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
370000
380000
390000
400000
450000 460000 470000 480000
Uz − elastic
5
10
15
20
25
30[mm]
370000
380000
390000
400000
450000 460000 470000 480000
|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]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 2 / 11
Crustal response to surface loads
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
50
100
150
200[mm]
370000
380000
390000
400000
450000 460000 470000 480000
|Ur| − final−relaxed
2
4
6
8
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]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 2 / 11
Crustal response to surface loads
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
50
100
150
200[mm]
370000
380000
390000
400000
450000 460000 470000 480000
|Ur| − final−relaxed
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]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 2 / 11
Crustal response to surface loads
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
50
100
150
200[mm]
370000
380000
390000
400000
450000 460000 470000 480000
|Ur| − final−relaxed
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]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 2 / 11
Motivation for this work
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
50
100
150
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 3 / 11
Motivation for this work
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 3 / 11
Motivation for this work
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 3 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 4 / 11
Chamber depth issues (conceptual!)
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
ISAK
MOHN
50
100
150
200[mm]
[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 km
27.5 mm 33.1 km
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 4 / 11
Identification of signal composition 1/2
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 5 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 6 / 11
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]
[Sturkell et al., 2008]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 7 / 11
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]
[Sturkell et al., 2008]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 7 / 11
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]
[Sturkell et al., 2008]
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 7 / 11
InSAR observations 2/2
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]
−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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 8 / 11
InSAR observations 2/2
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]
−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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 8 / 11
Derivation of crustal parameters (concept)
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
200
400
600
800
1000
1200
1400
1600
1800
[mm]
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)
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 9 / 11
Derivation of crustal parameters (concept)
370000
380000
390000
400000
450000 460000 470000 480000
Uz − final−relaxed
200
400
600
800
1000
1200
1400
1600
1800
[mm]
370000
380000
390000
400000
450000 460000 470000 480000
Uz − displacement−rate
t=60
2
4
6
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)
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 9 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 10 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 10 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 10 / 11
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
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 10 / 11
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.
Grapenthin et al. (UAFGI) Pressure sources vs. surface loads 22.08.2008 11 / 11