cose
ism
ic
Time since earthquake (yr)
Rapid deformationAfterslip?Transient viscosity?Poroelastic rebound?
IGS WORKSHOP 2017 | PARIS 17
Constraints on the asthenosphere transient viscosity
Burger rheology in the asthenosphere derived from postseismic studies
Compatible with seasonal deformation?
η
ηT
µT
µ
Burgers material
Elastic material
Elastic material
H
He
, κ
µ, κ
µ, κ
η
Burger material
η1
η2
µ2
µ1
⌘Tµ ⌘
µTTransient viscosity
Long-term viscosity
Maxwell
IGS WORKSHOP 2017 | PARIS 18
Datasets - Degree-1 - Earth rheology
Constraints on the asthenosphere transient viscosity
−10
−5
0
5
10
2002 2004 2006 2008 2010 2012
−10
−5
0
5
10
2002 2004 2006 2008 2010 2012
SAGA (Brazil)
−30
−20
−10
0
10
20
30
2002 2004 2006 2008 2010 2012
Det
. Nor
th (m
m)
Det
. Eas
t (m
m)
Det
. Ver
tical
(mm
)
Time (years)
Burger 1 Elastic Burger 2= µ/10µT1.1017 Pa.sηT = ,( ) = µ/10µT1.1018 Pa.sηT = ,( ) = µµT1.1017 Pa.sηT = ,( )
Burger 3
(Values from published postseismic studies)
IGS WORKSHOP 2017 | PARIS 19
Datasets - Degree-1 - Earth rheology
Constraints on the asthenosphere transient viscosity
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance 1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
Global Admittance (195 cGPS stations)
Transient Viscosities lower than
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
Pa.s
0.2
0.4
0.6
0.8
1µ/ 10
µ/ 5
µ1.1017 5.1017 1.1018
µ T
ηT (Pa.s)
(frac
tion
of
) µ
a) Effect of transient viscosity and shear modulus (H=200km, He=70km)
Horizontal Adm
ittance
b) Effect asthenospheric thickness and transient viscosity (He=70km, = µ/5)µT
0.2
0.4
0.6
0.8
Horizontal Adm
ittance
1
1.1017 5.1017 1.1018ηT (Pa.s)
200
150
100As
then
osph
eric
thic
knes
s (km
)
c) Effect asthenospheric thickness and transient shear modulus (He=70km, = )ηT 1 10 17. Pa.s
0.4
0.6
0.8
Horizontal Adm
ittance
1200
150
100
Asth
enos
pher
ic th
ickn
ess (
km)
µ µ/ 10µ/ 50.2
µT (fraction of )µ
are not compatible with seasonal observations Shear modulus smaller than
1.2
1
0.8
0.6
0.4
Other mechanisms may play a role when low transient viscosities are required to explain observations
Transposable to longer periods of loading, constraining larger viscosities
IGS WORKSHOP 2017 | PARIS 20
Datasets - Degree-1 - Earth rheology
Phase transformations in the mantle transition zone (400-660km)
Peak to Peak Pressure at 400km
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
0 1 2 3 4 5 6 7 8 9 10kPa
Influence of seasonal surface loading in the Earth mantle:
Unconstrained reactions kinetics between seismic waves and postglacial rebound
IGS WORKSHOP 2017 | PARIS 21
Datasets - Degree-1 - Earth rheology
Induced pressure variations at 400km depth Pressure variations in the mantle from seasonal surface
loading
Mineral transformations
Volume variations at 400-660km(effect on compressibility)
Charge saisonnière
400k
m66
0km
Zone de Transition du
ManteauEquilibre
1 2Seasonal load
➡➡
Mineral Equilibrium
IGS WORKSHOP 2017 | PARIS 22
Datasets - Degree-1 - Earth rheology
Bulk modulus rheology
ηκ
κ0
κ∞
Bulk modulus rheology
ηκ
κ0
κ∞
Bulk modulus rheology
ηκ
κ0
κ∞
Bulk modulus rheology
ηκ
κ0
κ∞, ~transformation kinetics
, elastic incompressibility, relaxed incompressibility
Incompressibility is frequency dependent
Phase transformations in the mantle are divariantAt thermodynamic equilibrium:
Modeling phase transformations:
0 = ⇢�P
�⇢
0 10 20 30 40 50 600
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Spherical harmonic order
Am
plitu
de
of
Ve
rtic
al d
isp
./E
WH
Elastic
Phase transition
Constraints on Phase transformations in the mantle transition zone
0 10 20 30 40 50 600
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
Am
plitu
de o
f H
orizonta
l dis
p./E
WH
Spherical harmonic order
Elastic
Phase transition
+ phase shift < 10days
IGS WORKSHOP 2017 | PARIS 23
Datasets - Degree-1 - Earth rheology
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
LHAZ
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson PREM/Deg1-estimated Phase transtions
Best fitting model for completion of 22% of total reaction, kinetics ~ 250 days
−10
−5
0
5
10
Det
. Eas
t (m
m)
2002 2004 2006 2008 2010 2012
GOLD
−10
−5
0
5
10
Det
. Nor
th (m
m)
2002 2004 2006 2008 2010 2012
−30
−20
−10
0
10
20
30
Det
. Ver
tical
(mm
)
2002 2004 2006 2008 2010 2012
PREM/Deg1-Swenson PREM/Deg1-estimated Phase transtions
IGS WORKSHOP 2017 | PARIS 24
Datasets - Degree-1 - Earth rheology
Best fitting model for completion of 22% of total reaction, kinetics ~ 250 days
North − Mantle Phase Transitions
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
East − Mantle Phase Transitions
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
Vertical − PREM/Deg1−estimated
−180˚
−180˚
−120˚
−120˚
−60˚
−60˚
0˚
0˚
60˚
60˚
120˚
120˚
180˚
180˚
−60˚ −60˚
−30˚ −30˚
0˚ 0˚
30˚ 30˚
60˚ 60˚
−100 −80 −60 −40 −20 0 20 40 60 80 100 WRMS reduction (%)
IGS WORKSHOP 2017 | PARIS 25
WRMS Obs. - Phase transitions
EAST
NORTH
VERTICAL
WRMS reduction (%)
North: 1054 sites (mean 56% )East: 1015 sites (mean 41%)Vert.: 943 sites (mean 39%)
Datasets - Degree-1 - Earth rheology
IGS WORKSHOP 2017 | PARIS 26
Conclusions
Seasonal horizontal and vertical displacements are indeed related to surface hydrology
GRACE can be used to accurately model seasonal deformation providing that degree-1 loads coefficients are re-estimated
Seasonal deformation may provide insights on the Earth rheology:
- lower bound on asthenospheric transient viscosities,
- partial occurrence of mantle phase transitions at an annual time scale
Summer
Winter
Pattern of Mw>7 deep earthquakes (>70km) from 1900 to present
(Zhan & Shearer, 2015)