A novel technique for automatic seismic data processing using both integral and local feature of seismograms was presented in this paper. Here, the term integral feature of seismograms refers to feature which may depi...A novel technique for automatic seismic data processing using both integral and local feature of seismograms was presented in this paper. Here, the term integral feature of seismograms refers to feature which may depict the shape of the whole seismograms. However, unlike some previous efforts which completely abandon the DIAL approach, i.e., signal detection, phase identifi- cation, association, and event localization, and seek to use envelope cross-correlation to detect seismic events directly, our technique keeps following the DIAL approach, but in addition to detect signals corresponding to individual seismic phases, it also detects continuous wave-trains and explores their feature for phase-type identification and signal association. More concrete ideas about how to define wave-trains and combine them with various detections, as well as how to measure and utilize their feature in the seismic data processing were expatiated in the paper. This approach has been applied to the routine data processing by us for years, and test results for a 16 days＇ period using data from the Xinjiang seismic station network were presented. The automatic processing results have fairly low false and missed event rate simultaneously, showing that the new technique has good application prospects for improvement of the automatic seismic data processing.展开更多
A source-time function plays an important role in generating finite-difference synthetic seismograms.In this regard,we consider the amplitude spectra of five different time functions.This investigation shows that when...A source-time function plays an important role in generating finite-difference synthetic seismograms.In this regard,we consider the amplitude spectra of five different time functions.This investigation shows that when the high-frequency signals of the time function carry more power than the main signal,the tailing phenomena would be associated with the main signal which is not desirable in producing finite-difference synthetic seismograms.It is illustrated that the time function denoted by is the optimal source-time function among those examined in this paper for generating finite-difference synthetic seismograms.This matter is also verified by making finite-difference synthetic seismograms over an elastic earth model consisting of a layer over a half space.展开更多
In order to obtain a finite-difference synthetic seismogram, the finite earth model must be subdivided into cells.If the cell size becomes too large in comparison with wavelength of the source signal, waves disperse w...In order to obtain a finite-difference synthetic seismogram, the finite earth model must be subdivided into cells.If the cell size becomes too large in comparison with wavelength of the source signal, waves disperse with increasing traveltime. This phenomenon is known as grid dispersion. The grid dispersion produces a variation of velocity with different frequencies; that is the higher signal frequencies travel more slowly than the lower signal frequencies. Consequently, substantial tailing of the signal arises with increasing traveltime. This may happpen if: (1) the grid spacing is large; (2) the sampling rate is large; or (3) the source wavelength is too short compared with grid size. In other words, an important parameter in generating finite-difference synthetic seismograms is the number of grid points per wavelength of the source signal. In this paper, it is shown that the frequency of a source function has great effects on grid dispersion when P-Sv coupled waves propagate through elastic models by finite-differences. The two-dimensional elastic models considered in this paper consist of : (1) a normal fault, and (2) a layer over a half-space. This study verifies that, when generating finite-difference synthetic seismograms, the grid dispersion will be reduced to a satisfactory level if the grid points per wavelength at the half-power frequency of the source signal for the lowest velocity of the medium exceeds ten.展开更多
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
At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters（FGBS） are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a...At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters（FGBS） are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.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
Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain MS=8.1 (MW=7.8) earth- q...Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain MS=8.1 (MW=7.8) earth- quake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The sec- ond stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position.展开更多
A global cross-section of the Earth parallel to the tectonic equator（TE） path,the great circle representing the equator of net lithosphere rotation,shows a difference in shear wave velocities between the western and...A global cross-section of the Earth parallel to the tectonic equator（TE） path,the great circle representing the equator of net lithosphere rotation,shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift basins.The lowvelocity layer in the upper asthenosphere,at a depth range of 120 to 200 km,is assumed to represent the decoupling between the lithosphere and the underlying mantle.Along the TE-perturbed（TE-pert） path,a ubiquitous LVZ,about 1,000-km-wide and 100-km-thick,occurs in the asthenosphere.The existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the Earth.Ground-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis（NDSHA）,using realistic and duly validated synthetic time series,and generating a data bank of several thousands of seismograms that account for source,propagation,and site effects.Accordingly,with basic selforganized criticality concepts,NDSHA permits the integration of available information provided by the most updated seismological,geological,geophysical,and geotechnical databases for the site of interest,as well as advanced physical modeling techniques,to provide a reliable and robust background for the development of a design basis for cultural heritage and civil infrastructures.Estimates of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory,and a case-study is discussed.In order to enable a reliable estimation of the ground motion response to an earthquake,three-dimensional velocity models have to be considered,resulting in a new,very efficient,analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.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
