The Effect of S-Velocity Heterogeneity in the North American Crust and Mantle on Waveforms of Regional Surface Waves from the Fe

The Effect of S-Velocity Heterogeneity in the North American Crust and Mantle on Waveforms of Regional Surface Waves from the February 2008 Nevada Earthquake (a) The Nevada Earthquake (Mw 6.0) indicated as a star was recorded at over 400 broadband stations in USArray indicated as triangles. Some stations are surrounded by red circles where observed waveforms are obtained to be compared with synthetics. (b) Comparison between observed wave- forms and several synthetics at stations surrounded by red circles in (a).
We compare observed waveforms recorded at the USArray Transportable Array stations from the 02/21/08 Nevada earthquake (Mw 6.0) with synthetics through three-dimensional (3D) velocity models such as S20RTS [Ritsema et al., 1999] and NA04 [Van der Lee and Frederiksen, 2005]. A crustal model CRUST2.0 is incorporated into the mantle velocity model S20RTS. We calculate synthetics down to 17 s through: 1) mode summation for a 1D model obtained by averaging velocity variations in the 3D model between the epicenter and the station (path-average method), and 2) the Spectral Element Method [Komatitsch and Tromp, 1999]. Because the Nevada earthquake occurred almost at the center of the Transportable Array stations at that time, distances between the epicenter and stations are typically less than 1000 km. In general, the 3D models predict the observed waveforms better than a reference 1D model, but some waveform fits need to be significantly improved by better 3D models of velocity heterogeneity and discontinuity depth. We find the spectral element method and path- averaging method produce similar waveforms for inland, while a little different synthetics are generated with the two methods for ocean-continent boundary.
</p><p>Komatitsch, D. and J. Tromp (1999), Introduction to the spectral-element method for 3-D seismic wave propagation, Geophys. J. Int., 139, 806-822.
</p><p>Ritsema, J., H. J. van Heijst, and J. H. Woodhouse (1999), Complex shear wave velocity structure imaged beneath Africa and Iceland, Science, 286, 1925-1928.
</p><p>Van der Lee, S. and A. Frederiksen (2005), Surface wave tomography applied to the North American upper mantle, in Seismic Earth: Array analysis of broadband seismograms, pp. 67-80, eds. A. Levander and G. Nolet, Geophys. Mono. 157, AGU, Washington, DC.
</p><p>Acknowledgements: We thank the IRIS DMC for providing waveform data used in this research. This study was supported by NSF EAR-0645752.</p>


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