Anisotropic Rayleigh-Wave Tomography of the Western United States
This example reproduces SurfATT-tests/examples/05_westUS_ani: a large-scale azimuthally anisotropic inversion of Rayleigh-wave phase-velocity travel times recorded by USArray and regional networks in the western United States.
Scientific background
The western United States hosts a dense broadband array and a spectrum of tectonic settings — active Cascadia subduction, Basin-and-Range extension, the Snake River Plain / Yellowstone track, and stable Colorado Plateau / craton. Rayleigh-wave phase velocities at 5–40 s periods sample the crust and uppermost mantle and exhibit two kinds of structure:
- Isotropic heterogeneity — slow extensional / magmatic provinces vs. fast cratonic and slab interiors.
- Azimuthal anisotropy — lattice-preferred orientation of olivine in the upper mantle and aligned cracks/fabrics in the crust produce velocity differences along different propagation directions. Mapping the fast-axis direction provides first-order constraints on flow patterns and tectonic fabric.
SurfATT’s adjoint-state framework jointly inverts both contributions in a single optimization loop.
What is included
- input_params.yml
- src_rec_data_wus.csv
- csem.nc
| File | Size | Description |
|---|---|---|
input_params.yml | ~3 KB | Anisotropic inversion configuration |
src_rec_data_wus.csv | ~26 MB | Rayleigh-wave phase-velocity travel-time table |
csem.nc | ~6.6 MB | CSEM 3-D Vs reference model (optional) |
The default input_params.yml uses init_model_type: 1 (1-D inversion of average travel times) as the starting model. csem.nc is provided so you can optionally switch to a 3-D initial model (init_model_type: 2) after converting the NetCDF file to HDF5.
Workflow overview
- Data Preparation — inspect
src_rec_data_wus.csv, optionally convertcsem.nctocsem.h5for a 3-D starting model. - Parameters & Run — review
input_params.yml(grid, smoothing, LBFGS,is_anisotropy: True) and launchSURFATT_tomowith MPI. - Visualization — plot the isotropic Vs maps, the anisotropy magnitude, and the fast-axis direction.
- Checkerboard Test — assess lateral resolution for both the isotropic and anisotropic components.