22 - Analysis of Digital Earthquake Signals

Progress in seismology has been mainly stimulated by the availability of plentiful and improved seismic data. The ability to collect, process, and analyze earthquake data is aided by rapid advances in electronics and digital computers. Modern digital seismograph systems consist of a cascade of analog and digital stages. The analog part of the system involves the seismometer, possible (pre-) amplifiers, and the analog antialias filter. The analog to digital (A/D) conversion is commonly based on the use of oversampling and decimation techniques. The output of the seismometer channels is first sampled at very high sampling frequencies (kHz range) and subsequently decimated to the desired sampling rate. Digital seismograms are merely sequences of numbers that must be processed in the context of analysis. This involves basic processes such as trace editing, integration, differentiation, Hilbert transformation of traces, rotation of components, and more advanced tasks such as frequency filtering of traces, detection and identification of different wavegroups, determination of exact onset times and true ground motion amplitudes, spectral analysis, and polarization analysis. Digital signal processing and system theory is considered an integral part of digital seismometry and seismology.

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