A P-wave velocity model was built in the central southern of the Tanlu Fault based on double-difference tomography.The results suggest the presence of a low-velocity anomaly extending from the surface to a depth of 25...A P-wave velocity model was built in the central southern of the Tanlu Fault based on double-difference tomography.The results suggest the presence of a low-velocity anomaly extending from the surface to a depth of 25 km around the Tanlu and Feixi Faults,representing fault-related fluids caused by partial melting.The relocated earthquakes indicate a significant concentration of seismic activity above 20 km around the Tanlu and Feixi Faults,suggesting that prominent fault systems possibly serve as conduits for the upward migration of deep minerals.The proposed geodynamic model,supported by geological and geophysical data,suggests that the migration of deep mineralized materials extends along the Tanlu Fault.The obtained results serve as a crucial foundation for elucidating the intricate process of mineralization in the central southern segment of the Tanlu Fault,thereby enhancing comprehension regarding the interaction among ore body formation,fault fluids,localized melting,and seismic activity.展开更多
Rockburst is a common dynamic geological hazard,frequently occurring in underground engineering(e.g.,TBM tunnelling and deep mining).In order to achieve rockburst monitoring and warning,the microseismic moni-toring te...Rockburst is a common dynamic geological hazard,frequently occurring in underground engineering(e.g.,TBM tunnelling and deep mining).In order to achieve rockburst monitoring and warning,the microseismic moni-toring technique has been widely used in the field.However,the microseismic source location has always been a challenge,playing a vital role in the precise prevention and control of rockburst.To this end,this study proposes a novel microseismic source location model that considers the anisotropy of P-wave velocity.On the one hand,it assigns a unique P-wave velocity to each propagation path,abandoning the assumption of a homogeneous ve-locity field.On the other hand,it treats the P-wave velocity as a co-inversion parameter along with the source location,avoiding the predetermination of P-wave velocity.To solve this model,three various metaheuristic multi-objective optimization algorithms are integrated with it,including the whale optimization algorithm,the butterfly optimization algorithm,and the sparrow search algorithm.To demonstrate the advantages of the model in terms of localization accuracy,localization efficiency,and solution stability,four blasting cases are collected from a water diversion tunnel project in Xinjiang,China.Finally,the effect of the number of involved sensors on the microseismic source location is discussed.展开更多
We examined the spatial variation of velocity structures around the 660-kin discontinuity at the western Pacific subduction zones by waveform modeling of triplication data. Data from two deep earthquakes beneath Izu-B...We examined the spatial variation of velocity structures around the 660-kin discontinuity at the western Pacific subduction zones by waveform modeling of triplication data. Data from two deep earthquakes beneath Izu-Bonin and Northeast China are used. Both events were well recorded by a dense broadband seismic network in China （CEArray）. The two events are located at approximately the same distance to the CEArray, yet significant differences are observed in their records： （1） the direct arrivals traveling above the 660-km discontinuity （AB branch） are seen in a different distance extent： -29° for the NE China event, -23° for Izu-Bonin event; （2） the direct （AB） and the refracted waves at the 660-km （CD branch） cross over at 19.5° and 17° for the NE China and the Izu-Bonin event, respectively. The best fitting model for the NE China event has a broad 660-km discontinuity and a constant high velocity layer upon it; while the Izu-Bonin model differs from the standard IASP91 model only with a high velocity layer above the 660-km discontinuity. Variations in velocity models can be roughly explained by subduction geometry.展开更多
Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of hori...Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of horizontal strata.Although the full-elastic orthorhombic anisotropic wave equation can accurately simulate seismic wave propagation in the underground media,a huge computational cost is required in seismic modeling,migration,and inversion.The conventional coupled pseudo-acoustic wave equations based on acoustic approximation can be used to significantly reduce the cost of calculation.However,these equations usually suffer from unwanted shear wave artifacts during wave propagation,and the presence of these artifacts can significantly degrade the imaging quality.To solve these problems,we derived a new pure P-wave equation for orthorhombic media that eliminates shear wave artifacts while compromising computational efficiency and accuracy.In addition,the derived equation involves pseudo-differential operators and it must be solved by 3D FFT algorithms.In order to reduce the number of 3D FFT,we utilized the finite difference and pseudo-spectral methods to conduct 3D forward modeling.Furthermore,we simplified the equation by using elliptic approximation and implemented 3D reverse-time migration(RTM).Forward modeling tests on several homogeneous and heterogeneous models confirm that the accuracy of the new equation is better than that of conventional methods.3D RTM imaging tests on three-layer and SEG/EAGE 3D salt models confirm that the ORT media have better imaging quality.展开更多
