Teleseismic P-wave receiver functions at 20 broadband seismic stations in the Longmenshan fault zone(LMFZ)and its vicinity were extracted,and the crustal thickness and the P-and S-wave velocity ratio were calculated b...Teleseismic P-wave receiver functions at 20 broadband seismic stations in the Longmenshan fault zone(LMFZ)and its vicinity were extracted,and the crustal thickness and the P-and S-wave velocity ratio were calculated by use of the H-k stacking algorithm.With the results as constraints,the S-wave ve-locity structures beneath each station were determined by the inversion of receiver functions.The crustal structure of the Rear-range zone is similar to that of the Songpan-Garze Block,whereas the velocity structure of the Fore-range zone resembles that of Sichuan Basin,implying that the Central Principal Fault of LMFZ is the boundary between the eastern Tibetan Plateau and the Yangtze Block.Lower velocity zone exists in lower crust of the Songpan-Garze Block and the central-southern seg-ment of the Rear-range zone,which facilitates the detachment of the material in upper and middle crust.Joint analysis of the receiver functions and the Bouguer gravity anomalies supports the thesis on the detachment-thrust mode of the LMFZ.A double-detachment pattern is suggested to the tectonic setting in the Songpan-Garze Block.The upper detachment occurs at the depth of 10-15 km,and represents a high-temperature ductile shear zone.There is a lower detachment at the depth of about 30 km,below which the lower crust flow exists in the eastern Tibetan Plateau.Interpretation of the Bouguer gravity anomalies indicates that the Sichuan Basin is of higher density in upper and middle crust in compari-son with that of the Songpan-Garze Block.The LMFZ with higher density is the result from the thrusting of the Songpan-Garze Block over the Sichuan Basin.In the lower crust,higher P velocity and higher density in the Sichuan Basin are related to more rigid material,while lower S velocity and lower density in the Songpan-Garze Block are related to the softened and weakened material.The higher density block beneath the Sichuan Basin obstructs the eastward flow of lower crustal material from the Tibetan Plateau,which is driven by the compression of northward movement of Indian Plate.The eastward movement of upper and middle crustal material is also obstructed by the rigid Yangtze Block,resulting in the stress concentrated and accumulated along the LMFZ.When the stress releases sharply,the Wenchuan Ms8.0 earthquake occurs.展开更多
The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as G...The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as GHF and ZDF,respectively).Although the extension of the ZDF to the northeast,which represents the amalgamation of the two sub-blocks has been confirmed,the development of the GHF to the southwest remains to be verified.To better constrain the detailed deep structure beneath the southwest Cathaysia,which hold great significance for revealing the evolution of the SCB,a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin(SSB).Combining with the regional 10 permanent stations(PA),we obtained two profiles with teleseismic P-wave receiver function stacking.The most obvious feature in our results is the ascending Moho towards the coastal area,which is consistent with the passive margin continental and extensional tectonic setting.The stacking profile from the dense nodal array(DNA)shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB.We deduce that this offset may be casued by the deep extension of the GHF,which represents the remnants of the amalgamation of the Cathaysia block.From the other evidences,we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface.The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB.The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF,which serves as a channel for upwelling hot materials.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.40334041,40774037)Joint Foundation of Earthquake Science(Grant No.1040062)
文摘Teleseismic P-wave receiver functions at 20 broadband seismic stations in the Longmenshan fault zone(LMFZ)and its vicinity were extracted,and the crustal thickness and the P-and S-wave velocity ratio were calculated by use of the H-k stacking algorithm.With the results as constraints,the S-wave ve-locity structures beneath each station were determined by the inversion of receiver functions.The crustal structure of the Rear-range zone is similar to that of the Songpan-Garze Block,whereas the velocity structure of the Fore-range zone resembles that of Sichuan Basin,implying that the Central Principal Fault of LMFZ is the boundary between the eastern Tibetan Plateau and the Yangtze Block.Lower velocity zone exists in lower crust of the Songpan-Garze Block and the central-southern seg-ment of the Rear-range zone,which facilitates the detachment of the material in upper and middle crust.Joint analysis of the receiver functions and the Bouguer gravity anomalies supports the thesis on the detachment-thrust mode of the LMFZ.A double-detachment pattern is suggested to the tectonic setting in the Songpan-Garze Block.The upper detachment occurs at the depth of 10-15 km,and represents a high-temperature ductile shear zone.There is a lower detachment at the depth of about 30 km,below which the lower crust flow exists in the eastern Tibetan Plateau.Interpretation of the Bouguer gravity anomalies indicates that the Sichuan Basin is of higher density in upper and middle crust in compari-son with that of the Songpan-Garze Block.The LMFZ with higher density is the result from the thrusting of the Songpan-Garze Block over the Sichuan Basin.In the lower crust,higher P velocity and higher density in the Sichuan Basin are related to more rigid material,while lower S velocity and lower density in the Songpan-Garze Block are related to the softened and weakened material.The higher density block beneath the Sichuan Basin obstructs the eastward flow of lower crustal material from the Tibetan Plateau,which is driven by the compression of northward movement of Indian Plate.The eastward movement of upper and middle crustal material is also obstructed by the rigid Yangtze Block,resulting in the stress concentrated and accumulated along the LMFZ.When the stress releases sharply,the Wenchuan Ms8.0 earthquake occurs.
基金the National Natural Science Foun-dation of China(Grant Nos.41874052 and 41730212)the Guangdong Province Introduced Innovative R&D Team(Grant No.2017ZT072066)+2 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0701)the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311021002)the Guangdong Collaborative Innovation Center for Earthquake Prevention and Mitigation(Grant No.2018B020207011).
文摘The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as GHF and ZDF,respectively).Although the extension of the ZDF to the northeast,which represents the amalgamation of the two sub-blocks has been confirmed,the development of the GHF to the southwest remains to be verified.To better constrain the detailed deep structure beneath the southwest Cathaysia,which hold great significance for revealing the evolution of the SCB,a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin(SSB).Combining with the regional 10 permanent stations(PA),we obtained two profiles with teleseismic P-wave receiver function stacking.The most obvious feature in our results is the ascending Moho towards the coastal area,which is consistent with the passive margin continental and extensional tectonic setting.The stacking profile from the dense nodal array(DNA)shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB.We deduce that this offset may be casued by the deep extension of the GHF,which represents the remnants of the amalgamation of the Cathaysia block.From the other evidences,we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface.The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB.The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF,which serves as a channel for upwelling hot materials.
