Passive surface wave imaging has been a powerful tool for near-surface characterization in urban areas,which extracts surface wave signals from ambient seismic noise and then estimates subsurface shear wave velocity b...Passive surface wave imaging has been a powerful tool for near-surface characterization in urban areas,which extracts surface wave signals from ambient seismic noise and then estimates subsurface shear wave velocity by inversion of the measured phase velocity.The high-frequency(approximately>1 Hz)seismic noise fields in urban environments are dominantly induced by human activities such as the vehicle traffic.Traffic seismic sources are nonrandomly distributed in time and space.Applying standard interferometric techniques to recordings from these nonrandom noise sources makes the Green’s function liable to estimation errors.We analyze the influence of using nonrandom traffic seismic sources for surface wave imaging.With nonrandom traffic seismic sources in time,spurious signals are generated in the cross-correlation function.With nonrandom traffic seismic sources in space,surface-wave phase velocities could be overestimated in the dispersion measurement.We provide an overview of solutions for surface-wave imaging with nonrandom traffic seismic sources in time and space,aiming to improve the retrieval of high-frequency surface waves and achieve reliable results from ultrashort(tens of seconds)observations for near-surface characterization.展开更多
Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been sy...Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been systematically discussed.This study investigates the influence of various parameter assumptions on the results of surface-wave inversion,including the compressional and shear velocity ratio(v_(P)/v_(S)),shear-wave attenuation(Q_(S)),density(ρ),Moho interface,and sedimentary layer.We constructed synthetic models to generate dispersion data and compared the obtained results with different parameter assumptions with those of the true model.The results indicate that the v_(P)/v_(S) ratio,Q_(S),and density(ρ) have minimal effects on absolute velocity values and perturbation patterns in the inversion.Conversely,assumptions about the Moho interface and sedimentary layer significantly influenced absolute velocity values and perturbation patterns.Introducing an erroneous Mohointerface depth in the initial model of the inversion significantly affected the v_(S) model near that depth,while using a smooth initial model results in relatively minor deviations.The assumption on the sedimentary layer not only affects shallow structure results but also impacts the result at greater depths.Non-linear inversion methods outperform linear inversion methods,particularly for the assumptions of the Moho interface and sedimentary layer.Joint inversion with other data types,such as receiver functions or Rayleigh wave ellipticity,and using data from a broader period range or higher-mode surface waves,can mitigate these deviations.Furthermore,incorporating more accurate prior information can improve inversion results.展开更多
The principle of surface wave plasma discharge in a rectangular cavity is introduced and the distribution of the electromagnetic field within a rectangular waveguide is analysed. A novel structure of a slot antenna ar...The principle of surface wave plasma discharge in a rectangular cavity is introduced and the distribution of the electromagnetic field within a rectangular waveguide is analysed. A novel structure of a slot antenna array is presented. In comparison with the traditional slotantenna, it is shown that the designed slot antenna array can excite effectively the surface wave coupling into the chamber, and generate a stable large-area high-density plasma. These results are useful for exploring the optimized design of the slot-antenna for surface wave plasmas.展开更多
A three-dimensional model of a surface-wave plasma （SWP） source is built numerically using the finite-difference time-domain （FDTD） method to investigate the structure of the surface wave propagation along the pla...A three-dimensional model of a surface-wave plasma （SWP） source is built numerically using the finite-difference time-domain （FDTD） method to investigate the structure of the surface wave propagation along the plasma-dielectric interface and the distributions of electromagnetic fields in the whole system. A good-performance excitation source technique for the waveguide which is pivotal to the simulation is presented. The technique can avoid the dc distortions of magnetic fields caused by the forcing electric wall. An example of simulation is given to confirm the existence of the surface waves. The simulation also shows that the code developed is a useful tool in the computer-aided design of the antenna of the SWP source.展开更多
