By analyzing the deep seismic sounding profiles across the Longmen Shan,this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake.The Lo...By analyzing the deep seismic sounding profiles across the Longmen Shan,this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake.The Longmen Shan thrust belt marks not only the topographical change,but also the lateral velocity variation between the eastern Tibetan Plateau and the Sichuan Basin.A low-velocity layer has consistently been found in the crust beneath the eastern edge of the Tibetan Plateau,and ends beneath the western Sichuan Basin.The low-velocity layer at a depth of-20 km beneath the eastern edge of the Tibetan Plateau has been considered as the deep condition for favoring energy accumulation that formed the great Wenchuan earthquake.展开更多
Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with t...Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the ex-posed basins, uplifts and faults. The low velocity anomaly corresponding to the volcano also has been revealed. There exists a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrocks are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust maybe shallow. On the other hand, known as the plates seam, the Honghe fault has a distinct evi-dence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a close relationship with the earthquakes occurrence nowadays. Despite of the ceasing of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. As the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and the upper mantle cannot be released; therefore it accumulates at some appropriate tectonic locations. Moreover, the saturation of the water from the basin, the action of other fluids, and the effects of the outer stress maybe another direct reason ac-count for the strong earthquakes occurrence in Yunnan region.展开更多
Cenozoic basalt in eastern China contains abundant ultramafic xenoliths which are specimens of pyrolitesreleased during basaltic magma eruption. A total of 405 P-T data of pyroxene in the ultramafic rocks have beencol...Cenozoic basalt in eastern China contains abundant ultramafic xenoliths which are specimens of pyrolitesreleased during basaltic magma eruption. A total of 405 P-T data of pyroxene in the ultramafic rocks have beencollected, which present a more precise pyroxene geotherm. The average geothermal gradient in the upper man-tle represented by the pyroxene geotherm is about 3.3℃ / km, which is much less than that derived from theconductive thermal model (≈14℃ / km), implying the great significance of convective heat transfer. The calcu-lation shows that the contributions of convective and conductive heat transfers are 79% and 21%, respectively.The perturbation in the thermal structure of the upper mantle is an important manifestation of thetectonothermal event of Cenozoic continental rifting and intense basaltic volcanism in eastern China. Based onthe pyroxene geotherm and its comparison with the current geothermal field derived from the measurements ofthe surface heat flows, it is suggested that the Moho may be a secondary thermal boundary. The currentgeothermal field and the thermal structure of the lithosphere in eastern China may mainly reflect the result ofthe tectonothermal disturbance in the Neogene-Quaternary, in other words, the lithosphere has just begun toCool.展开更多
A method of three dimensional (3-D) model parameterization is presented that makes forward and inverse problems become easy. The velocity and interface structure of crust and upper mantle are described by a set of hig...A method of three dimensional (3-D) model parameterization is presented that makes forward and inverse problems become easy. The velocity and interface structure of crust and upper mantle are described by a set of highly smoothed functions. Shooting ray tracing method is chosen to calculate the ray paths for both forward and inverse problems. The partial derivatives of traveltime with respect to parameters of the model grids are calculated analytically while rays are being traced. Because velocity and interface functions have second-order continuous partial derivatives, the geometrical shadow zones at the surface caused by scattering and focusing of ray paths can be prevented. After ray tracing, an equation consisting of matrix and vectors for inverse problem is obtained. We use singular value decomposition method with damped factor to solve the equation. A synthetic data set which consists of several in-line profiles is used to test the methods. The results show that the methods are robust. Compared with the two dimensional method, the 3-D inversion method can give the right position of interfaces and the velocity structure when the crustal model is complicated.展开更多
