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Research

Broad-band Ambient Noise Surface Wave Tomography of North America

Rayleigh wave group and phase speed tomography using permanent and temporary seismic stations

Gregory Bensen
Center for Imaging of the Earth's Interior
Department of Physics, University of Colorado at Boulder

Ambient Noise Tomography

We are working to improve the understanding of the compositional and thermal structure of North America using high resolution surface wave tomography maps. These maps are being created using ambient noise Green's functions between pairs of permanent and temporary seismic stations across North America. Using nearly 200 stations yielding up to 9000 high quality measurements, we create Rayleigh wave group and phase velocity maps from 8 to 60 seconds period; this provides information from roughly 8 km to over 100 km depth. <\p>

Details of this work are being written up for submission to Geophysical Research Letter. Please request a preprint via email if you're intereste in more details

Changes to Data Processing

As this is a new technique, we are still determining optimal data processing procedures. Starting with the initial methods, applied at relatively short periods and for small scales, I have incorporated more data over a continental scale. Through a series of improvements in signal preprocessing, increased stacking and uncertainty analysis, the method has been improved significantly. Details of these method improvements can be seen in the paper below. <\p>

Summary of processing procedures and changes:

Starting with the technique described by Shapiro et al. 2004, we have adjusted the technique to allow greater extensibility to a broad range of geographic scales and a broad range of periods.

The details of this technique are described in Bensen et al. (2007) submitted to GJI. (caution, pdf file is 2.5 Mb)

Preliminary Results:

Using the technique outlined in the paper above, we have begun writing up the results for submission to Journal of Geophysical Research. Group and phase speed dispersion maps for the continental United States are presented along with some guidelines about the reliability of resulting maps. Results are presented from 10 to 70 seconds period. Details of resulting resolution and relative reliability of group and phase measurements are presented. Feel free to read the manuscript in preparation for full details Bensen et al. (2006) in preparation for JGR.(caution, pdf file is 5 Mb)

References

  • Bensen, G.D., M.H. Ritzwoller, M.P. Barmin, A.L. Levshin, F. Lin, M.P. Moschetti, N.M. Shapiro, and Y. Yang, Processing seismic ambient noise data to obtain reliable broad-band surface wave dispersion measurements, submitted to Geophys. J. Int.
  • Shapiro, N.M. M. Campillo, L. Stehly, and M.H. Ritzwoller, High resolution surface wave tomography from ambient seismic noise, Science, 307(5715), 1615-1618, 11 March 2005.