Site engineering seismic survey provides basic data for seismic effect analysis. As an important parameter of soil, shear-wave velocity is usually obtained through wave velocity testing in borehole. In this paper, the...Site engineering seismic survey provides basic data for seismic effect analysis. As an important parameter of soil, shear-wave velocity is usually obtained through wave velocity testing in borehole. In this paper, the passive source surface-wave method is introduced into the site engineering seismic survey and practically applied in an engineering site of Shijingshan District. By recording the ubiquitous weak vibration on the earth surface, extract the dispersion curve from the surface-wave components using the SPAC method and obtain the shear-wave velocity structure from inversion. Over the depth of 42 m under- ground, it totally consists of five layers with interface depth of 3.31, 4.50, 7.23, 17.41, and 42.00 m; and shear-wave velocity of 144.0, 198.3, 339.4, 744.2, and 903.7 m/s, respectively. The inversion result is used to evaluate site classification, determine the maximum shear modulus of soil, provide basis for further seismic hazard analysis and site assessment or site zoning, etc. The result shows that the passive source surface-wave method is feasible in the site engineering seismic survey and can replace boreholes,shorten survey period, and reduce engineering cost to some extent.展开更多
The plasma parameters of planar-type surface-wave plasmas （SWPs） are diagnosed based on the resonant excitation of surface plasmon polaritons （SPPs）. The plasma parameter distributions are obtained by changing the...The plasma parameters of planar-type surface-wave plasmas （SWPs） are diagnosed based on the resonant excitation of surface plasmon polaritons （SPPs）. The plasma parameter distributions are obtained by changing the discharge conditions of gas pressure and incident power. The measured experimental results show that the plasma near the heating layer is excited by surface waves of SPPs while the plasma located downstream originates from diffusion Moreover, the influence of high-frequency oscillations plays a significant role in producing the proposed SWPs with bi-Maxwellian electron energy distributions.展开更多
Surface-wave tomography is an important and widely used method for imaging the crust and upper mantle velocity structure of the Earth.In this study,we proposed a deep learning(DL)method based on convolutional neural n...Surface-wave tomography is an important and widely used method for imaging the crust and upper mantle velocity structure of the Earth.In this study,we proposed a deep learning(DL)method based on convolutional neural network(CNN),named SfNet,to derive the vS model from the Rayleigh wave phase and group velocity dispersion curves.Training a network model usually requires large amount of training datasets,which is labor-intensive and expensive to acquire.Here we relied on synthetics generated automatically from various spline-based vS models instead of directly using the existing vS models of an area to build the training dataset,which enhances the generalization of the DL method.In addition,we used a random sampling strategy of the dispersion periods in the training dataset,which alleviates the problem that the real data used must be sampled strictly according to the periods of training dataset.Tests using synthetic data demonstrate that the proposed method is much faster,and the results for the vS model are more accurate and robust than those of conventional methods.We applied our method to a dataset for the Chinese mainland and obtained a new reference velocity model of the Chinese continent(ChinaVs-DL1.0),which has smaller dispersion misfits than those from the traditional method.The high accuracy and efficiency of our DL approach makes it an important method for vS model inversions from large amounts of surface-wave dispersion data.展开更多
The basic equations of free capillary_gravity surface_waves in a circular cylindrical basin were derived from Luke's principle. Taking Galerkin's expansion of the velocity potential and the free surface elevat...The basic equations of free capillary_gravity surface_waves in a circular cylindrical basin were derived from Luke's principle. Taking Galerkin's expansion of the velocity potential and the free surface elevation, the second_order perturbation equations were derived by use of expansion of multiple scale. The nonlinear interactions with the second order internal resonance of three free surface_waves were discussed based on the above. The results include:derivation of the couple equations of resonant interactions among three waves and the conservation laws; analysis of the positions of equilibrium points in phase plane; study of the resonant parameters and the non_resonant parameters respectively in all kinds of circumstances; derivation of the stationary solutions of the second_order interaction equations corresponding to different parameters and analysis of the stability property of the solutions; discussion of the effective solutions only in the limited time range. The analysis makes it clear that the energy transformation mode among three waves differs because of the different initial conditions under nontrivial circumstance. The energy may either exchange among three waves periodically or damp or increase in single waves.展开更多
