Basic Earth Science and Society - Basic Research Opportunities in Earth Science - page 20

constraints on how the hydrological cycle operates. Samples from more recent
deep drilling of a Hawaiian volcano are yielding a better understanding of the
physics and chemistry of deep-seated sources of volcanism. Deep drilling of
active faults such as the San Andreas offers great promise for elucidating
earthquake processes, including the role of fluids in fault mechanics.
Earthquakes and controlled (artificial) seismic sources generate a variety of
elastic waves that encode an immense amount of information about the Earth
through which they propagate. This illumination can be captured on arrays of
seismic sensors and digitally processed into three-dimensional images of Earth
structure and moving pictures of earthquake ruptures. Seismology thus gives
geoscientists the eyes to observe fundamental processes within the planetary
interior. In the past 15 years, the NSF-funded Incorporated Research Institutions
for Seismology (IRIS) have provided new tools of seismological imaging to a
broadly based user community, and the results have transformed the study of the
solid Earth. The USArray program, a part of the recently proposed EarthScope
initiative, would greatly extend these seismological capabilities, allowing the
Earth beneath North America to be imaged at much higher resolution than with
existing instrumentation (see Chapter 2 , Box 2.2 ).
Measurements of the gravitational potential and electromagnetic fields
constrain the mass variations and electrical properties of the interior, information
that is complementary to seismological imaging and critical to its interpretation in
terms of dynamic processes. The upcoming Gravity Recovery and Climate
Experiment (GRACE) mission, for example, will measure the time-dependent
component of gravity and thereby significantly advance studies of postglacial
rebound, structure, and evolution of the crust and lithosphere; the hydrologic
cycle; and mantle dynamics and plumes. 15
Geophysical interpretation also requires the understanding of Earth materials
at the extreme pressures, high temperatures, and special chemical environments
of the deep interior. Only by characterizing materials at these conditions can one
translate the observations of remote sensing and geochemical sampling into a
concrete understanding of the current state, evolution, and ultimately, origin of
the planet. State-of-the-art laboratories and apparatus are needed for this purpose.
Both static and dynamic (shockwave) methods are employed, with the NSF
Center for High-Pressure Research (CHiPR) being a leader for the United States
in the application of synchrotron facilities to static high-pressure experiments
with diamond-anvil cells and multianvil presses. High-pressure techniques
developed for the study of the deep interiors of the Earth and other planets now
allow the
15 Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth
and Its Fluid Envelope, National Academy Press, 112 pp., 1997.