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[SVC31-02] Relationship between volcanic activity and shallow volcanic earthquakes at Owakudani, Hakone volcano
Keywords:Hakone volcano, Volcanic earthquake, Matched filter technique, Phreatic eruptions
Many earthquakes occur at the Hakone volcano and swarm earthquakes are often observed. Recently, swarm seismic activity was observed during phreatic eruptions in 2015 and volcanic unrest in 2019, and these earthquakes are distributed from 0 km to 5 km depth around Owakudani, Komagatake, and Lake Ashinoko (cf. Harada et al. 2015, Yukutake et al. 2020). In addition, many volcanic earthquakes also occur in other period. Earthquakes in Hakone volcano are observed by Hot Springs Research Institute of Kanagawa prefecture (called as HSRI in bellow).
In May and July 2022, small earthquakes which were observed at only few stations near the Owakudani. These earthquakes were inferred to have occurred near surface based on the few observed stations and apparent velocity. The arrival phases of P and S waves were not clear. The hypocentral location is estimated at the depth of 0 km around the Owakudani. To investigate the activity of this earthquake, we used matched filter technique to detect the earthquake and reveal the activity history in the one year of 2015, when the phreatic eruption occurred, and four years from 2019 to 2022. Four stations of HSRI were used in the analysis. 73 earthquakes occurred in 2019-2022 were used as templates.
The results of the year of 2015 revealed a significant increase in the shallow earthquakes between April and July 2015. This period corresponds roughly to the period May and June 2015, when earthquake swarms and a small eruption actually occurred. In order to confirm that the earthquakes occur actually in shallow depths, we focused on the cumulative number of events where the ratio of the amplitudes of the OWD station near Owakudani and the TNM station about 6 km far from Owakudani exceeds 100. The earthquake may occur at very shallow region. We found that the earthquakes with the high amplitude in OWD station were detected in the period of the swarm activity. This result suggests that the earthquakes associate with volcanic activities.
The results from 2019 to 2022 show that the earthquakes were increased from May 2022 to July 2022. The earthquakes were not activated in 2019, when the volcano was more active. There is no other observation, such as crustal deformation or deep earthquakes, which suggest volcanic activity between May 2022 and July 2022, when the shallow earthquakes were activated. Therefore, the result suggests that these earthquakes were triggered by hydrothermal activity near the surface. The results of the two periods suggest that this earthquake may be activated by hydrothermal activity near the surface. The hydrothermal activity sometimes corresponds to volcanic activity, however, sometimes do not correspond to volcanic activity.
In May and July 2022, small earthquakes which were observed at only few stations near the Owakudani. These earthquakes were inferred to have occurred near surface based on the few observed stations and apparent velocity. The arrival phases of P and S waves were not clear. The hypocentral location is estimated at the depth of 0 km around the Owakudani. To investigate the activity of this earthquake, we used matched filter technique to detect the earthquake and reveal the activity history in the one year of 2015, when the phreatic eruption occurred, and four years from 2019 to 2022. Four stations of HSRI were used in the analysis. 73 earthquakes occurred in 2019-2022 were used as templates.
The results of the year of 2015 revealed a significant increase in the shallow earthquakes between April and July 2015. This period corresponds roughly to the period May and June 2015, when earthquake swarms and a small eruption actually occurred. In order to confirm that the earthquakes occur actually in shallow depths, we focused on the cumulative number of events where the ratio of the amplitudes of the OWD station near Owakudani and the TNM station about 6 km far from Owakudani exceeds 100. The earthquake may occur at very shallow region. We found that the earthquakes with the high amplitude in OWD station were detected in the period of the swarm activity. This result suggests that the earthquakes associate with volcanic activities.
The results from 2019 to 2022 show that the earthquakes were increased from May 2022 to July 2022. The earthquakes were not activated in 2019, when the volcano was more active. There is no other observation, such as crustal deformation or deep earthquakes, which suggest volcanic activity between May 2022 and July 2022, when the shallow earthquakes were activated. Therefore, the result suggests that these earthquakes were triggered by hydrothermal activity near the surface. The results of the two periods suggest that this earthquake may be activated by hydrothermal activity near the surface. The hydrothermal activity sometimes corresponds to volcanic activity, however, sometimes do not correspond to volcanic activity.