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- 1Machine learning and its application in seismology
- 2A review on microtremor H/V spectral ratio method
- 3Numerical methods of geodynamics in big data era: Review and outlook
- 4EikoNet traveltime calculation method and application based on deep neural network
- 5Revisiting the cross-correlation and SPatial AutoCorrelation (SPAC) of the seismic ambient noise based on the plane wave model
- 6Progress and prospect of deformation theory in the viscoelastic earth
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Advances in soft X-ray emission of the Earth's magnetosphere
Sun Tianran, Zhang Yingjie, Wei Fei et al.
Abstract：The coupling between solar wind and the magnetosphere and the dynamic processes in geo-space are the basic driving factors of space weather. Understanding these processes on the system level is essential to the studies of space physics and space weather. Recent solar wind charge exchange (SWCX) X-ray emission discoveries provide a novel approach to detect the large-scale magnetosphere through soft X-ray imaging. SWCX occurs when high-charge heavy ions such as C6+, N7+, O7+, and O8+ in the solar wind interact with neutral atoms or molecules, such as neutral hydrogen atoms in near-Earth space, neutral hydrogen and helium atoms in the heliosphere, and H2O and CO2 molecules on comets and other planets. Solar wind ions become excited by receiving one or more electrons, and then return to the ground state by releasing one or more photons in the soft X-ray band. The characteristics of the SWCX emissions include the X-ray spectrum showing line emissions corresponding to different species of solar wind particles and neutrons, and fast time variations closely related to solar wind variations. The SWCX soft X-ray emission of the Earth's magnetosphere mainly occurs in the magnetosheath on the dayside and the cusp regions. Therefore, the magnetosphere can be remotely imaged using large-scale soft X-ray imaging technology, allowing the fundamental modes of the interaction between the solar wind and magnetosphere to be recognized on a systematic scale.In this context, the European Space Agency (ESA) and Chinese Academy of Sciences (CAS) jointly proposed the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE). SMILE was approved in 2016 and implemented thereafter. SMILE aims to provide remote sensing measurements of the magnetopause and bow shock around the subsolar region, part of the cusp regions, and the aurora, as well as simultaneous in situ observations of the solar wind plasma and magnetic field. SMILE is planned to be launched in 2024–2025. Other missions have also been proposed to image the Earth's magnetosphere, such as the GEOspace X-ray imager (GEO-X) in Japan, Lunar Environment heliospherics X-ray Imager (LEXI) in the United States, and Lunar-based soft X-ray imager (LSXI) in China.With the advent of soft X-ray imaging missions to detect the magnetopause, evaluating the expected soft X-ray images and developing appropriate techniques to extract 3-dimentional boundary information from the 2-dimentional images is essential. Global magnetohydrodynamic (MHD) and instrument simulations are used to generate expected X-ray images under different solar wind conditions with different viewing geometries. Based on these images, several approaches have been developed to analyze the signals, composing the 'arsenal' or 'toolkit' for magnetopause reconstruction. Each approach has its own advantages and disadvantages, applicable to different situations.This paper introduces the mechanism of magnetospheric X-ray emission, reviews the research on the observational evidence and characteristics of SWCX X-ray emissions, summarizes the progress of simulation studies, presents the missions (or concept) of the magnetospheric X-ray detection, and discusses the possibility of future implementation of X-ray imaging for detecting other planets. 【details】
Direct surface wave tomography for three dimensional structure based on surface wave traveltimes: Methodology review and applications
Yao Huajian, Luo Song, Li Cheng et al.
Abstract：Surface wave tomography using dispersion data to obtain isotropic and anisotropic shear wave velocity structures is a very efficient approach to study regional and global tectonics and deformation and to probe high-resolution crustal, upper mantle and near surface structures. Conventional surface wave tomography based on dispersion data usually has two steps, that is, inverting for 2D phase/group velocity maps first and then conducting point-wise inversion to obtain a 1D shear wave velocity model at each geographical grid point, which are then combined to obtain a 3D shear wave velocity model. In this paper, we review in detail the direct surface wave tomography framework based on surface wave dispersion traveltimes, that is, the one-step surface wave tomography. This framework includes direct inversion of 3D isotropic shear wave velocity model using all dispersion measurements at different periods and from all paths (DSurfTomo), direct inversion of both isotropic and azimuthally anisotropic shear wave velocity model (DAzimSurfTomo), and direct inversion of radially anisotropic shear wave velocity model (DRadiSurfTomo).The new direct tomography method computes surface wave ray paths at different periods, thus better considering the ray path bending effect of surface waves in complex media on the precision of tomographic images. We then introduce some applications of the new direct tomography methods, including multi-scale isotropic and anisotropic shear wave velocity tomography in the crust and upper mantle as well as shallow crust. These tomographic studies provide important constraints on regional tectonic evolution, seismogenic structures, shallow fault zone structures, ore deposit structures, and urban subsurface structures. At last, we discuss the dispersion data and model parameterization problems in surface wave tomography, direct surface wave tomography based on finite frequency theory and full waveform inversion, and perspective research of joint tomography problems using surface wave dispersion data and other seismological or geophysical data in the framework of direct surface wave tomography. 【details】
Recent progress on full waveform inversion
Zhu Hejun, Liu Qinya, Yang Jidong
Abstract：Full waveform inversion is an acoustic/elastic/anelastic wave equation-based high accuracy seismic imaging method for studying the Earth's interior structure. To date, it has been widely used in exploration seismology, studies on crustal and mantle structures at both regional and global scales. With this approach, we are able to build a unified theory and algorithm platform to constrain multi-parameter seismic models for the Earth's interior, including P and S wave velocities, anisotropy, attenuation, density and reflectivity, etc. By jointly interpreting these seismic parameters, we hope to better constrain variations in temperature and composition, mantle convection and distribution of water and volatiles. Recent developments include selection of optimal misfit functions, multi-parameter inversion, model regularization, resolution and uncertainty quantification, as well as its applications to special types of datasets, such as ambient-noise recordings and teleseismic scattered waves recorded by dense linear arrays. Furthermore, in order to better interpret inverted multi-parameters and investigate related problems in Earth sciences, we need collaboration among different disciplines, such as synthesizing results from seismology, mineral physics and geodynamic modeling. These results enable us to better understand reservoirs, basin structures, fault distribution and mantle convection. 【details】
Recent progress on the retrieval and modeling of thermosphere mass density
Lei Jiuhou, Li Ruoxi, Ren Dexin et al.
Abstract：The thermosphere is the atmospheric layer extending from about 90 km to nearly 1000 kilometers, which is an important interreaction area between the Sun and the Earth. Under the effects of solar radiation flux changes, geomagnetic activities, and low atmospheric forcings, the thermosphere could undergo significant changes. On the other hand, the thermospheric molecule flow collides with space objects, leading to the drag effect, which impacts significantly on the trajectories of space objects. In this paper, we first survey multiple density retrieval methods. The space object tracking data has the advantage of a large amount of data and has long been used for density retrieval since the 1960s. However, the density from this method suffers from low accuracy and time resolution. With the development of the Global Navigation Satellite System (GNSS), satellite Precise Orbit Determination (POD) data was utilized to derive thermospheric density with higher accuracy and time resolution. The accelerometers of some geodesic satellites offer the highest accuracy of measurements. Subsequently, three widely-used empirical thermospheric models (Mass Spectrometer Incoherent Scatter MSIS, Jacchia, and Drag Temperature Model DTM) were summarized. The methodologies and data sources were further compared. Based on the derived neutral densities and thermospheric models, several new approaches in improving the previous atmospheric models were overviewed. Since the exospheric temperature is the crucial parameter for empirical models, one of the effective ways to improve models is to modify the exospheric temperature using accelerometer-based densities. The polynomial fitting as well as the Principal Component Analysis (PCA) techniques, were utilized to reconstruct the global density. Other methods such as assimilation and particle filter were also applied to improve atmospheric models. Finally, based on the derived neutral densities, the thermospheric responses to solar and astronomical events such as geomagnetic storms, solar flares, and solar eclipses were further reviewed. 【details】
Research progress in coronal magnetic field measurements
Yang Zihao, Tian Hui, Li Wenxian et al.
Abstract：Different solar atmospheric layers are connected by the magnetic field of the Sun, which is the primary source for various types of solar activity. The magnetic activity of the Sun has a significant impact on the solar-terrestrial environment and human life. Understanding the phenomena occurring in the solar atmosphere relies on a thorough understanding of the solar magnetic field. However, up to now, only the magnetic field at the photospheric level can be measured with precision on a daily basis. No routine measurements have been carried out for the magnetic field in the upper layers of the solar atmosphere, particularly the solar corona. The lack of coronal magnetic field measurements has limited our investigation of many important topics in solar physics research including the driving mechanism of solar eruptions and the heating process of corona. In the past several decades, a number of techniques that may be useful for coronal magnetic field diagnostics have been developed, such as the techniques based on infrared spectro-polarimetry of coronal lines, the diagnosis utilizing coronal radio observations, magneto-seismology using observations of coronal magnetohydrodynamics waves and the measurements based on the magnetic-field-induced transition of coronal extreme ultraviolet spectral lines. Meanwhile, a few attempts have been made to measure the coronal magnetic field based on these techniques. This review summarizes the physical principles and important progress of coronal magnetic field measurements, and discuss future perspectives on related research. 【details】
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, Available online ,
doi: 10.19975/j.dqyxx.2022-084
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Abstract:
The region along the border between China and Myanmar is situated at the intersection of the eastern edge of the Myanmar arc, the southeast edge of the Qinghai Tibet Plateau, and the Sunda Plate. This region is characterized by its complex geological structure and strong tectonic activity. To investigate the contemporary pattern of crustal deformation and the tectonics of the border region, the entire regional GNSS network data from 1998 to 2020 in both countries were analyzed. The multi-scale spherical wavelet algorithm was used to estimate the regional strain rate field for the crust deformation and earthquake risk. The following key findings were obtained: (1) The strong compression and subduction of the Indian plate towards the eastern side of the Myanmar block has caused the GPS stations on the Myanmar arc to move towards the Qinghai-Tibet Plateau in the direction of the Indian plate, at a rate of approximately 30 mm/a. The shear strain accumulation is evident in the Myanmar arc region. The primary compressive stress in the Myanmar arc is nearly east-west compression with a vertical tectonic trend on the outer side of the arc and nearly south-north compression with a parallel structure on the inner side of the arc and the Irrawaddy River basin. The Sagaing fault is situated in a region of high principal and shear strain rates, and its subsection activity has been observed. Significant velocity differences exist between the two sides of the northern segment, with significant shear strain accumulation indicating dextral shear movement and shortening. The middle segment of the Sagaing fault moves towards NNW at a rate of approximately 20 mm/a, characterized by dextral strike-slip movement and tension. (2) The Sichuan-Yunnan block rotates clockwise around the eastern Himalayan tectonic belt, with the GPS velocity direction deflecting from the nearly east-west movement on the northern side of the Himalayan tectonic knot towards the Sichuan-Yunnan rhombus block moving southward or southeastward. The pattern of velocity distribution in the southwestern part of Yunnan is dispersed, with the rate gradually decreasing in a southeastward direction. The Xiaojiang fault zone is generally characterized by sinistral strike-slip movement. The middle segment of the Honghe fault has a low strike-slip rate, while the north and south segments have high shear rates. The Dayingjiang fault in southwestern Yunnan exhibits characteristics of east-west extension and an apparent sinistral strike-slip trend. The Longling-Ruili fault is characterized by dextral strike-slip movement and extension. The NE-trending Nantinghe fault, Menglian fault, and Jinghong-Daluo fault are in a low shear state and are dominated by left lateral strike-slip movement. The NW-SE-trending Lancang fault and Wuliangshan fault are characterized by dextral strike-slip movement, while the NW-trending Longling-Lancang fault zone is characterized by dextral strike-slip movement and tension. The magnitude of the strain rate accumulation is related to seismic activity. (3) Based on these findings, it is important to pay attention to the future seismic risk associated with the Sagaing fault, Wanding fault, Nantinghe fault, and the middle part of Wuliangshan fault, all of which are located in the high strain rate area. The results of this study are of great significance for earthquake disaster assessment and furthering our understanding of the tectonic dynamic characteristics of the borderland between China and Myanmar.
The region along the border between China and Myanmar is situated at the intersection of the eastern edge of the Myanmar arc, the southeast edge of the Qinghai Tibet Plateau, and the Sunda Plate. This region is characterized by its complex geological structure and strong tectonic activity. To investigate the contemporary pattern of crustal deformation and the tectonics of the border region, the entire regional GNSS network data from 1998 to 2020 in both countries were analyzed. The multi-scale spherical wavelet algorithm was used to estimate the regional strain rate field for the crust deformation and earthquake risk. The following key findings were obtained: (1) The strong compression and subduction of the Indian plate towards the eastern side of the Myanmar block has caused the GPS stations on the Myanmar arc to move towards the Qinghai-Tibet Plateau in the direction of the Indian plate, at a rate of approximately 30 mm/a. The shear strain accumulation is evident in the Myanmar arc region. The primary compressive stress in the Myanmar arc is nearly east-west compression with a vertical tectonic trend on the outer side of the arc and nearly south-north compression with a parallel structure on the inner side of the arc and the Irrawaddy River basin. The Sagaing fault is situated in a region of high principal and shear strain rates, and its subsection activity has been observed. Significant velocity differences exist between the two sides of the northern segment, with significant shear strain accumulation indicating dextral shear movement and shortening. The middle segment of the Sagaing fault moves towards NNW at a rate of approximately 20 mm/a, characterized by dextral strike-slip movement and tension. (2) The Sichuan-Yunnan block rotates clockwise around the eastern Himalayan tectonic belt, with the GPS velocity direction deflecting from the nearly east-west movement on the northern side of the Himalayan tectonic knot towards the Sichuan-Yunnan rhombus block moving southward or southeastward. The pattern of velocity distribution in the southwestern part of Yunnan is dispersed, with the rate gradually decreasing in a southeastward direction. The Xiaojiang fault zone is generally characterized by sinistral strike-slip movement. The middle segment of the Honghe fault has a low strike-slip rate, while the north and south segments have high shear rates. The Dayingjiang fault in southwestern Yunnan exhibits characteristics of east-west extension and an apparent sinistral strike-slip trend. The Longling-Ruili fault is characterized by dextral strike-slip movement and extension. The NE-trending Nantinghe fault, Menglian fault, and Jinghong-Daluo fault are in a low shear state and are dominated by left lateral strike-slip movement. The NW-SE-trending Lancang fault and Wuliangshan fault are characterized by dextral strike-slip movement, while the NW-trending Longling-Lancang fault zone is characterized by dextral strike-slip movement and tension. The magnitude of the strain rate accumulation is related to seismic activity. (3) Based on these findings, it is important to pay attention to the future seismic risk associated with the Sagaing fault, Wanding fault, Nantinghe fault, and the middle part of Wuliangshan fault, all of which are located in the high strain rate area. The results of this study are of great significance for earthquake disaster assessment and furthering our understanding of the tectonic dynamic characteristics of the borderland between China and Myanmar.
, Available online ,
doi: 10.19975/j.dqyxx.2022-082
Abstract:
Herein, the technical characteristics and programme of Qujing incoherent scatter radar (the first one in China Mainland) are described. The measurement ability in the ionosphere, space debris, and the Moon was investigated using the data. The results showed that this radar is of importance useful for the measuring ionospheric climatologic property, analyzing storm-time and abnormal enhancement events analysis, studying E-F valley and its variations, the determining and modeling space debris distribution characteristics and model, and identifying the scatter echo characteristics from the different regions of the Moon. The next work will focus on the measurement of the structure and evolution of the lower ionosphere and the northern ionosphere crest, storm-time variations, and disturbance characteristics property.
Herein, the technical characteristics and programme of Qujing incoherent scatter radar (the first one in China Mainland) are described. The measurement ability in the ionosphere, space debris, and the Moon was investigated using the data. The results showed that this radar is of importance useful for the measuring ionospheric climatologic property, analyzing storm-time and abnormal enhancement events analysis, studying E-F valley and its variations, the determining and modeling space debris distribution characteristics and model, and identifying the scatter echo characteristics from the different regions of the Moon. The next work will focus on the measurement of the structure and evolution of the lower ionosphere and the northern ionosphere crest, storm-time variations, and disturbance characteristics property.
, Available online ,
doi: 10.19975/j.dqyxx.2022-067
Abstract:
The eastern Himalayan syntaxis is located at the front of the collision between the Indian and Eurasian continents. This region is affected by the interaction of the Himalayan, Lhasa, Qiangtang, and Sichuan-Yunnan blocks and the Indian plate and is characterized by strong tectonic deformation with frequent earthquakes primarily distributed linearly. In this study, various seismological methods were used to reveal the seismicity, seismogenic mechanism, and tectonic stress field in this region. First, we used the double-difference location method (HypoDD) to relocate 65663 earthquakes with M ≥1.0 during 2008-2018. Then, the Cut-And-Paste (CAP) method was adopted to invert the focal mechanism solutions of 163 events with M ≥3.5 from 2009 to 2021. Combining the focal mechanisms inverted in this study and 1156 solutions collected from the GlobalCMT catalog and other published studies, we obtained the regional stress field with the damped regional-scale stress tensor inversion method. The results show that the earthquakes in this region are mainly distributed along mapped faults, among which the eastern Himalayan syntaxis, the extensional rift in the middle of the plateau, the Sichuan-Yunnan block, and the Yunnan-Burma block experience significant seismic activity. The earthquakes are distributed in the upper and middle crust (5-25 km), and there is a significant increase in the number and dominant depth distribution of earthquakes within the Sichuan-Yunnan and Yunnan-Myanmar blocks from those in the Lhasa and Qiangtang blocks. Earthquakes of various mechanisms occur frequently at the eastern Himalayan syntaxis; strike-slip earthquakes are mainly distributed along large boundary faults; normal earthquakes primarily occur along the western boundary faults of the Sichuan-Yunnan block, and thrust earthquakes are concentrated at the front of the collision between the Indian and Eurasian plates. The horizontal direction of the principal compressive stress axis rotates nearly clockwise around the eastern Himalayan syntaxis, from the Himalayas, Lhasa, Qiangtang, Sichuan-Yunnan to Yunnan-Burma blocks. Moreover, strong local inhomogeneity in the stress fields are found in the shallow eastern Himalayan syntaxis and northwest Sichuan-Yunnan block.
The eastern Himalayan syntaxis is located at the front of the collision between the Indian and Eurasian continents. This region is affected by the interaction of the Himalayan, Lhasa, Qiangtang, and Sichuan-Yunnan blocks and the Indian plate and is characterized by strong tectonic deformation with frequent earthquakes primarily distributed linearly. In this study, various seismological methods were used to reveal the seismicity, seismogenic mechanism, and tectonic stress field in this region. First, we used the double-difference location method (HypoDD) to relocate 65663 earthquakes with M ≥1.0 during 2008-2018. Then, the Cut-And-Paste (CAP) method was adopted to invert the focal mechanism solutions of 163 events with M ≥3.5 from 2009 to 2021. Combining the focal mechanisms inverted in this study and 1156 solutions collected from the GlobalCMT catalog and other published studies, we obtained the regional stress field with the damped regional-scale stress tensor inversion method. The results show that the earthquakes in this region are mainly distributed along mapped faults, among which the eastern Himalayan syntaxis, the extensional rift in the middle of the plateau, the Sichuan-Yunnan block, and the Yunnan-Burma block experience significant seismic activity. The earthquakes are distributed in the upper and middle crust (5-25 km), and there is a significant increase in the number and dominant depth distribution of earthquakes within the Sichuan-Yunnan and Yunnan-Myanmar blocks from those in the Lhasa and Qiangtang blocks. Earthquakes of various mechanisms occur frequently at the eastern Himalayan syntaxis; strike-slip earthquakes are mainly distributed along large boundary faults; normal earthquakes primarily occur along the western boundary faults of the Sichuan-Yunnan block, and thrust earthquakes are concentrated at the front of the collision between the Indian and Eurasian plates. The horizontal direction of the principal compressive stress axis rotates nearly clockwise around the eastern Himalayan syntaxis, from the Himalayas, Lhasa, Qiangtang, Sichuan-Yunnan to Yunnan-Burma blocks. Moreover, strong local inhomogeneity in the stress fields are found in the shallow eastern Himalayan syntaxis and northwest Sichuan-Yunnan block.
, Available online ,
doi: 10.19975/j.dqyxx.2022-073
Abstract:
The lower mantle accounts for more than 50% of the total volume of the earth, and influences the evolution of the earth. Early studies showed that the lower mantle is relatively homogeneous, but since the 1970s, seismic tomography revealed the velocity structure of the deep earth and found many velocity anomalies in the lower mantle. The accumulation of new array data and the progress of computer technology in the present century have enabled us to further constrain the seismic structures of these anomalous zones. Since these structures could be closely related to subduction plates and mantle plumes, it is of great significance to understand the fine structure of these wave velocity anomalies to study the reconstruction of ancient plates and the mantle tectonic mechanism. This study focuses on summarizing the methods and results in revealing the lower mantle anomalies using seismic data in the past 30 years, especially the distribution and characteristics of different types of velocity anomalous zones worldwide. African and Pacific LLSVP are the two most important LLSVPs in the lower mantle. Their lateral and vertical extents span approximately a thousand and more than a thousand kilometers, respectively. The present study found sharp velocity contrasts along the boundary of the LLSVP, which argues for chemical anomalies in the LLSVP. The ULVZ is located at the bottom of the lower mantle, with extremely low S-wave velocities that are 20%-40% smaller than the average. The lateral extent of the ULVZ is generally smaller than a thousand kilometers, but some ULVZ exceed that extent; the heights range from ten kilometers to dozens of kilometers. Partial melting, particularly related to chemical anomalies, is thought to be the most plausible explanation for ULVZ. D" discontinuities were also observed in many regions, especially where high-velocity subducted slabs were found. The slabs reduce the temperature near the core-mantle boundary, which yields stable pPv and D" discontinuities. In addition, the seismic anisotropy of the lower mantle is also a focus because it reflects the flow conditions of the mantle. The existing results show that several wave velocity anomaly structures (LLSVP, ULVZ, D", anisotropy) in the lower mantle may be closely related and connected to the subducting slabs in space, and the difference in mantle temperature and chemical composition may be an important factor that produces these anomalies. Finally, this study also summarizes the results of the velocity structure of the lower mantle in China and looks forward to the future research direction of the velocity anomaly and anisotropy of the lower mantle in China.
The lower mantle accounts for more than 50% of the total volume of the earth, and influences the evolution of the earth. Early studies showed that the lower mantle is relatively homogeneous, but since the 1970s, seismic tomography revealed the velocity structure of the deep earth and found many velocity anomalies in the lower mantle. The accumulation of new array data and the progress of computer technology in the present century have enabled us to further constrain the seismic structures of these anomalous zones. Since these structures could be closely related to subduction plates and mantle plumes, it is of great significance to understand the fine structure of these wave velocity anomalies to study the reconstruction of ancient plates and the mantle tectonic mechanism. This study focuses on summarizing the methods and results in revealing the lower mantle anomalies using seismic data in the past 30 years, especially the distribution and characteristics of different types of velocity anomalous zones worldwide. African and Pacific LLSVP are the two most important LLSVPs in the lower mantle. Their lateral and vertical extents span approximately a thousand and more than a thousand kilometers, respectively. The present study found sharp velocity contrasts along the boundary of the LLSVP, which argues for chemical anomalies in the LLSVP. The ULVZ is located at the bottom of the lower mantle, with extremely low S-wave velocities that are 20%-40% smaller than the average. The lateral extent of the ULVZ is generally smaller than a thousand kilometers, but some ULVZ exceed that extent; the heights range from ten kilometers to dozens of kilometers. Partial melting, particularly related to chemical anomalies, is thought to be the most plausible explanation for ULVZ. D" discontinuities were also observed in many regions, especially where high-velocity subducted slabs were found. The slabs reduce the temperature near the core-mantle boundary, which yields stable pPv and D" discontinuities. In addition, the seismic anisotropy of the lower mantle is also a focus because it reflects the flow conditions of the mantle. The existing results show that several wave velocity anomaly structures (LLSVP, ULVZ, D", anisotropy) in the lower mantle may be closely related and connected to the subducting slabs in space, and the difference in mantle temperature and chemical composition may be an important factor that produces these anomalies. Finally, this study also summarizes the results of the velocity structure of the lower mantle in China and looks forward to the future research direction of the velocity anomaly and anisotropy of the lower mantle in China.
, Available online ,
doi: 10.19975/j.dqyxx.2023-001
Abstract:
The Chinese Meridian Project (Phase II) plans to construct ionospheric Doppler sounding arrays around Mohe, Beijing, Wuhan, and Shenzhen. Each array consists of one transmitter station and three stations equipped with the ionospheric high-frequency Doppler shift monitor, which is described in this paper in terms of system design and preliminary results from its pilot operation. By comparison with a collocated ionosonde, the performance capability of the sounder is validated. At present, the sounders have been installed at seven stations and have been running continuously for about 1 year. This paper presents observations of various ionospheric disturbances caused by solar flare eruptions, travelling ionosphere disturbances, and probable large-scale electric field variations. Once established, the chain of sounder arrays will continuously monitor ionospheric disturbances over eastern China and contribute to the sophisticated space environment monitoring network of the Chinese Meridian Project.
The Chinese Meridian Project (Phase II) plans to construct ionospheric Doppler sounding arrays around Mohe, Beijing, Wuhan, and Shenzhen. Each array consists of one transmitter station and three stations equipped with the ionospheric high-frequency Doppler shift monitor, which is described in this paper in terms of system design and preliminary results from its pilot operation. By comparison with a collocated ionosonde, the performance capability of the sounder is validated. At present, the sounders have been installed at seven stations and have been running continuously for about 1 year. This paper presents observations of various ionospheric disturbances caused by solar flare eruptions, travelling ionosphere disturbances, and probable large-scale electric field variations. Once established, the chain of sounder arrays will continuously monitor ionospheric disturbances over eastern China and contribute to the sophisticated space environment monitoring network of the Chinese Meridian Project.
, Available online ,
doi: 10.19975/j.dqyxx.2022-080
Abstract:
A finite-fault earthquake slip model can characterize the kinematics of rupture, which is essential for earthquake mechanism studies and seismic hazard assessments. The finite-fault model of an earthquake can be inverted from a wide range of geodetic measurements and seismic recordings. The linear least squares method minimizes misfits between observations and forward modeling and is a common approach in finite-fault inversion problems. This method may not yield the most plausible finite-fault model and has four main limitations. First, total parameter spaces are challenging to explore, and non-Gaussian parameter uncertainties cannot be evaluated. Second, to improve the stability of the fault slip inversion, fault slip smoothing operators (regularization techniques) are usually applied; however, determining the strength of smoothing a fault slip distribution is subjective. Third, the fault geometry needs to be predetermined, and different fault geometry settings can result in varying inversion results. Fourth, it is difficult to account for uncertainties in forward modeling because of imprecise Earth velocity models. In contrast, Bayesian inversion determines the probability density distribution of the model parameters, providing a globally optimized solution to all model parameters and characterizing trade-offs between pairs of model parameters. Therefore, the Bayesian approach effectively overcomes the problems encountered in linear inversion. With the rapid improvement in computer technology, Bayesian inversion has become highly developed, especially in the past decade. This review reports the results of recent Bayesian finite-fault inversion studies and explains the theory and methodology of Bayesian finite-fault inversion.
A finite-fault earthquake slip model can characterize the kinematics of rupture, which is essential for earthquake mechanism studies and seismic hazard assessments. The finite-fault model of an earthquake can be inverted from a wide range of geodetic measurements and seismic recordings. The linear least squares method minimizes misfits between observations and forward modeling and is a common approach in finite-fault inversion problems. This method may not yield the most plausible finite-fault model and has four main limitations. First, total parameter spaces are challenging to explore, and non-Gaussian parameter uncertainties cannot be evaluated. Second, to improve the stability of the fault slip inversion, fault slip smoothing operators (regularization techniques) are usually applied; however, determining the strength of smoothing a fault slip distribution is subjective. Third, the fault geometry needs to be predetermined, and different fault geometry settings can result in varying inversion results. Fourth, it is difficult to account for uncertainties in forward modeling because of imprecise Earth velocity models. In contrast, Bayesian inversion determines the probability density distribution of the model parameters, providing a globally optimized solution to all model parameters and characterizing trade-offs between pairs of model parameters. Therefore, the Bayesian approach effectively overcomes the problems encountered in linear inversion. With the rapid improvement in computer technology, Bayesian inversion has become highly developed, especially in the past decade. This review reports the results of recent Bayesian finite-fault inversion studies and explains the theory and methodology of Bayesian finite-fault inversion.
, Available online ,
doi: 10.19975/j.dqyxx.2022-083
Abstract:
Mars is the sister star of Earth. Studying Mars is important to understand its evolution as well as that of Earth and even the solar system. Since the launch of American Mariner 4 in 1964 and the first successful use of radio occultation technology to explore the environmental characteristics of Mars, many international missions to Mars have conducted occultation experiments and made important progress. This article investigates Mars probes based on their launch time sequence, which utilized radio occultation techniques for exploration, focusing on groundbreaking missions such as the Mariner series, Mars Global Surveyor, Mars Express, Mars Atmosphere and Volatile Evolution, and Tianwen-1. We review, analyze, and summarize the product information, including the number and distribution of profile measurements, and the methods of acquisition obtained from each mission's radio occultation. Additionally, this article analyzes the limitations of the current Mars radio occultation approaches and explores possible countermeasures. Mars radio occultation can be further improved by considering the mode of star-star occultation combined with star-ground occultation to form occultation constellation, choosing an appropriate signal detection frequency, and improving the inversion algorithm. It can also be combined with the Mars top detection radar and direct detection means to develop multi-source data fusion. With the continuous improvement of detection modes, radio occultation detection will be an important tool for Mars exploration in the future. Detections will grow in number and become increasingly more comprehensive in time and space coverage, and more accurate occultation data for the entire space environment of Mars will be obtained, including large, mesoscale, and even small-scale structure characteristics and evolution laws.
Mars is the sister star of Earth. Studying Mars is important to understand its evolution as well as that of Earth and even the solar system. Since the launch of American Mariner 4 in 1964 and the first successful use of radio occultation technology to explore the environmental characteristics of Mars, many international missions to Mars have conducted occultation experiments and made important progress. This article investigates Mars probes based on their launch time sequence, which utilized radio occultation techniques for exploration, focusing on groundbreaking missions such as the Mariner series, Mars Global Surveyor, Mars Express, Mars Atmosphere and Volatile Evolution, and Tianwen-1. We review, analyze, and summarize the product information, including the number and distribution of profile measurements, and the methods of acquisition obtained from each mission's radio occultation. Additionally, this article analyzes the limitations of the current Mars radio occultation approaches and explores possible countermeasures. Mars radio occultation can be further improved by considering the mode of star-star occultation combined with star-ground occultation to form occultation constellation, choosing an appropriate signal detection frequency, and improving the inversion algorithm. It can also be combined with the Mars top detection radar and direct detection means to develop multi-source data fusion. With the continuous improvement of detection modes, radio occultation detection will be an important tool for Mars exploration in the future. Detections will grow in number and become increasingly more comprehensive in time and space coverage, and more accurate occultation data for the entire space environment of Mars will be obtained, including large, mesoscale, and even small-scale structure characteristics and evolution laws.
, Available online ,
doi: 10.19975/j.dqyxx.2022-079
Abstract:
The north-south convergence and east-west extension of the Tibet Plateau are accommodated by a series of active strike-slip and normal faults, and normal-fault earthquakes are very active in the plateau. During 2020 to 2021, there were three normal-fault earthquakes, namely, the Dingri MS5.9 (2020-03-20), Biru MS6.1 (2021-03-19), and Shuanghu MS5.81 (2021-03-30) earthquakes. These three earthquakes were evenly distributed in the middle and southern parts of the plateau, which provides a favorable case for us to study the seismic deformation characteristics using interferometric synthetic aperture radar (InSAR) technology. We used InSAR technology and Sentinel-1 SAR image data to generate the coseismic deformation field of the three normal-fault earthquakes in the Tibetan Plateau. The results showed that the normal-fault earthquakes in the plateau were not pure normal-fault types, and the coseismic deformation field showed both subsidence deformation and strike-slip deformation. Based on the Okada elastic dislocation model and the coseismic deformation fields, we constrained and inverted the geometric parameters and the slip distribution of the fault plane to accurately determine the locations of the seismogenic faults. The seismogenic faults were mainly secondary concealed faults with dip angles < 60°, all of which were shallow earthquakes. The slip distribution was mainly concentrated within 12 km. Combined with geophysical recognition, we inferred that normal-fault earthquakes are widely distributed in the Qinghai-Tibet Plateau, and not limited to areas related to half-graben structure, and that the occurrence of normal-fault earthquakes largely depends on the gravitational potential energy in the extensional environment.
, Available online ,
doi: 10.19975/j.dqyxx.2022-074
Abstract:
The lithology and pore structure of conglomerate reservoir in the Mahu sag, China, are complex, which makes it difficult to identify reservoir fluids. In this study, the body relaxation characteristics of crude oil at different temperatures were obtained from block crude oil samples, and two simulated oil samples with different body relaxation characteristics were used to conduct experiments. The saturated water, bound water, and saturated oil states of some conglomerate samples were quickly established by vacuum compression saturation, high-speed centrifugation, and vacuum saturation simulation of oil, and the fluid and different simulated oil-water saturation states were analyzed by nuclear magnetic resonance (NMR) experiments. The experimental results showed that the distribution range of the water-saturated core NMR T2 spectrum is mainly affected by surface relaxation. The NMR spectra of saturated oil with different viscosity values are different from those of saturated water because of the relaxation property of the oil phase. The samples of this experiment indicated that the difference is more obvious when the oil is thinner. The distribution pattern of the oil-bearing NMR results was affected by the relaxation of the oil phase, surface relaxation, pore structure, and wettability. With consideration of the relaxation characteristics of the oil samples, the NMR T2 spectra of two oil-saturated conglomerates were analyzed by multi-component Gaussian fitting, and the relaxation signals of the oil phase were evaluated quantitatively.
The lithology and pore structure of conglomerate reservoir in the Mahu sag, China, are complex, which makes it difficult to identify reservoir fluids. In this study, the body relaxation characteristics of crude oil at different temperatures were obtained from block crude oil samples, and two simulated oil samples with different body relaxation characteristics were used to conduct experiments. The saturated water, bound water, and saturated oil states of some conglomerate samples were quickly established by vacuum compression saturation, high-speed centrifugation, and vacuum saturation simulation of oil, and the fluid and different simulated oil-water saturation states were analyzed by nuclear magnetic resonance (NMR) experiments. The experimental results showed that the distribution range of the water-saturated core NMR T2 spectrum is mainly affected by surface relaxation. The NMR spectra of saturated oil with different viscosity values are different from those of saturated water because of the relaxation property of the oil phase. The samples of this experiment indicated that the difference is more obvious when the oil is thinner. The distribution pattern of the oil-bearing NMR results was affected by the relaxation of the oil phase, surface relaxation, pore structure, and wettability. With consideration of the relaxation characteristics of the oil samples, the NMR T2 spectra of two oil-saturated conglomerates were analyzed by multi-component Gaussian fitting, and the relaxation signals of the oil phase were evaluated quantitatively.
, Available online ,
doi: 10.19975/j.dqyxx.2022-075
Abstract:
Strong diagenesis and reservoir heterogeneity as well as complex pore structure in the late stage of No. 4 structure in Nanpu sag make assessment of the petrophysical characteristics of its high-quality reservoir and evaluation of its effectiveness difficult. To address this, the sedimentary, diagenetic, and pore structure characteristics of the reservoir were comprehensively studied using core thin section analysis, scanning electron microscopy, X-ray diffraction, capillary analysis, and logging and oil tests. The results showed that the sedimentary facies of the Ed2 and Ed3 of the study area were mainly braided river delta types, and the sedimentary microfacies mainly developed in an underwater distributary channel, interdistributary bay, and mouth bar. Diagenetic facies can be divided into four types based on diagenesis and mineral types: weak dissolution facies, clay mineral filling facies, carbonate cementation facies, and compacted dense facies. The pore structure facies can be divided into four types based on the reservoir physical properties and mercury injection, I: macropore coarse throat type, II: macropore medium throat type, III: mesopore thin throat type, and IV: micropore throat type. Based on the superimposed cluster analysis of sedimentary, diagenesis, and pore structure, the reservoir petrophysical facies can be divided into PF1-PF4, and the corresponding quantitative classification and evaluation criteria can be established. PF1 is an advantageous reservoir with high oil, gas, and water productivity; PF2 is an oil-bearing reservoir with average productivity; PF3 is a poor reservoir with low productivity after reservoir reconstruction; and PF4 is an invalid reservoir. The quantitative classification and evaluation criteria of petrophysical facies are established by logging response rules, which provide technical support and a solid theoretical basis for the evaluation of reservoir effectiveness, superior reservoir prediction, and subsequent ongoing development in the study area.
Strong diagenesis and reservoir heterogeneity as well as complex pore structure in the late stage of No. 4 structure in Nanpu sag make assessment of the petrophysical characteristics of its high-quality reservoir and evaluation of its effectiveness difficult. To address this, the sedimentary, diagenetic, and pore structure characteristics of the reservoir were comprehensively studied using core thin section analysis, scanning electron microscopy, X-ray diffraction, capillary analysis, and logging and oil tests. The results showed that the sedimentary facies of the Ed2 and Ed3 of the study area were mainly braided river delta types, and the sedimentary microfacies mainly developed in an underwater distributary channel, interdistributary bay, and mouth bar. Diagenetic facies can be divided into four types based on diagenesis and mineral types: weak dissolution facies, clay mineral filling facies, carbonate cementation facies, and compacted dense facies. The pore structure facies can be divided into four types based on the reservoir physical properties and mercury injection, I: macropore coarse throat type, II: macropore medium throat type, III: mesopore thin throat type, and IV: micropore throat type. Based on the superimposed cluster analysis of sedimentary, diagenesis, and pore structure, the reservoir petrophysical facies can be divided into PF1-PF4, and the corresponding quantitative classification and evaluation criteria can be established. PF1 is an advantageous reservoir with high oil, gas, and water productivity; PF2 is an oil-bearing reservoir with average productivity; PF3 is a poor reservoir with low productivity after reservoir reconstruction; and PF4 is an invalid reservoir. The quantitative classification and evaluation criteria of petrophysical facies are established by logging response rules, which provide technical support and a solid theoretical basis for the evaluation of reservoir effectiveness, superior reservoir prediction, and subsequent ongoing development in the study area.
, Available online ,
doi: 10.19975/j.dqyxx.2022-077
Abstract:
This paper mainly reviews the history and prospects of the atmospheric motion vector (AMV) of meteorological satellites. The development history of AMV and some milestone events are first introduced before briefly discussing them in the contexts of China, the United States, Europe, and Japan. The first section provides a detailed summary of the characteristics and key technologies of various traditional AMV algorithms, introduces the cross-correlation, pattern recognition, and nested tracking approaches, and describes five commonly used height assignment algorithms and their basic principles. The second section discusses several recently developed AMV products based on computer vision and machine learning technologies and introduces the advantages and research histories of the optical flow method, and three-dimensional and mesoscale AMVs. Finally, we compare the advantages and disadvantages of new and traditional AMV algorithms before examining the potential for future applications and development trends. We specifically highlight the higher spatial resolution obtained by the advanced optical flow method, better wind field information from three-dimensional AMV, and finer spatial and temporal resolutions of special weather from mesoscale AMV such as cyclones. Furthermore, we predict more promising three-dimensional and mesoscale AMVs in the upcoming future.
This paper mainly reviews the history and prospects of the atmospheric motion vector (AMV) of meteorological satellites. The development history of AMV and some milestone events are first introduced before briefly discussing them in the contexts of China, the United States, Europe, and Japan. The first section provides a detailed summary of the characteristics and key technologies of various traditional AMV algorithms, introduces the cross-correlation, pattern recognition, and nested tracking approaches, and describes five commonly used height assignment algorithms and their basic principles. The second section discusses several recently developed AMV products based on computer vision and machine learning technologies and introduces the advantages and research histories of the optical flow method, and three-dimensional and mesoscale AMVs. Finally, we compare the advantages and disadvantages of new and traditional AMV algorithms before examining the potential for future applications and development trends. We specifically highlight the higher spatial resolution obtained by the advanced optical flow method, better wind field information from three-dimensional AMV, and finer spatial and temporal resolutions of special weather from mesoscale AMV such as cyclones. Furthermore, we predict more promising three-dimensional and mesoscale AMVs in the upcoming future.
, Available online ,
doi: 10.19975/j.dqyxx.2022-078
Abstract:
The 2020 MW6.3 Nima earthquake occurred in the northern Yibug Caka graben on the Qiangtang Block of the Tibetan Plateau. The epicentral area has complex geological structures, topography, and geomorphology, and there are few near-field ground observation stations and data. Interferometric Synthetic Aperture Radar (InSAR) has all-weather, wide ranging and high spatial resolution monitoring advantages, which can make up for the shortage of near-field ground deformation observations. However, previous studies have obtained different viewpoints regarding the seismogenic fault and coseismic and postseismic fault slip characteristics of this event. In addition, only the kinematic model has been used to extract the postseismic fault afterslip characteristics. In this study, we used ascending and descending Sentinel-1 Synthetic Aperture Radar (SAR) images and differential interferometry technology to extract the coseismic deformation fields at different viewing angles. The coseismic fault geometry and slip distribution were then inverted based on an elastic half-space dislocation model. The stress-driven postseismic afterslip model was used to model and analyze the postseismic fault slip. Finally, the earthquake seismogenic fault and the friction property characteristics of seismogenic fault zone were discussed. The ascending and descending InSAR coseismic deformation fields were continuous and smooth around the epicenter, trending NNE-SSW overall. The deformation on the southeastern side of the fault was relatively significant, and mainly decreased along the line-of-sight direction. The coseismic fault rupture was mainly normal, with a sinistral strike-slip component. The strike angle was 31.43°, and the dip angle was 45.79°. The coseismic fault slip was mainly located at 3.58-10.75 km underground, with a maximum slip of 1.33 m, and the moment magnitude was MW6.33. The stress-driven postseismic afterslip model could better explain the almost six-month InSAR postseismic deformation field of this event. The postseismic afterslip mainly occurred on the upper, lower and southwestern sides of the southwestern segment of the significant slip area of coseismic fault, with a maximum afterslip of 47.2 cm. The seismogenic fault of this event might be a normal fault located in the middle of the Yibug Caka-Riganpei Co fault and dipping SEE, and the friction property of the seismogenic fault zone might be uneven.
The 2020 MW6.3 Nima earthquake occurred in the northern Yibug Caka graben on the Qiangtang Block of the Tibetan Plateau. The epicentral area has complex geological structures, topography, and geomorphology, and there are few near-field ground observation stations and data. Interferometric Synthetic Aperture Radar (InSAR) has all-weather, wide ranging and high spatial resolution monitoring advantages, which can make up for the shortage of near-field ground deformation observations. However, previous studies have obtained different viewpoints regarding the seismogenic fault and coseismic and postseismic fault slip characteristics of this event. In addition, only the kinematic model has been used to extract the postseismic fault afterslip characteristics. In this study, we used ascending and descending Sentinel-1 Synthetic Aperture Radar (SAR) images and differential interferometry technology to extract the coseismic deformation fields at different viewing angles. The coseismic fault geometry and slip distribution were then inverted based on an elastic half-space dislocation model. The stress-driven postseismic afterslip model was used to model and analyze the postseismic fault slip. Finally, the earthquake seismogenic fault and the friction property characteristics of seismogenic fault zone were discussed. The ascending and descending InSAR coseismic deformation fields were continuous and smooth around the epicenter, trending NNE-SSW overall. The deformation on the southeastern side of the fault was relatively significant, and mainly decreased along the line-of-sight direction. The coseismic fault rupture was mainly normal, with a sinistral strike-slip component. The strike angle was 31.43°, and the dip angle was 45.79°. The coseismic fault slip was mainly located at 3.58-10.75 km underground, with a maximum slip of 1.33 m, and the moment magnitude was MW6.33. The stress-driven postseismic afterslip model could better explain the almost six-month InSAR postseismic deformation field of this event. The postseismic afterslip mainly occurred on the upper, lower and southwestern sides of the southwestern segment of the significant slip area of coseismic fault, with a maximum afterslip of 47.2 cm. The seismogenic fault of this event might be a normal fault located in the middle of the Yibug Caka-Riganpei Co fault and dipping SEE, and the friction property of the seismogenic fault zone might be uneven.
, Available online ,
doi: 10.19975/j.dqyxx.2022-076
Abstract:
Sudden stratospheric warming (SSW) is a violent atmospheric disturbance in the polar region of the winter hemisphere. The drastic changes in temperature and wind during SSWs are considered to be the main reasons for the abnormal increase in the energy of atmospheric waves in the upper and middle atmosphere in the winter hemisphere. Meteor radar is an important ground-based detection equipment that can stably and continuously detect neutral wind in the mesosphere and lower thermosphere (MLT) region. Based on one of the National Major Science Infrastructure Projects, the "Meridian Project", China has built several meteor radar observation stations to conduct long-term stable and continuous monitoring of the neutral wind in the MLT region, which provides important observation data for revealing the physical mechanism of abnormal changes in atmospheric waves during SSWs. Here, we briefly review the research progress on planetary waves in the middle and upper atmosphere during SSWs in recent years, especially the scientific findings based on the meteor radars in the Chinese "Meridian Project". The trigger mechanisms of the enhanced planetary waves during SSWs are discussed. With the completion of ten meteor radars in the second phase of the "Meridian Project", this paper prospects the use of its meteor radar monitoring network to further study the characteristics of atmospheric waves in the middle and upper atmosphere during SSWs.
Sudden stratospheric warming (SSW) is a violent atmospheric disturbance in the polar region of the winter hemisphere. The drastic changes in temperature and wind during SSWs are considered to be the main reasons for the abnormal increase in the energy of atmospheric waves in the upper and middle atmosphere in the winter hemisphere. Meteor radar is an important ground-based detection equipment that can stably and continuously detect neutral wind in the mesosphere and lower thermosphere (MLT) region. Based on one of the National Major Science Infrastructure Projects, the "Meridian Project", China has built several meteor radar observation stations to conduct long-term stable and continuous monitoring of the neutral wind in the MLT region, which provides important observation data for revealing the physical mechanism of abnormal changes in atmospheric waves during SSWs. Here, we briefly review the research progress on planetary waves in the middle and upper atmosphere during SSWs in recent years, especially the scientific findings based on the meteor radars in the Chinese "Meridian Project". The trigger mechanisms of the enhanced planetary waves during SSWs are discussed. With the completion of ten meteor radars in the second phase of the "Meridian Project", this paper prospects the use of its meteor radar monitoring network to further study the characteristics of atmospheric waves in the middle and upper atmosphere during SSWs.
, Available online ,
doi: 10.19975/j.dqyxx.2022-069
Abstract:
The Longgang volcanic field is one of the most active volcanoes in modern China. It is situated in the central region of the Longgang mountains on the west slopes of Changbaishan in Jilin. The present three-dimensional crustal movement velocity fields in the different periods were obtained by processing Global Navigation Satellite System (GNSS) observations from 2010 to 2020 and data for the leveling profiles from 1970s to 2010s in the area. The horizontal velocities of GNSS stations were larger in the eastern region than in the western regions, indicating that the eastern region is mainly tensile. The results of the continuous surface strain rates showed that a volcanic field is located in the expansion area. The results of the first-order leveling data for the Changfu profile and the Danfu profile showed that the vertical movements were predominantly uplift, with rates of 0.55~1.83 mm/a for most of the sites. The area with relatively higher uplifting rates of more than 1.0 mm/a was Fusong-Xianrenqiao-Laoshandui, which is rich in geothermal resources and prone to earthquakes. At the adjacent area, Meitong, the rates of the second-class leveling profile were relatively small, at 0.23~0.77 mm/a. The deep electrical structure of the volcanic area was obtained through the three-dimensional inversion of 99 broadband magnetotelluric soundings. The clear structures of the low resistivity in the middle and lower crusts corresponded to the uplift area, which is suggested to be a magmatic system. The position of the magma was relatively shallow. The electrical boundary zone at the northeast end of the Hunjiang fault was speculated to be the northern extension of the fault. The low-resistivity body had the largest scale and extended downward to the mantle. The shallowest low-resistivity body was approximately 10 km below the youngest Jinlongdingzi volcano, and the above high-resistivity structure was considered to be the retreat and consolidation magma after the overflow eruption ended. A comprehensive analysis showed that the ongoing inflation, uplift, and seismic activities of the crust in the volcanic area were related to the upwelling of mantle materials and fault movements caused by intermittent magma migration.