The 3-D P- and S-wave velocity models of the upper crust beneath Southwest Iberia are determined by inverting arrival time data from local earthquakes using a seismic tomo^raphy method. We used a total of 3085 P- and ...The 3-D P- and S-wave velocity models of the upper crust beneath Southwest Iberia are determined by inverting arrival time data from local earthquakes using a seismic tomo^raphy method. We used a total of 3085 P- and 2780 S-wave high quality arrival times from 886 local earthquakes recorded by a per- manent seismic network, which is operated by the Institute of Meteorology （IM）, Lisbon, Portugal. The computed P- and S-wave velocities are used to determine the 3-D distributions of Vp/Vs ratio. The 3-D velocity and Vp/Vs ratio images display clear lateral heterogeneities in the study area. Significant veloc- ity variations up to ~6% are revealed in the upper crust beneath Southwest lberia, At 4 km depth, both P- and S-wave velocity take average to high values relative to the initial velocity model, while at 12 km, low P-wave velocities are clearly visible along the coast and in the southern parts. High S-wave velocities at 12 km depth are imaged in the central parts, and average values along the coast; although some scattered patches of low and high S-wave velocities are also revealed. The Vp/Vs rztio is generally high at depths of 4 and 12 km along the coastal parts with some regions of high Vp/Vs ratio in the north at 4 km depth, and low Vp/Vs ratio in the central southern parts at a depth of 12 km, The imaged low velocity and high Vp/Vs ratios are related to the thick saturated and unconsolidated sediments covering the region; whereas the high velocity regions are generally associated with the Mesozoic basement rocks.展开更多
Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A＇nyemaqên suture zo...Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A＇nyemaqên suture zone. The upper crust structures around eastern A＇nyemaqên suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoigê basin and depressed in eastern A＇nyemaqên suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A＇nyemaqên suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined to- ward the south. Hoh Sai Hu-Maqên fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqên fault and Zhouqu-Liangdang fault, which are main tectonic boundaries of A＇nyemaqên suture zone. Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A＇nyemaqên suture zone implies crushed zone features under pinching action.展开更多
Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), the Q R of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino ...Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), the Q R of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino Korean paraplatform in this paper. The Q β models of the crust and upper mantle are respectively obtained for the 4 paths, with the aid of stochastic inverse method. It shows that in the eastern Sino Korean paraplatform, the average crustal Q β is about 200, and that there exists a weak attenuation layer in the middle crust (about 10～20 km deep) which is possibly related to earthquake prone layer. A strong attenuation layer (low Q ) of 70 km thick extensively exists in the uppermost mantle, with the buried depth about 80 km. The average Q R of fundamental mode Rayleigh wave is between the value of stable tectonic region and that of active tectonic region, and much close to the latter.展开更多
-Mainly on the basis of the data obtained during PRC/US bilateral TOGA cruises, abnormal variation occurred during the 1986/1987 El Nino is shown in this paper about the thermal structure and circulation of the upper ...-Mainly on the basis of the data obtained during PRC/US bilateral TOGA cruises, abnormal variation occurred during the 1986/1987 El Nino is shown in this paper about the thermal structure and circulation of the upper western tropical Pacific Ocean. The effects of the abmormal variation on the subtropical high over the Northwest Pacific Ocean are discussed. During the El Nino: (1) In the east part of the western tropical Pacific Ocean (the subsurface temperature data on the 165° E section are taken as an example), the water wanner than 29 C in the upper layer spread on the longitudinal section and positive temperature anormalies appeared in a large area of the sea surface. (2) In the west part of the western tropical Pacific Ocean (the subsurface temperature data on the 137°E section are representative ), the cross section occupied by the upper layer warmer water ( T >28 ℃ ) became shrunk, and the sea surface temperature showed negative amomalies. (3) The eastward flows in the upper layer of the 165°E section strengthened. (4)The northward flow volume of warm water from the origin area of Kuroshio, i. e. , the tropical oceanic area south of 18?0' N and from the west of 130?E to the Philippine coast, decreased. When those kinds of abnomal variation occurred, air divergence on the low level (1 000 hPa) over the Northwest Pacific Ocean was intensified, favourable to the strengthening of subtropical high over the Northwest Pacific Ocean.展开更多