Using the data set of 20±2 sec and(A/T)max of surface waves recorded by Type-763 and Type-SK seismographs from five stations in Beijing and elsewhere,the mean square deviations u and relative mean deviations D of...Using the data set of 20±2 sec and(A/T)max of surface waves recorded by Type-763 and Type-SK seismographs from five stations in Beijing and elsewhere,the mean square deviations u and relative mean deviations D of Ms values determined by five calibration functions(a,a763,a300 aN and from Msz(NEIS)are compared and analyzed.Results show that a and a763 are rather good between 20° and 160°;and a763 are rather good between 10 and 30 for 20 sec; a300 is relatively good between 160 and 179.展开更多
Seismic anisotropy reveals that seismic wave velocity, amplitude, and other physical properties show variations in different directions, which can be divided into lattice-preferred orientation(LPO) and shape-preferred...Seismic anisotropy reveals that seismic wave velocity, amplitude, and other physical properties show variations in different directions, which can be divided into lattice-preferred orientation(LPO) and shape-preferred orientation(SPO) according to its physical mechanisms. The main methods for studying seismic anisotropy include shearwave splitting analysis, P-wave travel time inversion and surface-wave tomography, etc. There are some differences and correlations among these methods. Seismic anisotropy is an important way to reveal the dynamic processes of crust-mantle evolution, and it is significant for monitoring crustal stress changes and improve seismic exploration studies. With the help of long-term observation, the application of machine learning techniques and combining inversion based on multiple phases would become potential developments in seismic anisotropy studies. This may improve the understanding of complex seismic anisotropic models, such as multiple layers anisotropy with an oblique axis of symmetry.展开更多
During seismic wave propagation on a free surface, a strong material contrast boundary develops in response to interference by P- and S- waves to create a surface-wave phenomenon. To accurately determine the effects o...During seismic wave propagation on a free surface, a strong material contrast boundary develops in response to interference by P- and S- waves to create a surface-wave phenomenon. To accurately determine the effects of this interface on surface-wave propagation, the boundary conditions must be accurately modeled. In this paper, we present a numerical approach based on the dynamic poroelasticity for a space–time-domain staggered-grid finite-difference simulation in porous media that contain a free-surface boundary. We propose a generalized stess mirror formulation of the free-surface boundary for solids and fluids in porous media for the grid mesh on which lays the free-surface plane. Its analog is that used for elastic media, which is suitable for precise and stable Rayleigh-type surface-wave modeling. The results of our analysis of first kind of Rayleigh （R1） waves obtained by this model demonstrate that the discretization of the mesh in a similar way to that for elastic media can realize stable numerical solutions with acceptable precision. We present numerical examples demonstrating the efficiency and accuracy of our proposed method.展开更多
Aliased surface waves are caused by large-space sampling intervals in three- dimensional seismic exploration and most current surface-wave suppression methods fail to account for. Thus, we propose a surface-wave suppr...Aliased surface waves are caused by large-space sampling intervals in three- dimensional seismic exploration and most current surface-wave suppression methods fail to account for. Thus, we propose a surface-wave suppression method using phase-shift and phase-filtering, named the PSPF method, in which linear phase-shift is performed to solve the coupled problem of surface and reflected waves in the FKXKY domain and then used phase and FKXKY filtering to attenuate the surface-wave energy. Processing of model and field data suggest that the PSPF method can reduce the surface-wave energy while maintaining the low-frequency information of the reflected waves.展开更多
In this paper, the diffraction of water waves by a vertically floating cylinder in a two-layer fluid of a finite depth is studied. Analytical expressions for the hydrodynamic loads on the vertically floating cylinder ...In this paper, the diffraction of water waves by a vertically floating cylinder in a two-layer fluid of a finite depth is studied. Analytical expressions for the hydrodynamic loads on the vertically floating cylinder are obtained by use of the method of eigenfunction expansions. The hydrodynamic loads on the vertically floating cylinder in a two-layer fluid inelude not only the surge, heave and pitch exciting forces due to the incident wave of the surface-wave mode, but also those due to the incident wave of the internal-wave mode. This is different from the case of a homogenous fluid. Some given examples show that, for a two-layer fluid system with a small density difference, the hydrodynamic loads for the surface-wave mode do not differ significantly from those due to surface waves in a single-layer fluid, but the hydrodynamic loads for the internal-wave mode are important over a wide range of frequencies. Moreover, also considered are the free surface and interface elevations generated by the diffraction wave due to the incident wave of the surface-wave and interhal-wave modes, and transfer of energy between modes.展开更多