The Longgang volcanic field is one of the most active volcanoes in modern China. It is situated in the central region of the Longgang mountains on the west slopes of Changbaishan in Jilin. The present three-dimensional crustal movement velocity fields in the different periods were obtained by processing Global Navigation Satellite System (GNSS) observations from 2010 to 2020 and data for the leveling profiles from 1970s to 2010s in the area. The horizontal velocities of GNSS stations were larger in the eastern region than in the western regions, indicating that the eastern region is mainly tensile. The results of the continuous surface strain rates showed that a volcanic field is located in the expansion area. The results of the first-order leveling data for the Changfu profile and the Danfu profile showed that the vertical movements were predominantly uplift, with rates of 0.55~1.83 mm/a for most of the sites. The area with relatively higher uplifting rates of more than 1.0 mm/a was Fusong-Xianrenqiao-Laoshandui, which is rich in geothermal resources and prone to earthquakes. At the adjacent area, Meitong, the rates of the second-class leveling profile were relatively small, at 0.23~0.77 mm/a. The deep electrical structure of the volcanic area was obtained through the three-dimensional inversion of 99 broadband magnetotelluric soundings. The clear structures of the low resistivity in the middle and lower crusts corresponded to the uplift area, which is suggested to be a magmatic system. The position of the magma was relatively shallow. The electrical boundary zone at the northeast end of the Hunjiang fault was speculated to be the northern extension of the fault. The low-resistivity body had the largest scale and extended downward to the mantle. The shallowest low-resistivity body was approximately 10 km below the youngest Jinlongdingzi volcano, and the above high-resistivity structure was considered to be the retreat and consolidation magma after the overflow eruption ended. A comprehensive analysis showed that the ongoing inflation, uplift, and seismic activities of the crust in the volcanic area were related to the upwelling of mantle materials and fault movements caused by intermittent magma migration.
, Available online ,
doi: 10.19975/j.dqyxx.2022-037
Abstract:
If coseismic deformation of the earthquake region can be obtained in a short time, it is important for timely evaluate the disaster and cooperate with the development of earthquake relief work. Space geodesy technology has the advantages of high monitoring accuracy and high spatial resolution, and has been widely used in seismic deformation monitoring related fields. The coseismic deformation obtained by processing space geodetic data can intuitively show the surface deformation caused by the earthquake and provide a reference for judging the disaster situation. However due to the lag of data acquisition, it is often impossible to provide coseismic deformation map in a short time after the earthquake. In this paper, using the near real-time focal mechanism solutions of the USGS NEIC, seismic elastic dislocation model and seismic empirical formula, a seismic deformation simulation application based on Android smartphone (namely Codefmap APP) is developed based on Java and Python language. The program has the functions of earthquake catalog query at any time in the world, actively obtaining USGS NEIC source parameters, displaying epicenter position and automatically calculating coseismic deformation. For important events, the deformation simulation results can be given within one day, especially for blind earthquakes. It can provide a reference basis for determining potentially dangerous areas and early earthquake relief to a certain extent.
If coseismic deformation of the earthquake region can be obtained in a short time, it is important for timely evaluate the disaster and cooperate with the development of earthquake relief work. Space geodesy technology has the advantages of high monitoring accuracy and high spatial resolution, and has been widely used in seismic deformation monitoring related fields. The coseismic deformation obtained by processing space geodetic data can intuitively show the surface deformation caused by the earthquake and provide a reference for judging the disaster situation. However due to the lag of data acquisition, it is often impossible to provide coseismic deformation map in a short time after the earthquake. In this paper, using the near real-time focal mechanism solutions of the USGS NEIC, seismic elastic dislocation model and seismic empirical formula, a seismic deformation simulation application based on Android smartphone (namely Codefmap APP) is developed based on Java and Python language. The program has the functions of earthquake catalog query at any time in the world, actively obtaining USGS NEIC source parameters, displaying epicenter position and automatically calculating coseismic deformation. For important events, the deformation simulation results can be given within one day, especially for blind earthquakes. It can provide a reference basis for determining potentially dangerous areas and early earthquake relief to a certain extent.
, Available online ,
doi: 10.19975/j.dqyxx.2022-023
Abstract:
Interferometry Synthetic Aperture Radar (InSAR) technology has become an important tool for monitoring surface deformation with its all-day, all-weather ground monitoring and high spatial resolution, and has been widely applied to seismic deformation monitoring. Currently, the most commonly used technique for coseismic deformation monitoring is differential InSAR (D-InSAR). However, the traditional D-InSAR is susceptible to spatial and temporal uncorrelation in areas such as waters and densely vegetated areas, resulting in serious contamination of the coseismic deformation field. In addition, the seismic deformation field sometimes contains obvious atmospheric delay that can affect source parameter inversions. Therefore, improving the quality of coseismic deformation is of great significance for future seismic deformation monitoring and parameter inversion. The multi-temporal InSAR (MT-InSAR) technique, which is widely used in inter-seismic and post-seismic deformation monitoring, is able to suppress the effects of spatiotemporal decorrelation and atmospheric noise. In this paper, we propose a high-precision coseismic deformation monitoring method based on time-series InSAR analysis to obtain high-precision coseismic deformation results. The accuracy of coseismic deformation field is mainly improved by selecting appropriate interferograms and selecting stable points. With the support of sufficient Sentinel-1A/B satellite SAR data, numerous interferograms were generated using a large number of pre- and post-earthquake images. Interferograms that are less affected by errors are selected for study according to certain criteria to reduce the impact caused by atmospheric delay errors. At the same time, setting threshold to select stable point target to improve the accuracy of deformation field. Taking the 2018 Hualian MW6.4 earthquake in Taiwan China as an example, the data processing flow of high-precision coseismic deformation monitoring method is introduced in detail. Compared with the results of the traditional D-InSAR method, the proposed method can reduce the noise error and improve the signal-to-noise ratio of coseismic deformation. The high-precision coseismic deformation monitoring method is applied to obtain the seismic deformation of 14 different magnitudes and locations. The deformation results show that the method can improve the accuracy of deformation field by selecting stable points, and it is generally applicable.
Interferometry Synthetic Aperture Radar (InSAR) technology has become an important tool for monitoring surface deformation with its all-day, all-weather ground monitoring and high spatial resolution, and has been widely applied to seismic deformation monitoring. Currently, the most commonly used technique for coseismic deformation monitoring is differential InSAR (D-InSAR). However, the traditional D-InSAR is susceptible to spatial and temporal uncorrelation in areas such as waters and densely vegetated areas, resulting in serious contamination of the coseismic deformation field. In addition, the seismic deformation field sometimes contains obvious atmospheric delay that can affect source parameter inversions. Therefore, improving the quality of coseismic deformation is of great significance for future seismic deformation monitoring and parameter inversion. The multi-temporal InSAR (MT-InSAR) technique, which is widely used in inter-seismic and post-seismic deformation monitoring, is able to suppress the effects of spatiotemporal decorrelation and atmospheric noise. In this paper, we propose a high-precision coseismic deformation monitoring method based on time-series InSAR analysis to obtain high-precision coseismic deformation results. The accuracy of coseismic deformation field is mainly improved by selecting appropriate interferograms and selecting stable points. With the support of sufficient Sentinel-1A/B satellite SAR data, numerous interferograms were generated using a large number of pre- and post-earthquake images. Interferograms that are less affected by errors are selected for study according to certain criteria to reduce the impact caused by atmospheric delay errors. At the same time, setting threshold to select stable point target to improve the accuracy of deformation field. Taking the 2018 Hualian MW6.4 earthquake in Taiwan China as an example, the data processing flow of high-precision coseismic deformation monitoring method is introduced in detail. Compared with the results of the traditional D-InSAR method, the proposed method can reduce the noise error and improve the signal-to-noise ratio of coseismic deformation. The high-precision coseismic deformation monitoring method is applied to obtain the seismic deformation of 14 different magnitudes and locations. The deformation results show that the method can improve the accuracy of deformation field by selecting stable points, and it is generally applicable.
Display Method:
2023, 54(5): 477-497.
doi: 10.19975/j.dqyxx.2022-071
Abstract:
Research on fault interaction and earthquake triggering, which is a hot issue in the field of source physics, can facilitate understanding of the underlying mechanisms of strong earthquakes and also has good application prospects in earthquake risk analysis and prediction research. Previous review articles provided detailed explanations from the perspectives of basic principles, methods, and applicability, as well as multiple earthquake case studies of stress triggering. However, the introduction to earthquake triggering from the perspective of seismicity analysis is not exhaustive, and the combination and complementarity of these two perspectives are not provided in detail. This paper summarizes the achievements and progress of research on fault interaction and earthquake triggering mechanism through the past few decades from the perspectives of physical and statistical models. The current challenges and possible future directions are reviewed and evaluated. From the perspective of the physical model, three important mechanisms of sources of fault interaction are analyzed: static stress triggering, dynamic stress triggering, and viscoelastic stress triggering, as well as the basic principles and methods of calculation. In the aspect of the statistical model, the basic principles and methods of seismicity analysis are introduced, and applications of the epidemic-type aftershock sequence (ETAS) model and b-value in fault interaction and earthquake triggering mechanism are analyzed. From the perspective of the combination of these two models, the unified connotation of mutual verification and the basic principle of the rate-and-state friction law are introduced. The analysis points out that the stress interaction between multiple faults or earthquakes can be comprehensively studied through the two different schools of Coulomb stress calculation and the ETAS model and that cross-validation can increase the reliability of the results. Retroactive application of rate-and-state friction law can provide a new perspective for understanding the earthquake triggering relationship and fault interaction.
