Andrea ManconiAndrea Manconi, T.R. Walter, T.R. Walter
M. Motagh, J. Ruch, M. Shirzaei, R. Wang & J. ZschauM. Motagh, J. Ruch, M. Shirzaei, R. Wang & J. Zschau
Helmholtz Centre GFZ Potsdam, Telegrafenberg, 14473 Potsdam (Germany)Helmholtz Centre GFZ Potsdam, Telegrafenberg, 14473 Potsdam (Germany)
Deformation sources derived Deformation sources derived from InSAR analysis at from InSAR analysis at volcanoes: volcanoes: How realistic are the models?How realistic are the models?
Geodetic data (InSAR)Geodetic data (InSAR)
InversionInversion
Volcanic unrest:
Inflation/deflation of the magma chamber, dyke/sill
intrusion, hydrothermal activity, ring fault
dislocation…
Surface displacementSurface displacement
InterpretationInterpretation
Source depth, Source depth, volume/pressure change, volume/pressure change,
position, shape, orientation, position, shape, orientation, evolution over time…evolution over time…
Model’s Assumptions
- Simplified geometries (points, spheres, rectangular planes, ellipsoidal, etc.)
- Earth’s lithosphere is an elastic, isotropic, and homogeneous half-space…
Skaergaard,Greenland
…however, in nature volcanic plumbing systems and volcanic areas look differently! Gran Canaria, Spain
…differences in the source parameters
(Depth and Pressure) are up to 60%
depending on the mechanical contrast
Manconi et al., 2007
Homogeneous models and layered models may lead to the same fitness of the data, but…
(Darwin Volcano, Galápagos, ca. 20 cm uplift between 1992-1998 Amelung et al., 2000)
L
A
Y
E
R
E
D
Pritchard et al., 2004; Trasatti et al., 2005; Newman et al., 2006; Ellis et al., 2007; Crescentini et al., 2007; Masterlark, 2007; Amoruso et al., 2008; etc…
NAPOLI Bay
WE ARE HERE !
CAMPI FLEGREI CALDERA
View from Vesuvius crater
Long and accurate observation of the surface displacements…SBAS-DInSAR (1992-2008, ERS – ENVISAT), M.Manzo, G.Zeni, P. Tizzani, E. Sansosti & R.Lanari
…Standard approach: joint inversion of Asc & Desc data assuming as source a Mogi source.
E(km) N(km) d(km) P(MPa/yr)
min 426.3 4518.8 2.5 9.4
max 427.2 4519.1 2.9 12.5
rms=0.3 cm/year
A priori information about the sub-surface structure
Chiarabba et al., 2006
Berrino et al., 1998
Judenherc et al.,2004
Zamora et al., 1994
3-D Finite Element models
constrained by independent
geophysical observations and
constraints
Forward model considering
20 MPa overpressure(Sartoris,1990)
Chiarabba et al., 2006 Low Vp/Vs anomaly 3 km depth
Seismicity between 2-4 km depth During unrest, gas chemistry andgravity changes compatible withhydrothermal reservoir (De Natale et al., 1991, Chiodini et al., 2001;
Battaglia et al., 2006)
Our FE model
Forward model on a 3D
heterogeneous
medium
E(km) N(km) d(km) P(MPa/yr)min 426.4 4519.2 2.8 23.5 (+15%)max 426.9 4519.5 3.1 26.5 (+25%)
E(km) N(km) d(km) P(MPa/yr)
426.82 4519.3 3 20
rms=0.3 cm/year
Inversion using Mogi and
assuming an “equivalent”
homogeneous half-space
Synthetic displacement on 3D
Finite Element heterogeneous
model (3DHET)
Best-fit model assuming an
“equivalent”
homogeneous half-space
(HHS)
This procedure retrieves the source location (coordinates and
depth) but OVERESTIMATES the pressure changes…
INVERSION
PHHS > P3DHET
3DHET HHSP3DHET
Ppropertiesmech
positiongeometryU yx
.
&)0,,(
The surface displacement U(x,y,0) is linearly
related to the source strengthP
If we consider the same source
parameters (x, y, z, P) in
both models…
KU
U
HHS
DHET 3
“K” represent the factor of amplification or reduction of the surface displacements due to the 3-D heterogeneities
3DHET
HHS
U3DHET
UHHS < U3DHET
*InSARInSAR UK
U
Applying this “correction
factors” to the real
data…
The inversion of UThe inversion of UInSARInSAR* will retrieve pressure changes as* will retrieve pressure changes asthey occur in a fully 3D heterogeneous model!they occur in a fully 3D heterogeneous model!
InSAR Data
“corrected” for the 3D heterogeneity effects
“Reality”
Similarly to seismology applications, “correction factors” might be
calculated for every “station” to take into account the local effects
and will be then applied to the real measured data
UUInSARInSAR
InterpretationInterpretation
3D FEM3D FEM
Synthetic testsSynthetic testsInversionInversion
The source position is The source position is not affected (like CF) not affected (like CF)
A priori constraints ?A priori constraints ?
*InSARInSAR UK
U
E(km) N(km) d(km) P(MPa/yr)
min 426.3 4518.8 2.5 9.4
max 427.2 4519.1 2.9 12.5
E(km) N(km) d(km) P(MPa/yr)
min 426.5 4519.3 2.5 5.4
(-40%)
max 427.1 4520.2 3 8.5
(- 32%)
Standard approach
“Corrected” dataset
Application to the complete SBAS time series
Manconi et al., in preparation
Summary and ConclusionSummary and Conclusion
- The use of InSAR data The use of InSAR data alonealone to constrain source to constrain source
parameters parameters MAYMAY lead to uncertainties! lead to uncertainties!
- The simplified analytical models fit the data…The simplified analytical models fit the data…
Numerical tests help to understand why!Numerical tests help to understand why!
- Good news…under certain conditions we can still Good news…under certain conditions we can still
use the simplified models (e.g. use the simplified models (e.g. monitoringmonitoring)!)!
Thanks for your attention!