Anovel compact E shape High Impedance Surface(HIS) Electromagnetic Band-Gap(EBG) comprising Amended Minkowski Fractal Boundary(AMFB),Added Metal Strips(AMS),and metal plated via printed on a Rogers TMM 10i substrate i...Anovel compact E shape High Impedance Surface(HIS) Electromagnetic Band-Gap(EBG) comprising Amended Minkowski Fractal Boundary(AMFB),Added Metal Strips(AMS),and metal plated via printed on a Rogers TMM 10i substrate is presented.The first order AMFB and ABS are introduced for equivalent capacitance enhancement and miniaturization with effective space-filling characteristics.The dimension of lattice size is only The proposed structure exhibits a most compact characteristic about 35% size reduction as compared with conven-tional mushroom-like HIS-EBG,and better surface-wave decoupling of around 9 dB at the operating frequency band.Details of design parameters which affect the whole performance of certain band-gap are intensively investigated.A constructed prototype is potential candidate for antenna system per-formance enhancement.展开更多
There are strong interactions between the crust and the mantle in the Abaga area.To study the structure of the crust and upper mantle in that area,the fundamental-mode Rayleigh-wave phase velocity dispersion along 3,3...There are strong interactions between the crust and the mantle in the Abaga area.To study the structure of the crust and upper mantle in that area,the fundamental-mode Rayleigh-wave phase velocity dispersion along 3,331 inter-station paths were estimated by the continuous wavelet transformation method.The dispersion data were used to construct the first 2-D phase velocity maps for waves with periods of 12-80 s and a horizontal resolution of 0.5°×0.5°by applying a linear inversion.The results show that the short-period phase velocity distributions(12-20 s)are affected by exposed Cenozoic volcanoes and the thickness of the sedimentary layer.Phase velocity maps for waves with periods of 30-40 s indicate that the direction of the Solonker suture zone is in good agreement with the extension of the high-speed anomalous connection in the study area.It is concluded that the Solonker suture zone extends throughout the entire lithosphere.For periods of 30-80 s,stable low-velocity anomalies were observed near the Holocene volcanoes in the northeast and south of the study area,suggesting that the low-velocity anomaly is related to volcanic activity.Moreover,the two low-velocity anomalies may be connected,suggesting that the Darigan Volcano may have the same thermal source as the Honggeertu Volcano and even the Datong Volcano.And the thermal source of the two low-velocity anomalies is speculated to be upwelling of hot mantle material.In addition,the velocities in the crust and upper mantle are lower than those from the AK 135 model and are close to the velocity for the destroyed North China Craton,and very similar to that for the East African Rift Valley.This may indicate that the lithospheric structure in the Abaga area is active.展开更多
Sichuan Province,East Western of China,within the area of east longitude 97°21′-108°31′,north latitude 26°03′-34°19′,which is on the Mediterranean seismic zone;with its complicated geological b...Sichuan Province,East Western of China,within the area of east longitude 97°21′-108°31′,north latitude 26°03′-34°19′,which is on the Mediterranean seismic zone;with its complicated geological background,several strong shocks occurred in this district since ancient times.Earthquake catalogue of this area could date back to B.C.26,however,limited by the conditions—technology or funds,lots of minor earthquake have been lost,which could be展开更多
In order to give a more reliable shallow crust model for the Chinese mainland, the present study collected many short-period surface wave data which are better sensitive to shallow earth structures. Different from tra...In order to give a more reliable shallow crust model for the Chinese mainland, the present study collected many short-period surface wave data which are better sensitive to shallow earth structures. Different from traditional two-step surface wave tomography, we developed a new linearized surface wave dispersion inversion method to directly get a 3D S-wave velocity model in the second step instead of inverting for 1D S-velocity profile cell by cell. We convert all the regionalized dispersions into linear constraints for a 3D S-velocity model. Checkerboard tests show that this method can give reasonable results. The distribution of the middle- and upper-crust shear-wave velocity of the Chinese mainland in our model is strongly heterogeneous and related to different geotectonic terrains. Low-velocity anomalies delineated very well most of the major sedimentary basins of China. And the variation of velocities at different depths gives an indication of basement depth of the basins. The western Tethyan tectonic domain （on the west of the 95°E longitude） is characterized by low velocity, while the eastern Tethyan domain does not show obvious low velocity. Since petroleum resources often distribute in sedimentary basins where low-velocity anomaly appears, the low velocity anomalies in the western Tethyan domain may indicate a better petroleum prospect than in its eastern counterpart. Besides, low velocity anomaly in the western Tethyan domain and around the Xing＇an orogenic belt may be partly caused by high crustal temperature. The weak low-velocity belt along -105°E longitude corresponds to the N-S strong seismic belt of central China.展开更多
