Abstract :
An extensive observatory for the measurement of long-period and ultra-long-period earth strains is being operated in a mine of the St. Joseph Lead Company at Flat River, Mo. The principal instruments in the observatory, three 100-foot quartz extensometers, provide electrical outputs proportional to earth strain. Each extensometer output consists of a number of components at various levels and frequencies-ultra-long-period secular strains, earth tides, earthquake waves and resulting free earth oscillations, microseisms, and high-frequency noise. The various signal components are to be recorded on instruments designed for their respective frequency bands. A system is designed to divide the signal into various frequency bands, filter out high-frequency noise, and provide compatibility between the signal components and their desired recorders in terms of power amplification and signal attenuation. The design is accomplished by use of active RC networks. A general description of the system is given in the form of specifications, block diagram, and required circuitry. There is also a discussion of some special problems associated with the hardware required. Finally, there is an evaluation of the system as to fulfillment of the stated objectives.
