The Global-Scale Context for OMD Studies of the Lithosphere and Asthenosphere

Michael H. Ritzwoller and Nikolai M. Shapiro
University of Colorado at Boulder

Recent years have seen substantial improvements 
in global tomographic models of the oceanic lithosphere and 
asthenosphere. The ``Leapfrogging'' regional arrays of
OBS will be designed to refine and improve these global models.
These improvements are needed to provide a large-scale
context for the process-oriented seismic studies that
are the focus of the OMD initiative. In particular, 
advances in global models will be useful to understand
along-ridge variability, to investigate patterns of
large-scale convection beneath oceanic plates, to
illuminate the continent - ocean lithosphere transition
both at active and passive margins, to refine the intriguing 
set of hypothetical structures that appear in the Central Pacific 
(e.g., unique anisotropy, superplumes from the CMB to the 
lithosphere, the arrested cooling between 70 - 100 Ma), and 
to provide guidance for OMD experiments generally. 

In this talk we will briefly describe our surface wave study
of the Pacific and present evidence that the cooling of the
Pacific lithosphere arrests at ages between 70 - 100 Ma. We will
demonstrate the use of a physically motivated parameterization 
as the basis for seismic tomography which is based on a thermal 
model of lithospheric cooling. Finally, we will assess how
the leapfrogging array will improve lateral and vertical resolution
of the upper mantle.