Seismological Observatories

This paper describes the instrumentation and principal operating characteristics of one of the seismological observatories being established in the United States under Project VELA UNIFORM. Seismic detectors are arranged in arrays to provide directional sensitivity, noise cancellation, and velocity filtering. They are located in remote, seismically quiet areas. Signals in the frequency range of 0.001 to 10 cps are detected, amplified, and recorded by four individual instrumentation systems, each exhibiting a frequency response tailored to permit studies of a specific type of earth motion. Seismic detectors used produce output power levels of approximately 10
^-5
watts when driven by normal earth background vibrations. Amplification is provided by galvanometer-phototube bridge amplifiers. Data are recorded on magnetic tape, 16-mm strip film and on heat-sensitive paper.