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 transmis...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
In the past two decades numerous studies were made to develop and improve the theory and practical computation techniques of synthesizing theoretical seismograms for the model of multi-layered half-space. Today, synth...In the past two decades numerous studies were made to develop and improve the theory and practical computation techniques of synthesizing theoretical seismograms for the model of multi-layered half-space. Today, synthesizing theoretical seismograms in multi-layered half-space is an important tool for understanding the structure of the Earth’s interior as well as the seismic source process from well-recorded seismograms data. As part of a review of the state-of-the-art, in this article I shall present a systematic and self-contained theory of elastic waves in multi-layered half-space media based on the developments in the past two decades.展开更多
The extensive application of pre-stack depth migration has produced huge volumes of seismic data,which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth...The extensive application of pre-stack depth migration has produced huge volumes of seismic data,which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth domain.It is difficult to estimate seismic wavelets directly from seismic data due to the nonstationarity of the data in the depth domain.We conduct a velocity transformation of seismic data to make the seismic data stationary and then apply the ridge regression method to estimate a constant seismic wavelet.The estimated constant seismic wavelet is constructed as a set of space-variant seismic wavelets dominated by velocities at different spatial locations.Incorporating the weighted superposition principle,a synthetic seismogram is generated by directly employing the space-variant seismic wavelets in the depth domain.An inversion workflow based on the model-driven method is developed in the depth domain by incorporating the nonlinear conjugate gradient algorithm,which avoids additional data conversions between the time and depth domains.The impedance inversions of the synthetic and field seismic data in the depth domain show good results,which demonstrates that seismic inversion in the depth domain is feasible.The approach provides an alternative for forward numerical analyses and elastic property inversions of depth-domain seismic data.It is advantageous for further studies concerning the stability,accuracy,and efficiency of seismic inversions in the depth domain.展开更多
Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic...Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic seismograms may require large amount of computing resources. Conventional high-performance computer clusters may not provide a cost-effective solution to this type of applications. The newly emerging cloud-computing platform provides an alternative solution. In this paper, we describe our implementation of a synthetic seismogram generator based on the reciprocity principle using the Windows Azure cloud application framework. Our preliminary experiment shows that our cloud-based synthetic seismogram generator provides a costeffective and numerically efficient approach for computing synthetic seismograms based on the reciprocity principle.展开更多
Study of seismic wave excitation and propagation in laterally heterogeneous media was an active and important subject in seismology in the past two decades, numerous analytical and numerical efforts have been made in ...Study of seismic wave excitation and propagation in laterally heterogeneous media was an active and important subject in seismology in the past two decades, numerous analytical and numerical efforts have been made in this research field. In this article, I have, first, made a brief review on those developments and then introduced and summarized a unified and efficient method, global generalized reflection-transmission (abbreviated to R/T thereafter) matrices method, for synthetic seismograms in multi-layered media with irregular interfaces developed by the author [24~26]. As demonstrated in this article, this method could be regarded as an extension of the generalized R/T coefficients method for the horizontally layered case [2,5] to the layered media with irregularly shaped interfaces by incorporating the T matrices technique [27,28]. Because of the use of a recursive scheme in computing the global generalized R/T matrices, this method is efficient, particularly for the case with a large number of展开更多