An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as ...An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies.展开更多
基金supported by the National Natural Science Foundation of China(No.42374177)。
文摘Passive surface wave imaging has been a powerful tool for near-surface characterization in urban areas,which extracts surface wave signals from ambient seismic noise and then estimates subsurface shear wave velocity by inversion of the measured phase velocity.The high-frequency(approximately>1 Hz)seismic noise fields in urban environments are dominantly induced by human activities such as the vehicle traffic.Traffic seismic sources are nonrandomly distributed in time and space.Applying standard interferometric techniques to recordings from these nonrandom noise sources makes the Green’s function liable to estimation errors.We analyze the influence of using nonrandom traffic seismic sources for surface wave imaging.With nonrandom traffic seismic sources in time,spurious signals are generated in the cross-correlation function.With nonrandom traffic seismic sources in space,surface-wave phase velocities could be overestimated in the dispersion measurement.We provide an overview of solutions for surface-wave imaging with nonrandom traffic seismic sources in time and space,aiming to improve the retrieval of high-frequency surface waves and achieve reliable results from ultrashort(tens of seconds)observations for near-surface characterization.
基金supported by the Special Fund of the Institute of Geophysics, China Earthquake Administration (No. DQJB21B32)the National Key R&D Program of China (No. 2022YFF0800601)。
文摘Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been systematically discussed.This study investigates the influence of various parameter assumptions on the results of surface-wave inversion,including the compressional and shear velocity ratio(v_(P)/v_(S)),shear-wave attenuation(Q_(S)),density(ρ),Moho interface,and sedimentary layer.We constructed synthetic models to generate dispersion data and compared the obtained results with different parameter assumptions with those of the true model.The results indicate that the v_(P)/v_(S) ratio,Q_(S),and density(ρ) have minimal effects on absolute velocity values and perturbation patterns in the inversion.Conversely,assumptions about the Moho interface and sedimentary layer significantly influenced absolute velocity values and perturbation patterns.Introducing an erroneous Mohointerface depth in the initial model of the inversion significantly affected the v_(S) model near that depth,while using a smooth initial model results in relatively minor deviations.The assumption on the sedimentary layer not only affects shallow structure results but also impacts the result at greater depths.Non-linear inversion methods outperform linear inversion methods,particularly for the assumptions of the Moho interface and sedimentary layer.Joint inversion with other data types,such as receiver functions or Rayleigh wave ellipticity,and using data from a broader period range or higher-mode surface waves,can mitigate these deviations.Furthermore,incorporating more accurate prior information can improve inversion results.
基金the scientific fund of returnees for studying abroad of the Ministry of Education of China of 2006
文摘The principle of surface wave plasma discharge in a rectangular cavity is introduced and the distribution of the electromagnetic field within a rectangular waveguide is analysed. A novel structure of a slot antenna array is presented. In comparison with the traditional slotantenna, it is shown that the designed slot antenna array can excite effectively the surface wave coupling into the chamber, and generate a stable large-area high-density plasma. These results are useful for exploring the optimized design of the slot-antenna for surface wave plasmas.
文摘A three-dimensional model of a surface-wave plasma （SWP） source is built numerically using the finite-difference time-domain （FDTD） method to investigate the structure of the surface wave propagation along the plasma-dielectric interface and the distributions of electromagnetic fields in the whole system. A good-performance excitation source technique for the waveguide which is pivotal to the simulation is presented. The technique can avoid the dc distortions of magnetic fields caused by the forcing electric wall. An example of simulation is given to confirm the existence of the surface waves. The simulation also shows that the code developed is a useful tool in the computer-aided design of the antenna of the SWP source.
