Flank dynamic of Mt. Etna by combining ascending and descending Permanent

Scatterer analysis and GPS data

(1) Istituto Nazionale di Geofisica e Vulcanologia – Sez. di Catania, Piazza Roma, 2, 95123 Catania, Italy(2) Tele-Rilevamento Europa - T.R.E. s.r.l., Via Vittoria Colonna, 7, 20149 Milano, Italy(3) DEI - Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy

Puglisi, G. (1), Basilico, M.(2), Bonforte, A. (1), Coltelli M. (1), Ferretti A (2), Fumagalli, A. (2), Guglielmino, F. (1), Palano, M. (1), Prati, C. (3)

FRINGE 2005ESSRIN-ESA, November 28th – December 2nd 2005

Ground deformations monitoring at Mt. Etna is carried out using both continuous and discontinuous (or discrete) techniques:

ContinuousUsing sensors installed permanently on field• GPS permanent Net (11 stations)• Tilt Net (10 stations)• Strainmeter sensors (2 stations)

DiscreteSurveys measures.• GPS (82 benchmarks)• Leveling (230 benchmarks = 230 km)• EDM (44 benchmarks)• SAR interferometry

The monitoring systems now existing on Mt. Etna are the result of a continuous evolution for improving both quality and quantity of data

N

CASTELMOLA

CESARO’

CENTURIPE

IIV

ROCCELLA

CATANIA

CAPOMULINI

RIPOSTO

GIARDINI

IONIAN SE

A

LegendPermanent GPS statione tilt

Permanent GPS station

Tilt station

GPS benchmarkEDM benchmark 0 5 10 km

The deformation pattern of Mt.Etna (1993-2004) is characterized by continuous inflation (the summit activity and 2001 e 2002-03 eruptions seem to produce secondary effects )

Cumulate areal dilatation(inversion of strain tensor from GPS surveys comparisons).

Cumulative Areal Dilatation: GPS Mt.Etna network - from 1990 to 2004

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gen-90 gen-91 gen-92 gen-93 gen-94 gen-95 gen-96 gen-97 gen-98 gen-99 gen-00 gen-01 gen-02 gen-03 gen-04

Dil.

(mic

rost

rain

)

1991

- 93

eru

ptio

n

Bocca Nuova activity

NE Crater activity

SE Crater activity

Voragine Cr. Act.

2001

eru

ptio

n

2002

-03

erup

tion

2004

-05

erup

tion

The “inflation” results from the sum of two phenomena

Radial expansion(due to pressure source = magma)

+the “sliding” of S and SE flanks

Velocity form 1993 to 2001 (before eruption)

INFLATION

Which is the origin of East and South-East flanks

movements

Lundgren et al. (JGR, 2003) by analysing ascendingand descending ERS data from 1993 to 1996 proposed an eastward moving sub-horizontal plane together with a pressure (magmatic) source.

SWNNW

Mas-Trec. Fault Syst.

Pernicana Fault Syst.

Timpe

??

From Rasà et al.1996 Eastern flank dynamics was discussed in geological studies since ‘70 (Kieffer, 1977), and suggested several models (Borgia et al., 1992; Rasà et al., 1996, etc.).Only GPS studies confirmed these movements on ’90 (Azzaro et al. 2001; Bonforte & Puglisi, 2003).

Eastern and south-eastern flank dynamics

Researches performed during the last years confirmed that the movements of the eastern and southeastern flanks are inexplicable by adopting only a magmatic source (e.g. Mogi), during both eruptive and un-eruptive periods.

The movements require the presence of “a sliding surface”(how many ?) beneath the eastern and southeastern flanks .

References:

From geological studies: Tibaldi and Groppelli (2002), Acocella et al. (2003), Neri et al. (2005).

From GPS data analysis: Bonforte & Puglisi (2003), Puglisi & Bonforte (2004)

From SAR interferometry: Lundgren & Rosen (2003), Lundgren et al. (2004), Palano et al. (EPSL submitted).

