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[SCG54-P04] Activity of deep low-frequency earthquake at the period of the 2018 eruptions
Keywords:Deep low-frequency earthquake, Kirishima volcano, Matched filter technique
Deep low-frequency (DLF) earthquakes, of which waveforms are characterized by predominant frequencies around 1–8 Hz, occur at the depth of 10–50 km in the volcanic regions. At the Kirishima volcano, the rate of DLF earthquakes at the depths of 20–25 km increased in the two years before and after the 2011 eruption of the volcano (Kurihara et al., 2019). In contrast, during the 2018 eruption, there appears to be only a weak activity of DLF earthquakes, based on the catalog constructed by Kurihara et al. (2019).
To describe it more precisely, we applied a new matched filter method developed by Kurihara et al. (2021) to waveforms of a single station from 2017 to 2018. The new method can accurately detect microearthquakes using a single station, by adopting mutual information (MI) in addition to CC to measure the similarity between the template and target waveforms. We used waveforms recorded at the N.SUKH station (Hi-net) with a distance of about 20 km from the volcano, operated by the National Research Institute for Earth Science and Disaster Resilience (NIED). After the detection, we visually checked the waveforms of each potential detection and removed some misdetections (false positives) caused by surface waveforms of teleseismic events and shallow low-frequency volcanic tremors. For the comparison, we performed the same analysis for waveforms from 2010 to 2011.
As a result, a total of 514 events were detected in the two-year period of 2017–2018, while we detected more than 2000 events in the two-year period of 2010–2011. After the visual checking, we finally identified a total of 76 DLF events. Although the number of events within this period was much less than that of 2010–2011, we can find two clusters in March and July 2017, respectively. The cluster in July 2017 seems to coincide with the starting of the crustal deformation associated with the inflation of magma reservoir at the depth of 10 km. In addition, the rate of the DLF earthquakes slightly increased after the 2018 eruption. Although the rate of DLF earthquakes associated with the 2018 eruption was much lower than that in 2010-2011, the weak activity of the DLF earthquakes implies a connection from deep magmatic fluid to shallow volcanic unrest observed in the period of the 2018 eruptions.
To describe it more precisely, we applied a new matched filter method developed by Kurihara et al. (2021) to waveforms of a single station from 2017 to 2018. The new method can accurately detect microearthquakes using a single station, by adopting mutual information (MI) in addition to CC to measure the similarity between the template and target waveforms. We used waveforms recorded at the N.SUKH station (Hi-net) with a distance of about 20 km from the volcano, operated by the National Research Institute for Earth Science and Disaster Resilience (NIED). After the detection, we visually checked the waveforms of each potential detection and removed some misdetections (false positives) caused by surface waveforms of teleseismic events and shallow low-frequency volcanic tremors. For the comparison, we performed the same analysis for waveforms from 2010 to 2011.
As a result, a total of 514 events were detected in the two-year period of 2017–2018, while we detected more than 2000 events in the two-year period of 2010–2011. After the visual checking, we finally identified a total of 76 DLF events. Although the number of events within this period was much less than that of 2010–2011, we can find two clusters in March and July 2017, respectively. The cluster in July 2017 seems to coincide with the starting of the crustal deformation associated with the inflation of magma reservoir at the depth of 10 km. In addition, the rate of the DLF earthquakes slightly increased after the 2018 eruption. Although the rate of DLF earthquakes associated with the 2018 eruption was much lower than that in 2010-2011, the weak activity of the DLF earthquakes implies a connection from deep magmatic fluid to shallow volcanic unrest observed in the period of the 2018 eruptions.