Data users have occasionally observed pulse-like transients in the long-period waveforms recorded at the Seismic Research Observatories (SRO) and at the Modified High-Gain Long-Period (ASRO) stations. In a recent paper, Dziewonski et al (1981) reported transients associated with earthquake signals record at some SRO stations, and the authors ascribed these transients to an unpredictable nonlinear system response. While some transients in the SRO and ASRO data are indeed generated by a nonlinear response (clipping), others are the result of linear processes. All event-associated transients are predictable in the sense that they are produced by large impulsive body-wave signals.
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A Note on Transients in the SRO and ASRO Long-Period Data