Tidal Effects on Volcanic Earthquakes and Deep-sea Hydrothermal Activity Revealed by Ocean Bottom Seismometer Measurements

Abstract

For a long time, the question of, whether or not tidal forces control volcanic activity and/or seismic activity, has been unsolved. The authors obtained remarkable results for tidal control of volcanic earthquakes and ocean bottom hydrothermal activity. An OBSIH (Ocean Bottom Seismometers with Hydrophone) was used for all observations. Volcanic earthquake activity associated with the 1983 Miyake Island eruption was high at high-tide and/or low-tide. Observations in three hydrothermal areas, the southern Mariana Trough, the TAG area in the Mid-Atlantic Ridge and the middle Okinawa Trough, showed the existence of low-frequency pulses called pressure pulses having a good correlation with semi-diurnal and diurnal changes in relation to tidal forces. An increase of pressure pulses suggests a hydrothermal upwelling from the vents. It is difficult to state why volcanic and hydrothermal activities are controlled by the ocean tide or the earth-tide. Similar variations occurred during the most resent volcanic activity on Miyake Island in July-September, 2000. Using the 2000 Miyake Island volcanism, a hypothetical interpretation is presented.