2:15 PM - 2:30 PM
[SCG48-08] Detection of slow earthquakes in the microseism frequency band (0.05–1.0 Hz) by large-scale waveform stacking
Keywords:slow earthquakes, LFE, microseism, matched filter, Nankai subduction zone
In this study, we first report the observation of slow earthquake signals in the microseism frequency band in the western Shikoku region of the Nankai subduction zone, Japan, by stacking a lot of seismograms relative to the timing of high-frequency signals. First, we made synthetic template waveforms and conducted a matched filter analysis using these template waveforms (Ohta & Ide, 2017). Utilizing GPU, we detected about 700,000 events in continuous records at 9 Hi-net stations, operated by National Research Institute for Earth Science and Disaster Resilience, from 2005 to 2015. Their temporal distribution suggests that LFEs are episodic phenomena and their spatial distribution indicates the sources are concentrated in several patches, as reported by previous researches (e.g., Ohta & Ide, 2017). Then we stacked seismograms at the timing of these detected events, after band-pass filtering in different frequency bands (4-8 Hz, 2-4 Hz, 1-2 Hz, 0.5-1 Hz, 0.25-0.5 Hz, and 0.125-0.25 Hz). In-phase waveforms are confirmed in all frequency bands, despite low sensitivity of Hi-net seismometers in lower frequencies than 1 Hz. This result suggests that slow earthquakes radiate broadband signals without characteristic frequencies from 0.125 to 8 Hz.