Particular opportunities exist for high-resolution geodetic measurements near active faults and other regions of concentrated deformation. The multiagency EarthScope initiative (Box 6.2) will provide denser and more complete geodetic coverage of North America. The Plate Boundary Observatory (PBO) will expand existing geodetic networks with additional permanent Global Positioning System (GPS) stations and campaign-style observations, allowing secular deformations to be separated from the transient signals associated with individual earthquakes and filling major gaps in measurements of the western United States plate boundary deformation zone. GPS receivers located with millimeter precision over baselines of thousands of kilometers will be deployed to map long-term strain rates across the width of the Pacific-North American plate boundary, while arrays of GPS stations will be used to measure the short-term deformations associated with volcanoes and earthquakes (Figure 6.1). PBO will also augment the presently sparse array of borehole strainmeters and seismometers along the main active faults from Alaska to Mexico to better characterize transient tectonic strain signals. Another geodetic component of EarthScope is a satellite-based system for interferometric synthetic aperture radar (InSAR) imaging, proposed as a joint initiative between the National Aeronautics and Space Administration (NASA), National Science Foundation (NSF), and the USGS. InSAR will be used to map decimeter-level deformations of fault ruptures continuously over areas tens to hundreds of kilometers wide, as well as a range of other phenomena such as strain accumulation between earthquakes, magma inflation of volcanoes, and ground subsidence. InSAR data are currently available to U.S. researchers only from foreign satellite systems, and the amount of data available is limited. A dedicated U.S. mission with free access to InSAR data is needed to complement PBO and exploit the exceptional scientific promise of spatially contiguous deformation mapping.

No initiative comparable to ANSS and EarthScope exists to organize the gathering of much-needed geologic data. Current plans call for the sponsorship of geologic field work in conjunction with the deployment of all four instrumental components of the EarthScope system. It is crucial that this planning provide mechanisms for the compilation and synthesis of fault-related data using geographic information systems and other information technologies. Geologic data tend to be more diverse and require more complex semantics and descriptive metadata to place them in the appropriate scientific context than the instrumental time series of seismology and geodesy. Perhaps owing to this complexity, few resources have thus far been allocated to consolidate geological information into community data bases. There is now a critical need for a substantial data-basing effort, ideally as a component of larger efforts now being discussed in the new field of “geoinformatics.”



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