10:15 AM - 10:30 AM
[SVC26-06] Relationship between volcano-tectonic earthquakes and eruption styles at Aso Volcano
Keywords:Aso Volcano, Volcano-tectonic earthquake, Eruption Styles
Volcanic earthquakes are classified into A-type earthquakes, B-type earthquakes, explosive earthquakes, and microtremors based on their predominant frequency and waveform characteristics (Minakami, 1960). Type A earthquakes, also called volcano-tectonic earthquakes, have predominant high-frequency components in the 5 to 20 Hz range, with distinct P and S waves, and are believed to be caused by stress changes due to magma intrusion. Therefore, it is believed that the mode of occurrence of volcano-tectonic earthquakes preceding an eruption is one of the indicators of the movement of magma and other substances.
In recent years, the epicenters of many of the volcano-tectonic earthquakes at Aso Volcano have been determined by improving the observation network in the vicinity of the crater. However, the amplitude of continuous volcanic tremors before and during eruptions is large, and the details of seismic activity during these periods have not been clarified.
In this study, we detected volcano-tectonic earthquakes preceding eruptions that occurred in 2014-2021 at Aso Volcano using the Matched Filter method and investigated the relationship between seismic activity and eruption style.
We used some of the earthquakes whose hypocenters were determined by the JMA as template earthquakes. We calculated the cross-correlation function between them and continuous waveforms by shifting the waveform every 0.02 seconds, setting the threshold value at 0.2. The magnitude was calculated from the amplitude ratio of the detected earthquake to the template.
As a result, for example, more than 2,000 earthquakes of M>-1 were detected in the 20 days before the November 2014 eruption. This is about 50 times the number of earthquakes determined by the JMA. Phreatic, phreatomagmatic, and magmatic eruptions occurred at Aso volcano. We investigated the differences in precursory seismic activity by eruption style and found that differences by eruption style appeared in the number of detected earthquakes, temporal changes in magnitude, and integrated earthquake energy. In particular, the energy of precursor earthquakes was larger for phreatic, phreatomagmatic, and magmatic eruptions, in that order. Comparing the precursor earthquakes of phreatomagmatic eruptions in 2015 and 2016, the rate of change in the integrated earthquake energy immediately before the 2016 eruption, which was an explosive eruption, was about 50 times greater than that before the 2015 eruption.
As described above, it is clear that the mode of occurrence of precursor earthquakes varies greatly depending on the eruption style. This result suggests the predictability of eruption styles.
Acknowledgments
The present study was financially supported by the Ministry of Education, Culture, Sports, and Technology of Japan under its Earthquake and Volcano Hazards Observation and Research Program.
In recent years, the epicenters of many of the volcano-tectonic earthquakes at Aso Volcano have been determined by improving the observation network in the vicinity of the crater. However, the amplitude of continuous volcanic tremors before and during eruptions is large, and the details of seismic activity during these periods have not been clarified.
In this study, we detected volcano-tectonic earthquakes preceding eruptions that occurred in 2014-2021 at Aso Volcano using the Matched Filter method and investigated the relationship between seismic activity and eruption style.
We used some of the earthquakes whose hypocenters were determined by the JMA as template earthquakes. We calculated the cross-correlation function between them and continuous waveforms by shifting the waveform every 0.02 seconds, setting the threshold value at 0.2. The magnitude was calculated from the amplitude ratio of the detected earthquake to the template.
As a result, for example, more than 2,000 earthquakes of M>-1 were detected in the 20 days before the November 2014 eruption. This is about 50 times the number of earthquakes determined by the JMA. Phreatic, phreatomagmatic, and magmatic eruptions occurred at Aso volcano. We investigated the differences in precursory seismic activity by eruption style and found that differences by eruption style appeared in the number of detected earthquakes, temporal changes in magnitude, and integrated earthquake energy. In particular, the energy of precursor earthquakes was larger for phreatic, phreatomagmatic, and magmatic eruptions, in that order. Comparing the precursor earthquakes of phreatomagmatic eruptions in 2015 and 2016, the rate of change in the integrated earthquake energy immediately before the 2016 eruption, which was an explosive eruption, was about 50 times greater than that before the 2015 eruption.
As described above, it is clear that the mode of occurrence of precursor earthquakes varies greatly depending on the eruption style. This result suggests the predictability of eruption styles.
Acknowledgments
The present study was financially supported by the Ministry of Education, Culture, Sports, and Technology of Japan under its Earthquake and Volcano Hazards Observation and Research Program.