基金supported by National Natural Science Foundation of China (No. 41174085)Chinese Academy of Sciences (KZZD-EW-TZ-19)China Geological Survey (12120113101400)
文摘Site engineering seismic survey provides basic data for seismic effect analysis. As an important parameter of soil, shear-wave velocity is usually obtained through wave velocity testing in borehole. In this paper, the passive source surface-wave method is introduced into the site engineering seismic survey and practically applied in an engineering site of Shijingshan District. By recording the ubiquitous weak vibration on the earth surface, extract the dispersion curve from the surface-wave components using the SPAC method and obtain the shear-wave velocity structure from inversion. Over the depth of 42 m under- ground, it totally consists of five layers with interface depth of 3.31, 4.50, 7.23, 17.41, and 42.00 m; and shear-wave velocity of 144.0, 198.3, 339.4, 744.2, and 903.7 m/s, respectively. The inversion result is used to evaluate site classification, determine the maximum shear modulus of soil, provide basis for further seismic hazard analysis and site assessment or site zoning, etc. The result shows that the passive source surface-wave method is feasible in the site engineering seismic survey and can replace boreholes,shorten survey period, and reduce engineering cost to some extent.
基金supported by National Natural Science Foundation of China(No.11105002)Doctoral Scientific Research Fund of AUST(No.2010yb011)ITER Domestic Matching Item of China(No.GB105003)
文摘The plasma parameters of planar-type surface-wave plasmas （SWPs） are diagnosed based on the resonant excitation of surface plasmon polaritons （SPPs）. The plasma parameter distributions are obtained by changing the discharge conditions of gas pressure and incident power. The measured experimental results show that the plasma near the heating layer is excited by surface waves of SPPs while the plasma located downstream originates from diffusion Moreover, the influence of high-frequency oscillations plays a significant role in producing the proposed SWPs with bi-Maxwellian electron energy distributions.
基金the Open Fund from SinoProbe Laboratory(Grant No.Sinoprobe Lab 202201)the National Natural Science Foundation of China(No.U1939204).
文摘Surface-wave tomography is an important and widely used method for imaging the crust and upper mantle velocity structure of the Earth.In this study,we proposed a deep learning(DL)method based on convolutional neural network(CNN),named SfNet,to derive the vS model from the Rayleigh wave phase and group velocity dispersion curves.Training a network model usually requires large amount of training datasets,which is labor-intensive and expensive to acquire.Here we relied on synthetics generated automatically from various spline-based vS models instead of directly using the existing vS models of an area to build the training dataset,which enhances the generalization of the DL method.In addition,we used a random sampling strategy of the dispersion periods in the training dataset,which alleviates the problem that the real data used must be sampled strictly according to the periods of training dataset.Tests using synthetic data demonstrate that the proposed method is much faster,and the results for the vS model are more accurate and robust than those of conventional methods.We applied our method to a dataset for the Chinese mainland and obtained a new reference velocity model of the Chinese continent(ChinaVs-DL1.0),which has smaller dispersion misfits than those from the traditional method.The high accuracy and efficiency of our DL approach makes it an important method for vS model inversions from large amounts of surface-wave dispersion data.
文摘The basic equations of free capillary_gravity surface_waves in a circular cylindrical basin were derived from Luke's principle. Taking Galerkin's expansion of the velocity potential and the free surface elevation, the second_order perturbation equations were derived by use of expansion of multiple scale. The nonlinear interactions with the second order internal resonance of three free surface_waves were discussed based on the above. The results include:derivation of the couple equations of resonant interactions among three waves and the conservation laws; analysis of the positions of equilibrium points in phase plane; study of the resonant parameters and the non_resonant parameters respectively in all kinds of circumstances; derivation of the stationary solutions of the second_order interaction equations corresponding to different parameters and analysis of the stability property of the solutions; discussion of the effective solutions only in the limited time range. The analysis makes it clear that the energy transformation mode among three waves differs because of the different initial conditions under nontrivial circumstance. The energy may either exchange among three waves periodically or damp or increase in single waves.
文摘Using the data set of 20±2 sec and(A/T)max of surface waves recorded by Type-763 and Type-SK seismographs from five stations in Beijing and elsewhere,the mean square deviations u and relative mean deviations D of Ms values determined by five calibration functions(a,a763,a300 aN and from Msz(NEIS)are compared and analyzed.Results show that a and a763 are rather good between 20° and 160°;and a763 are rather good between 10 and 30 for 20 sec; a300 is relatively good between 160 and 179.