The three-dimension crustal and upper mantle structures in the region around Beijing were studied by seismic tomography. We used the P wave arrival times from local and teleseismic events. These events were recorded b...The three-dimension crustal and upper mantle structures in the region around Beijing were studied by seismic tomography. We used the P wave arrival times from local and teleseismic events. These events were recorded by 250 stations of the North China Seismic Array and 108 stations of the Beijing Telemetry Seismic Network. 118 869 P wave arrivals from 10 285 local events and 12 189 P wave arrivals from 107 teleseismic events were used in the inversion. We obtained the 3-D P wave velocity structure of the crust and upper mantle with the horizontal resolution of 0.3° in the studied region. The tomographic imaging shows the remarkably heterogeneous velocity variation. The velocity anomalies are in well agreement with the geological structure in the shallow crust. The different relationships between seismic activities and velocity anomalies may imply the different seismogenic structure and mechanism. Beneath the Moho under Taihangshan mountain and Yanshan mountain, we found the high velocity anomalies deep to 120 km and 200 km, respectively. The deep high velocity zone may be explained by the existence of the mountain root under Yanshan mountain. The high velocity anomalies in the upper mantle of North China basin may be the relics of the de-rooting from the former craton mantle lithosphere.展开更多
The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the ...The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.展开更多
The Tazhong paleouplift is divided into the upper and the lower structural layers, bounded by the unconformity surface at the top of the Ordovician carbonate rock. The reservoirs in the two layers from different parts...The Tazhong paleouplift is divided into the upper and the lower structural layers, bounded by the unconformity surface at the top of the Ordovician carbonate rock. The reservoirs in the two layers from different parts vary in number, type and reserves, but the mechanism was rarely researched before. Therefore, an explanation of the mechanism will promote petroleum exploration in Tazhong paleouplift. After studying the evolution and reservoir distribution of the Tazhong paleouplift, it is concluded that the evolution in late Caledonian, late Hercynian and Himalayan periods resulted in the upper and the lower structural layers. It is also defined that in the upper structural layer, structural and stratigraphic overlap reservoirs are developed at the top and the upper part of the paleouplift, which are dominated by oil reservoirs, while for the lower structural layer, lithological reservoirs are developed in the lower part of the paleouplift, which are dominated by gas reservoirs, and more reserves are discovered in the lower structural layer than the upper. Through a comparative analysis of accumulation conditions of the upper and the lower structural layers, the mechanism of enrichment differences is clearly explained. The reservoir and seal conditions of the lower structural layer are better than those of the upper layer, which is the reason why more reservoirs have been found in the former. The differences in the carrier system types, trap types and charging periods between the upper and the lower structural layers lead to differences in the reservoir types and distribution. An accumulation model is established for the Tazhong paleouplift. For the upper structural layer, the structural reservoirs and the stratigraphic overlap reservoirs are formed at the upper part of the paleouplift, while for the lower structural layer, the weathering crust reservoirs are formed at the top, the reef-flat reservoirs are formed on the lateral margin, the karst and inside reservoirs are formed in the lower part of the paleouplift.展开更多
Granular computing is a very hot research field in recent years. In our previous work an algebraic quotient space model was proposed,where the quotient structure could not be deduced if the granulation was based on an...Granular computing is a very hot research field in recent years. In our previous work an algebraic quotient space model was proposed,where the quotient structure could not be deduced if the granulation was based on an equivalence relation. In this paper,definitions were given and formulas of the lower quotient congruence and upper quotient congruence were calculated to roughly represent the quotient structure. Then the accuracy and roughness were defined to measure the quotient structure in quantification. Finally,a numerical example was given to demonstrate that the rough representation and measuring methods are efficient and applicable. The work has greatly enriched the algebraic quotient space model and granular computing theory.展开更多
The attenuation of seismic waves reflects the elastic nature of the media within which the waves propagate.In this study,we calculate the Coda-Q(Qc),frequency dependence(η),Vp/Vs and Poisson's(υ)ratios by using ...The attenuation of seismic waves reflects the elastic nature of the media within which the waves propagate.In this study,we calculate the Coda-Q(Qc),frequency dependence(η),Vp/Vs and Poisson's(υ)ratios by using 2621 vertical component seismograms generated by 987 earthquakes recorded by 13 seismic stations in Eastern Anatolia,and creat a 2-D seismic tomographic Qc model for the region.The obtained model provides significant information for exploring the boundaries of adjacent tectonic units within the upper crust and interpreting their dynamic characteristics.The 2-D Qc model and the other parameters are consistent with the seismotectonic features of Eastern Anatolia.Highly heterogeneous Qc values are observed in the study area dividing it into north-south directed bands of low and high attenuation.The highestηvalues were obtained beneath the northwestern and eastern parts of the study region.Clear,high and lowυvalues are obtained in the western and eastern parts of the study area,respectively.The spatial variations in the measured parameters are consistent with many geophysical observations including low Pn velocities,efficient Sn blockage,high heat flow,and widespread volcanism.Different upper crustal thicknesses and inhomogeneous stress distribution along the East and North Anatolian Fault Zones may also contribute to the observed heterogeneities.展开更多
