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Synthetic SeismogramsJeroen Tromp
Synthetic Seismograms – p.1
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Semi-Analytical Seismology
Global Seismology: Spherical models
� Normal-mode summation
� Reflectivity method (Earth flattening)
� WKBJ theory (Asymptotic)
Regional Seismology: layercake models
� Discrete wavenumber/Reflectivity method
Synthetic Seismograms – p.2
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Perturbation Methods
Tomographic inversions:
� Ray methods
� Path-average approximation
� Non-linear asymptotic coupling theory
� mode splitting/coupling
Source inversions:
� 1D models with path corrections
Synthetic Seismograms – p.3
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The Challenge of the Globe
� A slow, thin, highly variable crust
� Sharp radial discontinuities
� Fluid-solid boundaries
� Anisotropy
� Attenuation
� Ellipticity, topography & bathymetry
� Rotation
� Self-gravitation
Synthetic Seismograms – p.4
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Computational Seismology
Calculation of 3D synthetic seismograms:
� Modern numerical methods
� Hardware advances
Synthetic Seismograms – p.5
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The Seismo Lab Beowulf
� 312 processors
� 156 GB of RAM
� 733 MHz Pentium III� 133 MHz Tyan boards
� CISCO switch
� Linux OS
� MPICH communications
Synthetic Seismograms – p.6
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Topography & Crustal Model
Elevation from sea level (km)
-8 +8 10 30 39 50 65 75
Crustal thickness (km)
Bassin et al. (2000)Synthetic Seismograms – p.7
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Mantle Model
Shear velocity variation (%)
-6% +6%
Ritsema, Van Heijst & Woodhouse (1999)Synthetic Seismograms – p.8
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Hjörleifsdóttir, Kanamori & Tromp (2002)
Synthetic Seismograms – p.9
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The Earth Simulator
� 640 nodes
� 16 GB of memory pernode, 10 TB ofdistributed memory
� 8 processors pernode, 5120 total
Collaboration with Seiji Tsuboi (IFREE)
Synthetic Seismograms – p.10
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Earth Simulator
243 nodes (1944 processors), 3.4 TB memory, 14.8 billion degrees of freedom,5 teraflops
Soon: 512 nodes (4096 processors)
Synthetic Seismograms – p.11
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November 3, 2002, Denali
Tsuboi, Komatitsch, Chen & Tromp, 2003
Synthetic Seismograms – p.12
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November 3, 2002, Denali
PREM 3D
Tsuboi, Komatitsch, Chen & Tromp, 2003Synthetic Seismograms – p.13
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The World’s Fastest Computer
10
100
1000
10000
100000
1000000Ju
n− 93
Nov
− 94
Jun− 9
6Nov
− 97
Jun− 9
9Nov
− 00
Jun− 0
2Nov
− 03
Jun− 0
5Nov
− 06
Jun− 0
8Nov
− 09
Per
form
ance
(G
igaf
lops)
1 Teraflop/s
1 Petaflop/s
Courtesy T. Sterling (CACR, Caltech) Synthetic Seismograms – p.14
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Conclusions
� 3D global synthetics accurate up to4 seconds (1D mode synthetics are typicallyaccurate up to 8 seconds)
� Tool to probe/assess 3D structures
� 1D & 3D reference synthetics (need REMand CMT)
� 3D (finite) source inversions
Synthetic Seismograms – p.15