thesis graduate school complex processes in the earth – theory, experiment, simulation stefan...
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THESIS Graduate School
Complex Processes in the Earth – Theory, Experiment, Simulation
Stefan Wenk, Martin Käser, Christian Pelties, Alan Schiemenz, Heiner Igel, Hans-Peter Bunge
Global/regional wave propagation through complex 3D heterogeneous
Earth models
2
Outline
1. Why do we develop global simulation tools?
2. Why do we use the Discontinuous-Galerkin
method?
3. What are the experiences in applying the
method?
4. How do we have to focus the developments?
14.10.2011
Motivation
• Imaging the Earth/Study Earthquake physics
• Computational power increases exponentially Inversion of full waveforms
Numerical simulations for 3D heterogeneous Earth models
• Focus on Finite-Element methods High order accurate and fast enough
Different implementations for different applications
• There is no all in one algorithm
• SEM – “faster but simple models”
• DG – “slower but complex models”
• Many other…
314.10.2011Motivation Why DG? Experiences Focus
Project aim
• Adaptation of the new Discontinuous-Galerkin
method to global/regional wave propagation
• Code development
• Benchmarking with elaborated numerical methods
• High quality mesh generation
• Application to models of
complex geometries and
strong material gradients
4Motivation Why DG? Experiences Focus
Unstructured tetrahedral grid, PREM model
14.10.2011
5
Outline
1. Why do we develop global simulation tools?
2. Why do we use the Discontinuous-Galerkin
method?
3. What are the experiences in applying the
method?
4. How do we have to focus the developments?
14.10.2011
621.06.2011
FEM tools
Spectral-Element method
• High order method with spectral convergence
• Structured hexahedral grid
Why another algorithm?
• Ratio of element size: hmin/hmax <<1
• SEM: global time step -> simulation “explodes”
Discontinuous-Galerkin method
• Easy mesh refinement
• Local system → easier to parallelize
• SeisSol features: time integration as good as
spatial approximation, local time stepping, local
polynomial degreeMotivation Why DG? Experiences Focus
Structured hexahedral grid (Komatitsch et al. (2002)
Unstructured tetrahedral grid, PREM with refined Kernel
721.06.2011
Outline
1. Why do we develop global simulation tools?
2. Why do we use the Discontinuous-Galerkin
method?
3. What are the experiences in applying the
method?
4. How do we have to focus the developments?
Explosive source
PREM no crust PREM with crust
8Motivation Why DG? Experiences Focus
• High frequency simulation only on a regional scale
• Problem: Boundary reflections14.10.2011
Realistic source
9Motivation Why DG? Experiences Focus
CMT: Norwegian Sea (M=6.0, 20.08.2009)• Lat/Lon/Depth = 72.2°/0.84°/12km
• dip ≈ 30°, oblique slip
Raw Mineos datalook like this!
Any suggestions?
14.10.2011
Attenuation
10Motivation Why DG? Experiences Focus
1D iso PREM + explosive source + attenuation
Comparison of
Mineos and
SpecFEM
Difference in
relaxation
mechanisms or
attn. model?
14.10.2011
11
Outline
1. Why do we develop global simulation tools?
2. Why do we use the Discontinuous-Galerkin
method?
3. What are the experiences in applying the
method?
4. How do we have to focus the developments?
14.10.2011
12
Conclusions
• Benchmarking up to intermediate frequency and simple
1D isotropic Earth model works
• Modeling Tasks: 1D-Model: Investigate differences for real source and visco-
elastic modeling results 3D-Model: real source + attenuation (+ anisotropy) Application: Cascadia, Europe…
• Quest benchmark library
• Code development: Perfectly Matched Layers Load balancing using space filling curves Streamline routines
Motivation Why DG? Experiences Focus 14.10.2011