Comparison between observed (gray) and modeled (blue) GSP vectors.

Contour lines show the residuals between observed and modeled vertical movements (O-M) 1 cm interval; dot lines are positive, continuous lines are negative.

Sources locations:

Point = center of point source.

Rectangle= projection of the sub-horizontal plane boundaries.

from Palano et al., EPSL, submittedResults and limits of current modelling

Example from 1993-2000 GPS and DInSAR data analysis

… main limit: to model the local fault kinematics;it is important, e.g., for seismic risk reduction.

exampleThe actual structural setting in the south-eastern flank cannot be modeled by using analytical model.Numerical models require detailed information about the location and the kinematics of the active faults.

The first-order modeling is achieved, but ..

Results from the Ionica GPS network (e.g. comparison 1997-’98)

Constraints from GPS

Bonforte & Puglisi, JVGR, in printIs it enough ?

DInSAR vs. PS

Constraints from SAR ?

The detail provided by PS is enough to model the structural setting

PS (ascending orbits) from 1995 to 2000DInSAR map (ascending orbits) from 1993 to 2000

• We used the Catania benchmark as reference for GPS stations (LOSasc ≈ 2.7 mm/yr, with respect to the ITRF net; Houlié et al, GRL, in print).

PS vs GPS

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Ascending PS velocities (mm/y)G

PS v

eloc

ities

(mm

/y)

⇒ the two sets of velocities are consistent at ± 2.5 mm/y level .

PS Validation by using GPS • We compared the GPS velocity measured at 27 benchmarks (projected along the LOS) with the average of PS velocity measured surrounding each benchmark (radius 250 m)

STAZSGMB

PER1

NS05

similar results are obtained for descending passes.

PS (ascending orbits) from 1995 to 2000

Analysis of PS mapMain features of G.D. pattern

• Positive velocity on W flank (uplift) ⇒ “volcanic” inflation

• Linear features (faults ?) dividing East flank in “homogenous” zones

• Irregular features (neg. velocity) (subsidence) ⇒(lava flows compactions)

• Local circular features (neg. vel.) (subsidence) ⇒water wells

• Positive velocity on S flank (uplift) ⇒ anticline

To perform a detailed study of East flank we try to filter the effects of the “volcanic”inflation

PS (ascending orbits) from 1995 to 2000

(from Puglisi & Bonforte, JGR, 2004)

How “to filter” the magmatic source?

Active sources from 1990 al 1998(bibliography)

• Shallow intrusions (dikes) ⇒ local undetected effects

• Deep pressure sources (magma “storage”) ⇒ produce large measured effects

For modeling the cumulated effects of pressure sources we can use a simple Mogi source abut 7 km (b.s.l.) deep (form Houlié et al., in print).

Analysis of PS interpolated “filtered” map (ascending)

Whole East flank has negative velocity

Section A

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Distance (km)

LOS

velo

city

(mm

/y)

SW NE

A

A

gradient variations define different sectors (cross sections)

Section B

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Distance (km)

LOS

velo

city

(mm

/y)

WNW ESE

B

B

Section C

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0 5 10 15 20 25 30 35 40 45Distance (km)

LOS

velo

city

(mm

/y)

S

N

C

C

Giarrewedge

Giarrewedge

NE sector

NE sector NE

sect

or

SE sector

SE sector

SE sector

3 main domains:• SE sector• NE sector• Giarre wedge

Similar analysis has been performed on PS obtained from descending orbits

By combining PS maps from ascending and descending orbits we may estimate two displacement components: E-W and Vertical.

where:• UN, UE, UV are the component of the 3D vector displacement, N-S,

E-W and Vertical respectively. • φ and λ are the azimuth and incidence angles, respectively

λλ cossin VELOS UUd +±=

On Mt. Etna φ ≈ 11°, thus sin(φ) = 0.19 and cos(φ) = 0.98Considering sin(φ) ≈ 0 and cos(φ) ≈ 1

( ) λλφφ cossincossin VENLOS UUUd ++=

where: (-) for ascending and (+) for descending orbits

By adding and differencing (1) we can calculate two maps: E-W and Vertical motions

(1)

≈ E-W motions

- = (2 sin λ)

+ =

≈ vertical motion

(2 cos λ)

An evident eastward decrease of the vertical velocity also affect each block on the SE flank. This produce a westwards tilt of each block.THIS AGREE WITH GPS DATA ⇒

Analysis of PS vertical and E-W components maps≈ E-W motions ≈ vertical motions

Gradient on E-W motion is detected only on some faults: e.g. Fasano-S. Gregorio fault has E-W horizontal component.

