The relevance of high-frequency analysis artifacts to remote triggering

Zhigang Peng, Leland Timothy Long, & Peng Zhao

Published 2011, SCEC Contribution #1559

Recently studies have shown that shallow earthquakes and deep tremor can be triggered by surface waves of large distant earthquakes. An effective way to demonstrate triggered seismicity is spectrogram display, where the triggered event is characterized with elevated high-frequency spikes during large-amplitude surface waves. Here we show that an improper way to compute the spectrogram could also introduce high-frequency energy that tracks the zero crossings of the broadband signals, mimicking the behavior of remotely triggered seismic activity. The high-frequency signals only show in the spectrogram of broadband recording, but not in the band-pass-filtered seismogram, or the spectrogram of co-located short-period recording, suggesting that they are caused by a processing artifact. Such signals are mostly generated during the Fourier transform if the window length is shorter than the predominant periods of the surface waves. We introduce several procedures that can eliminate the artificial high-frequency signals in the spectrogram plot.

Citation
Peng, Z., Long, L., & Zhao, P. (2011). The relevance of high-frequency analysis artifacts to remote triggering. Seismological Research Letters, 82(5), 654-660. doi: 10.1785/gssrl.82.5.654.