TIME-VARIATIONS OF FLUID EXPULSION VELOCITIES AT THE TOE OF THE EASTERN NANKAI ACCRETIONARY COMPLEX

The temperatures in the bottom seawater and down to a depth of 60 cm in the sediment were measured over two active fluid seeps at the toe of the eastern Nankai accretionary complex for periods of 12 and 32 days successively. At the first station, the fluid advection velocity is low (less than 10 m/a) and the sediment temperature fluctuations closely reflect those of seawater. At the second location, the fluid advection velocity is greater. with a Darcy velocity of the order of 100 m/a, and sediment temperature fluctutations mainly reflect variations in the fluid velocity. The temperature data suggest amplitude fluctuations of the fluid velocity of the order of 15% over characteristic periods of about 14 days. They also suggest a 30% increase in the velocity over the one month period of the observation.