On the NE block, Giarre wedge and the central part of the SE block there is not gradient on E-W motion. THE EASTERN FLANK SHOWS A QUITE UNIFORM HORIZONTAL VELOCITY.The N-S component resulting form the right lateral strike-slip of “Timpe” faults produce secondary effects visible only on GPS vectors (azimuth rotation).

Gradient of the vertical motion shows significant dip-slip components along many faults (e.g.: Mascalucia, Trecastagni and Timpe).

480 490 500 510 520

Lon UTM

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LatU

TM

BAGL

CAS

FOPE

GIA

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MANG

MDGR

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MPLMTSE

SGBO STAZ

SVEN

TARC

TVOL

Tilt from GPS

Results from Ionica network(1997-2001)

By combining vertical and horizontal velocities we estimate the dip of each GPS vectors.The dip generally decrease towards the sea, with a few anomalies close the main faults.This results in a westwards tilt of the flank.

Bonforte & Puglisi, JVGR, in print

Summary of movements

Giarre WedgeESE GPS vector azimuthHorizontal component >> vertical

10 cm

N-E Sector E – ESE GPS vector azimuthHorizontal component > vertical.Splay block

S-E SectorGPS vector azimuth ranging from SSE to SESeveral blocks tilting westwards

By integrating PS and GPS

Conclusions on active structures of eastern flank• The information obtained by combining PS (1995-2000) and GPS (1997-2001)

results show that the eastern flank could be divided in at least 3 main domains :– The SE (Timpe) Domain; this is the most complex because it is formed by different blocks

with different azimuth of motion (GPS) due to the control of the local faults; each block is tilting westwards.

– The NE (Pernicana) Domain located along the northern boundary of the sliding flank shows higher velocity with respect to the Timpe Domain; except to the splay block, it shows a near constant velocity both on horizontal and vertical component.

– The Giarre Domain (or Wedge) shows the highest velocity of the eastern flank of Mt. Etna. Its motion is incompatible with a shallow gravitational sliding of eastern flank, but compatible with the regional tectonics (E-W extension).

• In the southern part of the eastern flank the dip of GPS vectors and the PS vertical components indicate a tilt in agreement with the rotational sliding of this flank; this agree with a “decollement” along listric surfaces (at least in SE flank).

• Those new observations provide new insights on how Etna works:– The regional tectonics, acting on the Giarre wedge, might drives the gravitation spreading

of sectors of east flank (e.g. SE sector tilt).

– This produce in turn the depressurization on the upper part of volcano plumbing system, facilitating magma rising.

Thank you

verticalMany (but not all) faults show large vertical component: Mascalucia, Trecastagni and Timpe. Blocks tilted westwards .

Analysis of PS interpolated “filtered” maps (vertical and E-W components)

First result: the Mogi source is too “strong” with respect to the vertical component. This is expected ! OK.

Palano et al., EPSL, submitted

• approaching of volcano (along LOS) on N,W,S flanks.

• departure of volcano (along LOS) of E and SE flanks.

93.10.17-97.05.28 93.11.21-97.03.19 93.11.21-97.09.10

97.03.19-97.09.10 97.05.28-98.05.13 97.03.19-00.04.17

97.03.19-00.10.04 97.09.10-00.10.04 97.10.15-00.06.21

93.11.21-00.05.17 93.11.21-00.10.04

By extending the data-set to 2000 and integrating the analysis with GPS data, the general pattern is confirmed