Multi-scale imaging of crustal and upper mantle structure beneath North America is a primary objective of the EarthScope program, as this is a starting point for quantifying the dynamical processes and history of the continent and its plate tectonic context. Another major objective is to analyze seismic sources, from microearthquakes to large ruptures, in an effort to understand the fundamental nature of earthquakes and their relationship to volcanic and tectonic events. Seismology provides one of the most important geophysical tools for imaging subsurface structure and recording earthquake signals. All EarthScope components involve seismological data acquisition; however, USArray is the principal seismological effort.

The progressive deployment of the Transportable Array across the 48 contiguous states and Alaska, and the pool of deployable seismometers in the Flexible Array, are key USArray activities and facilities. They will directly provide or allow acquisition of the requisite seismic data for imaging subsurface structure at multiple scales and for studying earthquakes in many environments. USArray also consists of permanent broadband seismic stations -- Reference Network -- that provide a large-aperture, fixed grid of observing sites essential for tying together the 70-km-spaced grid of sequential Transportable Array deployments. Data acquired by the USArray Magnetotelluric Facility supplements the seismic data by providing images of crustal and lithospheric conductivity structure. Transportable Array and Reference Network station distribution together provide unprecedented spatial coverage and uniformity of seismic wavefield sampling, enabling well-established and new seismological analyses to reveal deep Earth structure and to characterize earthquake sources throughout the continent. The scientific community will be able to conduct a host of research projects with Transportable Array data and with separately funded field deployments of Flexible Array sensors. Data collected from these EarthScope facilities are openly available to the scientific and educational communities.

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