A great number of calcareous nannofossils have been found in the deep-sea sediments of 2.32 Ma at ODP Site 1143 located in the Nansha area, the southern South China Sea. The number of coccoliths varies from about 0.5&...A great number of calcareous nannofossils have been found in the deep-sea sediments of 2.32 Ma at ODP Site 1143 located in the Nansha area, the southern South China Sea. The number of coccoliths varies from about 0.5×106 up to almost 53×106 coccoliths/g sediment, with an average of 16×106 coccoliths/g sediment. The accumulation rate of total coccoliths varies from 1×106 to 278×106 coccoliths/cm2 ka. The nannofossil assemblages are usually dominated by a lower-photic species-Florisphaera profunda, of which the average percentage is about 70% in all samples. The absolute abundance and the accumulation rate of nannofossils as well as the percentage ofF. profunda display significant oscillations on two different time scales. One is the fluctuation coincident with the glacial-interglacial cycle, and the other is the long-term changes on a time scale longer than 100 ka. Six evolutionary stages of calcareous nannofossils could be divided for the last 2.32 Ma, from which we can reconstruct the changes in the depth of nutricline of the Nansha area. In this paper, the possible mechanism resulting in these variations is also discussed.展开更多
From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associa...From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.展开更多
Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral accelerat...Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral acceleration region (AAR) in the southern hemisphere on February 14, 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~11100 km. Moreover, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~0.4°–1° invariantlatitude (ILAT), moving poleward at an average speed of ~0.2° ILAT per minute, before disappearing at ~71.5° ILAT.展开更多
We studied ultrastructurally the cancellons bone tissues of the upper femoral ends, collected from 12 patients undergoing endoprostbesis replacement for fractures of the femoral neck and from 7 fresh cadavers. The bon...We studied ultrastructurally the cancellons bone tissues of the upper femoral ends, collected from 12 patients undergoing endoprostbesis replacement for fractures of the femoral neck and from 7 fresh cadavers. The bone tissues were composed of meshwork of trabeculae, that constituted tier upon tier of anisotropic arch structures of different diameters and sizes. The arch structures of the cancellous bone tissues in the femoral heads assumed round or roundish configurations, whereas those of the femoral head-neck junctions revealed oval outlines and those of the femoral necks showed narrow oval profiles. The fine structures of the trabecnlae in the femoral head could be divided into superficial zone, central zone, and transitional zone. Under weight-bearing, the central zone suited to sustain the load, while the superficial zone could produce elastic deformation lest fracture of the trabecaulae should ensue. The long axes of the oval arch structures of the femoral head-neck junction and the narrow oval arch structures of the femoral neck coincided with those of the femoral neck, thereby facilitating weight-bearing under physiological conditions. However, external violence in the form of either adduction or abduction force would act in a horizontal direction on the long axes of the oval and narrow oval arches so as to produce subcapital or transverse fracture of the femur in the aged.展开更多
基金financed by International Sciences and Technology cooperation(2006DFA21340)the special funds for Sciences and technology research of public welfare trades(200811021)+2 种基金the key innovation project for sciences and technology of ministry of land and resources(1212010711813)the Basic outlay of scientific research work from Ministry of Science and Technology of the People's Republic of China(J0803)the National Natural Science Foundation of China(40830316 and 40874045)and SINOPPROBE-02
文摘By analyzing the deep seismic sounding profiles across the Longmen Shan,this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake.The Longmen Shan thrust belt marks not only the topographical change,but also the lateral velocity variation between the eastern Tibetan Plateau and the Sichuan Basin.A low-velocity layer has consistently been found in the crust beneath the eastern edge of the Tibetan Plateau,and ends beneath the western Sichuan Basin.The low-velocity layer at a depth of-20 km beneath the eastern edge of the Tibetan Plateau has been considered as the deep condition for favoring energy accumulation that formed the great Wenchuan earthquake.
