WAVES ACROSS AMERICA: USING A SEISMIC ARRAY FROM FLORIDA TO ALBERTA TO EXAMINE THE GEOLOGY BENEATH THE MIDDLE OF NORTH AMERICA

The Florida-to-Edmonton (FLED) array of 2001-2002 is providing a great deal of information about the sub-North American structure, crust to core. The project involved the placement of 26 broadband seismometers in a line across North America for a duration of 15 months. Together with a dozen permanent broadband stations, it formed the best seismic coverage of the mid-continent to date. The array spanned a wide range of different geological terranes, and two major fossil rift zones - the Mid-Continent Rift and the New Madrid Rift Zone. The broadband nature of the seismometers allows for an investigation of deep structure as well as shallow structure. The FLED array was installed perpendicular to an earlier array, the Missouri-to-Massachusetts (MOMA) deployment. Some of the projects investigated and being investigated with these arrays include: (1) The relationship of mantle anisotropy to lithospheric deformation and deeper mantle flow, using SKS and SKKS splitting (with emphasis on the MCR). (2) Deep structure of the Midcontinent Rift (MCR) and New Madrid Fault Zone (NMFZ), using receiver functions and surface wave inversions across a more-densely-spaced deployment of stations; (3) Variations in crust and mantle structure across the many cratons, orogens, fossil tectonic boundaries and accreted terranes between Alberta and Florida, using receiver functions and surface wave inversions; (4) The relationship of the 410-km, 660-km, and upper mantle discontinuities to the North American mantle (using Ps phases); (5) The nature of anisotropy at the base of the mantle, using the relative times and waveforms of SHdiff and SVdiff. In all of the CMB studies, a key focus will be discerning the transition between the distinct seismic characteristics of sub-Pacific and sub-Pacific-rim regions; (6) The vertical structure of the D" thermal and chemical boundary layers through (A) SPdKS times and waveforms (for the ultralow velocity layer), (B) the frequency dependence (dispersion) of Sdiff and Pdiff profile slownesses, (C) the frequency dependence of Sdiff and Pdiff profile amplitudes; (7) The lateral structure and dynamics of the CMB region through (A) relative slownesses of core-diffracted Sdiff and Pdiff waves, (B) SKS-SKKS-S/Sdiff differential travel times, (C) PKP-Pdiff differential travel times, (D) SdS and ScS (for investigating the D" discontinuity).