Very Low Frequency Earthquakes Modulate Regular Fast Earthquakes at the Central Range in Taiwan

Slow earthquakes in the form of tremors and low frequency earthquakes (low-frequency earthquakes) occur along the south-central range of Taiwan (Aguiar et al., 2017, ; Chao et al., 2012, ; Tang et al., 2010, ). This study detects discrete very low frequency earthquakes (VLFEs) using a grid-search moment tensor inversion algorithm (Ghosh et al., 2015, ; Hutchison & Ghosh, 2019, ). By applying a matched filtered technique, we have created a robust VLFE catalog for 3 years. The two VLFEs closer to the tremor-producing region show a temporal relationship, but the western VLFE is the most active among the three. Our VLFE catalog of high temporal resolution allows us to identify a significant increase in VLFE activities preceding earthquake swarms. An empirical comparison of the VLFE catalog with regional and local cataloged fast earthquakes reveals two such instances. We show that fluid migration from deeper to shallower crust explains this modulation of regular fast earthquakes by VLFEs.

Automated summary

This study reveals the occurrence of slow earthquakes, including tremors and low-frequency earthquakes, in the south-central range of Taiwan. Using a grid-search moment tensor inversion algorithm, very low frequency earthquakes (VLFEs) have been detected and a robust VLFE catalog for 3 years has been created. The study shows that there is a significant increase in VLFE activities preceding earthquake swarms and a correlation between VLFEs and fast earthquakes.