A seismograph complex consisting of short-period (SP), long-period (LP), and extended long-period (XLP) inertial and strain seismographs has been installed. Recordings are made on magnetic tape and photographic film. Routine magnifications on the 20-trace, 16-mm film recorders for all three components are: SP inertial, 500 K; LP inertial, 100 K. The noise levels permit equivalent magnifications on the strain seismographs. The complex provides seismic wave discrimination by directional response, which is independent of period, and by detection of differences in phase velocities between P, S, Love, or Rayleigh arrivals. The strain seismographs use 40-m-long rods and moving coil transducers with generator constants of 32,000 v/m/sec. They sense waves of 5 × 10-13 strain at 30 sec and reject the 2 × 10-8 earth-tide strain. A low-noise preamplifier drives a filter assembly which provides SP, LP, and XLP strain outputs. The complex is installed in an abandoned mine 50 km southeast of Phoenix, Arizona. Environmental control is provided by burial at a depth of about 110 m in a quartz diorite, by sealing the mine, and by insulating the seismometers.

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