Determination of Seismograph System Transfer Functions By Inversion of Transient and Steady-State Calibration Responses

The methods and software tools for the identification of the low-frequency portion of seismograph system transfer functions from transient (Dirac or step-impulse) calibration responses and of the high-frequency portion from steady-state (sinusoidal) calibration data are described. The presented procedures allow fast in-site determination of the overall Laplace transfer function of the analog stages of arbitrary seismograph systems. The developed identification software, which may also be employed for determining transfer functions in PAZ (p oles a nd zeros) format from steady-state calibration data given graphically or in the form of FAP (f requency- amplitude-p hase) triplets, has been made publicly available on the INTERNET. The paper is expected to prove useful especially for seismologists faced with the problem of specifying reliable calibration headers for digital upgrades of standard-class analog seismographs, for non-standard feedback-controlled seismograph systems, or for seismometric channels comprising inverse or simulation filters.