基金supported by State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences(SKL-202204 and SKL-202305)the National Natural Science Foundation of China (42274131 and 41774111)。
文摘Seismic anisotropy reveals that seismic wave velocity, amplitude, and other physical properties show variations in different directions, which can be divided into lattice-preferred orientation(LPO) and shape-preferred orientation(SPO) according to its physical mechanisms. The main methods for studying seismic anisotropy include shearwave splitting analysis, P-wave travel time inversion and surface-wave tomography, etc. There are some differences and correlations among these methods. Seismic anisotropy is an important way to reveal the dynamic processes of crust-mantle evolution, and it is significant for monitoring crustal stress changes and improve seismic exploration studies. With the help of long-term observation, the application of machine learning techniques and combining inversion based on multiple phases would become potential developments in seismic anisotropy studies. This may improve the understanding of complex seismic anisotropic models, such as multiple layers anisotropy with an oblique axis of symmetry.
基金sponsed by National Natural Science Foundation of China(NSFC,Grant No.41304077)the Natural Basic Research Program of China(the“973 Project,”Grant No.2013CB733303)Postdoctoral Science Foundation of China(Grant No.2014T70740)
文摘During seismic wave propagation on a free surface, a strong material contrast boundary develops in response to interference by P- and S- waves to create a surface-wave phenomenon. To accurately determine the effects of this interface on surface-wave propagation, the boundary conditions must be accurately modeled. In this paper, we present a numerical approach based on the dynamic poroelasticity for a space–time-domain staggered-grid finite-difference simulation in porous media that contain a free-surface boundary. We propose a generalized stess mirror formulation of the free-surface boundary for solids and fluids in porous media for the grid mesh on which lays the free-surface plane. Its analog is that used for elastic media, which is suitable for precise and stable Rayleigh-type surface-wave modeling. The results of our analysis of first kind of Rayleigh （R1） waves obtained by this model demonstrate that the discretization of the mesh in a similar way to that for elastic media can realize stable numerical solutions with acceptable precision. We present numerical examples demonstrating the efficiency and accuracy of our proposed method.
基金supported by the National Natural Science Foundation of China(No.41274124)the National Science and Technology Major Project(No.2016ZX05014-001-008HZ)
文摘Aliased surface waves are caused by large-space sampling intervals in three- dimensional seismic exploration and most current surface-wave suppression methods fail to account for. Thus, we propose a surface-wave suppression method using phase-shift and phase-filtering, named the PSPF method, in which linear phase-shift is performed to solve the coupled problem of surface and reflected waves in the FKXKY domain and then used phase and FKXKY filtering to attenuate the surface-wave energy. Processing of model and field data suggest that the PSPF method can reduce the surface-wave energy while maintaining the low-frequency information of the reflected waves.
基金This project was financially supported by the National Natural Science Foundation of China(Grant No.10572092)the High Technology Research and Development Programof China(863Program,Grant Nos.2006AA09Z352 and 2006AA09196-6)
文摘In this paper, the diffraction of water waves by a vertically floating cylinder in a two-layer fluid of a finite depth is studied. Analytical expressions for the hydrodynamic loads on the vertically floating cylinder are obtained by use of the method of eigenfunction expansions. The hydrodynamic loads on the vertically floating cylinder in a two-layer fluid inelude not only the surge, heave and pitch exciting forces due to the incident wave of the surface-wave mode, but also those due to the incident wave of the internal-wave mode. This is different from the case of a homogenous fluid. Some given examples show that, for a two-layer fluid system with a small density difference, the hydrodynamic loads for the surface-wave mode do not differ significantly from those due to surface waves in a single-layer fluid, but the hydrodynamic loads for the internal-wave mode are important over a wide range of frequencies. Moreover, also considered are the free surface and interface elevations generated by the diffraction wave due to the incident wave of the surface-wave and interhal-wave modes, and transfer of energy between modes.
