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High gain broad band velocity sensors and accelerometers distributed throughout the Central and Eastern parts of the United States. Stations were initially operated under the Transportable Array (TA) network. Roughly 1 in 4 (hence the network code!) TA stations were selected to remain permanently in the central and eastern US. N4 was operated by ANF/UC San Diego from 2013-2018 and adopted by the USGS in 2019.