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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
Sung-Joon Chang (Northwestern University), Suzan van der Lee (Northwestern University)
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 pathaveraging
method produce similar waveforms for
inland, while a little different synthetics are generated
with the two methods for ocean-continent
boundary.
References
Komatitsch, D. and J. Tromp (1999), Introduction to
the spectral-element method for 3-D seismic wave
propagation, Geophys. J. Int., 139, 806-822.
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.
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.
Acknowledgements: We thank the IRIS DMC for providing
waveform data used in this research. This
study was supported by NSF EAR-0645752.
(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 waveforms
and several synthetics at stations surrounded by red circles in (a).
II-210 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics