RELATIONSHIP BETWEEN THE NUMBER OF HYDROTHERMAL ACTIVITY FIELDS AND SPREADING RATE AND ITS APPLICATION IN THE OKINAWA TROUGH

The relationship between the number of hydrothermal activity fields and the sea floor spreading rate has been created based on the number of hydrothermal activity fields and the sea floor spreading rate of 11 segments of the ridge. The paper points out that there will be a larger number of hydrothermal fields on the faster spreading ridges than the lower ones. The linear equation:Ph=0.0002Us-0.0005 is obtained for the relationship between the number and the spreading rate, here Us for the spreading rate (in mm/a),and Ph for the possibility of number of hydrothermal activity fields (in 1/km). Based on the above given equation, the number of possible hydrothermal activity fields can be calculated if we know the spreading rate of a given ridge, and also we can calculate the spreading rate of the given ridge if we know the number of the hydrothermal activity fields along the given ridge. The spreading rate of Okinawa Trough has been discussed in this paper. During the past extension phase of Okinawa Trough, it has a lower spreading (extension) rate around 15 mm/a.The present spreading rate both based on the seismic profile and on the equation given by this paper is around 40 mm/a.The paper also points out that the spreading of the Okinawa Trough goes faster from past to present. There is possibly one or two more hydrothermal activity fields in the Okinawa Trough that we have not detected until now based on the equation and the current spreading rate of the Okinawa Trough.