Abstract
• The partitioned inversion is employed to calculate the depth of the Moho interface. • The depth of the Moho interface varies from 16 km to 26 km. • The stretching factor ranges from 1.4 to 2.5, increasing along the direction from north to south. • The inversion results indicate the crustal thinning in the Okinawa Trough. The Okinawa Trough is an active back-arc basin of the Ryukyu Island arc-trench system caused by the subduction of the Philippine Sea plate. The different controlling effects of plate subduction result in the unique characteristic of the crustal structure, fault development and magmatic activities. Studies on the crustal structure and properties are better to understand the origin and evolution of back-arc basins. To overcome the non-uniqueness of the gravity interface inversion and spatial limitation of seismic profiles, 19 published seismic results are selected for the soft constrained strategy. Furthermore, the partitioned interface inversion with the exponential density contrast model is utilized to obtain more detailed undulations of the Moho interface. The crustal thickness and the stretching factors of the Okinawa Trough are obtained as well. The results are reliable after the evaluation of the fitting degree of observed data, and the evaluation of recovered data and selected constraint points respectively. The results show that the overall variation trend of the crustal thickness in the study area gradually decreases from the west to east. The crustal thickness of the Okinawa Trough is larger than that of the East China Sea shelf basin, ranging from 12 to 22 km. The Okinawa Trough is a transitional crust formed during the transformation from continental crust to oceanic crust, with the overall characteristics of extensional and thinning continental crust. However, a new oceanic crust may have accreted in the central graben of the southern sections of the trough.
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