Paper published in JGR Solid Earth

Among the various slow earthquakes, tectonic tremors and low-frequency earthquakes (LFEs) are similar in that they can be observed with ordinary seismographs. A complex tremor signals is considered to be a series of simpler LFEs. It is easy to create a complex signal by supreposing simple signals. Is it possible to extract simple signals (LFEs) from complex signals (tremor)? This is the question of this research. If simple signals can be obtained, it opens the way to more advanced analysis. We call the extracted simple signal empirical low-frequency earthquake, eLFE.
In this study, we established an eLFE extraction method and demonstrated its effectiveness with examples. We were able to extract particularly good eLFE for tremors occurring beneath Okayama Prefecture. These microtremors are quite sensitive to tidal stress and occur only at low tide. With the new eLFE, we can detect many tremors that were buried in the noise, so the tidal dependence is much clearer than before. We also found out that the tremors occurred at 27 km, which is extremely shallow for tremors in this area. This is a new and difficult mystery in considering the plate subduction pattern in western Japan.

S. Ide, Empirical Low-Frequency Earthquakes Synthesized From Tectonic Tremor Records

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Illustration of the concept to make eLFE