Statistical properties of low-frequency earthquakes triggered by large earthquakes in southern Taiwan

• We examine the relationship between triggered tremors and low-frequency earthquakes.
• Low-frequency earthquakes could be triggered repeatedly by large distant earthquakes.
• Low-frequency earthquake is a basic element of triggered tremor.
• Locations of low-frequency earthquakes suggest that the source structure is complex.
• We analyze statistical properties of LFEs.

The recent discovery of triggered tremors (TTs) and low-frequency earthquakes (LFEs) in various tectonic environments provides an opportunity for studying the fundamental properties and physical mechanisms of deep tectonic tremor. Here, we quantify the relationship between TTs and LFEs beneath the Central Range in southern Taiwan and their statistical properties during the teleseismic waves of six large distant earthquakes. Using waveforms of 11 LFEs triggered by the 2005 Mw 8.6 Nias earthquake as templates, we scan through 12 hours of waveform data around six mainshocks and identify a total of 783 LFEs. The LFEs were mainly located in a compact region between 12 and 36 km in depth near the Chaochou–Lishan Fault. Most of LFEs occurred within TT during the passage of large-amplitude surface waves, and the increase of the LFE rate during the surface waves is statistically significant. The LFE rates do not follow an Omori's type decay, but rather abruptly return to the background rate immediately after the surface-wave passage. These findings suggest that LFEs do not trigger any additional LFEs at later times and are primarily driven by an external forcing. Our observations are consistent with the inference that TTs consist of many reoccurring LFEs.