Filtering Characteristics of Multiple Seismometer Groups, Long Cables, and the Amplifier Input Impedance

The vertical component of ground velocity to which the moving coil seismometer is sensitive undergoes significant filtering before appearing as the input voltage drive for the seismic amplifier. The characteristics of this filter are established by the seismometer parameters, the cable resistance and capacitance, and the input impedance of the amplifier. A solution for both the frequencyand time-domain behavior of this filter has been developed and programmed for a digital computer. The results of applying this network solution to field recording systems serve as a significant guide to the selection of seismometers and their connection pattern, amplifier input system design, and cable constants. Typical and illustrative solutions are given for the amplifier input voltage resulting from an impulse in vertical ground velocity at the seismometer location.