A tomographic study of the Vp and Vp/Vs structures in the crust and upper mantle beneath the Taiwan region of China is conducted by simultaneous inversion of P and S arrival times. Compared with the previous tomograph...A tomographic study of the Vp and Vp/Vs structures in the crust and upper mantle beneath the Taiwan region of China is conducted by simultaneous inversion of P and S arrival times. Compared with the previous tomographic results, the spherical finite difference technique is suitable for the strong heterogeneous velocity structure, and may improve the accuracy in the travel time and three-dimensional ray tracing calculations. The Vp and Vp/Vs structures derived from joint inversion and the relocated earthquakes can provide better constraints for analyzing the lateral heterogeneity and deep tectonic characters in the crust and upper mantle. Our tomographic results reveal significant relations between the seismic wavespeed structure and the tectonic characters. In the shallow depth, sedimentary basins and orogen show distinct wavespeed anomalies, with low Vp, high Vp/Vs in basins and high Vp, low Vp/Vs in orogen. As the suture zone of Eurasian Plate and Philippine Sea Plate, Longitudinal Valley is characterized by a significant high Vp/Vs anomaly extending to the middle-lower crust and upper mantle, which reflects the impact of rock cracking, partial melting, and the presence of fluids. In the northeast Taiwan, the Vp, Vp/Vs anomalies and relocated earthquakes depict the subducting Philippine Sea Plate under the Eurasian Plate. The high Vp of oceanic plate and the low Vp, high Vp/Vs atop the subducted oceanic plate extend to 80 km depth. Along the east-west profiles, the thickness of crust reaches 60 km at the east of Central Range with eastward dipping trend, which reveals the eastward subduction of the thickened and deformed crust of the Eurasian continental plate.展开更多
We estimated crustal v p/ v s ratio of Tibetan Plateau by combined inversion of Love and Rayleigh wave dispersion data. It is developed by us that the joint inversion methods using both Love and Rayleigh wave dispersi...We estimated crustal v p/ v s ratio of Tibetan Plateau by combined inversion of Love and Rayleigh wave dispersion data. It is developed by us that the joint inversion methods using both Love and Rayleigh wave dispersion data. Thickness and S\|wave velocity of each sub layer are taken from Love wave dispersion data, then P\|wave velocity structure was deduced using Rayleigh wave dispersion data. Densities of sub layers were estimated by the empirical relationships between seismic velocity and rock density. Having S\| and P\|wave velocities, v p/ v s ratio is calculated for each sub layer. Six sub layers in crust of Tibetan Plateau has been identified, which are 0～8km, 8～30km, 30～40km, 40～62km, 62～68km and 68～75km respectively. The S\|wave velocity structure of the Plateau is 3 13, 3 32, 3 15, 3 92, 3 45 and 3 87 km/s for each sub layer; and P\|wave velocities are 6 00, 6 10, 5 72, 6 35, 6 78 and 6 64km/s respectively v p/ v s ratios in sub layers are 1 92, 1 84, 1 82, 1 62, 1 96 and 1 72; and corresponding Poisson ratios are 0 31, 0 29, 0 28, 0 19, 0 32 and 0 24. Our result on Poisson ratios of Tibetan crust was supported by seismic waveform modelling by Rodgers and Schwartz (1998).展开更多
The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structur...The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structures of this tectonically active,rapidly developing region are yet poorly understood because of many limitations.For this reason,a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network（ENSN） from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai.Because the velocity model used for routine earthquake location by ENSN is one-dimensional,the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures.Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west.The crustal V_P/V_S ratio is 1.74 from shallow（depth≤10 km） earthquakes and 1.76 from deeper（depth 〉 10 km） crustal events.The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model（PREM）,implying that the seismic stations are located above widely distributed,tectonically-induced low-velocity zones.These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures.The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities,which should be excluded from major future development projects and large constructions in central and southern Sinai.展开更多
基金Supported by Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX3-SW-234-2)National Basic Research Program of China (Grant No. 2007CB411701)+1 种基金National High Technology Research and Development Pro-gram of China (Grant No. 2006AA09A101-0201) National Natural Science Foundation of China (Grant Nos. 40804016, 40704013)
文摘A tomographic study of the Vp and Vp/Vs structures in the crust and upper mantle beneath the Taiwan region of China is conducted by simultaneous inversion of P and S arrival times. Compared with the previous tomographic results, the spherical finite difference technique is suitable for the strong heterogeneous velocity structure, and may improve the accuracy in the travel time and three-dimensional ray tracing calculations. The Vp and Vp/Vs structures derived from joint inversion and the relocated earthquakes can provide better constraints for analyzing the lateral heterogeneity and deep tectonic characters in the crust and upper mantle. Our tomographic results reveal significant relations between the seismic wavespeed structure and the tectonic characters. In the shallow depth, sedimentary basins and orogen show distinct wavespeed anomalies, with low Vp, high Vp/Vs in basins and high Vp, low Vp/Vs in orogen. As the suture zone of Eurasian Plate and Philippine Sea Plate, Longitudinal Valley is characterized by a significant high Vp/Vs anomaly extending to the middle-lower crust and upper mantle, which reflects the impact of rock cracking, partial melting, and the presence of fluids. In the northeast Taiwan, the Vp, Vp/Vs anomalies and relocated earthquakes depict the subducting Philippine Sea Plate under the Eurasian Plate. The high Vp of oceanic plate and the low Vp, high Vp/Vs atop the subducted oceanic plate extend to 80 km depth. Along the east-west profiles, the thickness of crust reaches 60 km at the east of Central Range with eastward dipping trend, which reveals the eastward subduction of the thickened and deformed crust of the Eurasian continental plate.
文摘We estimated crustal v p/ v s ratio of Tibetan Plateau by combined inversion of Love and Rayleigh wave dispersion data. It is developed by us that the joint inversion methods using both Love and Rayleigh wave dispersion data. Thickness and S\|wave velocity of each sub layer are taken from Love wave dispersion data, then P\|wave velocity structure was deduced using Rayleigh wave dispersion data. Densities of sub layers were estimated by the empirical relationships between seismic velocity and rock density. Having S\| and P\|wave velocities, v p/ v s ratio is calculated for each sub layer. Six sub layers in crust of Tibetan Plateau has been identified, which are 0～8km, 8～30km, 30～40km, 40～62km, 62～68km and 68～75km respectively. The S\|wave velocity structure of the Plateau is 3 13, 3 32, 3 15, 3 92, 3 45 and 3 87 km/s for each sub layer; and P\|wave velocities are 6 00, 6 10, 5 72, 6 35, 6 78 and 6 64km/s respectively v p/ v s ratios in sub layers are 1 92, 1 84, 1 82, 1 62, 1 96 and 1 72; and corresponding Poisson ratios are 0 31, 0 29, 0 28, 0 19, 0 32 and 0 24. Our result on Poisson ratios of Tibetan crust was supported by seismic waveform modelling by Rodgers and Schwartz (1998).
文摘The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structures of this tectonically active,rapidly developing region are yet poorly understood because of many limitations.For this reason,a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network（ENSN） from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai.Because the velocity model used for routine earthquake location by ENSN is one-dimensional,the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures.Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west.The crustal V_P/V_S ratio is 1.74 from shallow（depth≤10 km） earthquakes and 1.76 from deeper（depth 〉 10 km） crustal events.The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model（PREM）,implying that the seismic stations are located above widely distributed,tectonically-induced low-velocity zones.These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures.The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities,which should be excluded from major future development projects and large constructions in central and southern Sinai.
