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Mantle Heterogeneity West and East of the Rocky Mountains
Xiaoting Lou (Northwestern University), Suzan van der Lee (Northwestern University)
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.
References
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.
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.
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.
Figure 1: Station average S relative delay times for the two groups of stations west and east of the Rocky Mountains, respectively.
Figure 2: Measured individual relative S delays plotted against P delays for the
two groups of stations west and east of the Rocky Mountains, respectively.
2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics | II-211