[S-VC36] Volcanoes in the sea

[SVC36-01] Volcanic tremor controlled by heat flux: implication for the mid-long term evaluation for volcanic hydrothermal activity

★Invited Papers

*Eisuke Fujita¹ (1.National research Institute for Earth science, Department of Catastrophic Geohazard Research, Research Division for Volcanic Disasters)

Keywords:heat flux, volcanic tremor, mid-long term evaluation

In the activity of submarine volcanoes, the interaction between hydrothermal systems and magma beneath the volcanic body is a crucial factor. The 2000 eruption of Miyakejima revealed that magma had been retained in the shallow subsurface for several years after the eruption, and in recent activities at Iwoto, the first magma eruption in recorded history occurred, indicating that magma has risen to the shallow subsurface. Seismic observation in volcanoes is a particularly robust observational method, and the interpretation of the mechanisms of volcanic earthquakes and volcanic tremor plays an important role in assessing volcanic activity. At Miyakejima and Iwoto, monotonic tremor and banded tremor, which occur at regular intervals, can sometimes be observed. Fujita (2008) and Fujita et al. (2011) propose a volcanic tremor model based on heat flux. This model formulates the vibrations caused by the instability of two-phase flow of water and water vapor using a two-fluid model, allowing for a quantitative interpretation of the periodicity of the vibrations from its characteristic equation. It has been found that the banded tremor (with a period of 20 to 45 minutes) occurring on Miyakejima from 2003 to 2005 is realized by a heat supply of approximately 10 MW. Additionally, individual volcanic tremor can be interpreted as density wave oscillations caused by shifts in density due to water flow and steam generation. For this oscillation phenomenon to occur, there is a range of heat quantity, specifically a lower limit (the amount of heat sufficient for steam generation) and an upper limit (beyond which too much steam is generated). The occurrence of volcanic tremor can be interpreted in relation to the amount of heat flux. Based on this, it is proposed to conduct continuous thermodynamic observations, such as temperature and crustal heat flow, for medium to long-term (several years to several decades) assessments of hydrothermal volcanic systems, including marine areas. The recently spreading observation using optical fibers (DAS) will be expanded in boreholes to continuously monitor earthquakes and temperature, and understanding these fluctuations will serve as an indicator.