According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed...According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed in this paper, and the paper suggests that: ① The Tokara Channel fault belt is a fault belt with seismicity, cutting through lithosphere. ② The different stress state in the both subducting slabs on the both sides of Tokara Channel fault belt are caused by the difference of subducting depth of the both slabs. ③ The seismicity and stress field in the Okinawa Trough and Ryukyu regions are related not only to the subduction of the Philippine Sea Plate but also to the self-expanding action of Okinawa Trough.展开更多
In this paper,two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system:one data set was from the ‘Geological-geophysical map series of China S...In this paper,two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system:one data set was from the ‘Geological-geophysical map series of China Seas and adjacent areas' database and the other was newly collected by R/V Kexue III in 2011.Magnetic and gravity data were reorganized and processed using the software MMDP,MGDP and RGIS.In addition to the description of the anomaly patterns in different areas,deep and shallow structure studies were performed by using several kinds of calculation,including a spectrum analysis,upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly.The depth of the Moho and magnetic basement were calculated.Based on the above work,several controversial tectonic problems were discussed.Compared to the shelf area and Ryukyu Arc,the Okinawa Trough has an obviously thinned crust,with the thinnest area having thickness less than 14 km in the southern part.The Taiwan-Sinzi belt,which terminates to the south by the NW-SE trending Miyako fault belt,contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough.As an important tectonic boundary,the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments.A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate.Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area.The gravity and magnetic data support the existence of a Great East China Sea,which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions,and might have extended southwestward and connected with the northern South China Sea shelf basin.展开更多
The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deforma...The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.展开更多
文摘According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed in this paper, and the paper suggests that: ① The Tokara Channel fault belt is a fault belt with seismicity, cutting through lithosphere. ② The different stress state in the both subducting slabs on the both sides of Tokara Channel fault belt are caused by the difference of subducting depth of the both slabs. ③ The seismicity and stress field in the Okinawa Trough and Ryukyu regions are related not only to the subduction of the Philippine Sea Plate but also to the self-expanding action of Okinawa Trough.
基金funded by the National Key Basic Research Program of China (973 ProgramGrant No.2013CB429701)National Natural Science Foundations of China (Grant Nos.41206050 and 41202081)
文摘In this paper,two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system:one data set was from the ‘Geological-geophysical map series of China Seas and adjacent areas' database and the other was newly collected by R/V Kexue III in 2011.Magnetic and gravity data were reorganized and processed using the software MMDP,MGDP and RGIS.In addition to the description of the anomaly patterns in different areas,deep and shallow structure studies were performed by using several kinds of calculation,including a spectrum analysis,upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly.The depth of the Moho and magnetic basement were calculated.Based on the above work,several controversial tectonic problems were discussed.Compared to the shelf area and Ryukyu Arc,the Okinawa Trough has an obviously thinned crust,with the thinnest area having thickness less than 14 km in the southern part.The Taiwan-Sinzi belt,which terminates to the south by the NW-SE trending Miyako fault belt,contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough.As an important tectonic boundary,the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments.A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate.Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area.The gravity and magnetic data support the existence of a Great East China Sea,which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions,and might have extended southwestward and connected with the northern South China Sea shelf basin.
文摘The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.
