HR: 11:55h
AN: S52B-06    [Abstracts]
TI: IRIS and the S-velocity structure of the North American upper mantle
AU: * van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Northwestern University, Dept. of Geological Sciences 1850 Campus Drive, Evanston, IL 60208 United States
AU: Frederiksen, A W
EM: frederik@cc.umanitoba.ca
AF: University of Manitoba, Dept. of Geological Sciences, Winnipeg, MB R3T 2N2 Canada
AB: Owing to its US-based origin and resulting seismogram holdings the Data Management Center (DMC) of the Incorporated Research Institutions for Seismology (IRIS) has greatly facilitated waveform tomographic studies worldwide, and for North America in particular. We report on one such undertaking, in which nearly one and a half thousand seismograms from the IRIS DMC and the Canadian National Seismic Network have been interactively analyzed and used in a Partitioned Waveform Inversion for a tomographic model for the three-dimensional S-velocity structure of the North American upper mantle. A predecessor (NA95) of this new model is consistent with global tomographic models and revealed additional detail such as an upper-mantle component of subducted Farallon lithosphere, an enigmatic structure for the Wyoming lithosphere, and a V-shaped dent in the new England cratonic lithosphere. These details in turn helped spark additional IRIS activity in the form of further analyses of the data holdings of the DMC and PASSCAL experiments addressing these details. The new model provides relatively high-resolution images of the high-velocity rigid root beneath the Canadian shield and central US, which extends to depths of 200-300 km, the low velocities beneath the tectonically active Cordillera and the continent west of it, which also reach depths of 200-300 km, and details herein such as those mentioned above. Below these structures, high-velocity features in the transition zone are not as steep as but in line with the dipping high-velocity Farallon slab imaged in the lower mantle with tomographic methods that include teleseismic body waves. Increased accuracy in the new model, relative to its predecessors, is largely a result of extending the data base that constrains it. We checked the effects of using sensitivity kernels that cover elliptical areas around the great circles and found that they do not lead to better a posteriori data fits.
DE: 8180 Tomography
DE: 9350 North America
DE: 7207 Core and mantle
DE: 7218 Lithosphere and upper mantle
DE: 3260 Inverse theory
SC: Seismology [S]
MN: 2004 AGU Fall Meeting