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CCS Seminar
Professor Paul Hall
Boston University - Department of Earth Sciences
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FRIDAY - February 29, 2008
12:00 noon
Physics Research Building - Room 595
3 Cummington Street
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"Computational Geodynamics: Exploring the Earth's Deep Interior from the 
Comfort of the Computer Lab"

Abstract: The development of the theory of plate tectonics in the late 
1960's revolutionized our understanding of the solid Earth, providing a 
framework through which phenomena such as earthquakes and volcanoes can 
be understood as the surface manifestation of convective motion in the 
Earth's deep interior. Over the 40 years since the advent of this new 
paradigm, the exquisitely slow motions of the Earth's rocky mantle have 
been investigated using a variety of both geophysical and geo-chemical 
methods, and they are now thought to be intimately tied to the origin 
and evolution of life, as well as to a number of mass extinction events 
that nearly destroyed life on Earth. However, because the Earth's 
interior is physically inaccessible, we are unable to directly observe 
convection in the mantle, and therefore many basic questions about the 
morphology and timescale of these motions remain unresolved. In an 
effort to answer these questions, Earth scientists have increasingly 
turned to computational fluid dynamics (CFD) to develop models of mantle 
convection.

By treating the mantle as a highly viscous fluid, using material 
properties obtained from high-pressure, high-temperature mineral physics 
experiments and applying boundary and initial conditions derived from 
geophysical and geochemical observations, it is possible to produce 
meaningful CFD models of flow in the Earth's mantle. This type of 
computational modeling poses many challenges that are not normally 
encountered within more traditional applications of CFD. For example, 
the relevant physical processes being modeled cover a vast range of 
length scales (from the flow of magma along the boundaries of individual 
mineral grains (L < 0.000001 m) to the dimensions of individual 
convective cells (L > 1,000,000 m)), and pressures (from 0 GPa at the 
surface to >100 GPa at the base of the mantle). Furthermore, ductile 
deformation within the mantle is governed by a range of mechanisms, from 
diffusion creep (e.g., Coble, Nabarro-Herring) to dislocation creep, 
resulting in an effective viscosity that is highly non-linear and varies 
with temperature, pressure, composition, grain size and strain rate. 
Finally, mantle minerals undergo a variety of both solid-solid and 
solid-liquid phase transitions as they move around within the mantle, 
significantly altering their physical properties quite abruptly over 
very short distances. By way of illustration, a case study using a 
finite element CFD model in conjunction with a Lagrangian particle 
method to model the interaction between a thermo-chemically buoyant 
mantle plume and a mid-ocean ridge system (an analog for the creation of 
the Easter Island - Salas y Gomez seamount chain) will be presented.


Cheryl Endicott
Administrative Assistant
Center for Computational Science
3 Cummington Street
Boston, MA 02215
tel: 617-358-1470
fax: 617-358-2487
http://ccs.bu.edu

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