Between 2004 and 2013 the Transportable Array moved eastward across the contiguous U.S., with each station operating about 2 years, and is now being redeployed to Alaska. The spacing between each station is 70 km (~42 miles) for the lower-48 and 85 km for Alaska. Similarly the Magnetotelluric Array has been operating stations in similarly spaced footprints across the Pacific Northwest, Midwest, and Southeast. Flexible Array experiments have been distributed across the U.S. in a variety of different configurations. To find out where USArray stations are right now, navigate lists and maps available here.
Several factors affect where we construct and install Transportable Array stations. Some questions we ask are: Is the site accessible with two-wheel drive vehicles? Is the site near a busy road, railroad, or other sources of noise? Is the site likely to be subject to vandalism? Will the site have direct, unobstructed sunlight? Regarding when a station will be installed, we prefer to take advantage of a season where weather conditions will be optimal.
The instruments of the Flexible Array are deployed as prioritized through the peer review process of the scientific community. These transient arrays provide high-resolution, short-term observations of key geologic targets within the footprint of the larger Transportable Array. The Flexible Array uses high-density sensor spacing and both natural and artificial sources of seismic energy.