基金Supported by the 2010 Natural Science Foundation of Shanghai (No. 09ZR1430400)
文摘Anovel compact E shape High Impedance Surface(HIS) Electromagnetic Band-Gap(EBG) comprising Amended Minkowski Fractal Boundary(AMFB),Added Metal Strips(AMS),and metal plated via printed on a Rogers TMM 10i substrate is presented.The first order AMFB and ABS are introduced for equivalent capacitance enhancement and miniaturization with effective space-filling characteristics.The dimension of lattice size is only The proposed structure exhibits a most compact characteristic about 35% size reduction as compared with conven-tional mushroom-like HIS-EBG,and better surface-wave decoupling of around 9 dB at the operating frequency band.Details of design parameters which affect the whole performance of certain band-gap are intensively investigated.A constructed prototype is potential candidate for antenna system per-formance enhancement.
基金National Natural Science Foundation of China(Nos.41674094 and 41504073)。
文摘There are strong interactions between the crust and the mantle in the Abaga area.To study the structure of the crust and upper mantle in that area,the fundamental-mode Rayleigh-wave phase velocity dispersion along 3,331 inter-station paths were estimated by the continuous wavelet transformation method.The dispersion data were used to construct the first 2-D phase velocity maps for waves with periods of 12-80 s and a horizontal resolution of 0.5°×0.5°by applying a linear inversion.The results show that the short-period phase velocity distributions(12-20 s)are affected by exposed Cenozoic volcanoes and the thickness of the sedimentary layer.Phase velocity maps for waves with periods of 30-40 s indicate that the direction of the Solonker suture zone is in good agreement with the extension of the high-speed anomalous connection in the study area.It is concluded that the Solonker suture zone extends throughout the entire lithosphere.For periods of 30-80 s,stable low-velocity anomalies were observed near the Holocene volcanoes in the northeast and south of the study area,suggesting that the low-velocity anomaly is related to volcanic activity.Moreover,the two low-velocity anomalies may be connected,suggesting that the Darigan Volcano may have the same thermal source as the Honggeertu Volcano and even the Datong Volcano.And the thermal source of the two low-velocity anomalies is speculated to be upwelling of hot mantle material.In addition,the velocities in the crust and upper mantle are lower than those from the AK 135 model and are close to the velocity for the destroyed North China Craton,and very similar to that for the East African Rift Valley.This may indicate that the lithospheric structure in the Abaga area is active.
文摘Sichuan Province,East Western of China,within the area of east longitude 97°21′-108°31′,north latitude 26°03′-34°19′,which is on the Mediterranean seismic zone;with its complicated geological background,several strong shocks occurred in this district since ancient times.Earthquake catalogue of this area could date back to B.C.26,however,limited by the conditions—technology or funds,lots of minor earthquake have been lost,which could be
基金National Natural Science Foundation of China (40504011, 40674058)State Special Project of Oil-Gas of the Minis-try of Land and Resources (XQ-2004-01)
文摘In order to give a more reliable shallow crust model for the Chinese mainland, the present study collected many short-period surface wave data which are better sensitive to shallow earth structures. Different from traditional two-step surface wave tomography, we developed a new linearized surface wave dispersion inversion method to directly get a 3D S-wave velocity model in the second step instead of inverting for 1D S-velocity profile cell by cell. We convert all the regionalized dispersions into linear constraints for a 3D S-velocity model. Checkerboard tests show that this method can give reasonable results. The distribution of the middle- and upper-crust shear-wave velocity of the Chinese mainland in our model is strongly heterogeneous and related to different geotectonic terrains. Low-velocity anomalies delineated very well most of the major sedimentary basins of China. And the variation of velocities at different depths gives an indication of basement depth of the basins. The western Tethyan tectonic domain （on the west of the 95°E longitude） is characterized by low velocity, while the eastern Tethyan domain does not show obvious low velocity. Since petroleum resources often distribute in sedimentary basins where low-velocity anomaly appears, the low velocity anomalies in the western Tethyan domain may indicate a better petroleum prospect than in its eastern counterpart. Besides, low velocity anomaly in the western Tethyan domain and around the Xing＇an orogenic belt may be partly caused by high crustal temperature. The weak low-velocity belt along -105°E longitude corresponds to the N-S strong seismic belt of central China.
基金Project supported by the Foundation of the Excellent State Key Laboratory (Grant No. 50323004) the KSJ Foundation of the Education Ministry of China.
文摘An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies.
