Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been wi...Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been widely used in reflection wave raytracing,and both of them are characterized by high efficiency and ac-curacy.However,the MSPM does not strictly follow Snell's law at the interface because it treats the interface point as a sub-source,resulting in a decrease in accuracy.The MFMM achieves high accuracy by solving the Eikonal equation in local triangular mesh.However,the implementation process is complex.Here we propose a new method which uses linear interpolation to compute the incident travel time of interface points and then using Snell's law to compute the reflection travel time of grid points just above the interface.Our new method is much simpler than the MFMM;furthermore,numerical simulations show that the accuracy of the MFMM and our new method are basically the same,thus the reflection tomography algorithms which use our new method are easier to implement without decreasing accuracy.Besides,our new method can be extended easily to other grid-based raytracing methods.展开更多
In order to investigate the interrelations of crust and upper mantle tectonics and its velocity distribution as well as seismicity in the Yanhuai basin and its surrounding area, a nearly EW trending Beijing Huailai ...In order to investigate the interrelations of crust and upper mantle tectonics and its velocity distribution as well as seismicity in the Yanhuai basin and its surrounding area, a nearly EW trending Beijing Huailai Fengzhen wide angle reflection/refraction profile, which obliquely passes through seismic zone of Zhangjiakou Bohai Sea and coincides with a deep reflection profile in the Yanhuai basin, was completed recently. The results show: The crust presents layered structures and its thickness gradually increases from 35.0 km in Shunyi to 42.0 km in the west end of the profile; the interior crustal interfaces appear approximately horizontal or slowly sloping down from east to west; In the Yanhuai basin, the crust presents the characteristics of higher velocities alternating with the lower ones and the low velocity bodies obviously exist in the lower part of upper crust. Moreover, there are two deep crustal fault zones which stretch to the Moho discontinuity, are closely related with the seismicity in the Yanhuai area.展开更多
In this paper, the typical velocity structures and average velocities of the crust in six different active tectonic block regions are presented on the basis of previous studies and their tectonic implications are disc...In this paper, the typical velocity structures and average velocities of the crust in six different active tectonic block regions are presented on the basis of previous studies and their tectonic implications are discussed. The results show that different tectonic units have different features of crustal velocity structures. In general, there are low velocity distributions in the crust in regions with strong tectonic activities, and the scales of low velocity distributions are related to the tectonic activities. The average velocities are relatively low in such regions. This reflects strong crustal deformation and the variations of states of matter in the crust resulting from strong tectonic movements. These regions are also seismically active zones frequented by strong earthquakes. Therefore, studying crustal velocity structures of these regions is of great importance to understanding crustal geodynamic process and seismogenic tectonic background.展开更多
The paper presents the results of a ground penetrating radar （GPR） application for the detection of ground ice. We com- bined a reflection traveltime curves analysis with a frequency spectrogram analysis. We found s...The paper presents the results of a ground penetrating radar （GPR） application for the detection of ground ice. We com- bined a reflection traveltime curves analysis with a frequency spectrogram analysis. We found special anomalies at specific traces in the traveltime curves and ground boundaries analysis, and obtained a ground model for subsurface structure which allows the ground ice layer to be identified and delineated.展开更多
In this paper,we propose and experimentally demonstrate a method to realize a polarization detector by using a commercially available polymethyl methacrylate（PMMA） pipe.An asymmetric polarization-related structure i...In this paper,we propose and experimentally demonstrate a method to realize a polarization detector by using a commercially available polymethyl methacrylate（PMMA） pipe.An asymmetric polarization-related structure is fabricated by etching different grating structures on the external surface of the pipe.The results show that when the pipe rotates up to 90°,the peak of the transmission spectrum can evidently shift towards the low frequency,which means the pipe with grating structures can serve as a polarization detector.This design possesses the merits of a simple structure and easy fabrication.展开更多
An improved reconstructing field method for measuring sound reflection coefficient of a large impedance surface at arbitrary incident angles is proposed in this paper. In order to get the reflection coefficient by the...An improved reconstructing field method for measuring sound reflection coefficient of a large impedance surface at arbitrary incident angles is proposed in this paper. In order to get the reflection coefficient by the Spatial Transformation of Sound Fields (STSF), the complex pressure on two parallel planes near by the material surface or the reflection surface must be measured. By the acoustic intensity measurement, the phases of complex pressure on two parallel planes are given. The results of the numerical simulations are shown that the error due to the finite size of the measurement area, and it may be reduced by using a dipole sound source.展开更多
A new type of optical fiber is presented here. It consists of a coaxial optical fiber, bounded by dielectric, multilayer and omnidirectional reflecting mirrors. Jones matrix method is used to analyze the influence of ...A new type of optical fiber is presented here. It consists of a coaxial optical fiber, bounded by dielectric, multilayer and omnidirectional reflecting mirrors. Jones matrix method is used to analyze the influence of the layer number of one Dimensional (1D) photonic crystals on their reflectivity. The numerical results show that this type of fiber can be used to guide light around sharp bends whose radius of curvature can be as small as the wavelength of light without significant scattering losses.展开更多
基金This research is jointly sponsored by National Natural Science Foundation of China(Grant No.U1901602)Shenzhen Key Laboratory of Deep Offshore Oil and Gas Exploration Technology(Grant No.ZDSYS20190902093007855)+1 种基金Shenzhen Science and Technology Program(KQTD20170810111725321)This study is also sponsored by the China Earthquake Science Experiment Project of China Earthquake Administration(Grant No.2018CSES0101).
