Continuous seismic monitoring of Nishinoshima volcano, Izu-Ogasawara, by using long-term ocean bottom seismometers

Abstract

Nishinoshima in Izu-Ogasawara started erupting in November 2013, and the island size increased. Continuous monitoring is important for study of the formation process. Since it is difficult to make continuous observations on a remote uninhabited island, we started seismic observations near Nishinoshima using ocean bottom seismometers (OBSs) from February 2015. Our OBSs have a recording period of 1 year, and recovery and re-deployment of OBSs were repeated to make continuous observations. The OBSs were deployed with distances of less than 13 km from the crater. Events with particular characteristics were frequently recorded during the eruption period and are estimated to correlate with the release of plumes from the crater by comparison with temporal on-site records using a video camera and microphones. We estimated the number of events using the amplitude average of records to monitor volcanic activity.

The Seismo‐Acoustics of Submarine Volcanic Eruptions

“…Targeted deployments of campaign instruments are complementary to real-time monitoring and typically have a scientific goal in mind, either specific to one seamount or a larger region. However, nonreal-time instruments can also be used for monitoring on-going eruptions by swapping out instruments periodically, such as the OBS monitoring efforts at Nishinoshima (Shinohara et al, 2017 ocean-bottom hydrophones or OBSs located within a few kilometers of the seamount or ridge of interest (e.g., Chadwick et al, 2008;Crone & Bohnenstiehl, 2019;Dziak et al, 2015;Tolstoy et al, 2006). Regional studies may use a widely spaced network of moored hydrophones or other instruments, similar to most land-based seismic studies (e.g., Bohnenstiehl et al, 2013;Dziak et al, 2005;Helffrich et al, 2006), or they may take advantage of SOFAR propagation and use a single small-aperture array of a few instruments (e.g., Bohnenstiehl et al, 2013;.…”

The 2017 Nishinoshima eruption: combined analysis using Himawari-8 and multiple high-resolution satellite images

“…Landing for surveying was performed once in October 2016 long after decline of the 2013-2015 activity, but it was only a 3-h stay (Takeo et al 2018). Geophysical research was conducted by observing seismic activity with ocean-bottom seismometers installed about 4 km offshore from the island (Shinohara et al 2017) also by a seismometer installed in the island in October 2016 (Takeo et al 2018), which was destroyed by the 2017 eruption. However, continuous or systematic observation of island surface activity could not be carried out, and only aerial observations and images released by governmental agencies (e.g., the Japan Coast Guard (2019) or Geospatial Information Authority of Japan (2018)) or media were available for examining the eruptive conditions.…”

Two independent signals detected by ocean bottom electromagnetometers during a non-eruptive volcanic event: Ogasawara Island arc volcano, Nishinoshima

“…The radius is slightly smaller than the source depth below the seafloor, suggesting that the heat causing the demagnetization would have reached close to the seafloor. However, in November 2016, neither eruptions on the island were reported nor seismic signals observed by ocean bottom seismometers were not significantly increased (Shinohara et al 2017).…”

“…1a). The Nishinoshima volcano provides a unique opportunity to study island-forming eruption processes (e.g., Maeno et al 2016;Shinohara et al 2017;Takagi et al 2017;Kaneko et al 2019). The island has attracted the attention of geological researchers due to the development process of the continental crust associated with the subduction of the Pacific plate (e.g., Sano et al 2016;Tamura et al 2019).…”

“…After an absence of nearly 40 years, eruption activity has occurred since November 2013. Seafloor seismic observations showed numerous events associated with the surface activity of the volcano, which mostly ceased in November 2015 and became active again in May 2017 (Shinohara et al 2017). Active and quiet periods have alternated until the present time (April 2020).…”