Seismic Background Level (SBL) for Monitoring Active Volcanoes

Seismological methods are the most widely used for monitoring active volcanoes. While conventional methods focusing on noticeable events (e.g., event counting, classification, and integrating powers) are frequently useful and are being advanced with modern analysis techniques, there are cases of eruptions where no apparent precursors are observed as events. Recently, seismic background level (SBL) analyses were proposed for detecting subtle continuous vibrations and for monitoring years of volcanic activity (Ichihara et al., 2023). The SBL successfully revealed slowly developing long-term eruption precursors for the 2011 and 2017-2018 eruptions of Shinmoe-dake, Kirishima, Japan.

 

In this presentation, we compare the SBL and continuous tremor analyses carried out for multiple volcanoes. The cases are Shinmoe-dake and Iwo-yama of the Kirishima Volcanic Group (Ichihara et al., 2023), including the 2025 eruption of Shinmoe-dake, Hakone (Kurihara, 2023), Kusatsu-Shirane (Kobayashi et al., 2026), Whakaari, New Zealand (Ardid et al., 2025; Behr et al., 2025), and Northern Group of Volcanoes in Kamchatka (Galina et al., 2026). The relationships between the SBL variation and other parameters, such as eruptive activity, gas emission, and ground deformation, are compared, even though the available parameters and seismic observation sensitivity depend on the dataset. We demonstrate that the SBL is an efficient tool to assess the volcano’s activity condition and is particularly effective for inferring the end of an eruptive period.