The USArray component of EarthScope is a continental-scale seismic observatory designed to provide a foundation for integrated studies of continental lithosphere and deep Earth structure. Over the wide frequency range of seismic waves transmitted through the Earth (hundreds of seconds to ten cycles per second), the sensors of the permanent and transportable seismic and magnetotelluric arrays will resolve the smallest background motions at the quietest of sites, while remaining “on scale” for all but the largest ground motions from regional earthquakes. USArray consists of of a portable array (the Transportable Array) of 400 seismometers that have been deployed across the United States over a 10-year period. In addition a "flexible component" array will be available to be deployed in areas where a denser network of seismometers is required. The Magnetotelluric Transportable (MT) Array comprises shorter-period investigations at hundreds of sites in the continental USA. Data from these sites are collected on a regular schedule through recovery of data storage modules. The USArray project is guided by the USArray Advisory Committee. For more information about the USArray observatory, visit the USArray website.
USArray has a large traveling network of 400 high-quality, portable seismographs that are being placed in temporary sites across the United States in a rolling fashion. Station spacing is ~70 km (42 mi) called the Transportable Array. Transportable Array data are extremely useful for mapping the structure of Earth's uppermost 70 km. The array was initially deployed in the westernmost United States. Unless adopted and made into a permanent installation, after 18-24 months, each instrument is picked up and moved to the next carefully spaced array location to the east. When completed, over 2000 locations will have been occupied during this program. More information about adopting a station can be found at the USArray webpage on adopted stations.
Each of the Transportable Array stations consists of a three-component broadband seismometer with associated signal processing, power, and communications equipment. In the early phase of the experiment, significant effort was devoted to the design of the temporary vaults to house the instruments, which resulted in a configuration that provides both high-quality data and a data return of greater than 90%. Data from each station are continuously transmitted to the Array Network Facility at the University of California, San Diego, where initial operational and quality checks are performed, and then sent to the IRIS Data Management Center, where all data and associated metadata are archived.
Atmospheric Sensors on Transportable Array
TA stations are now being equipped with Atmospheric Sensors as of 2010. In addition to the Micro-Electro-Mechanical (MEMS) state-of-health barometer included within the vault at all installations since 2004, each station also features an external high frequency infrasound microphone (NCPA model IFS-4532) and a low to intermediate frequency microbarometer (Setra 278). The compared responses of all three instruments demonstrate the wide spectrum of atmospheric signals now recorded. More information about these sensors can also be found at the USArray website.
The magnetotelluric (MT) component of EarthScope’s USArray consists of both permanent and portable elements that measure naturally occurring electric and magnetic fields. The backbone component consists of seven permanent MT stations installed across the United States as a reference network. These data are integrated with other geophysical data to identify Earth's thermal structure and study the significance of fluids in the crust.
Twenty-one transportable MT systems complement the seven permanent MT stations. The transportable MT instruments are being used for deployments of approximately one-month duration on a nominal 70-km grid spacing for imaging of crustal and lithospheric conductivity structure in areas of special interest as proposed by the MT community and approved by NSF.The MT stations and instruments are operated and maintained by Oregon State University under a subaward from IRIS.