The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an...The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an exotic microcontinent,the Glenburgh Terrane,to form the West Australia Craton(WAC)through two collisional orogenic events,the 2215–2145 Ma Ophthalmian and 2005–1950 Ma Glenburgh Orogenies(Johnson et al.,2013;Fig.1).Compared to other Proterozoic orogenic belts in Australia,the Capricorn Orogen preserves‘complete'opposing continental margin successions,together with intervening arc fragments associated with oceanic closure and foreland basins associated with collisional loading(Cawood et al.,2009).展开更多
We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion ...We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.展开更多
We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equa...We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equal-radius penny-shaped crack inclusions in each layer. The P-wave velocity and amplitude were measured parallel and perpendicular to the layers of cracks at frequencies of 0.1 MHz to 1 MHz. The experiments show that as the crack aperture increases from 0.l mm to 0.34 mm, the amplitude of the P-waves parallel to the crack layers decreases linearly with increasing frequency and the P-wave velocity dispersion varies from 1.5% to 2.1%, whereas the amplitude of the P-wave perpendicular to the crack layers decreases quadratically with increasing frequency and the velocity dispersion varies from 1.9% to 4.7%. The variation in the velocity dispersion parallel and perpendicular to the cracks intensifies the anisotropy dispersion of the P-waves in the crack models （6.7% to 83%）. The P-wave dispersion strongly depends on the scattering characteristics of the crack apertures.展开更多
Finite-frequency travel time tomography is a newly developing method.The main procedure in this new method is to compute the traveltime sensitive kernel.The travel time of the same scatterer needs to be used for compu...Finite-frequency travel time tomography is a newly developing method.The main procedure in this new method is to compute the traveltime sensitive kernel.The travel time of the same scatterer needs to be used for computing the traveltime sensitive kernel many times.It is a time-consuming task.It is easy and fast to get the travel time from analytic equations in a simple model such as a homogenous or linear velocity media.However,most of the earth models are layered.It is cumbersome to get the travel time from analytic equations.In order to enhance the computation efficiency,we used the table look-up method to compute the finite-frequency travel time sensitive kernel for P-waves in a layered structure model.We chose the AK135 earth model for the velocity model.The table look-up method saved about 50% of the computation time.We enhanced the computation speed by using the table lookup method in the same velocity model,which was very useful for enhancing the computation efficiency for the finite-frequency travel time tomography.展开更多
The effects of plasma screening on the ^(1)P^(o) resonance states of H-and He below the n=3 and n=4 thresholds of the respective subsystemsare investigated using the stabilization method and correlated exponential wav...The effects of plasma screening on the ^(1)P^(o) resonance states of H-and He below the n=3 and n=4 thresholds of the respective subsystemsare investigated using the stabilization method and correlated exponential wave functions.Two plasma mediums,namely,the Debye plasma and quantum plasma environments are considered.The screened Coulomb potential(SCP)obtained from Debye-Hückel model is used to represent Debye plasma environments and the exponential cosine screened Coulomb potential(ECSCP)obtained from a modified Debye-Hückel model is used to represent quantum plasma environments.The resonance parameters(resonance positions and widths)are presented in terms of the screening parameters.展开更多
Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining st...Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining strength parameters by incorporating the dependence of uniaxial compressive strength(UCS)on P-wave velocity into the Hoek-Brown criterion.Additionally,a new approach is introduced to process triaxial test data efficiently using Python libraries such as SciPy,NumPy,Matplotlib,and Pandas.Furthermore,the paper addresses challenges in determining elastic parameters through triaxial testing.A Python script is developed to automate the calculation of elastic modulus and Poisson's ratio,over-coming subjectivity in selecting the linear portion of stress-strain curves.The script optimally identifies the linear region by minimizing the fit error with appropriate constraints,ensuring a more objective and standardized approach.The proposed methodologies are demonstrated using limestone specimens from Central Asian gas fields.These innovations offer faster,more reliable results,reducing error and enhancing the comparability of analyses in geomechanics,with potential applications across various geological settings.展开更多
Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorabili...Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorability and irreversible plastic deformation,even in the linear elastic stage.The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation.In this study,ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes.The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages.A numerical model based on the discrete element method(DEM)was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures.The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens.The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks.The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes.Such evolution of microcracks is highly dependent on the stress path.The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions.The study can provide insight into the microstructure evolution during cyclic loading and unloading processes.展开更多
P-wave waveforms in the distance range between 12°and 30°were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas.The waveform data from 504 earthquak...P-wave waveforms in the distance range between 12°and 30°were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas.The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30°from the center of the Plateau were modelled.We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately.The results show that the uppermantle P-wave velocity structures beneath India,the Himalayas,and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick.The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane,the Tarim Basin,and especially the Songpan-GarzêTerrane are lower than those in the south.The 410-km discontinuity beneath these two terranes is elevated by about 20 km.Highvelocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes.The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet.Portions of the thickened Eurasian mantle lithosphere were delaminated;they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.展开更多
The recently built China Digital Seismic Network consists of the China National Digital Seismic Network （CNDSN）, 31 regional seismic networks and several small aperture arrays with more than 1 000 stations including...The recently built China Digital Seismic Network consists of the China National Digital Seismic Network （CNDSN）, 31 regional seismic networks and several small aperture arrays with more than 1 000 stations including 850＋ broadband stations. It forms a gigantic seismic array that provides an unprecedented opportunity to study the Earth＇s deep interior besides its routine task of seismic monitoring. Many modern seismic studies rely on rotation of vertical and horizontal components in order to separate different types of seismic waves. Knowledge of the orientations of the two horizontal components thus is important to perform a correction rotation. We analyzed particle motions of teleseismic P waves recorded by the network and used them to estimate the northcomponent azimuth of each station. An SNR-weighted-multi-event method was introduced to obtain component azimuths that best explain the P-wave particle motions of all the events recorded at a station. The method provides robust estimates including a measurement error calculated from background noise levels. We found that about one third of the stations have some sort of problems, including misorientation of the two horizontal components, mislabeling and polarity reversal in one or more components. These problems need to be taken into account for any rotation based seismic studies.展开更多
Fast and accurate P-wave arrival picking significantly affects the performance of earthquake early warning(EEW)systems.Automated P-wave picking algorithms used in EEW have encountered problems of falsely picking up no...Fast and accurate P-wave arrival picking significantly affects the performance of earthquake early warning(EEW)systems.Automated P-wave picking algorithms used in EEW have encountered problems of falsely picking up noise,missing P-waves and inaccurate P-wave arrival estimation.To address these issues,an automatic algorithm based on the convolution neural network(DPick)was developed,and trained with a moderate number of data sets of 17,717 accelerograms.Compared to the widely used approach of the short-term average/long-term average of signal characteristic function(STA/LTA),DPick is 1.6 times less likely to detect noise as a P-wave,and 76 times less likely to miss P-waves.In terms of estimating P-wave arrival time,when the detection task is completed within 1 s,DPick′s detection occurrence is 7.4 times that of STA/LTA in the 0.05 s error band,and 1.6 times when the error band is 0.10 s.This verified that the proposed method has the potential for wide applications in EEW.展开更多
