5:15 PM - 6:45 PM
[SSS05-P08] The waveform characteristics of volcanic earthquakes observed in Ogasawara Ioto
Keywords:Volcanic earthquakes, Ioto Island (Iwo-jima)
The Ioto Island (Iwo-jima) is a very active volcanic island in Japan, where the remarkable crustal deformation and high ground temperature have been continuously observed. Many volcanic earthquakes have been routinely detected on the Ioto Island since the National Research Institute for Earth Science and Disaster Resilience (NIED) began routine observations in 1982. Seismic activity on the Ioto Island is characterized by an increase in the number of events associated with increased volcanic activity such as the crustal deformation, which indicates that a relationship between seismic activity and eruption (Ueda et al. 2018). The first magmatic eruption was observed on the Ioto Island in July 2022, and understanding the interaction between volcanic earthquakes and eruption is important for disaster prevention in order to capture the precursor phenomena of future large-scale eruptions. In this study, we investigated the waveform characteristics of volcanic earthquakes on the Ioto Island and performed the classifications of volcanic earthquakes based on waveform cross-correlation.
Two types of events have observed on the Ioto Island: volcano tectonic earthquakes with predominant high-frequency components and low-frequency earthquakes dominated with low-frequency components. The source locations of them have been routinely determined by the NIED. Based on the catalog during the 2022-2023 period, we classified for volcano tectonic earthquakes with magnitude 0 or more. A total of five three-component velocity seismographs were used, consisting of three stationary stations installed by the NIED and two stations by the Japan Meteorological Agency. We calculated the cross-correlation coefficients for each station and component of each event pair, and the sum of them was used as the index for clustering. After applying a 2-15 Hz band-pass filter, we calculated cross-correlation functions using the 8-second window from the theoretical P-wave arrival, and the maximum value was regarded as the correlation coefficient for one component at each station. We used DBSCAN (Ester et al. 1996) as the clustering algorithm in this study.
As a result of analysis, volcano tectonic earthquakes were classified into 25 clusters. The observed waveforms included in the same cluster are very similar, indicating that there are many characteristic volcanic earthquakes in the Ioto Island. This result suggests that repeated ruptures occur at small faults localized at certain locations and that the increase in the number of earthquakes prior to the eruption reflects the injection of volcanic fluids. In addition, the complicated waveforms with various converted waves in addition to P and S waves imply that the Ioto Island has a highly heterogeneous inner structure.
Two types of events have observed on the Ioto Island: volcano tectonic earthquakes with predominant high-frequency components and low-frequency earthquakes dominated with low-frequency components. The source locations of them have been routinely determined by the NIED. Based on the catalog during the 2022-2023 period, we classified for volcano tectonic earthquakes with magnitude 0 or more. A total of five three-component velocity seismographs were used, consisting of three stationary stations installed by the NIED and two stations by the Japan Meteorological Agency. We calculated the cross-correlation coefficients for each station and component of each event pair, and the sum of them was used as the index for clustering. After applying a 2-15 Hz band-pass filter, we calculated cross-correlation functions using the 8-second window from the theoretical P-wave arrival, and the maximum value was regarded as the correlation coefficient for one component at each station. We used DBSCAN (Ester et al. 1996) as the clustering algorithm in this study.
As a result of analysis, volcano tectonic earthquakes were classified into 25 clusters. The observed waveforms included in the same cluster are very similar, indicating that there are many characteristic volcanic earthquakes in the Ioto Island. This result suggests that repeated ruptures occur at small faults localized at certain locations and that the increase in the number of earthquakes prior to the eruption reflects the injection of volcanic fluids. In addition, the complicated waveforms with various converted waves in addition to P and S waves imply that the Ioto Island has a highly heterogeneous inner structure.