surface wave tomography of northern europe · surface wave tomography of northern europe •global...
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![Page 1: Surface wave tomography of Northern Europe · Surface wave tomography of Northern Europe •global tomography: many models, coarse resolution > 500km, global average •regional tomography:](https://reader033.vdocument.in/reader033/viewer/2022050523/5fa73ac21b94dc0b6069fa5c/html5/thumbnails/1.jpg)
Christian Weidle, Valérie Maupin
Dept. of Geosciences, Univ. Oslo, Norway
Acknowledgements: J. Schweitzer (NORSAR), A. Levshin (Univ. Colorado, USA)
Surface wave tomography of Northern Europe
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• global tomography: many models, coarse resolution > 500km, global average
• regional tomography:
body waves – strong resolution but limited on land areas
surface waves – used for mapping hotspots and contrasts, resolution ~ 400km (Pilidou et al.)
• `local` tomography: temporary deployments, very good local models, restricted to land (so far)
Bijwaard et al., 1998
Marquering & Snieder, 1996
Goes et al., 2000
Pilidou et al., 2005
Shomali et al., 2006
Bruneton et al.,2004
Eken et al., 2007
?
What do we know?
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Data statistics
• group velocity measurements (FTAN)
• Love and Rayleigh waves
• periods 14s to 200s
• dominant periods around 30s
• intermediate size of earthquakes
• for inversion 16s to 150s
• 2-D inversion code by Barmin et al. (2000)
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Data statistics
HOTSPOT and NORSAR recordings removed• decrease in number of data• increase in azimuthal coverage
geometries in group velocity maps persist
Full dataset
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Group velocity tomography
• 2-D reference model CUB
• inversion on 1x1 deg grid
• lateral resolution < 300km even at 80s
• strong enhancement in details and amplitudes
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Group velocity tomography
Synthetic reconstruction tests:
• without noise, reconstruction is convenient
• with added noise lateral smearing and change in geometries is observed, however smeared amplitudes are significantly smaller than structural ampl.
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1-D linear inversion – reference models
Inversion of 2-D g.v. maps for S-wave velocity
• point-by-point 1-D inversions
• approach Maupin & Cara (1992) modified for group
velocities
• correlation length 20 km in all `layers`, uncoupled across
interfaces
• interfaces fixed
Reference models:
1-D model PREM insufficient due to tectonic variety
3-D crust & 1-D mantle (ak135):
a) CRUST2.0 oceanic regions interpolated
b) EUCRUST07 incl. offshore models
(standard conversions where necessary)
3-D model: CUB20 (Shapiro & Ritzwoller, 2002)
Invert on 1x1 deg (PREM & EUCRUST07) and 2x2 deg (CRUST2.0 & CUB20) grids
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1-D linear anisotropic inversion
• Group vel. in the mantle most sensitive to VSV and
• VP in the crust non-negligible but better constrained through ref.models
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3-D model for Northern Europe
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3-D model for Northern Europe
CM
CM
CM
CTFCM
SNFCTF
EW
EW SENW
SENW
Radial profiles from Iceland
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3-D model for Northern Europe
STZ
DSHZ
ThS
STZ SNF
DSHZ
STZ
SNFSNF
ISZ?STZ?
CM
CMCM SNFTESZ
STZThSThS
N(E)S(W) (N)E(S)W SENW
Radial profiles centered in Southern Norway
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3-D model for Northern Europe
Eken et al., 2007
ThS STZShomali et al., 2006
ThS
STZ
Comparison with TOR and SNSN tomographies
TOR
TOR
SNSN
SNSN
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3-D model for Northern Europe
Safe points:
• stable model at depths > 70km
• good correlation to previous studies
• good geometrical fit to ancient plate boundaries
• CM intersected offshore Norway
• low-velocity anomaly bounded by STZ and SNF
Careful points:
• 1x1deg grid lateral smearing
• amplitudes at < 70km depth (crustal correction)
• linearity of inversion vs. tectonic contrasts
• uncertainty in anisotropy amplitude
Impact for TopoScandiaDeep:
• model is readily available as reference and / or background for modelling
• S.Norway: major problem to be tackled is velocities between sub-Moho and ca. 70 km in conjunction with absolute receiver functions ?
• model could be updated in the course of project to include MAGNUS data, updated crustal model, …