Engineering rock mass classification,based on empirical relations between rock mass parameters and engineering applications,is commonly used in rock engineering and forms the basis for designing rock structures.The ba...Engineering rock mass classification,based on empirical relations between rock mass parameters and engineering applications,is commonly used in rock engineering and forms the basis for designing rock structures.The basic data required may be obtained from visual observation and laboratory or field tests.However,owing to the discontinuous and variable nature of rock masses,it is difficult for rock engineers to directly obtain the specific design parameters needed.As an alternative,the use of geophysical methods in geomechanics such as seismography may largely address this problem.In this study,25 seismic profiles with the total length of 543 m have been scanned to determine the geomechanical properties of the rock mass in blocks Ⅰ,Ⅲ and Ⅳ-2 of the Choghart iron mine.Moreover,rock joint measurements and sampling for laboratory tests were conducted.The results show that the rock mass rating（RMR） and Q values have a close relation with P-wave velocity parameters,including P-wave velocity in field(V;).P-wave velocity in the laboratory(V;) and the ratio of V;V;(i.e.K;= V;/V;.However,Q value,totally,has greater correlation coefficient and less error than the RMR,In addition,rock mass parameters including rock quality designation（RQD）,uniaxial compressive strength（UCS）,joint roughness coefficient（JRC） and Schmidt number（RN） show close relationship with P-wave velocity.An equation based on these parameters was obtained to estimate the P-wave velocity in the rock mass with a correlation coefficient of 91%.The velocities in two orthogonal directions and the results of joint study show that the wave velocity anisotropy in rock mass may be used as an efficient tool to assess the strong and weak directions in rock mass.展开更多
It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and syst...It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20C or 25C)to 800C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400C,400Ce600C,and 600Ce800C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.展开更多
If the thickness of coal seams and the lithology of both roofs and floors of coal seams have not changed at all or only a little, then it is thought that the elastic anisotropy of coal seams depends mainly on fracture...If the thickness of coal seams and the lithology of both roofs and floors of coal seams have not changed at all or only a little, then it is thought that the elastic anisotropy of coal seams depends mainly on fractures and obeys the horizontally symmetric model of an azimuth anisotropy. For a fixed offset, the amplitude A of the reflection P-wave and the cosine of 2φ has an approximately linear relation, (φ is the source-detector azimuth with respect to the fracture strike. Based on this relationship, many things can be done, such as the extraction of macro bins, the correction of residual normal moveout, the formation of azimuth gather, the transformation and normalization of azimuth gathers and the extraction of reflection wave amplitudes of coal seams. The least squares method was used to inverse theoretically the direction and density of fractures of coal seams. The result is in good agreement with the regional geological structure, indicating that the azimuth anisotropic analysis of the P-wave is feasible in evaluating the density and direction of fractures in coal seams.展开更多
Model-driven and data-driven inversions are two prominent methods for obtaining P-wave impedance,which is significant in reservoir description and identification.Based on proper initial models,most model-driven method...Model-driven and data-driven inversions are two prominent methods for obtaining P-wave impedance,which is significant in reservoir description and identification.Based on proper initial models,most model-driven methods primarily use the limited frequency bandwidth information of seismic data and can invert P-wave impedance with high accuracy,but not high resolution.Conventional data-driven methods mainly employ the information from well-log data and can provide high-accuracy and highresolution P-wave impedance owing to the superior nonlinear curve fitting capacity of neural networks.However,these methods require a significant number of training samples,which are frequently insufficient.To obtain P-wave impedance with both high accuracy and high resolution,we propose a model-data-driven inversion method using Res Nets and the normalized zero-lag cross-correlation objective function which is effective for avoiding local minima and suppressing random noise.By using initial models and training samples,the proposed model-data-driven method can invert P-wave impedance with satisfactory accuracy and resolution.Tests on synthetic and field data demonstrate the proposed method’s efficacy and practicability.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42574119,42274083,41974049)partly supported by the Urban Geological Survey Project of Linyi,Shandong Province,China(No.SDGP371300202102000468).