In process of seismic exploration,the noise of seismic signals produces serious interference. Conventional methods of wavelet threshold denoising cannot fully use the characteristics of seismic signals due to its limi...In process of seismic exploration,the noise of seismic signals produces serious interference. Conventional methods of wavelet threshold denoising cannot fully use the characteristics of seismic signals due to its limitations. There is always a certain degree of deviation between estimated value and actual value. In this study,a method of seismic data denoising is proposed,the authors use the current coefficients,the parent coefficients and the neighborhood coefficients based on dual-tree complex wavelet transform( DTCWT) and related sub-band denoising model( TrivaS hrink) to achieve the optimal estimation of shrinking factor and get the noise reduction of seismic records. It is found that the method is better than conventional methods of wavelet threshold denoising in removing random noise.展开更多
On May 29, 2017, the MW6.6 Poso earthquake occurred in Central Sulawesi, Indonesia, causing moderate damages. The mainshock rupture and primary aftershock cluster occurred in the active Palolo-Sausu tectonic zone, and...On May 29, 2017, the MW6.6 Poso earthquake occurred in Central Sulawesi, Indonesia, causing moderate damages. The mainshock rupture and primary aftershock cluster occurred in the active Palolo-Sausu tectonic zone, and some aftershocks also took place around the Tokararu fault. However, the rupture mechanism of this earthquake and its relation to regional tectonics are not clear. In this study, the rupture process of the Poso mainshock is estimated by finite-fault waveform inversion, which is constrained by teleseismic bodies and surface waves. The rupture propagates upward unilaterally in a southwest-dipping moderate-angle(~34°) normal fault beneath Tokorondo Mountains, with a notable~15% initial moment release at the first 4 s of the ~12 s rupture duration. The average and peak slip are0.5 m and 1.5 m, respectively. The rupture velocity is relatively slow(less than 2.5 km/s), and the Coulomb stress changes due to the mainshock are obtained using the inverted coseismic slip.展开更多
Based on the extensive-dilatancy anisotropy theory, the method of synthetic seismogram is used to estimate the anisotropic parameters. The advantages of the method lie in that it avoids the singularity resolution and ...Based on the extensive-dilatancy anisotropy theory, the method of synthetic seismogram is used to estimate the anisotropic parameters. The advantages of the method lie in that it avoids the singularity resolution and saves calculation time of computer by using the eigenvalue and eigenvector analytical expressions of Christoffel equation, at the same time, the result is tested by coherence function. The test result reveals that there exists a fine linear relation between original records and synthetic records, indicating the anisotropic parameters estimated by synthetic seismogram can reflect and describe the anisotropic characteristics of the given region medium.展开更多
In this article, we analyze the dynamic characteristics of head wave in multi-layered half-space media models with high-velocity layer or low-velocity layer, and the model with a continuous transition-zone between the...In this article, we analyze the dynamic characteristics of head wave in multi-layered half-space media models with high-velocity layer or low-velocity layer, and the model with a continuous transition-zone between the crust and the mantle by using synthetic seismogram. It is concluded that the dynamic characteristics of head wave are sensitive to the thickness and velocity of the high-velocity layer. There is obvious diffraction phenomenon of seismic wave if the thickness of high-velocity layer is very small compared with the characteristic wavelength. In this case, the high-velocity layer cannot shield the head wave propagating along the upper interface of the media below it, and the amplitude of this head wave is proportional to the thickness or the velocity of the high-velocity layer. When the thickness of high-velocity layer is nearly identical to the characteristic wavelength of seismic wave, the wave phases reflected from the bottom of the high-velocity layer and the head wave phase may have very close arrival and weaken each other because of destructive interference. As to low-velocity layer, the amplitude of the head wave is weak and decreases with the velocity of this layer. It is also found that if a continuous transition-zone between the crust and the mantle is introduced, we can get a strong apparent head wave phase in synthetic seismogram and the amplitude of this phase increases with the thickness or velocity gradient of the transition-zone.展开更多
The M_(W)7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_(W)9.2 great Alaska earthquake in the United States.In this study,high-rate GPS data and near-field broadband seismograms are used ...The M_(W)7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_(W)9.2 great Alaska earthquake in the United States.In this study,high-rate GPS data and near-field broadband seismograms are used in separate and joint inversions by the generalized Cut-and-Paste(gCAP)method to estimate the focal mechanism.In order to investigate the influence of crustal velocity structure on the focal mechanism inversion results,two velocity models(Crustl.0 and Alaska Earthquake Center(AEC))are used for detailed comparison and analysis.The results show that:(1)The two nodal planes of the optimal double-couple solution are nearly north-south striking,with dip angles of about 30°and 60°respectively,and the centroid focal depth is 54-55 km,which is an intraplate normal fault event.(2)The inversion results for the two types of data and the two velocity models are consistent with some previous studies,which indicates that the results are stable and reliable.The more accurate velocity structure model is helpful for focal mechanism inversion of the complex earthquake.(3)The inclusion of high-rate GPS data in joint inversion provides a more effective constraint on centroid depth.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
