Mantle Heterogeneity West and East of the Rocky Mountains

Mantle Heterogeneity West and East of the Rocky Mountains, Figure 1 Figure 1:
Station average S relative delay times for the two groups of stations west and east of the Rocky Mountains, respectively.
Separated by the Rocky Mountains, North America is divided into a tectonically active western part and a tectonically stable eastern part. We have measured teleseismic P and S relative delay times using waveforms from IRIS PASSCAL seismic arrays and EarthScopes Transportable Array sampling both western and eastern North America. Relative delay times were corrected for ellipticity, topography, Moho depth and sediments using the Crust 2.0 Model [Bassin et al., 2000]. To investigate the delay time differences between tectonically active and stable North America, seismic stations are divided into two groups: (1) TA stations west of the Rocky Mountains; (2) TA stations east of the Rocky Mountains and stations of MOMA, ABBA, FLED and Abitibi. Delay times within each group of stations are shifted relative to other groups using predicted average delay times by tracing 1D raypath through 3D model NA04 [Van der Lee and Frederiksen, 2005]. The range of relative delay times from seismic stations east of the Rocky Mountains is comparable to that for stations west of the Rocky Mountains, which holds for both station average delay times (Figure 1) and all individual measurements (Figure 2). This suggests that the mantle heterogeneity in the east is comparable to that in the west, despite there being relatively little surface or tectonic expression of this heterogeneity in the east. For both groups of stations, the measured S and P delay times have a significant linear correlation, with S delays at approximately 3 times the P delays, which confirms the dominant effect of mantle temperature on mantle velocity structure.
</p><p>Bassin, C., G. Laske, and G. Masters (2000), The current limits of resolution for surface wave tomography in North America, Eos Trans AGU, 81, F897.
</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, Geophys. Monogr. Ser., vol. 157, edited by A. Levander and G. Nolet, pp. 67–80, AGU, Washington, D. C.
</p><p>Acknowledgements: This study is supported by NSF EAR-0645752 grant to Suzan van der Lee. The authors are grateful to the IRIS DMC for providing seismic waveform data.</p>


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