文摘A P-wave velocity model was built in the central southern of the Tanlu Fault based on double-difference tomography.The results suggest the presence of a low-velocity anomaly extending from the surface to a depth of 25 km around the Tanlu and Feixi Faults,representing fault-related fluids caused by partial melting.The relocated earthquakes indicate a significant concentration of seismic activity above 20 km around the Tanlu and Feixi Faults,suggesting that prominent fault systems possibly serve as conduits for the upward migration of deep minerals.The proposed geodynamic model,supported by geological and geophysical data,suggests that the migration of deep mineralized materials extends along the Tanlu Fault.The obtained results serve as a crucial foundation for elucidating the intricate process of mineralization in the central southern segment of the Tanlu Fault,thereby enhancing comprehension regarding the interaction among ore body formation,fault fluids,localized melting,and seismic activity.
基金supported by the National Natural Science Founda-tion of China under Grant Nos.42472351,42177140,52404127,and 42207235the Natural Science Foundation of Hubei Province under Grant No.2024AFD359+1 种基金the Young Elite Scientist Sponsorship Program by CAST under Grant No.YESS20230742the China Postdoctoral Science Foundation Program under Grant No.2024T170684.
文摘Rockburst is a common dynamic geological hazard,frequently occurring in underground engineering(e.g.,TBM tunnelling and deep mining).In order to achieve rockburst monitoring and warning,the microseismic moni-toring technique has been widely used in the field.However,the microseismic source location has always been a challenge,playing a vital role in the precise prevention and control of rockburst.To this end,this study proposes a novel microseismic source location model that considers the anisotropy of P-wave velocity.On the one hand,it assigns a unique P-wave velocity to each propagation path,abandoning the assumption of a homogeneous ve-locity field.On the other hand,it treats the P-wave velocity as a co-inversion parameter along with the source location,avoiding the predetermination of P-wave velocity.To solve this model,three various metaheuristic multi-objective optimization algorithms are integrated with it,including the whale optimization algorithm,the butterfly optimization algorithm,and the sparrow search algorithm.To demonstrate the advantages of the model in terms of localization accuracy,localization efficiency,and solution stability,four blasting cases are collected from a water diversion tunnel project in Xinjiang,China.Finally,the effect of the number of involved sensors on the microseismic source location is discussed.
基金supported by National Natural Science Foundation of China under grant 40874095 and NSF under grant EAR-063566
文摘We examined the spatial variation of velocity structures around the 660-kin discontinuity at the western Pacific subduction zones by waveform modeling of triplication data. Data from two deep earthquakes beneath Izu-Bonin and Northeast China are used. Both events were well recorded by a dense broadband seismic network in China （CEArray）. The two events are located at approximately the same distance to the CEArray, yet significant differences are observed in their records： （1） the direct arrivals traveling above the 660-km discontinuity （AB branch） are seen in a different distance extent： -29° for the NE China event, -23° for Izu-Bonin event; （2） the direct （AB） and the refracted waves at the 660-km （CD branch） cross over at 19.5° and 17° for the NE China and the Izu-Bonin event, respectively. The best fitting model for the NE China event has a broad 660-km discontinuity and a constant high velocity layer upon it; while the Izu-Bonin model differs from the standard IASP91 model only with a high velocity layer above the 660-km discontinuity. Variations in velocity models can be roughly explained by subduction geometry.
基金supported by the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(No.2021QNLM020001)the Major Scientific and Technological Projects of Shandong Energy Group(No.SNKJ2022A06-R23)+2 种基金the Funds of Creative Research Groups of China(No.41821002)National Natural Science Foundation of China Outstanding Youth Science Fund Project(Overseas)(No.ZX20230152)the Major Scientific and Technological Projects of CNPC(No.ZD2019-183-003)。
文摘Compared with the transverse isotropic(TI)medium,the orthorhombic anisotropic medium has both horizontal and vertical symmetry axes and it can be approximated as a set of vertical fissures developed in a group of horizontal strata.Although the full-elastic orthorhombic anisotropic wave equation can accurately simulate seismic wave propagation in the underground media,a huge computational cost is required in seismic modeling,migration,and inversion.The conventional coupled pseudo-acoustic wave equations based on acoustic approximation can be used to significantly reduce the cost of calculation.However,these equations usually suffer from unwanted shear wave artifacts during wave propagation,and the presence of these artifacts can significantly degrade the imaging quality.To solve these problems,we derived a new pure P-wave equation for orthorhombic media that eliminates shear wave artifacts while compromising computational efficiency and accuracy.In addition,the derived equation involves pseudo-differential operators and it must be solved by 3D FFT algorithms.In order to reduce the number of 3D FFT,we utilized the finite difference and pseudo-spectral methods to conduct 3D forward modeling.Furthermore,we simplified the equation by using elliptic approximation and implemented 3D reverse-time migration(RTM).Forward modeling tests on several homogeneous and heterogeneous models confirm that the accuracy of the new equation is better than that of conventional methods.3D RTM imaging tests on three-layer and SEG/EAGE 3D salt models confirm that the ORT media have better imaging quality.
