pressure sources vs. surface loads: analyzing deformation ...pressure sources vs. surface loads:...

Pressure sources vs. surface loads: Analyzingdeformation signal composition at volcanoes – a

case study at Hekla volcano, Iceland

Ronni Grapenthin 1 Freysteinn Sigmundsson 2 Erik Sturkell 2

Benedikt G. Ofeigsson 2

1Geophysical Institute, Univ. of Alaska Fairbanks.

2Nordic Volcanological Center, Institute of Earth Sciences, Univ. of Iceland.

IAVCEI 2008, 22.08.2008

Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 1 / 11

Crustal response to surface loads

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Uz − elastic

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25

30[mm]

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|Ur| − elastic

1

2

3

4

[mm]

instantaneous response of elastic layer

followed by visco-elastic response of ductile crusttransition for Newtonian viscosity: exponential decaymodeled using Green’s functions derived by Pinel et al. (2007)implemented in simulation framework CRUSDE [Grapenthin, 2007]



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Uz − final−relaxed

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|Ur| − final−relaxed

2

4

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10

12

14

16

18[mm]

instantaneous response of elastic layerfollowed by visco-elastic response of ductile crust

transition for Newtonian viscosity: exponential decaymodeled using Green’s functions derived by Pinel et al. (2007)implemented in simulation framework CRUSDE [Grapenthin, 2007]



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50

100

150

200[mm]

370000

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450000 460000 470000 480000


2

4

6

8

10

12

14

16

18[mm]

instantaneous response of elastic layerfollowed by visco-elastic response of ductile crusttransition for Newtonian viscosity: exponential decay

modeled using Green’s functions derived by Pinel et al. (2007)implemented in simulation framework CRUSDE [Grapenthin, 2007]



370000

380000

390000

400000

450000 460000 470000 480000


50

100

150

200[mm]

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380000

390000

400000

450000 460000 470000 480000


2

4

6

8

10

12

14

16

18[mm]

instantaneous response of elastic layerfollowed by visco-elastic response of ductile crusttransition for Newtonian viscosity: exponential decaymodeled using Green’s functions derived by Pinel et al. (2007)implemented in simulation framework CRUSDE [Grapenthin, 2007]


Motivation for this work

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200[mm]

Uz − Mogi

volcano deformation often related to internal pressure sources[Yamakawa, 1955, Mogi, 1958]surface loads contribute a significant signal

gradual subsidence may be mistaken as source deflation – giveswrong chamber characteristicssignal can be exploited to derive crustal parameters



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450000 460000 470000 480000


50

100

150

200[mm]

Uz − Mogi

volcano deformation often related to internal pressure sources[Yamakawa, 1955, Mogi, 1958]surface loads contribute a significant signalgradual subsidence may be mistaken as source deflation – giveswrong chamber characteristics

signal can be exploited to derive crustal parameters



370000

380000

390000

400000

450000 460000 470000 480000


50

100

150

200[mm]

Uz − Mogi

volcano deformation often related to internal pressure sources[Yamakawa, 1955, Mogi, 1958]surface loads contribute a significant signalgradual subsidence may be mistaken as source deflation – giveswrong chamber characteristicssignal can be exploited to derive crustal parameters


Chamber depth issues (conceptual!)

Hekla 2000 lava

19˚54'W 19˚48'W 19˚42'W 19˚36'W 19˚30'W 19˚24'W63˚54'N

63˚57'N

64˚00'N

64˚03'N

64˚06'N

MOHN

Hekla 2000 lava

19˚54'W 19˚48'W 19˚42'W 19˚36'W 19˚30'W 19˚24'W63˚54'N

63˚57'N

64˚00'N

64˚03'N

64˚06'N

0 5

km

[Sturkell et al., 2005]

Uz = 45 mm, V = 0.189 km3 lava [Höskuldsson et al., 2007]

E = 40 GPa [Grapenthin et al., 2006], MOHNUz =17.5 mm:max vertical displacement hypothetical source depth (Mogi)

45 mm 25.8 km27.5 mm 33.1 km


Chamber depth issues (conceptual!)

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ISAK

MOHN

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100

150

200[mm]


Uz = 45 mm, V = 0.189 km3 lava [Höskuldsson et al., 2007]E = 40 GPa [Grapenthin et al., 2006], MOHNUz =17.5 mm:

max vertical displacement hypothetical source depth (Mogi)45 mm 25.8 km

27.5 mm 33.1 km


Identification of signal composition 1/2


Identification of signal composition 2/2

0 6.2 170

1/3

1

distance from center [km]

|Uh|/U

zDisplacement ratios

Mogi modelElasticFinal relaxedMax. elasticavg GPS


InSAR observations 1/2

MOHN

−12−10−8 −6 −4 −2 0 2 4 6 8

LOS Velocity (mm/yr)

Mean LOS velocity 23.05.1997−15.10.1999

20˚00'W 19˚44'W 19˚28'W 19˚12'W

63˚52'N

64˚03'N

0 5 10

km

[Ófeigsson et al., last Tuesday, 2008]




MOHN

−12−10−8 −6 −4 −2 0 2 4 6 8



20˚00'W 19˚44'W 19˚28'W 19˚12'W

63˚52'N

64˚03'N

0 5 10

km


−5

0

8.5

Mogi anomaly

−12−8−4

048

12

Mea

n LO

S v

eloc

ity [m

m/y

r]

−20 −15 −10 −5 0 5 10 15 20

−5

0

8.5

Distance from profile junction [km]

Mogi source depth d = 11.6 km, Sturkell et al. (2008, submitted) :d = 10 km

surface loading (and/or other source) has to account forsubsidence of 13.5 mm/yr



MOHN

−12−10−8 −6 −4 −2 0 2 4 6 8



20˚00'W 19˚44'W 19˚28'W 19˚12'W

63˚52'N

64˚03'N

0 5 10

km


−5

0

8.5

Mogi anomaly

−12−8−4

048

12

Mea

n LO

S v

eloc

ity [m

m/y

r]

−20 −15 −10 −5 0 5 10 15 20

−5

0

8.5

Distance from profile junction [km]

Mogi source depth d = 11.6 km, Sturkell et al. (2008, submitted) :d = 10 kmsurface loading (and/or other source) has to account forsubsidence of 13.5 mm/yr


Derivation of crustal parameters (concept)

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elastic thickness: H = 3.5 km (matches 15 km subsidencediameter)

effective relaxation time: tR = 100 yrsboth compare well with previous results (i.e., Pinel 2007)


Derivation of crustal parameters (concept)

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[mm]

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Uz − displacement−rate

t=60

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8

10

12[mm/yr]

elastic thickness: H = 3.5 km (matches 15 km subsidencediameter)effective relaxation time: tR = 100 yrsboth compare well with previous results (i.e., Pinel 2007)


Take home messages . . .

gradual subsidence may be mistaken as source deflation . . .

. . . or at least has significant impact on interpretationshorizontal deformation field gives clues about signal source(s)visco-elastic response to (recent) loads must be considered

signal can be exploited to derive crustal parameters . . .

a combination of GPS, InSAR data, and inverse approaches isnecessarywe had: Young’s modulus, Poisson’s ratiowe got (approx.): source depth, elastic plate thickness, effectiverelaxation time (viscosity)

Download CRUSDE: http://www.gps.alaska.edu/ronniThanks to: Jeff Freymueller, Rósa Ólafsdóttir, and HalldórGeirsson



gradual subsidence may be mistaken as source deflation . . .. . . or at least has significant impact on interpretationshorizontal deformation field gives clues about signal source(s)visco-elastic response to (recent) loads must be considered

signal can be exploited to derive crustal parameters . . .

a combination of GPS, InSAR data, and inverse approaches isnecessarywe had: Young’s modulus, Poisson’s ratiowe got (approx.): source depth, elastic plate thickness, effectiverelaxation time (viscosity)




gradual subsidence may be mistaken as source deflation . . .. . . or at least has significant impact on interpretationshorizontal deformation field gives clues about signal source(s)visco-elastic response to (recent) loads must be considered

signal can be exploited to derive crustal parameters . . .a combination of GPS, InSAR data, and inverse approaches isnecessarywe had: Young’s modulus, Poisson’s ratiowe got (approx.): source depth, elastic plate thickness, effectiverelaxation time (viscosity)



References

Grapenthin, R., Sigmundsson, F., Geirsson, H., Árnadóttir, T., Pinel, V (2006) Icelandic rhythmics: Annual modulation ofland elevation and plate spreading by snow load, Geophys. Res. Lett., 33, L24305.

Grapenthin (2007), CRUSDE: A plug-in based simulation framework for composable CRUStal DEformation simulationsusing Green’s functions Ms thesis, Humboldt-Universität zu Berlin, pp. 127.

Höskuldsson, Á., Óskarsson, N., Pedersen, R., Grönvold, K., Vogfjörd, K., Ólafsdóttir, R. (2007) The millennium eruptionof Hekla in February 2000 Bull. Volc., doi:10.1007/s00445-007-0128-3.

Mogi, K. (1958) Relations between eruptions of various volcanoes and the deformations of the ground surface aroundthem, Bull. Earthquake Res. Inst. Univ. Tokyo, 36, 99–134.

Pinel, V., Sigmundsson F., Sturkell, E., Geirsson, H., Einarsson, P., Gudmundsson, M.T., Högnadóttir, Th. (2007)Discriminating volcano deformation due to magma movements and variable surface loads: Application to Katla subglacialvolcano, Iceland Geophys. J. Int., 169, 325–338.

Sturkell, E., Ágústsson, K. ,Linde, A.T., Sacks, S.I., Einarsson, P., Sigmundsson, F., Geirsson, H., Pedersen, R.,

LaFemina, P.C., Ólafsson, H. (2008) New insights into volcanic activity from strain and other deformation data from theHekla 2000 eruption Science, submitted.

Yamakawa, N. (1955) On the Strain Produced in a Semi-infinite Elastic Solid by an Interior Source of Stress, Zisin (J. Seis.

Soc. Japan), II, 8, 84–98.


pressure sources vs. surface loads: analyzing deformation ...pressure sources vs. surface loads:...

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