Determination of the isostatic and gravity Moho in the East China Sea and its implications

Abstract

The East China Sea (ECS) is located among the Eurasian, Pacific and Philippine Sea plates, whose crustal structure and evolution are very complex. Elevation, geoid and gravity anomaly data are used in this study to determine the isostatic and gravity Moho topography of the ECS and surroundings. The gravity effects of sediments and subducting slabs are computed using recent datasets during estimation of the gravity Moho, and the results show good agreement between the gravity Moho and seismic results. The crustal isostatic implications of the difference between the isostatic and gravity Moho are discussed, and the decreasing Moho depth from the coast of the mainland China to the western margin of the Okinawa Trough suggests continental crust-type features, similar to the Yellow Sea. A combined isostatic analysis, which takes the difference between the isostatic and gravity Moho into account, indicates that the shallower Moho beneath the Okinawa Trough and the depressed Moho beneath the Ryukyu Arc may have implications for rifting in the Okinawa Trough. The steep Moho along the Ryukyu Trench marks the continent-ocean boundary at the crustal scale, which is consistent with the subduction of the Philippine Sea Plate. Taking the eastward extension of the ECS into account, it is expected that this would be steeper if it was generated by the isostatic over- and under-compensation beneath the Ryukyu Arc and Trench, respectively.