文摘Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been widely used in reflection wave raytracing,and both of them are characterized by high efficiency and ac-curacy.However,the MSPM does not strictly follow Snell's law at the interface because it treats the interface point as a sub-source,resulting in a decrease in accuracy.The MFMM achieves high accuracy by solving the Eikonal equation in local triangular mesh.However,the implementation process is complex.Here we propose a new method which uses linear interpolation to compute the incident travel time of interface points and then using Snell's law to compute the reflection travel time of grid points just above the interface.Our new method is much simpler than the MFMM;furthermore,numerical simulations show that the accuracy of the MFMM and our new method are basically the same,thus the reflection tomography algorithms which use our new method are easier to implement without decreasing accuracy.Besides,our new method can be extended easily to other grid-based raytracing methods.
文摘In order to investigate the interrelations of crust and upper mantle tectonics and its velocity distribution as well as seismicity in the Yanhuai basin and its surrounding area, a nearly EW trending Beijing Huailai Fengzhen wide angle reflection/refraction profile, which obliquely passes through seismic zone of Zhangjiakou Bohai Sea and coincides with a deep reflection profile in the Yanhuai basin, was completed recently. The results show: The crust presents layered structures and its thickness gradually increases from 35.0 km in Shunyi to 42.0 km in the west end of the profile; the interior crustal interfaces appear approximately horizontal or slowly sloping down from east to west; In the Yanhuai basin, the crust presents the characteristics of higher velocities alternating with the lower ones and the low velocity bodies obviously exist in the lower part of upper crust. Moreover, there are two deep crustal fault zones which stretch to the Moho discontinuity, are closely related with the seismicity in the Yanhuai area.
文摘In this paper, the typical velocity structures and average velocities of the crust in six different active tectonic block regions are presented on the basis of previous studies and their tectonic implications are discussed. The results show that different tectonic units have different features of crustal velocity structures. In general, there are low velocity distributions in the crust in regions with strong tectonic activities, and the scales of low velocity distributions are related to the tectonic activities. The average velocities are relatively low in such regions. This reflects strong crustal deformation and the variations of states of matter in the crust resulting from strong tectonic movements. These regions are also seismically active zones frequented by strong earthquakes. Therefore, studying crustal velocity structures of these regions is of great importance to understanding crustal geodynamic process and seismogenic tectonic background.
文摘The paper presents the results of a ground penetrating radar （GPR） application for the detection of ground ice. We com- bined a reflection traveltime curves analysis with a frequency spectrogram analysis. We found special anomalies at specific traces in the traveltime curves and ground boundaries analysis, and obtained a ground model for subsurface structure which allows the ground ice layer to be identified and delineated.
文摘In this paper,we propose and experimentally demonstrate a method to realize a polarization detector by using a commercially available polymethyl methacrylate（PMMA） pipe.An asymmetric polarization-related structure is fabricated by etching different grating structures on the external surface of the pipe.The results show that when the pipe rotates up to 90°,the peak of the transmission spectrum can evidently shift towards the low frequency,which means the pipe with grating structures can serve as a polarization detector.This design possesses the merits of a simple structure and easy fabrication.
文摘An improved reconstructing field method for measuring sound reflection coefficient of a large impedance surface at arbitrary incident angles is proposed in this paper. In order to get the reflection coefficient by the Spatial Transformation of Sound Fields (STSF), the complex pressure on two parallel planes near by the material surface or the reflection surface must be measured. By the acoustic intensity measurement, the phases of complex pressure on two parallel planes are given. The results of the numerical simulations are shown that the error due to the finite size of the measurement area, and it may be reduced by using a dipole sound source.
文摘A new type of optical fiber is presented here. It consists of a coaxial optical fiber, bounded by dielectric, multilayer and omnidirectional reflecting mirrors. Jones matrix method is used to analyze the influence of the layer number of one Dimensional (1D) photonic crystals on their reflectivity. The numerical results show that this type of fiber can be used to guide light around sharp bends whose radius of curvature can be as small as the wavelength of light without significant scattering losses.
