Science Opportunities - Basic Research Opportunities in Earth Science - page 65

Seismology
The academic community undertook an ambitious program to modernize the
collection of seismological data by establishing the Incorporated Research
Institutions for Seismology (IRIS), initiated under NSF support in 1984. The
growth in the Global Seismic Network has been phenomenal and has prompted
other countries to participate in this expansion. The enlarging archive of
seismographic recordings has helped to clarify the structure of the Earth's
interior, substantially increasing, for example, the resolution of tomographic
imaging ( Figure 2.14 ). These images provide a snapshot view of the internal
dynamics that control the geological evolution of the planet.
The USArray component of the EarthScope initiative ( Box 2.2 , Figure 2.15 )
will greatly enhance the ability to investigate Earth's interior at many scales: (1)
the mantle structure beneath North America will be resolved to horizontal scales
of 50-200 km down to a depth of at least 1000 km; (2) the topography and
transition widths of major seismic discontinuities in the upper mantle will be
resolved to tens of kilometers; and (3) the CMB structure beneath portions of the
Pacific, the Caribbean, and near the Aleutians will be mapped with similar
resolution. USArray will also provide the high-quality, high-density data sets
needed for the joint interpretation of compressional and shear velocities.
Observatory-type studies on a planetary scale offer a number of important
scientific opportunities. Large gaps exist in the global network of seismic stations
that cannot be filled with island stations, particularly in the eastern Pacific and
Southern Oceans. Improved spatial sampling provided by long-term, broadband
seismic stations at approximately 20 ocean sites would provide much improved
tomographic imaging of the structure of the lower mantle (especially in the
Southern Hemisphere), the CMB, and subducting slabs and rising plumes of
mantle circulation. Seafloor observatories will also provide close-in data for
studies of oceanic earthquakes, which differ in substantial and poorly understood
ways from continental earthquakes. A new program sponsored by the Ocean
Sciences Division of NSF (Dynamics of Earth and Ocean Systems) advocates
such an undertaking.
Increased computational speeds, coupled with high-speed networks and
languages capable of managing parallel computations, allow calculations to be
made at higher resolution and with fewer compromises than ever before. These
information technologies will play a central role in the processing of very large
seismic data sets and the numerical simulations of seismic wave-fields in
heterogeneous, anisotropic media needed for data interpretation. These efforts
could be facilitated through a better coupling between EAR and NSF information
technology programs.