ANALOG COMPUTATION OF TIME-VARYING POWER SPECTRA OF SEISMIC WAVES
Abstract
An analog computing technique for measuring time varying power spectra of seismic signals was developed. The signal to be analyzed is re corded on a magnetic-tape loop so that it may be played back repeatedly, and the analog com puting equipment, connected to the output of the tape-playback apparatus, measures as a func tion of time the power level at a different specific frequency for each passage of the tape. The concept of a time-varying spectrum is de veloped and the theory of the analysis method used is derived. It is shown that in measuring time-varying power spectra, there is a theoret ical relationship between the time resolution and frequency resolution such that any adjustment which gives an improvement in one results in a degradation of the other. This conflict is not caused by equipment limitations, but instead is a result of theoretical relations between the time and frequency domains. A plot of the energy- or power-density spectrum of a seismic wave is not smooth, but instead shows a number of sharply defined peaks. It was found experi mentally that a filter bandwidth of 2 1/2% for the analyzing apparatus gave satisfactory fre quency resolution without seriously degrading time resolution when magnetic- tape seismograms were analyzed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1963
- Accession Number
- AD0403084
Entities
People
- Raymond E. Crabtree
- Vernon L. Larrowe
Organizations
- University of Michigan