文摘A novel technique for automatic seismic data processing using both integral and local feature of seismograms was presented in this paper. Here, the term integral feature of seismograms refers to feature which may depict the shape of the whole seismograms. However, unlike some previous efforts which completely abandon the DIAL approach, i.e., signal detection, phase identifi- cation, association, and event localization, and seek to use envelope cross-correlation to detect seismic events directly, our technique keeps following the DIAL approach, but in addition to detect signals corresponding to individual seismic phases, it also detects continuous wave-trains and explores their feature for phase-type identification and signal association. More concrete ideas about how to define wave-trains and combine them with various detections, as well as how to measure and utilize their feature in the seismic data processing were expatiated in the paper. This approach has been applied to the routine data processing by us for years, and test results for a 16 days＇ period using data from the Xinjiang seismic station network were presented. The automatic processing results have fairly low false and missed event rate simultaneously, showing that the new technique has good application prospects for improvement of the automatic seismic data processing.
文摘A source-time function plays an important role in generating finite-difference synthetic seismograms.In this regard,we consider the amplitude spectra of five different time functions.This investigation shows that when the high-frequency signals of the time function carry more power than the main signal,the tailing phenomena would be associated with the main signal which is not desirable in producing finite-difference synthetic seismograms.It is illustrated that the time function denoted by is the optimal source-time function among those examined in this paper for generating finite-difference synthetic seismograms.This matter is also verified by making finite-difference synthetic seismograms over an elastic earth model consisting of a layer over a half space.
文摘In order to obtain a finite-difference synthetic seismogram, the finite earth model must be subdivided into cells.If the cell size becomes too large in comparison with wavelength of the source signal, waves disperse with increasing traveltime. This phenomenon is known as grid dispersion. The grid dispersion produces a variation of velocity with different frequencies; that is the higher signal frequencies travel more slowly than the lower signal frequencies. Consequently, substantial tailing of the signal arises with increasing traveltime. This may happpen if: (1) the grid spacing is large; (2) the sampling rate is large; or (3) the source wavelength is too short compared with grid size. In other words, an important parameter in generating finite-difference synthetic seismograms is the number of grid points per wavelength of the source signal. In this paper, it is shown that the frequency of a source function has great effects on grid dispersion when P-Sv coupled waves propagate through elastic models by finite-differences. The two-dimensional elastic models considered in this paper consist of : (1) a normal fault, and (2) a layer over a half-space. This study verifies that, when generating finite-difference synthetic seismograms, the grid dispersion will be reduced to a satisfactory level if the grid points per wavelength at the half-power frequency of the source signal for the lowest velocity of the medium exceeds ten.
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.
基金supported by the Special Fund for Earthquake Research in the Public Interest(No.201108009)
文摘At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters（FGBS） are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.
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Joint Seismological Science Foundation of China (103066) and Foundation of the Seismic Pattern and Digital Seis- mic Data Application Research Office of Institute of Earthquake Science of the China Earthquake Administration.
文摘Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain MS=8.1 (MW=7.8) earth- quake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The sec- ond stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position.
文摘A global cross-section of the Earth parallel to the tectonic equator（TE） path,the great circle representing the equator of net lithosphere rotation,shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift basins.The lowvelocity layer in the upper asthenosphere,at a depth range of 120 to 200 km,is assumed to represent the decoupling between the lithosphere and the underlying mantle.Along the TE-perturbed（TE-pert） path,a ubiquitous LVZ,about 1,000-km-wide and 100-km-thick,occurs in the asthenosphere.The existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the Earth.Ground-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis（NDSHA）,using realistic and duly validated synthetic time series,and generating a data bank of several thousands of seismograms that account for source,propagation,and site effects.Accordingly,with basic selforganized criticality concepts,NDSHA permits the integration of available information provided by the most updated seismological,geological,geophysical,and geotechnical databases for the site of interest,as well as advanced physical modeling techniques,to provide a reliable and robust background for the development of a design basis for cultural heritage and civil infrastructures.Estimates of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory,and a case-study is discussed.In order to enable a reliable estimation of the ground motion response to an earthquake,three-dimensional velocity models have to be considered,resulting in a new,very efficient,analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.