基金State Scientific and Technological Development program (95-13-02-03).
文摘Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the ex-posed basins, uplifts and faults. The low velocity anomaly corresponding to the volcano also has been revealed. There exists a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrocks are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust maybe shallow. On the other hand, known as the plates seam, the Honghe fault has a distinct evi-dence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a close relationship with the earthquakes occurrence nowadays. Despite of the ceasing of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. As the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and the upper mantle cannot be released; therefore it accumulates at some appropriate tectonic locations. Moreover, the saturation of the water from the basin, the action of other fluids, and the effects of the outer stress maybe another direct reason ac-count for the strong earthquakes occurrence in Yunnan region.
文摘Cenozoic basalt in eastern China contains abundant ultramafic xenoliths which are specimens of pyrolitesreleased during basaltic magma eruption. A total of 405 P-T data of pyroxene in the ultramafic rocks have beencollected, which present a more precise pyroxene geotherm. The average geothermal gradient in the upper man-tle represented by the pyroxene geotherm is about 3.3℃ / km, which is much less than that derived from theconductive thermal model (≈14℃ / km), implying the great significance of convective heat transfer. The calcu-lation shows that the contributions of convective and conductive heat transfers are 79% and 21%, respectively.The perturbation in the thermal structure of the upper mantle is an important manifestation of thetectonothermal event of Cenozoic continental rifting and intense basaltic volcanism in eastern China. Based onthe pyroxene geotherm and its comparison with the current geothermal field derived from the measurements ofthe surface heat flows, it is suggested that the Moho may be a secondary thermal boundary. The currentgeothermal field and the thermal structure of the lithosphere in eastern China may mainly reflect the result ofthe tectonothermal disturbance in the Neogene-Quaternary, in other words, the lithosphere has just begun toCool.
文摘A method of three dimensional (3-D) model parameterization is presented that makes forward and inverse problems become easy. The velocity and interface structure of crust and upper mantle are described by a set of highly smoothed functions. Shooting ray tracing method is chosen to calculate the ray paths for both forward and inverse problems. The partial derivatives of traveltime with respect to parameters of the model grids are calculated analytically while rays are being traced. Because velocity and interface functions have second-order continuous partial derivatives, the geometrical shadow zones at the surface caused by scattering and focusing of ray paths can be prevented. After ray tracing, an equation consisting of matrix and vectors for inverse problem is obtained. We use singular value decomposition method with damped factor to solve the equation. A synthetic data set which consists of several in-line profiles is used to test the methods. The results show that the methods are robust. Compared with the two dimensional method, the 3-D inversion method can give the right position of interfaces and the velocity structure when the crustal model is complicated.
文摘The 3-D P- and S-wave velocity models of the upper crust beneath Southwest Iberia are determined by inverting arrival time data from local earthquakes using a seismic tomo^raphy method. We used a total of 3085 P- and 2780 S-wave high quality arrival times from 886 local earthquakes recorded by a per- manent seismic network, which is operated by the Institute of Meteorology （IM）, Lisbon, Portugal. The computed P- and S-wave velocities are used to determine the 3-D distributions of Vp/Vs ratio. The 3-D velocity and Vp/Vs ratio images display clear lateral heterogeneities in the study area. Significant veloc- ity variations up to ~6% are revealed in the upper crust beneath Southwest lberia, At 4 km depth, both P- and S-wave velocity take average to high values relative to the initial velocity model, while at 12 km, low P-wave velocities are clearly visible along the coast and in the southern parts. High S-wave velocities at 12 km depth are imaged in the central parts, and average values along the coast; although some scattered patches of low and high S-wave velocities are also revealed. The Vp/Vs rztio is generally high at depths of 4 and 12 km along the coastal parts with some regions of high Vp/Vs ratio in the north at 4 km depth, and low Vp/Vs ratio in the central southern parts at a depth of 12 km, The imaged low velocity and high Vp/Vs ratios are related to the thick saturated and unconsolidated sediments covering the region; whereas the high velocity regions are generally associated with the Mesozoic basement rocks.
