17:15 〜 19:15
[SCG45-P36] Spatio-Temporal Variability of Very Low-Frequency Earthquakes: A Novel Detection Approach Using Waveform Correlation
Very low-frequency earthquakes (VLFEs) have been observed along subduction zones, including the Nankai Trough and the Japan Trench, both of which host megathrust earthquakes along the plate interface. In the Nankai Trough, the VLFEs occur both updip and downdip of the seismogenic zone, suggesting that VLFE activity often regarded as a proxy for slow earthquakes may be associated with stress accumulation in regions susceptible to future coseismic slip. Therefore, continuous monitoring of the spatio-temporal evolution of VLFEs is crucial for understanding the underlying physical process in subduction zones.
Previous studies have mapped the distribution of VLFEs using various detection methods. In the updip side of the seismogenic zone, VLFEs are localized within specific areas and exhibit showing clear hypocenter migration, while in the downdip side tend to form a belt-like distribution. However, detailed spatio-temporal characteristics of VLFEs remain poorly constrained due to the limited spatial coverage and duration of high-density seismic observations. Addressing this gap requires the development of novel detection techniques that enable long-term monitoring, even with relatively sparse seismic networks.
In this study, we propose a new VLFE detection method based on direct waveform correlation. Unlike conventional approaches such as matched-filter and envelope-correlation techniques, our method calculates waveform similarity at individual stations, allowing for the detection of VLFEs with fewer constraints. To investigate the detailed spatio-temporal characteristics of VLFE activity, we applied this method to the nationwide broadband seismic network, F-net, and investigated shallow VLFE activity.
Our analysis focused on VLFE activity offshore of the Kii Peninsula in September 2004. We identified a marked increase in VLFE activity following the Mw 7.4 earthquake on September 5, 2004. Additionally, our results reveal periodic fluctuation in VLFE activity, characterized by intermittent quiescence lasting 1–2 hours approximately every half-day. Future studies should refine station selection and enhance detection techniques to further improve the accuracy and resolution of VLFE monitoring.
Previous studies have mapped the distribution of VLFEs using various detection methods. In the updip side of the seismogenic zone, VLFEs are localized within specific areas and exhibit showing clear hypocenter migration, while in the downdip side tend to form a belt-like distribution. However, detailed spatio-temporal characteristics of VLFEs remain poorly constrained due to the limited spatial coverage and duration of high-density seismic observations. Addressing this gap requires the development of novel detection techniques that enable long-term monitoring, even with relatively sparse seismic networks.
In this study, we propose a new VLFE detection method based on direct waveform correlation. Unlike conventional approaches such as matched-filter and envelope-correlation techniques, our method calculates waveform similarity at individual stations, allowing for the detection of VLFEs with fewer constraints. To investigate the detailed spatio-temporal characteristics of VLFE activity, we applied this method to the nationwide broadband seismic network, F-net, and investigated shallow VLFE activity.
Our analysis focused on VLFE activity offshore of the Kii Peninsula in September 2004. We identified a marked increase in VLFE activity following the Mw 7.4 earthquake on September 5, 2004. Additionally, our results reveal periodic fluctuation in VLFE activity, characterized by intermittent quiescence lasting 1–2 hours approximately every half-day. Future studies should refine station selection and enhance detection techniques to further improve the accuracy and resolution of VLFE monitoring.