Title: INT 97-21  NSF/Tokyo Report:  Numerical Modelling and Rehological
          Properties of the Transition Zone
Date:  5/21/97

The National Science Foundation's offices in Tokyo and in Paris periodically
report on developments abroad that are related to the Foundation's mission.
These documents present facts for the use of NSF program managers and policy
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Special Scientific Report #97-15 (May 09, 1997)

NUMERICAL MODELLING AND RHEOLOGICAL PROPERTIES OF THE TRANSITION ZONE

The following report was submitted by Dr. David Yuen, Professor of Geophysics,
University of Minnesota, Minneapolis, MN 55415. Dr. Yuen is in the third year
of a three year collaborative study with Professor Satoru Honda, Department of
Earth and Planetary Systems, Horoshima University, Higashi-Hiroshima, Japan.
Dr. Yuen's participation in the project is supported by the NSF Japan and
Korea Program; Professor Honda's support is provided by the Japan Society for
the Promotion of Science (JSPS). This project is one of the joint projects
supported under the U.S.-Japan Cooperative Science Program. Dr. Yuen can be
reached via email at: davey@krissy.msi.umn.edu

Interim Report of work done on our US-Japan project:

In the last year, the group from the University of Minnesota and Hiroshima
University have focused their efforts on looking at the combined effects of
continental and oceanic plates on modulating mantle convection with phase
transitions. Since the continental lithosphere is considerably thicker than
the oceanic lithosphere by a factor of around two, the interaction with the
400 km phase transition is much stronger. Our results show that large
megaplumes have a tendency to form under thick continental lithosphere and
that the upper-mantle under continents are hotter  than under oceanic plates.
We have also developed a model for fault creep incorporating the grain-size
dependence of the viscosity into the deformation process.  By using over
10,000 grid points along the fault we have successfully captured all of the
nonlinearities associated with the deformation. Features down to one hundred
meters were resolved within a zone of 40 km.  We found that under certain
conditions a runaway process can take place, leading to melting inside the
fault zone.