文摘The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an exotic microcontinent,the Glenburgh Terrane,to form the West Australia Craton(WAC)through two collisional orogenic events,the 2215–2145 Ma Ophthalmian and 2005–1950 Ma Glenburgh Orogenies(Johnson et al.,2013;Fig.1).Compared to other Proterozoic orogenic belts in Australia,the Capricorn Orogen preserves‘complete'opposing continental margin successions,together with intervening arc fragments associated with oceanic closure and foreland basins associated with collisional loading(Cawood et al.,2009).
文摘We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.
基金supported by the Major National Project Program (No.2011ZX05007-006)
文摘We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equal-radius penny-shaped crack inclusions in each layer. The P-wave velocity and amplitude were measured parallel and perpendicular to the layers of cracks at frequencies of 0.1 MHz to 1 MHz. The experiments show that as the crack aperture increases from 0.l mm to 0.34 mm, the amplitude of the P-waves parallel to the crack layers decreases linearly with increasing frequency and the P-wave velocity dispersion varies from 1.5% to 2.1%, whereas the amplitude of the P-wave perpendicular to the crack layers decreases quadratically with increasing frequency and the velocity dispersion varies from 1.9% to 4.7%. The variation in the velocity dispersion parallel and perpendicular to the cracks intensifies the anisotropy dispersion of the P-waves in the crack models （6.7% to 83%）. The P-wave dispersion strongly depends on the scattering characteristics of the crack apertures.
基金supported by the National Natural Science Foundation of China (Grant No. 90814013)
文摘Finite-frequency travel time tomography is a newly developing method.The main procedure in this new method is to compute the traveltime sensitive kernel.The travel time of the same scatterer needs to be used for computing the traveltime sensitive kernel many times.It is a time-consuming task.It is easy and fast to get the travel time from analytic equations in a simple model such as a homogenous or linear velocity media.However,most of the earth models are layered.It is cumbersome to get the travel time from analytic equations.In order to enhance the computation efficiency,we used the table look-up method to compute the finite-frequency travel time sensitive kernel for P-waves in a layered structure model.We chose the AK135 earth model for the velocity model.The table look-up method saved about 50% of the computation time.We enhanced the computation speed by using the table lookup method in the same velocity model,which was very useful for enhancing the computation efficiency for the finite-frequency travel time tomography.
基金Supported by the Natural Science Foundation of Heilongjiang Province(LH2024A025)。
文摘The effects of plasma screening on the ^(1)P^(o) resonance states of H-and He below the n=3 and n=4 thresholds of the respective subsystemsare investigated using the stabilization method and correlated exponential wave functions.Two plasma mediums,namely,the Debye plasma and quantum plasma environments are considered.The screened Coulomb potential(SCP)obtained from Debye-Hückel model is used to represent Debye plasma environments and the exponential cosine screened Coulomb potential(ECSCP)obtained from a modified Debye-Hückel model is used to represent quantum plasma environments.The resonance parameters(resonance positions and widths)are presented in terms of the screening parameters.
