[SVC45-P03] Detection of long-period volcanic earthquakes using continuous wavefield processing system
Keywords:volcanic earthquake, seismic wavefield, realtime processing
Our continuous wavefield processing system is being developed to analyze continuous seismic wavefield using seismic interferometry, back projection, and spectral analyses. The back projection analysis in the system is based on the slant stack of wavefield assuming predefined virtual sources, and it is almost similar to the Source-Scanning Algorithm by Kao and Shan (2004). Because the dominant period of long-period events occurring at shallow depth is around 10 s and the observed wavefield at far stations is dominated by surface waves, we stack the observed wavefield assuming the propagation of Rayleigh wave from the virtual source. To obtain the travel times of Rayleigh wave propagating between the focal area and far stations, we use the ambient noise seismic interferometry between the station in the vicinity of postulated source location and far stations.
In this study, to verify the detectability of long-period earthquakes and the robustness of the method, we apply this processing to the analysis of long-period events at Zao volcano. In the analysis, we use the vertical component data at stations operated by Tohoku Univ., JMA, and NIED, and apply the method for several frequency bands. As the result, we find that the method successfully detects almost all the events which are detected by manual inspection, and the estimated source energy well correlates with the amplitude of long-period events observed at nearby stations.
We are now operating the continuous back projection analysis at three volcanoes (Zao, Azuma, and Asama) as a trial, and we expect further optimization of the processing will contribute the monitoring of volcanic activities as well as the systematical detection of long-period events.
Acknowledgments: This work was supported by MEXT Integrated Program for Next Generation Volcano Research and Human Resource Development.