抄録
Hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone and a composite measuring system including CTD, current meter, transmission meter and cameras at a small depression on the TAG hydrothermal mound in the Mid-Atlantic Ridge and the southern East Pacific Rise. Low-frequency pressure pulses detected by the hydrophone with semi-diurnal periodicity seems to correspond to cycles of hydrothermal upflow from a small and short-lived smoker vent close to the observing site. The peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release. Microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting. Temporal variations in bottom water temperature and bottom currents have semi-diurnal and diurnal periodicity but are more complicated than the pressure events. Temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide.
