Geoscience Reference
In-Depth Information
observations from many disciplines. In the study of active faulting, for example,
geologists map faults, geomorphologists date fault motion, seismologists locate
earthquakes, geodesists measure deformations, and rock mechanists investigate
the frictional properties of fault materials. Numerical simulations of active fault
systems attempt to bring together these various types of observations in the
context of a self-consistent model. The success of such a model in reconciling
diverse types of information can thus be used to confirm the compatibility of the
data from different disciplines and ferret out inconsistencies, in addition to giving
researchers confidence in their underlying assumptions and hypotheses.
The problems of relating observations and simulations are particularly
difficult in the research fields sponsored by EAR, because the solid Earth is
characterized by physical and chemical processes that generally have shorter
ranges and longer durations than the fluid systems investigated by meteorologists
and oceanographers. Two representative examples illustrate this point. First, the
global circulation time is on the order of a month for the troposphere and about a
thousand years for the deep ocean, but it exceeds 100 million years for mantle
convection. Second, chemical diffusion is an important process both above and
below the Earth's solid surface, but the diffusivities of the common cations are 10
to 15 orders of magnitude lower in solid rock than in liquid water.
Fluid-bearing geosystems in the Critical Zone and upper crust—rock bodies
containing magmas, petroleum, or water—present special challenges in this
regard because the relevant processes range from the atomic level (i.e., sorption-
desorption on mineral surfaces) to tens of kilometers or more. Their elucidation
requires systematic, coordinated observations involving multiple disciplinary
techniques that are spatially dense and extend over long time intervals. Field
studies of this type are often most efficiently accomplished through the joint
efforts of several groups of investigators in carefully chosen localities.
Measurements and experiments within such “natural laboratories” may have to
continue for many years. This mode of research is becoming more common as the
trend toward the quantification of geological processes and system-level
behaviors accelerates. Hence, the demand for basic research funds to invest in
natural laboratories can be expected to increase.
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