基金National Natural Science Foundation of China (40334040).
文摘Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A＇nyemaqên suture zone. The upper crust structures around eastern A＇nyemaqên suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoigê basin and depressed in eastern A＇nyemaqên suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A＇nyemaqên suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined to- ward the south. Hoh Sai Hu-Maqên fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqên fault and Zhouqu-Liangdang fault, which are main tectonic boundaries of A＇nyemaqên suture zone. Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A＇nyemaqên suture zone implies crushed zone features under pinching action.
文摘Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), the Q R of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino Korean paraplatform in this paper. The Q β models of the crust and upper mantle are respectively obtained for the 4 paths, with the aid of stochastic inverse method. It shows that in the eastern Sino Korean paraplatform, the average crustal Q β is about 200, and that there exists a weak attenuation layer in the middle crust (about 10～20 km deep) which is possibly related to earthquake prone layer. A strong attenuation layer (low Q ) of 70 km thick extensively exists in the uppermost mantle, with the buried depth about 80 km. The average Q R of fundamental mode Rayleigh wave is between the value of stable tectonic region and that of active tectonic region, and much close to the latter.
文摘-Mainly on the basis of the data obtained during PRC/US bilateral TOGA cruises, abnormal variation occurred during the 1986/1987 El Nino is shown in this paper about the thermal structure and circulation of the upper western tropical Pacific Ocean. The effects of the abmormal variation on the subtropical high over the Northwest Pacific Ocean are discussed. During the El Nino: (1) In the east part of the western tropical Pacific Ocean (the subsurface temperature data on the 165° E section are taken as an example), the water wanner than 29 C in the upper layer spread on the longitudinal section and positive temperature anormalies appeared in a large area of the sea surface. (2) In the west part of the western tropical Pacific Ocean (the subsurface temperature data on the 137°E section are representative ), the cross section occupied by the upper layer warmer water ( T >28 ℃ ) became shrunk, and the sea surface temperature showed negative amomalies. (3) The eastward flows in the upper layer of the 165°E section strengthened. (4)The northward flow volume of warm water from the origin area of Kuroshio, i. e. , the tropical oceanic area south of 18?0' N and from the west of 130?E to the Philippine coast, decreased. When those kinds of abnomal variation occurred, air divergence on the low level (1 000 hPa) over the Northwest Pacific Ocean was intensified, favourable to the strengthening of subtropical high over the Northwest Pacific Ocean.
基金supported by the National Special Fund of Science and Technological Basic Work under grant No. 2006FY110100partially by the 2007 Special Fund of Seismological Industry "Seismic Travel Time Table in the Capital Area" under grant No. 200708009Contribution No. is 09FE3003 of Institute of Geophysics,China Earthquake Administration
文摘The three-dimension crustal and upper mantle structures in the region around Beijing were studied by seismic tomography. We used the P wave arrival times from local and teleseismic events. These events were recorded by 250 stations of the North China Seismic Array and 108 stations of the Beijing Telemetry Seismic Network. 118 869 P wave arrivals from 10 285 local events and 12 189 P wave arrivals from 107 teleseismic events were used in the inversion. We obtained the 3-D P wave velocity structure of the crust and upper mantle with the horizontal resolution of 0.3° in the studied region. The tomographic imaging shows the remarkably heterogeneous velocity variation. The velocity anomalies are in well agreement with the geological structure in the shallow crust. The different relationships between seismic activities and velocity anomalies may imply the different seismogenic structure and mechanism. Beneath the Moho under Taihangshan mountain and Yanshan mountain, we found the high velocity anomalies deep to 120 km and 200 km, respectively. The deep high velocity zone may be explained by the existence of the mountain root under Yanshan mountain. The high velocity anomalies in the upper mantle of North China basin may be the relics of the de-rooting from the former craton mantle lithosphere.
