SEMum2

Welcome to the online home of the SEMum2 model, a global radially anisotropic shear-velocity model of the earth's upper mantle and transition zone.

This is the companion website to the SEMum2 model, presented in our recently published paper:

French, S.W., V. Lekic, and B. Romanowicz (2013), Waveform Tomography Reveals Channeled Flow at the Base of the Oceanic Asthenosphere, Science, accepted (Science Express).

Here you, you can download the model itself, as well as find information about the methods used to develop the model and various model visualizations (coming soon).

Methodology

The SEMum2 model represents an update to the model SEMum [1], incorporating an improved treatment of Earth's crust and inversion for shorter-wavelength mantle structure. Both models employ a "hybrid" full-waveform inversion methodology, combining accurate forward modeling of the seismic wavefield using the spectral element method (SEM) [2] with finite-frequency sensitivity kernels from non-linear asymptotic coupling theory (NACT) [3]. Together with the use of a smooth crustal model that mimics the seismic response of Earth's crust, this approach leads to considerable savings in computational cost.

  1. Lekic, V. and Romanowicz, B., 2011. Inferring upper-mantle structure by full waveform tomography with the spectral element method, Geophys. J Int., 185, 799-831.
  2. Komatitsch, D. and Vilotte, J.-P., 1998. The Spectral Element Method: An Efficient Tool to Simulate the Seismic Response of 2D and 3D Geological Structures, Bull. seism. Soc. Am., 88, 368-392.
  3. Li, X.D. and Romanowicz, B., 1995. Comparison of global waveform inversions with and without considering cross-branch modal coupling, Geophys. J Int., 121, 695-709.

hybrid waveform inversion

Hybrid full-waveform inversion

The combination of SEM for forward modeling with NACT sensitivity kernels leads to a quickly-converging Gauss-Newton model update scheme, in addition to the overall cost reduction due to the smooth crustal layer.

Media

Model visualization, etc ... Coming soon.

Download

Download the model distribution and evaluation tool (2.8M) here (Version 0.1).

This gzipped tar file (expand: tar xzf SEMum2_dist-v0.1.tar.gz) contains the raw spline-basis coefficients for the model, as well as a tool for evaluation at arbitrary (lon,lat) points and on regular grids at a specified radius. The latter is written in C and should compile without issue using, for example, the GNU C compiler.

More functionality for model evaluation will be added, so do check back for updated versions of this package.

Please report any bugs to Scott French (contact).

Contact

The SEMum2 model was developed at the Berkeley Seismological Laboratory. Contact the authors:

AuthorEmailCurrent affiliation
Scott Frenchsfrench at seismo dot berkeley dot eduBerkeley Seismological Laboratory, U.C. Berkeley
Vedran Lekicved at umd dot eduUniversity of Maryland
Barbara Romanowiczbarbara at seismo dot berkeley dot eduBerkeley Seismological Laboratory, U.C. Berkeley; Institut de Physique du Globe de Paris, Paris, France