文摘Triaxial testing serves as a fundamental method for evaluating the elastic and strength properties of rocks,crucial for developing accurate 3D geomechanical models.This paper presents a novel method for determining strength parameters by incorporating the dependence of uniaxial compressive strength(UCS)on P-wave velocity into the Hoek-Brown criterion.Additionally,a new approach is introduced to process triaxial test data efficiently using Python libraries such as SciPy,NumPy,Matplotlib,and Pandas.Furthermore,the paper addresses challenges in determining elastic parameters through triaxial testing.A Python script is developed to automate the calculation of elastic modulus and Poisson's ratio,over-coming subjectivity in selecting the linear portion of stress-strain curves.The script optimally identifies the linear region by minimizing the fit error with appropriate constraints,ensuring a more objective and standardized approach.The proposed methodologies are demonstrated using limestone specimens from Central Asian gas fields.These innovations offer faster,more reliable results,reducing error and enhancing the comparability of analyses in geomechanics,with potential applications across various geological settings.
基金supported by the National Natural Science Foundation of China(Grant No.U2244215)the Knowledge Innovation Program of Wuhan-Basic Research(Grant No.2022010801010159)the Major Project of Inner Mongolia Science and Technology(Grant No.2021ZD0034).
文摘Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorability and irreversible plastic deformation,even in the linear elastic stage.The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation.In this study,ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes.The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages.A numerical model based on the discrete element method(DEM)was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures.The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens.The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks.The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes.Such evolution of microcracks is highly dependent on the stress path.The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions.The study can provide insight into the microstructure evolution during cyclic loading and unloading processes.
基金supported by funding from the Strategic Priority Research Program(B)of Chinese Academy of Sciences through grant XDB18010304Natural Science Foundation of China through grant 41322027,41374060,41374079,41661164035
文摘P-wave waveforms in the distance range between 12°and 30°were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas.The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30°from the center of the Plateau were modelled.We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately.The results show that the uppermantle P-wave velocity structures beneath India,the Himalayas,and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick.The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane,the Tarim Basin,and especially the Songpan-GarzêTerrane are lower than those in the south.The 410-km discontinuity beneath these two terranes is elevated by about 20 km.Highvelocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes.The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet.Portions of the thickened Eurasian mantle lithosphere were delaminated;they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.
基金supported by NSF grant EAR-063566(F.N.)National Natural Science Foundation of China grant 40774042(J.L.)
文摘The recently built China Digital Seismic Network consists of the China National Digital Seismic Network （CNDSN）, 31 regional seismic networks and several small aperture arrays with more than 1 000 stations including 850＋ broadband stations. It forms a gigantic seismic array that provides an unprecedented opportunity to study the Earth＇s deep interior besides its routine task of seismic monitoring. Many modern seismic studies rely on rotation of vertical and horizontal components in order to separate different types of seismic waves. Knowledge of the orientations of the two horizontal components thus is important to perform a correction rotation. We analyzed particle motions of teleseismic P waves recorded by the network and used them to estimate the northcomponent azimuth of each station. An SNR-weighted-multi-event method was introduced to obtain component azimuths that best explain the P-wave particle motions of all the events recorded at a station. The method provides robust estimates including a measurement error calculated from background noise levels. We found that about one third of the stations have some sort of problems, including misorientation of the two horizontal components, mislabeling and polarity reversal in one or more components. These problems need to be taken into account for any rotation based seismic studies.
基金National Natural Science Foundation of China under Grant Nos.51968016 and 5197083806the Guangxi Innovation Driven Development Project(Science and Technology Major Project,Grant No.Guike AA18118008).
文摘Fast and accurate P-wave arrival picking significantly affects the performance of earthquake early warning(EEW)systems.Automated P-wave picking algorithms used in EEW have encountered problems of falsely picking up noise,missing P-waves and inaccurate P-wave arrival estimation.To address these issues,an automatic algorithm based on the convolution neural network(DPick)was developed,and trained with a moderate number of data sets of 17,717 accelerograms.Compared to the widely used approach of the short-term average/long-term average of signal characteristic function(STA/LTA),DPick is 1.6 times less likely to detect noise as a P-wave,and 76 times less likely to miss P-waves.In terms of estimating P-wave arrival time,when the detection task is completed within 1 s,DPick′s detection occurrence is 7.4 times that of STA/LTA in the 0.05 s error band,and 1.6 times when the error band is 0.10 s.This verified that the proposed method has the potential for wide applications in EEW.
