Elastic wave on seafloor caused by low frequency noise radiated from ship is called ship seismic wave which can be used to identify ship target. In order to analyze the wave components and the propagating properties o...Elastic wave on seafloor caused by low frequency noise radiated from ship is called ship seismic wave which can be used to identify ship target. In order to analyze the wave components and the propagating properties of ship seismic wave, the numerical calculation of synthetic seismograms on seafloor aroused by a low frequency point sound source is carried out using a wave number integration technique combined with inverse Fourier transform. According to the numerical example of hard seafloor, the time series of seismic wave on seafloor are mostly composed of interface waves and normal mode waves. Each normal mode wave has a well defined low cut-off frequency, while the interface wave doesn't have. The frequency dispersion of normal mode wave is obvious when frequency is lower than 100Hz, while the interface wave is dispersive only in the infra-sound frequency range. The time series of seismic wave is dominated by the interface wave when the source frequency is less than the minimal cut-off frequency of normal mode wave.展开更多
The extensive use of depth-imaged seismic data produced by pre-stack depth migration(PSDM)leads to the necessity to synthesize seismogram directly in depth domain.However,since seismic wavelet in depth domain is depen...The extensive use of depth-imaged seismic data produced by pre-stack depth migration(PSDM)leads to the necessity to synthesize seismogram directly in depth domain.However,since seismic wavelet in depth domain is dependent on media velocities.The time-domain convolution operation directly used in depth domain does not meet the linear time-invariant condition.In this paper,we present a new method for genuine depth-domain seismic synthesis.This method constructs the velocity-dependent seismic wavelets varying adaptively with the corresponding interval velocities in the depth direction and weights them by the reflectivities,then the synthetic seismic record is obtained by the superposition of these weighted depth-varying wavelets.We applied this method to synthesize the seismic record of both a multi-layered geological model and the field data.The results show that the method can accommodate the intrinsic velocity-dependent variation characteristics of seismic events in depth domain and avoid the redundant depth-to-time and time-to-depth transformations.展开更多
Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves.Observations of these so-called prompt elasto-gravity signals by ground-bas...Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves.Observations of these so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events,such as the 2011 M_(W)9.1 Tohoku earthquake.Recent studies have introduced prompt gravity strain signals(PGSSs)as a new type of observable seismic gravity perturbation that can be used to measure the spatial gradient of the perturbed gravity field.Theoretically,these types of signals can be recorded by indevelopment instruments termed gravity strainmeters,although no successful detection has been reported as yet.Herein,we propose an efficient approach for PGSSs based on a multilayered spherical Earth model.We compared the simulated waveforms with analytical solutions obtained from a homogeneous half-space model,which has been used in earlier studies.This comparison indicates that the effect of the Earth’s structural stratification is significant.With the help of the new simulation approach,we also demonstrated how the PGSSs depend on the magnitude of the seismic source.We further conducted synthetic tests estimating earthquake magnitude using gravity strain signals to demonstrate the potential application of this type of signal in earthquake early warning systems.These results provide essential information for future studies on the synthesis and application of earthquake-induced gravity strain signals.展开更多
Chen's technique of computing synthetic seismograms,which decomposes every vector with a set of basis of orthogonality and completeness before applying the Luco-Apsel-Chen(LAC)generalized reflection and transmissi...Chen's technique of computing synthetic seismograms,which decomposes every vector with a set of basis of orthogonality and completeness before applying the Luco-Apsel-Chen(LAC)generalized reflection and transmission coefficients method,is confirmed to be efficient in dealing with elastic waves in multi-layered media and accurate in any frequency range.In this article,we extend Chen's technique to the computation of coupled seismic and electromagnetic(EM)waves in layered porous media.Expanding the involved mechanical and electromagnetic fields by a set of scalar and vector wave-function basis,we obtain the fundamental equations which are subsequently solved by using a recently developed version of the LAC generalized reflection and transmission coefficients method.Our approach and corresponding program is validated by reciprocity tests.We also show a numerical example of a two-layer model with an explosion source.The P-to-EM conversion waves radiated from the interface may have potential application.展开更多
As is well known, Greece has a significant number of earthquakes each year. Ιn recent years, several earthquakes have occurred in Greece. For this scope, a methodology was used to determine the source parameters. Thi...As is well known, Greece has a significant number of earthquakes each year. Ιn recent years, several earthquakes have occurred in Greece. For this scope, a methodology was used to determine the source parameters. This methodology is based on minimizing the difference between the observed and the synthetic waveforms, using the method Source Parameters Calculation—SPCa <a href="#ref1" target="_blank">[1]</a>. The source parameters, using the proposed methodology, are calculated by comparing observed seismograms and synthetic by inverting data. The synthetics are calculated using the reflectivity method (Kennett, 1983) as implemented by Randall et al. (1994) for a given earth structure. This study includes inversion results for the strongest events that occurred in Greece from 2008 to 2014. For the same events calculated the main fault plane, using the method of Hypocenter Centroid-plot (HC-plot) <a href="#ref2" target="_blank">[2]</a> <a href="#ref3" target="_blank">[3]</a>. This methodology is a simple geometrical method based on the combination between the hypocentral position and the two possible fault planes.展开更多
基金Sponsored by National Nature Science Foundation of China ( 51179195)National Defense Foundation of China ( 513030203-02)
文摘Elastic wave on seafloor caused by low frequency noise radiated from ship is called ship seismic wave which can be used to identify ship target. In order to analyze the wave components and the propagating properties of ship seismic wave, the numerical calculation of synthetic seismograms on seafloor aroused by a low frequency point sound source is carried out using a wave number integration technique combined with inverse Fourier transform. According to the numerical example of hard seafloor, the time series of seismic wave on seafloor are mostly composed of interface waves and normal mode waves. Each normal mode wave has a well defined low cut-off frequency, while the interface wave doesn't have. The frequency dispersion of normal mode wave is obvious when frequency is lower than 100Hz, while the interface wave is dispersive only in the infra-sound frequency range. The time series of seismic wave is dominated by the interface wave when the source frequency is less than the minimal cut-off frequency of normal mode wave.
