EXPLORING WESTERN NORTH AMERICA WITH EARTHSCOPE: THE BEST PLACE TO STUDY PLATE BOUNDARY PROCESSES

Continents tend to be inactive bodies that hold the record of their construction in their structure. The western North American plate boundary however, is one of those places where continental construction - both the addition of new crust and the reprocessing and fabrication of older crust - is occurring now. Scientifically, the area offers as a diversity of tectonic, volcanic and continental evolutionary elements. The processes at work in the western U. S are diverse: gravitational collapse drives extension of the Basin and Range; transform Pacific-North America interaction imposes a broad shear zone across the western side of the margin; magmatism associated with subduction beneath the Pacific Northwest and Alaska is "continentalizing" oceanic lithosphere; and Yellowstone hotspot magmatism is reconstructing large portions of the continental interior. Active faults and volcanos, common throughout the western U.S., are the agents of this activity and the mountains, sedimentary basins and reconstructed crust are its products. In the western U.S., ancient features related to active processes provide a tie from the past to the present to the future. We suggest that western N. America is scientifically the best and most readily accessible place on Earth to study active and ancient continental evolution, i.e., a plate boundary laboratory of EarthScope. EarthScope will collect multi-disciplinary data to study system-level plate-scale tectonic interactions to small-scale processes such as faults and volcanoes. Continuously recording GPS receivers and borehole strain meters will measure the contemporary deformation field. A network of seismographic stations will be deployed to provide information on earthquakes and volcano processes and will provide a 3-D geologic image deep into the mantle. A 4-km deep observatory bored into the San Andreas fault will provide rock samples and conditions in which earthquakes occur. These data will be integrated into community 3-D geodynamic models along with a full scale of geologic information to understand plate boundary processes and continental evolution. EarthScope’s scientific goals, plans, and opportunities will be presented.