基金National Key Research Development Project (No. G1998 040700/sub-project 95-13-02-03).
文摘The Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE. Based on the travel times and the related amplitudes of phases in the record sections, the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quite strong lateral variation along the profile. The crust is divided into 5 layers, where the first, second and third layer belong to the upper crust, the forth and fifth layer belong to the lower crust. The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile, and it integrates into the overlying low velocity basement in the area to the north of Ma'erkang. The crustal structure in the section can be divided into 4 parts: in the south of Garze-Litang fault, between Garze-Litang fault and Xianshuihe fault, between Xianshuihe fault and Longriba fault and in the north of Longriba fault, which are basically coincided with the regional tectonics division. The crustal thickness decreases from southwest to northeast along the profile, that is, from 62 km in the region of the Jinshajiang River to 52 km in the region of the Yellow River. The Moho discontinuity does not obviously change across the Xianshuihe fault based on the PmP phase analysis. The crustal average velocity along the profile is lower, about 6.30 km/s. The Benzilan-Tangke profile reveals that the crust in the study area is orogenic. The Xianshuihe fault belt is located in the central part of the profile, and the velocity is positive anomaly on the upper crust, and negative anomaly on the lower crust and upper mantle. It is considered as a deep tectonic setting in favor of strong earthquake's accumulation and occurrence.
基金supported by the National 973 Key Development Program for Basic Research of China(S/N: 2006CB202308)the National Natural Science Foundation of China(Grant No.40972088)
文摘The Tazhong paleouplift is divided into the upper and the lower structural layers, bounded by the unconformity surface at the top of the Ordovician carbonate rock. The reservoirs in the two layers from different parts vary in number, type and reserves, but the mechanism was rarely researched before. Therefore, an explanation of the mechanism will promote petroleum exploration in Tazhong paleouplift. After studying the evolution and reservoir distribution of the Tazhong paleouplift, it is concluded that the evolution in late Caledonian, late Hercynian and Himalayan periods resulted in the upper and the lower structural layers. It is also defined that in the upper structural layer, structural and stratigraphic overlap reservoirs are developed at the top and the upper part of the paleouplift, which are dominated by oil reservoirs, while for the lower structural layer, lithological reservoirs are developed in the lower part of the paleouplift, which are dominated by gas reservoirs, and more reserves are discovered in the lower structural layer than the upper. Through a comparative analysis of accumulation conditions of the upper and the lower structural layers, the mechanism of enrichment differences is clearly explained. The reservoir and seal conditions of the lower structural layer are better than those of the upper layer, which is the reason why more reservoirs have been found in the former. The differences in the carrier system types, trap types and charging periods between the upper and the lower structural layers lead to differences in the reservoir types and distribution. An accumulation model is established for the Tazhong paleouplift. For the upper structural layer, the structural reservoirs and the stratigraphic overlap reservoirs are formed at the upper part of the paleouplift, while for the lower structural layer, the weathering crust reservoirs are formed at the top, the reef-flat reservoirs are formed on the lateral margin, the karst and inside reservoirs are formed in the lower part of the paleouplift.
基金Supported by the National Natural Science Foundation of China(No.61772031)the Special Energy Saving Foundation of Changsha,Hunan Province in 2017
文摘Granular computing is a very hot research field in recent years. In our previous work an algebraic quotient space model was proposed,where the quotient structure could not be deduced if the granulation was based on an equivalence relation. In this paper,definitions were given and formulas of the lower quotient congruence and upper quotient congruence were calculated to roughly represent the quotient structure. Then the accuracy and roughness were defined to measure the quotient structure in quantification. Finally,a numerical example was given to demonstrate that the rough representation and measuring methods are efficient and applicable. The work has greatly enriched the algebraic quotient space model and granular computing theory.
