Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian li...Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian lithospheric subduction are still controversial.Answering these questions requires additional information regarding crustal structure.In this study,the 2-D normalized full gradient(NFG)of the Bouguer gravity anomaly was used to investigate anomalous sources and interpret the crustal structure underneath the Qiangtang and Songpan-Ganzi terranes.The NFG-derived structures with loworder harmonic numbers(N=33 and N=43)showed that an anomalous source beneath the southern Qiangtang terrane had a characteristic northeastward-dipping shape,suggesting the northeastward motion of the crustal material induced by underthrusting Indian lithospheric mantle.The NFG images with harmonic number N=53 showed a large-scale anomalous source in the lower crust of the transformational zone from the Qiangtang terrane to the Songpan-Ganzi terrane,consistent with thickening crust and resistance of lower crustal flow.The anomalous source demonstrated by the NFG results with harmonic number N=71,located in the upper crust underneath the Ganzi-Yushu fault,suggested a seismogenic body of the 2010 M6.9 Yushu event.展开更多
The method of 3D polar transformation of full gravity potential gradient vectors is based on the geometric properties of the crossing points of complete gradient of the potential to localize the source region that cau...The method of 3D polar transformation of full gravity potential gradient vectors is based on the geometric properties of the crossing points of complete gradient of the potential to localize the source region that causes the observed anomaly. The cross-points—poles—are defined for rectangular polygons of different sizes where the full gradient vector is defined at every vertex. The polygon size range could be specified. The set of poles, positive and negative, is then represented on the 3D chart in the form of clusters of dots or cubes and can be considered as a model image of the sources, intended for visual analysis and further interpretation.展开更多
We present an estimation of depth of anomalous bodies using normalized full gradient （NFG） of gravity anomaly. Maxima in the NFG map can locate the bodies and indicate their depth. Model calculation using a sphere a...We present an estimation of depth of anomalous bodies using normalized full gradient （NFG） of gravity anomaly. Maxima in the NFG map can locate the bodies and indicate their depth. Model calculation using a sphere and application of the NFG method to gravity anomalies over salt domes in the USA and Denmark shows effectiveness of the method. However, the accuracy of depth estimation strongly depends on the number of term N in the Fourier series used to calculate the NFG. An optimum N for the calculation can be given from a test.展开更多
The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of thi...The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of this approach is prone to be influ- enced by the energy of reflected waves. To tackle this problem, the paper proposes a new gradient preconditioning method based on the energy of transmitted waves. The approach scales the gradient through a precondition factor, which is calculated by the ‘ap- proximate transmission wavefield’ simulation based on the nonreflecting acoustic wave equation. The method requires no computing nor storing of the Hessian matrix and its inverse matrix. Furthermore, the proposed method can effectively eliminate the effects of geometric spreading and disproportionality in the gradient illumination. The results of model experiments show that the time-domain full waveform inversion (FWI) using the gradient preconditioning based on transmitted wave energy can achieve higher inversion accuracy for deep high-velocity bodies and their underlying strata in comparison with the one using the gradient preconditioning based on seismic wave energy. The field marine seismic data test shows that our proposed method is also highly applicable to the FWI of field marine seismic data.展开更多
In the present work we calculate the energies,quadrupole moments,and electric field gradients（EFGs） of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force co...In the present work we calculate the energies,quadrupole moments,and electric field gradients（EFGs） of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force constant k2 is the product of charge and EFG at its equilibrium nuclear distance.The dipole charge distributions for these symmetrical molecules are all in equilibrium,however,the quadrupole charge distributions are far from equilibrium;among these,there is the most remarkable deviation from equilibrium for N2,for its many charges concentrate on two sides of the molecule,which is in agreement with the well-known characteristic of the nitrogen molecule.The relativistic effect is remarkable even for the same period.展开更多
With the development of gravity gradient full tensor measurement technique,three-dimensional( 3D) inversion based on gravity gradient tensor can provide more accurate information. But the forward calculation of 3D ful...With the development of gravity gradient full tensor measurement technique,three-dimensional( 3D) inversion based on gravity gradient tensor can provide more accurate information. But the forward calculation of 3D full tensor sensitivity matrix is very time-consuming,which restricts its development and application.According to the symmetry of the kernel function,the authors reconstruct the underground source of geological body to avoid repeat computation of the same value,and work out the corresponding relationship between the response of geological body to the observation point and the response of reconstructed geological body to the observation point. According to the relationship,rapid calculation of full tensor gravity sensitivity matrix can be achieved. The model calculation shows that this method can increase the speed of 30-45 times compared with the traditional calculation method. The sensitivity matrix is applied to the multi-component inversion of gravity gradient. The application of this method on the measured data provides the basis for the promotion of the method.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.42074090)
文摘Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau.However,crust-mantle evolution and crustal response to the Indian lithospheric subduction are still controversial.Answering these questions requires additional information regarding crustal structure.In this study,the 2-D normalized full gradient(NFG)of the Bouguer gravity anomaly was used to investigate anomalous sources and interpret the crustal structure underneath the Qiangtang and Songpan-Ganzi terranes.The NFG-derived structures with loworder harmonic numbers(N=33 and N=43)showed that an anomalous source beneath the southern Qiangtang terrane had a characteristic northeastward-dipping shape,suggesting the northeastward motion of the crustal material induced by underthrusting Indian lithospheric mantle.The NFG images with harmonic number N=53 showed a large-scale anomalous source in the lower crust of the transformational zone from the Qiangtang terrane to the Songpan-Ganzi terrane,consistent with thickening crust and resistance of lower crustal flow.The anomalous source demonstrated by the NFG results with harmonic number N=71,located in the upper crust underneath the Ganzi-Yushu fault,suggested a seismogenic body of the 2010 M6.9 Yushu event.