文摘Engineering rock mass classification,based on empirical relations between rock mass parameters and engineering applications,is commonly used in rock engineering and forms the basis for designing rock structures.The basic data required may be obtained from visual observation and laboratory or field tests.However,owing to the discontinuous and variable nature of rock masses,it is difficult for rock engineers to directly obtain the specific design parameters needed.As an alternative,the use of geophysical methods in geomechanics such as seismography may largely address this problem.In this study,25 seismic profiles with the total length of 543 m have been scanned to determine the geomechanical properties of the rock mass in blocks Ⅰ,Ⅲ and Ⅳ-2 of the Choghart iron mine.Moreover,rock joint measurements and sampling for laboratory tests were conducted.The results show that the rock mass rating（RMR） and Q values have a close relation with P-wave velocity parameters,including P-wave velocity in field(V;).P-wave velocity in the laboratory(V;) and the ratio of V;V;(i.e.K;= V;/V;.However,Q value,totally,has greater correlation coefficient and less error than the RMR,In addition,rock mass parameters including rock quality designation（RQD）,uniaxial compressive strength（UCS）,joint roughness coefficient（JRC） and Schmidt number（RN） show close relationship with P-wave velocity.An equation based on these parameters was obtained to estimate the P-wave velocity in the rock mass with a correlation coefficient of 91%.The velocities in two orthogonal directions and the results of joint study show that the wave velocity anisotropy in rock mass may be used as an efficient tool to assess the strong and weak directions in rock mass.
基金This work was supported by the National Natural Science Foundation of China(Grant No.41772333)the program of State Key Laboratory of Frozen Soil Engineering(Grant No.SKLFSE201713)the Shaanxi Province New-Star Talents Promotion Project of Science and Technology(Grant No.2019KJXX-049).
文摘It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20C or 25C)to 800C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400C,400Ce600C,and 600Ce800C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.
基金Projects 40574058 supported by the National Natural Science Foundation of China, 2005cb221500 the National Key Basic Research and Development(973) Program of China and 03(2007) the Scientific and Technological Project about Geology and Mineral Resources of Henan Land Resources Department
文摘If the thickness of coal seams and the lithology of both roofs and floors of coal seams have not changed at all or only a little, then it is thought that the elastic anisotropy of coal seams depends mainly on fractures and obeys the horizontally symmetric model of an azimuth anisotropy. For a fixed offset, the amplitude A of the reflection P-wave and the cosine of 2φ has an approximately linear relation, (φ is the source-detector azimuth with respect to the fracture strike. Based on this relationship, many things can be done, such as the extraction of macro bins, the correction of residual normal moveout, the formation of azimuth gather, the transformation and normalization of azimuth gathers and the extraction of reflection wave amplitudes of coal seams. The least squares method was used to inverse theoretically the direction and density of fractures of coal seams. The result is in good agreement with the regional geological structure, indicating that the azimuth anisotropic analysis of the P-wave is feasible in evaluating the density and direction of fractures in coal seams.
基金financially supported by the Important National Science&Technology Specific Project of China(Grant No.2017ZX05018-005)
文摘Model-driven and data-driven inversions are two prominent methods for obtaining P-wave impedance,which is significant in reservoir description and identification.Based on proper initial models,most model-driven methods primarily use the limited frequency bandwidth information of seismic data and can invert P-wave impedance with high accuracy,but not high resolution.Conventional data-driven methods mainly employ the information from well-log data and can provide high-accuracy and highresolution P-wave impedance owing to the superior nonlinear curve fitting capacity of neural networks.However,these methods require a significant number of training samples,which are frequently insufficient.To obtain P-wave impedance with both high accuracy and high resolution,we propose a model-data-driven inversion method using Res Nets and the normalized zero-lag cross-correlation objective function which is effective for avoiding local minima and suppressing random noise.By using initial models and training samples,the proposed model-data-driven method can invert P-wave impedance with satisfactory accuracy and resolution.Tests on synthetic and field data demonstrate the proposed method’s efficacy and practicability.