文摘The extensive use of depth-imaged seismic data produced by pre-stack depth migration(PSDM)leads to the necessity to synthesize seismogram directly in depth domain.However,since seismic wavelet in depth domain is dependent on media velocities.The time-domain convolution operation directly used in depth domain does not meet the linear time-invariant condition.In this paper,we present a new method for genuine depth-domain seismic synthesis.This method constructs the velocity-dependent seismic wavelets varying adaptively with the corresponding interval velocities in the depth direction and weights them by the reflectivities,then the synthetic seismic record is obtained by the superposition of these weighted depth-varying wavelets.We applied this method to synthesize the seismic record of both a multi-layered geological model and the field data.The results show that the method can accommodate the intrinsic velocity-dependent variation characteristics of seismic events in depth domain and avoid the redundant depth-to-time and time-to-depth transformations.
基金This work was supported by the National Natural Science Foundation of China(Nos.U1901602 and 42204060)Guangdong Provincial Key Laboratory of Geophysical High-Resolution Imaging Technology(No.2022B1212010002)+1 种基金Shenzhen Key Laboratory of Deep Offshore Oil and Gas Exploration Technology(No.ZDSYS20190902093007855)。
文摘Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves.Observations of these so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events,such as the 2011 M_(W)9.1 Tohoku earthquake.Recent studies have introduced prompt gravity strain signals(PGSSs)as a new type of observable seismic gravity perturbation that can be used to measure the spatial gradient of the perturbed gravity field.Theoretically,these types of signals can be recorded by indevelopment instruments termed gravity strainmeters,although no successful detection has been reported as yet.Herein,we propose an efficient approach for PGSSs based on a multilayered spherical Earth model.We compared the simulated waveforms with analytical solutions obtained from a homogeneous half-space model,which has been used in earlier studies.This comparison indicates that the effect of the Earth’s structural stratification is significant.With the help of the new simulation approach,we also demonstrated how the PGSSs depend on the magnitude of the seismic source.We further conducted synthetic tests estimating earthquake magnitude using gravity strain signals to demonstrate the potential application of this type of signal in earthquake early warning systems.These results provide essential information for future studies on the synthesis and application of earthquake-induced gravity strain signals.
基金supported by the Natural R&D Special Fund for Public Welfare Industry(No.200808069)National Natural Science Foundation of China(Nos.40974038,40774028 and 40821062)
文摘Chen's technique of computing synthetic seismograms,which decomposes every vector with a set of basis of orthogonality and completeness before applying the Luco-Apsel-Chen(LAC)generalized reflection and transmission coefficients method,is confirmed to be efficient in dealing with elastic waves in multi-layered media and accurate in any frequency range.In this article,we extend Chen's technique to the computation of coupled seismic and electromagnetic(EM)waves in layered porous media.Expanding the involved mechanical and electromagnetic fields by a set of scalar and vector wave-function basis,we obtain the fundamental equations which are subsequently solved by using a recently developed version of the LAC generalized reflection and transmission coefficients method.Our approach and corresponding program is validated by reciprocity tests.We also show a numerical example of a two-layer model with an explosion source.The P-to-EM conversion waves radiated from the interface may have potential application.
文摘As is well known, Greece has a significant number of earthquakes each year. Ιn recent years, several earthquakes have occurred in Greece. For this scope, a methodology was used to determine the source parameters. This methodology is based on minimizing the difference between the observed and the synthetic waveforms, using the method Source Parameters Calculation—SPCa <a href="#ref1" target="_blank">[1]</a>. The source parameters, using the proposed methodology, are calculated by comparing observed seismograms and synthetic by inverting data. The synthetics are calculated using the reflectivity method (Kennett, 1983) as implemented by Randall et al. (1994) for a given earth structure. This study includes inversion results for the strongest events that occurred in Greece from 2008 to 2014. For the same events calculated the main fault plane, using the method of Hypocenter Centroid-plot (HC-plot) <a href="#ref2" target="_blank">[2]</a> <a href="#ref3" target="_blank">[3]</a>. This methodology is a simple geometrical method based on the combination between the hypocentral position and the two possible fault planes.
