Science Opportunities - Basic Research Opportunities in Earth Science - page 59

EarthScope Project, a 10-year study of the North American continent ( Box 2.2 ).
A prime motivation for the project is the need for geological mapping in the third
dimension, which requires imaging of the subsurface with enough horizontal
resolution to observe how individual surface features— rift valleys, tectonic
blocks, major faults—are expressed at depth. Essential features such as mountain
belts, sedimentary basins, and province boundaries come into view only when the
horizontal resolution of the images is comparable to the crustal thickness itself,
about 30 km ( Figure 2.13 ). One of the observational components of EarthScope,
USArray, will take advantage of the recent advances in seismic technology that
can achieve this resolution. These seismological observations will be a principal
source of new structural information for modeling and interpreting a vast array of
existing geological and geochemical data.
A second component, SAFOD, will extend observations in the third
dimension by drilling into the San Andreas Fault, allowing direct sampling and in
situ measurements of crustal rocks and fluids under conditions where the
mechanics and chemistry of active deformation are very poorly known. SAFOD
will provide unique data on the composition and physical properties of fault zone
materials at depth, the constitutive laws governing fault behavior, the stress
conditions under which earthquakes initiate and propagate, and the role of fluids
in active faulting.
Two additional components, the Plate Boundary Observatory (PBO) and the
InSAR initiative, will improve the geodetic observations within the North
America-Pacific plate boundary zone of deformation. Continuously recording
GPS station arrays and satellite-based InSAR imaging will observe small
transient strains in the crust, complementing the more widely spaced GPS
measurements made during the past 15 years. InSAR is a particularly promising
technology that has the potential to monitor surface changes associated with a
wide range of geologic phenomena and natural hazards—earthquakes, volcanoes,
and landslides—as well as glacier flow and ground subsidence caused by fluid
withdrawal. The InSAR component of EarthScope will increase the availability
of synthetic aperture radar data to U.S. researchers, which is currently much too
limited for research needs. 10
10 The amount of data that can be obtained from the European Space Agency's ERS and
the Canadian RADARSAT satellites are limited, hindering application to geophysical
problems. For a discussion of conditions on the use of SAR data by U.S. researchers, see
Review of NASA's Distributed Active Archive Centers, National Academy Press,
Washington, D.C., 233 pp., 1998.