[A-OS16] Global ocean observing systems, their status, research results and future perspective

[AOS16-04] Two-year seismic observation by hydrophone floats

*Masayuki Obayashi¹, Hiroko Sugioka², Junko Yoshimitsu¹ (1.Japan Agency for Marine-Earth Science and Technology, 2. Department of Planetology, Kobe University)

Keywords:float, hydrophone, Pacific Plume, Nishinoshima, seismic observation

A new international joint seismic observation project using autonomous float instrument (MERMAID) started from 2018. More than 50 MERMAID instruments were deployed in the south Pacific to study the mantle beneath the South Pacific Superswell, broad seafloor anomalously elevated and concatenated by several volcanic island (hot spot) chain. The MERMAID is an autonomous robotic float equipped with a hydrophone and drifts passively at 1,500–2,000 m depth until an earthquake signal is detected. If this is identified as a strong P wave, the MERMAID ascends at speed of 10 cm/s for transmission of the recorded waveform within time window of a hundred seconds before and after the P wave arrival as well as its global positioning system coordinates at the surface. 9 Japanese MERMAIDs out of them were deployed in the winter and summer of 2019. So far, we obtained approximately 1700 P-wave records from about 480 earthquakes. One of the MEMRAID is recoding continuous pressure to search for a possibility to detect pressure changes due to tsunamis. Additionally, we launched two MERMAIDs to monitor the seismic activities of Nishinoshima volcano island that became active since 2013. We will introduce how we operate the Mermaid floats and what kind of data we obtained in the presentation.


Figure 1: Present locations of 11 Japanese MERMAIDs (9 in south Pacific and 2 near Nishinoshima volcano island)