13:45 〜 15:15
[SVC34-P01] Daily analysis of the IMS hydrophone array signals toward the detection of submarine volcano activities
キーワード：ハイドロフォン、海底火山、モニタリング
Following previous studies, for example Metz (2021), it has become clear that the IMS hydrophone array is useful for the monitoring of submarine volcanic activities. Especially for the submarine volcanoes in the western Pacific Ocean, we started to routinely analyze the signals of the hydrophone array, H11S, that locates off-south coast of the Wake Island since July, 2022. The SeedLink server of the Incorporated Research Institutions for Seismology (IRIS) provides the hydrophone array data. The SeisComP5 software (Helmholtz-Centre Potsdam - GFZ German Research Centre for Geosciences and gempa GmbH, 2008) is used for receive and storage of the data, which makes daily miniseed files. Every morning, we process the 1-day hydrophone array data as follows; 1. Removing the instrumental response, 2. Band-pass filtering with cut-off frequencies of 4 and 8 Hz, 3. Semblance indicating the multi-channel correlation (Taner and Koehler, 1969) is calculated to determine the most appropriate incoming direction and apparent velocity across the array per 10-s time window without overlapping using intervals of 1° and 0.002km/s from 1.45 to 1.55 km/s, 4. The graphic results are posted on our internal website. The obtained maximum semblance values vary from 0.5 to 0.9, then we think that the values greater than or equal to 0.7 can be interpreted to be significant.
To date, we have detected some interesting signals although we have no certain information to confirm volcanic eruptions by ourselves. The most noticeable events were coming from the azimuth of 278° that consisted of roughly two time periods continuing more than 1 month as it occurred. The first series of signals started late September, 2022 and suddenly weakened around the middle of November, the second one is observed from early December, 2022 to early January, 2023. The azimuth is very close to Ahyi Seamount that the United States Geological Survey reported unrest of this volcano based on the satellite, hydrophone, and seismic observations since mid-October to mid-November and after the week of November 30 to December 6, which are summarized in the website of Smithsonian Institutions (https://volcano.si.edu/volcano.cfm?vn=284141). Another interesting events are signals from the azimuth of approximately 291° that is very close to Kaitoku Seamount and are lasting 2 to 3 hours that are intermittently observed between August, 2022 and January, 2023. The Japan Meteorological Agency issued a warning for this submarine volcano based on the detection of water discoloration at the sea surface observed by an airplane. To confirm the relationship between the hydroacoustic signals and volcanic activities, we should compare the waveforms and spectrum characteristics with those from known eruptions, e.g., Fukutoku-Okanoba.
To date, we have detected some interesting signals although we have no certain information to confirm volcanic eruptions by ourselves. The most noticeable events were coming from the azimuth of 278° that consisted of roughly two time periods continuing more than 1 month as it occurred. The first series of signals started late September, 2022 and suddenly weakened around the middle of November, the second one is observed from early December, 2022 to early January, 2023. The azimuth is very close to Ahyi Seamount that the United States Geological Survey reported unrest of this volcano based on the satellite, hydrophone, and seismic observations since mid-October to mid-November and after the week of November 30 to December 6, which are summarized in the website of Smithsonian Institutions (https://volcano.si.edu/volcano.cfm?vn=284141). Another interesting events are signals from the azimuth of approximately 291° that is very close to Kaitoku Seamount and are lasting 2 to 3 hours that are intermittently observed between August, 2022 and January, 2023. The Japan Meteorological Agency issued a warning for this submarine volcano based on the detection of water discoloration at the sea surface observed by an airplane. To confirm the relationship between the hydroacoustic signals and volcanic activities, we should compare the waveforms and spectrum characteristics with those from known eruptions, e.g., Fukutoku-Okanoba.