文摘The attenuation of seismic waves reflects the elastic nature of the media within which the waves propagate.In this study,we calculate the Coda-Q(Qc),frequency dependence(η),Vp/Vs and Poisson's(υ)ratios by using 2621 vertical component seismograms generated by 987 earthquakes recorded by 13 seismic stations in Eastern Anatolia,and creat a 2-D seismic tomographic Qc model for the region.The obtained model provides significant information for exploring the boundaries of adjacent tectonic units within the upper crust and interpreting their dynamic characteristics.The 2-D Qc model and the other parameters are consistent with the seismotectonic features of Eastern Anatolia.Highly heterogeneous Qc values are observed in the study area dividing it into north-south directed bands of low and high attenuation.The highestηvalues were obtained beneath the northwestern and eastern parts of the study region.Clear,high and lowυvalues are obtained in the western and eastern parts of the study area,respectively.The spatial variations in the measured parameters are consistent with many geophysical observations including low Pn velocities,efficient Sn blockage,high heat flow,and widespread volcanism.Different upper crustal thicknesses and inhomogeneous stress distribution along the East and North Anatolian Fault Zones may also contribute to the observed heterogeneities.
基金the National Natural Science Foundation of China (Grant No. 49999560) and NKBRSF (Grant Nos. G1999043409 and G2000078500).
文摘A great number of calcareous nannofossils have been found in the deep-sea sediments of 2.32 Ma at ODP Site 1143 located in the Nansha area, the southern South China Sea. The number of coccoliths varies from about 0.5×106 up to almost 53×106 coccoliths/g sediment, with an average of 16×106 coccoliths/g sediment. The accumulation rate of total coccoliths varies from 1×106 to 278×106 coccoliths/cm2 ka. The nannofossil assemblages are usually dominated by a lower-photic species-Florisphaera profunda, of which the average percentage is about 70% in all samples. The absolute abundance and the accumulation rate of nannofossils as well as the percentage ofF. profunda display significant oscillations on two different time scales. One is the fluctuation coincident with the glacial-interglacial cycle, and the other is the long-term changes on a time scale longer than 100 ka. Six evolutionary stages of calcareous nannofossils could be divided for the last 2.32 Ma, from which we can reconstruct the changes in the depth of nutricline of the Nansha area. In this paper, the possible mechanism resulting in these variations is also discussed.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91014006, 90914005 & 41474073)
文摘From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41031065, 41421003)by the Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences
文摘Outflowing ion beams forming four successive inverted-V structures in the energy-time spectrograms of H+, He+, and O+ were observed at an altitude of 3.4 RE by Cluster satellites travelling above the auroral acceleration region (AAR) in the southern hemisphere on February 14, 2001. Energization by negative U-shaped potential structures in the AAR is believed to be responsible for the formation of these outflowing ion inverted-V structures. Thus, utilizing the different motion properties of the three ion species, the altitude of the upper boundary of the AAR is estimated to be ~11100 km. Moreover, based on multi-satellite observations, each of these U-shaped potential structures involved in this event crosses the latitudinal direction at ~0.4°–1° invariantlatitude (ILAT), moving poleward at an average speed of ~0.2° ILAT per minute, before disappearing at ~71.5° ILAT.
文摘We studied ultrastructurally the cancellons bone tissues of the upper femoral ends, collected from 12 patients undergoing endoprostbesis replacement for fractures of the femoral neck and from 7 fresh cadavers. The bone tissues were composed of meshwork of trabeculae, that constituted tier upon tier of anisotropic arch structures of different diameters and sizes. The arch structures of the cancellous bone tissues in the femoral heads assumed round or roundish configurations, whereas those of the femoral head-neck junctions revealed oval outlines and those of the femoral necks showed narrow oval profiles. The fine structures of the trabecnlae in the femoral head could be divided into superficial zone, central zone, and transitional zone. Under weight-bearing, the central zone suited to sustain the load, while the superficial zone could produce elastic deformation lest fracture of the trabecaulae should ensue. The long axes of the oval arch structures of the femoral head-neck junction and the narrow oval arch structures of the femoral neck coincided with those of the femoral neck, thereby facilitating weight-bearing under physiological conditions. However, external violence in the form of either adduction or abduction force would act in a horizontal direction on the long axes of the oval and narrow oval arches so as to produce subcapital or transverse fracture of the femur in the aged.