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.
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In the past two decades numerous studies were made to develop and improve the theory and practical computation techniques of synthesizing theoretical seismograms for the model of multi-layered half-space. Today, synthesizing theoretical seismograms in multi-layered half-space is an important tool for understanding the structure of the Earth’s interior as well as the seismic source process from well-recorded seismograms data. As part of a review of the state-of-the-art, in this article I shall present a systematic and self-contained theory of elastic waves in multi-layered half-space media based on the developments in the past two decades.
基金supported by the National Natural Science Foundation of China(No.41574130,41874143 and 41374134)the National Science and Technology Major Project of China(No.2016ZX05014-001-009)the Sichuan Provincial Youth Science&Technology Innovative Research Group Fund(No.2016TD0023)
文摘The extensive application of pre-stack depth migration has produced huge volumes of seismic data,which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth domain.It is difficult to estimate seismic wavelets directly from seismic data due to the nonstationarity of the data in the depth domain.We conduct a velocity transformation of seismic data to make the seismic data stationary and then apply the ridge regression method to estimate a constant seismic wavelet.The estimated constant seismic wavelet is constructed as a set of space-variant seismic wavelets dominated by velocities at different spatial locations.Incorporating the weighted superposition principle,a synthetic seismogram is generated by directly employing the space-variant seismic wavelets in the depth domain.An inversion workflow based on the model-driven method is developed in the depth domain by incorporating the nonlinear conjugate gradient algorithm,which avoids additional data conversions between the time and depth domains.The impedance inversions of the synthetic and field seismic data in the depth domain show good results,which demonstrates that seismic inversion in the depth domain is feasible.The approach provides an alternative for forward numerical analyses and elastic property inversions of depth-domain seismic data.It is advantageous for further studies concerning the stability,accuracy,and efficiency of seismic inversions in the depth domain.
文摘Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic seismograms may require large amount of computing resources. Conventional high-performance computer clusters may not provide a cost-effective solution to this type of applications. The newly emerging cloud-computing platform provides an alternative solution. In this paper, we describe our implementation of a synthetic seismogram generator based on the reciprocity principle using the Windows Azure cloud application framework. Our preliminary experiment shows that our cloud-based synthetic seismogram generator provides a costeffective and numerically efficient approach for computing synthetic seismograms based on the reciprocity principle.
文摘Study of seismic wave excitation and propagation in laterally heterogeneous media was an active and important subject in seismology in the past two decades, numerous analytical and numerical efforts have been made in this research field. In this article, I have, first, made a brief review on those developments and then introduced and summarized a unified and efficient method, global generalized reflection-transmission (abbreviated to R/T thereafter) matrices method, for synthetic seismograms in multi-layered media with irregular interfaces developed by the author [24~26]. As demonstrated in this article, this method could be regarded as an extension of the generalized R/T coefficients method for the horizontally layered case [2,5] to the layered media with irregularly shaped interfaces by incorporating the T matrices technique [27,28]. Because of the use of a recursive scheme in computing the global generalized R/T matrices, this method is efficient, particularly for the case with a large number of
基金Supported by the National "863" Project(No.2014AA06A605)
文摘In process of seismic exploration,the noise of seismic signals produces serious interference. Conventional methods of wavelet threshold denoising cannot fully use the characteristics of seismic signals due to its limitations. There is always a certain degree of deviation between estimated value and actual value. In this study,a method of seismic data denoising is proposed,the authors use the current coefficients,the parent coefficients and the neighborhood coefficients based on dual-tree complex wavelet transform( DTCWT) and related sub-band denoising model( TrivaS hrink) to achieve the optimal estimation of shrinking factor and get the noise reduction of seismic records. It is found that the method is better than conventional methods of wavelet threshold denoising in removing random noise.
