The Plate Boundary Observatory (PBO) component of EarthScope will use the science of geodesy to measure the slow deformations in the Earth's crust that are driven by plate tectonics and magmatism. Specifically, the Global Positioning System (GPS) will be used to measure the movements of approximately 1000 points spanning the North America-Pacific plate boundary. These motions must be defined relative to a terrestrial reference frame. Such a frame requires the definition of its Cartesian coordinate axes (including origin, orientation, and scale) and the evolution of these axes in time, as well as precise models of the dynamic Earth. The motions of the Earth's surface due to tectonic processes the region spanning the North America-Pacific plate boundary (the focus of PBO) are most naturally expressed with respect to the stable interiors of either the North America or Pacific plates. A standard reference frame will therefore make it easier to interpret the geodetic data in terms of where the total budget of relative plate motion is being accommodated (for example, how much deformation can be inferred to be offshore?), and how deeply the plate boundary dynamics penetrate into the plate interior (is the Rio Grande Rift in New Mexico still active?). It will also provide a common frame by which to compare results from different analysis groups.
The goal of this proposal is to continue research to improve and further develop SNARF, with the eventual goal of handing off operational and regular maintenance to the joint auspices of the US and Canadian national geodetic surveys, as part of their joint remit to maintain the "North American Datum". The research of the SNARF Working Group is based on a volunteer effort and would come at no cost to this grant.
In terms of science benefits to EarthScope, the accurate realization of the terrestrial reference frame in terms of scientific models (rather than arbitrary convention) will add significant interpretive value to measured station motions. SNARF will provide a common framework for comparison of geodetic data and geophysical models. Defining a stable frame at the sub-millimeter level requires adequate characterization of Earth deformation processes across the "stable plate interior," a region that by definition is relatively unaffected by plate boundary process. This plate interior provides a stable platform from which to view plate boundary deformation.
In terms of broad impacts, the outcome of the SNARF workshops will be a published series of improved reference frames that accurately define the precise coordinates and time evolution of a set of stations representing "stable North America," thus enabling the broad scientific community to realize a common, accurate reference frame for their own research purposes. The SNARF Working Group will provide tools and products for performing model calculations and model-data comparisons in the EarthScope reference frame. The EarthScope initiative will significantly broaden the community using geodetic techniques to study the Pacific-North American plate boundary. Therefore the SNARF working group will not only develop an accurate and stable reference frame, but will also properly describe the use of that reference frame to this larger scientific community. Educational information on using the frame correctly will be made available online. From a national perspective, the SNARF research product will become the US and Canadian national reference frame "NAREF" (North American Reference Frame) to supercede the current definition of the North American Datum (NAD83). This will have profound implications for the US geospatial infrastructure, and all govermental and commercial enterprises who depend on it.
