As an interoceanic arc,the Kyushu-Palau Ridge(KPR)is an exceptional place to study the subduction process and related magmatism through its interior velocity structure.However,the crustal structure and its nature of t...As an interoceanic arc,the Kyushu-Palau Ridge(KPR)is an exceptional place to study the subduction process and related magmatism through its interior velocity structure.However,the crustal structure and its nature of the KPR,especially the southern part with limited seismic data,are still in mystery.In order to unveil the crustal structure of the southern part of the KPR,this study uses deep reflection/refraction seismic data recorded by 24 ocean bottom seismometers to reconstruct a detailed P-wave velocity model along the ridge.Results show strong alongridge variations either on the crustal velocity or the thickness of the KPR.P-wave velocity model is featured with(1)a crustal thickness between 6–12 km,with velocity increases from 4.0 km/s to 7.0 km/s from top to bottom;(2)high gradient(~1 s^(-1))in the upper crust but low one(<0.2 s^(-1))in the lower crust;(3)a slow mantle velocity between 7.2 km/s and 7.6 km/s in the uppermost mantle;and(4)inhomogenous velocity anomalies in the lower crust beneath seamounts.By comparing with the mature arc in the Izu-Bonin-Mariana arc in the east,this study suggests the southern part of KPR is a thicken oceanic crust rather than a typical arc crust.The origin of low velocities in the lower crust and upper mantle may be related with crustal differentiation,which implies advanced crustal evolution from normal oceanic crust to partly thicken oceanic crust.High velocities in the lower crust are related to the difference in magmatism.展开更多
A new method is developed to constrain S-wave velocity structures of the shallow crust based on frequencydependent amplitudes of direct P-waves in P-wave receiver functions(P-RFs). This method involves the following t...A new method is developed to constrain S-wave velocity structures of the shallow crust based on frequencydependent amplitudes of direct P-waves in P-wave receiver functions(P-RFs). This method involves the following two steps:first, the high-frequency approximate amplitude formula of direct P-waves in P-RFs of individual stations is used to fit the observed amplitude distribution against the ray parameters at different frequencies, and second, the S-wave velocity depth profile beneath each station is constrained according to an empirical correlation between frequency and depth. Unlike traditional inversion techniques, the newly developed method is not dependent on initial velocity models, and the lateral and vertical resolutions of the results are controlled by the interstation distance and the data frequency, respectively. The effectiveness of the method is verified by synthetic tests on various models. The method is then applied to teleseismic P-RF data from a NW-SEtrending linear seismic array extending from the northeastern Tibetan Plateau to the central Sichuan Basin to construct an S-wave velocity image of the shallow crust along the array. The imaged velocity structure is further analysed and compared with the regional geology. In particular, the structural differences of sedimentary basins in the cratonic area of the stable Sichuan Basin and tectonically active belts in northeastern Tibet are investigated. By combining our results with previous observations, the relationship between the surficial geology and deep processes in the study region is also discussed.展开更多
基金The Scientific Research Fund of the Second Institute of OceanographyMNR under contract No.QNYC1801+3 种基金the National Natural Science Foundation of China under contract Nos 91858214,41776053,42025601,42076047,41890811 and 42006072the National Program on Global Change and Air-Sea InteractionMinistry of Natural Resources under contract No.GASI-02-PACDWZP02the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)under contract No.311020018。
文摘As an interoceanic arc,the Kyushu-Palau Ridge(KPR)is an exceptional place to study the subduction process and related magmatism through its interior velocity structure.However,the crustal structure and its nature of the KPR,especially the southern part with limited seismic data,are still in mystery.In order to unveil the crustal structure of the southern part of the KPR,this study uses deep reflection/refraction seismic data recorded by 24 ocean bottom seismometers to reconstruct a detailed P-wave velocity model along the ridge.Results show strong alongridge variations either on the crustal velocity or the thickness of the KPR.P-wave velocity model is featured with(1)a crustal thickness between 6–12 km,with velocity increases from 4.0 km/s to 7.0 km/s from top to bottom;(2)high gradient(~1 s^(-1))in the upper crust but low one(<0.2 s^(-1))in the lower crust;(3)a slow mantle velocity between 7.2 km/s and 7.6 km/s in the uppermost mantle;and(4)inhomogenous velocity anomalies in the lower crust beneath seamounts.By comparing with the mature arc in the Izu-Bonin-Mariana arc in the east,this study suggests the southern part of KPR is a thicken oceanic crust rather than a typical arc crust.The origin of low velocities in the lower crust and upper mantle may be related with crustal differentiation,which implies advanced crustal evolution from normal oceanic crust to partly thicken oceanic crust.High velocities in the lower crust are related to the difference in magmatism.
基金supported by the National Natural Science Foundation of China (Grant No. 41688103)the Strategic Priority Research Program (A) of the Chinese Academy of Sciences (Grant No. XDA20070302)+1 种基金the Independent Project of the State Key Laboratory of the Lithospheric Evolution, IGGCAS (SKL-Z201704-11712180)The field work for seismic data collection was financially supported by the Projects (Grant Nos. SinoProbe-02-03, 2011ZX05008-001)
文摘A new method is developed to constrain S-wave velocity structures of the shallow crust based on frequencydependent amplitudes of direct P-waves in P-wave receiver functions(P-RFs). This method involves the following two steps:first, the high-frequency approximate amplitude formula of direct P-waves in P-RFs of individual stations is used to fit the observed amplitude distribution against the ray parameters at different frequencies, and second, the S-wave velocity depth profile beneath each station is constrained according to an empirical correlation between frequency and depth. Unlike traditional inversion techniques, the newly developed method is not dependent on initial velocity models, and the lateral and vertical resolutions of the results are controlled by the interstation distance and the data frequency, respectively. The effectiveness of the method is verified by synthetic tests on various models. The method is then applied to teleseismic P-RF data from a NW-SEtrending linear seismic array extending from the northeastern Tibetan Plateau to the central Sichuan Basin to construct an S-wave velocity image of the shallow crust along the array. The imaged velocity structure is further analysed and compared with the regional geology. In particular, the structural differences of sedimentary basins in the cratonic area of the stable Sichuan Basin and tectonically active belts in northeastern Tibet are investigated. By combining our results with previous observations, the relationship between the surficial geology and deep processes in the study region is also discussed.