文摘On May 29, 2017, the MW6.6 Poso earthquake occurred in Central Sulawesi, Indonesia, causing moderate damages. The mainshock rupture and primary aftershock cluster occurred in the active Palolo-Sausu tectonic zone, and some aftershocks also took place around the Tokararu fault. However, the rupture mechanism of this earthquake and its relation to regional tectonics are not clear. In this study, the rupture process of the Poso mainshock is estimated by finite-fault waveform inversion, which is constrained by teleseismic bodies and surface waves. The rupture propagates upward unilaterally in a southwest-dipping moderate-angle(~34°) normal fault beneath Tokorondo Mountains, with a notable~15% initial moment release at the first 4 s of the ~12 s rupture duration. The average and peak slip are0.5 m and 1.5 m, respectively. The rupture velocity is relatively slow(less than 2.5 km/s), and the Coulomb stress changes due to the mainshock are obtained using the inverted coseismic slip.
基金National Natural Science Foundation of China (D4007410) and Joint Seismological Science Foundation of China (603006).
文摘Based on the extensive-dilatancy anisotropy theory, the method of synthetic seismogram is used to estimate the anisotropic parameters. The advantages of the method lie in that it avoids the singularity resolution and saves calculation time of computer by using the eigenvalue and eigenvector analytical expressions of Christoffel equation, at the same time, the result is tested by coherence function. The test result reveals that there exists a fine linear relation between original records and synthetic records, indicating the anisotropic parameters estimated by synthetic seismogram can reflect and describe the anisotropic characteristics of the given region medium.
基金State Natural Science Foundation of China (40074008) and State Key Basic Research Development and Program-ming Project (G1998040702).
文摘In this article, we analyze the dynamic characteristics of head wave in multi-layered half-space media models with high-velocity layer or low-velocity layer, and the model with a continuous transition-zone between the crust and the mantle by using synthetic seismogram. It is concluded that the dynamic characteristics of head wave are sensitive to the thickness and velocity of the high-velocity layer. There is obvious diffraction phenomenon of seismic wave if the thickness of high-velocity layer is very small compared with the characteristic wavelength. In this case, the high-velocity layer cannot shield the head wave propagating along the upper interface of the media below it, and the amplitude of this head wave is proportional to the thickness or the velocity of the high-velocity layer. When the thickness of high-velocity layer is nearly identical to the characteristic wavelength of seismic wave, the wave phases reflected from the bottom of the high-velocity layer and the head wave phase may have very close arrival and weaken each other because of destructive interference. As to low-velocity layer, the amplitude of the head wave is weak and decreases with the velocity of this layer. It is also found that if a continuous transition-zone between the crust and the mantle is introduced, we can get a strong apparent head wave phase in synthetic seismogram and the amplitude of this phase increases with the thickness or velocity gradient of the transition-zone.
基金co-supported by the National Natural Science Foundation of China under Grants No.41721003,No.42074007the National Key Research and Development Program of China under Grant No.2018YFC1503604。
文摘The M_(W)7.1 Anchorage earthquake is the most destructive earthquake since the 1964 M_(W)9.2 great Alaska earthquake in the United States.In this study,high-rate GPS data and near-field broadband seismograms are used in separate and joint inversions by the generalized Cut-and-Paste(gCAP)method to estimate the focal mechanism.In order to investigate the influence of crustal velocity structure on the focal mechanism inversion results,two velocity models(Crustl.0 and Alaska Earthquake Center(AEC))are used for detailed comparison and analysis.The results show that:(1)The two nodal planes of the optimal double-couple solution are nearly north-south striking,with dip angles of about 30°and 60°respectively,and the centroid focal depth is 54-55 km,which is an intraplate normal fault event.(2)The inversion results for the two types of data and the two velocity models are consistent with some previous studies,which indicates that the results are stable and reliable.The more accurate velocity structure model is helpful for focal mechanism inversion of the complex earthquake.(3)The inclusion of high-rate GPS data in joint inversion provides a more effective constraint on centroid depth.
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.
