CRUSTAL STRUCTURE OF THE OKINAWA TROUGH: EVIDENCE FROM WIDE-ANGLE REFLECTION AND SEISMIC REFRACTION SURVEYS

Seismic refraction/wide-angle reflection survey is used in this paper to ascertain the crustal structure of the Okinawa Trough. The seismic refraction/wide-angle reflection survey data shows that the Okinawa Trough has a thin crust, of which the major part is a thinned continental crust. However, the existance of oceanic crust in some local areas cannot be excluded. The northern, middle and southern parts of the Okinawa Trough are in different stages of tectonic evolution with different crustal thicknesses, structures and thinning forms. All of the differences of the Okinawa Trough from north to south are closely related to the variation in the kinematics and dynamics of the Ryukyu subduction zone. The newborn oceanic crusts will be confined in the narrow axial part of the Trough if exist. In this regard, longitudinal OBS profiles are recommended being used in the axial grabens. It would be helpful in determination of the existence of the newborn oceanic crust.