文摘The method of 3D polar transformation of full gravity potential gradient vectors is based on the geometric properties of the crossing points of complete gradient of the potential to localize the source region that causes the observed anomaly. The cross-points—poles—are defined for rectangular polygons of different sizes where the full gradient vector is defined at every vertex. The polygon size range could be specified. The set of poles, positive and negative, is then represented on the 3D chart in the form of clusters of dots or cubes and can be considered as a model image of the sources, intended for visual analysis and further interpretation.
基金supported by the Ministry of Science,Researches and Technology,Iran
文摘We present an estimation of depth of anomalous bodies using normalized full gradient （NFG） of gravity anomaly. Maxima in the NFG map can locate the bodies and indicate their depth. Model calculation using a sphere and application of the NFG method to gravity anomalies over salt domes in the USA and Denmark shows effectiveness of the method. However, the accuracy of depth estimation strongly depends on the number of term N in the Fourier series used to calculate the NFG. An optimum N for the calculation can be given from a test.
基金support of the NSFCShandong Joint Fund for Marine Science Research Centers (No. U1606401)the National Natural Science Foundation of China (Nos. 41574105 and 41704114)+1 种基金the National Science and Technology Major Project of China (No.2016ZX05027-002)Taishan Scholar Project Funding (No. tspd20161007)
文摘The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of this approach is prone to be influ- enced by the energy of reflected waves. To tackle this problem, the paper proposes a new gradient preconditioning method based on the energy of transmitted waves. The approach scales the gradient through a precondition factor, which is calculated by the ‘ap- proximate transmission wavefield’ simulation based on the nonreflecting acoustic wave equation. The method requires no computing nor storing of the Hessian matrix and its inverse matrix. Furthermore, the proposed method can effectively eliminate the effects of geometric spreading and disproportionality in the gradient illumination. The results of model experiments show that the time-domain full waveform inversion (FWI) using the gradient preconditioning based on transmitted wave energy can achieve higher inversion accuracy for deep high-velocity bodies and their underlying strata in comparison with the one using the gradient preconditioning based on seismic wave energy. The field marine seismic data test shows that our proposed method is also highly applicable to the FWI of field marine seismic data.
基金Project supported by the Fundamental Research Funds for the Central Universities
文摘In the present work we calculate the energies,quadrupole moments,and electric field gradients（EFGs） of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force constant k2 is the product of charge and EFG at its equilibrium nuclear distance.The dipole charge distributions for these symmetrical molecules are all in equilibrium,however,the quadrupole charge distributions are far from equilibrium;among these,there is the most remarkable deviation from equilibrium for N2,for its many charges concentrate on two sides of the molecule,which is in agreement with the well-known characteristic of the nitrogen molecule.The relativistic effect is remarkable even for the same period.
基金Support by Project of Geophysical Comprehensive Survey and Information Extraction of Deep Mineral Resources(2016YFC0600505)
文摘With the development of gravity gradient full tensor measurement technique,three-dimensional( 3D) inversion based on gravity gradient tensor can provide more accurate information. But the forward calculation of 3D full tensor sensitivity matrix is very time-consuming,which restricts its development and application.According to the symmetry of the kernel function,the authors reconstruct the underground source of geological body to avoid repeat computation of the same value,and work out the corresponding relationship between the response of geological body to the observation point and the response of reconstructed geological body to the observation point. According to the relationship,rapid calculation of full tensor gravity sensitivity matrix can be achieved. The model calculation shows that this method can increase the speed of 30-45 times compared with the traditional calculation method. The sensitivity matrix is applied to the multi-component inversion of gravity gradient. The application of this method on the measured data provides the basis for the promotion of the method.
