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!