Research on fault interaction and earthquake triggering, which is a hot issue in the field of source physics, can facilitate understanding of the underlying mechanisms of strong earthquakes and also has good application prospects in earthquake risk analysis and prediction research. Previous review articles provided detailed explanations from the perspectives of basic principles, methods, and applicability, as well as multiple earthquake case studies of stress triggering. However, the introduction to earthquake triggering from the perspective of seismicity analysis is not exhaustive, and the combination and complementarity of these two perspectives are not provided in detail. This paper summarizes the achievements and progress of research on fault interaction and earthquake triggering mechanism through the past few decades from the perspectives of physical and statistical models. The current challenges and possible future directions are reviewed and evaluated. From the perspective of the physical model, three important mechanisms of sources of fault interaction are analyzed: static stress triggering, dynamic stress triggering, and viscoelastic stress triggering, as well as the basic principles and methods of calculation. In the aspect of the statistical model, the basic principles and methods of seismicity analysis are introduced, and applications of the epidemic-type aftershock sequence (ETAS) model and b-value in fault interaction and earthquake triggering mechanism are analyzed. From the perspective of the combination of these two models, the unified connotation of mutual verification and the basic principle of the rate-and-state friction law are introduced. The analysis points out that the stress interaction between multiple faults or earthquakes can be comprehensively studied through the two different schools of Coulomb stress calculation and the ETAS model and that cross-validation can increase the reliability of the results. Retroactive application of rate-and-state friction law can provide a new perspective for understanding the earthquake triggering relationship and fault interaction.
2023, 54(5): 498-511.
doi: 10.19975/j.dqyxx.2022-058
Abstract:
Rapid, accurate, and nearly real-time aftershock forecasting has attracted increasing public and social attention in dealing with disaster risk and taking effective disposal measures after the mainshock. Many aftershock forecasting methods are seriously affected by catalogue incompleteness in the early stage after the mainshock, which makes it difficult to carry out aftershock forecasting with a disaster reduction effect in time. In recent years, with the development of technology and models, the forecasting of early aftershocks has become possible. In this study, aiming at the "bottleneck period" of aftershock forecasting in the early stage after the mainshock, we elaborated the matched filtering technology and deep learning technology from the perspective of improving aftershock detection rate, the bi-scale empirical transformation technology from the perspective of statistical seismology, and the research progress of the Omi and Lippiello models from the perspective of maximizing the use of aftershock information for real-time forecasting. We analyzed the advantages and disadvantages of various methods and proposed a technical route to comprehensively solve the "bottleneck period" of aftershock forecasting in the early stage after the mainshock. This study provides a scientific reference for researchers to engage in microearthquake detection, aftershock forecasting, and post-earthquake trend research.
Rapid, accurate, and nearly real-time aftershock forecasting has attracted increasing public and social attention in dealing with disaster risk and taking effective disposal measures after the mainshock. Many aftershock forecasting methods are seriously affected by catalogue incompleteness in the early stage after the mainshock, which makes it difficult to carry out aftershock forecasting with a disaster reduction effect in time. In recent years, with the development of technology and models, the forecasting of early aftershocks has become possible. In this study, aiming at the "bottleneck period" of aftershock forecasting in the early stage after the mainshock, we elaborated the matched filtering technology and deep learning technology from the perspective of improving aftershock detection rate, the bi-scale empirical transformation technology from the perspective of statistical seismology, and the research progress of the Omi and Lippiello models from the perspective of maximizing the use of aftershock information for real-time forecasting. We analyzed the advantages and disadvantages of various methods and proposed a technical route to comprehensively solve the "bottleneck period" of aftershock forecasting in the early stage after the mainshock. This study provides a scientific reference for researchers to engage in microearthquake detection, aftershock forecasting, and post-earthquake trend research.
2023, 54(5): 512-531.
doi: 10.19975/j.dqyxx.2022-038
Abstract:
Stress drop measures the stress release level over a fault during an earthquake rupture. As one of the important parameters for characterizing source mechanisms and predicting strong ground motions, the stress drop is controlled by the tectonic environment, focal mechanism, and type of earthquake sequence. The stress drop measurements from the seismic data also depend on the observation frequency band. Therefore, the values obtained from various seismic phases, such as body and surface waves, may be different. Previous studies have often used indirect methods to remove the attenuation effects along the propagation path to obtain the source spectra and then estimate the stress drops. Using a broadband high-resolution Lg-wave attenuation model, the attenuation effect can be directly corrected to obtain the Lg-wave source excitation spectra. By fitting the observed spectra to the theoretical source model, we can calculate the seismic moments and corner frequencies from which the stress drops can be calculated. Taking a typical tectonic earthquake and a potentially induced earthquake, that is, the 2017 MS7.0 Jiuzhaigou earthquake sequence and the 2019 MS 6.0 Changning earthquake sequence, in the eastern margin of the Tibetan Plateau as examples, we explored the potential physical differences between tectonic and induced earthquakes. The stress drop in the 2017 Jiuzhaigou mainshock was approximately 27 MPa. The stress drops, and the magnitude of its aftershocks rapidly decay. However, for the 2019 Changning earthquake sequence, the temporal variation of stress drops declined slowly, with two aftershocks having stress drops comparable to the main shock. For an area with long-term water injection, it takes a long time to recover to its equilibrium status once a large earthquake disturbs the regional stress field. Given that no apparent difference in the absolute level of stress drops can be observed between the two types of earthquake sequences, the stress drops alone cannot be used to distinguish between induced and tectonic earthquakes in this area. The increasingly accumulated underground water may have created pathways linking multiple fault systems in the changing salt mining. Thus, the possibility of future induced earthquakes cannot be ruled out.
Stress drop measures the stress release level over a fault during an earthquake rupture. As one of the important parameters for characterizing source mechanisms and predicting strong ground motions, the stress drop is controlled by the tectonic environment, focal mechanism, and type of earthquake sequence. The stress drop measurements from the seismic data also depend on the observation frequency band. Therefore, the values obtained from various seismic phases, such as body and surface waves, may be different. Previous studies have often used indirect methods to remove the attenuation effects along the propagation path to obtain the source spectra and then estimate the stress drops. Using a broadband high-resolution Lg-wave attenuation model, the attenuation effect can be directly corrected to obtain the Lg-wave source excitation spectra. By fitting the observed spectra to the theoretical source model, we can calculate the seismic moments and corner frequencies from which the stress drops can be calculated. Taking a typical tectonic earthquake and a potentially induced earthquake, that is, the 2017 MS7.0 Jiuzhaigou earthquake sequence and the 2019 MS 6.0 Changning earthquake sequence, in the eastern margin of the Tibetan Plateau as examples, we explored the potential physical differences between tectonic and induced earthquakes. The stress drop in the 2017 Jiuzhaigou mainshock was approximately 27 MPa. The stress drops, and the magnitude of its aftershocks rapidly decay. However, for the 2019 Changning earthquake sequence, the temporal variation of stress drops declined slowly, with two aftershocks having stress drops comparable to the main shock. For an area with long-term water injection, it takes a long time to recover to its equilibrium status once a large earthquake disturbs the regional stress field. Given that no apparent difference in the absolute level of stress drops can be observed between the two types of earthquake sequences, the stress drops alone cannot be used to distinguish between induced and tectonic earthquakes in this area. The increasingly accumulated underground water may have created pathways linking multiple fault systems in the changing salt mining. Thus, the possibility of future induced earthquakes cannot be ruled out.
2023, 54(5): 532-540.
doi: 10.19975/j.dqyxx.2022-072
Abstract:
Strong pulse-like ground motions have caused extensive damage to many engineering structures and are one of the main factors influencing earthquake damage in near-fault regions. Therefore, it is necessary to study near-fault velocity pulse-like ground motions to reveal the seismic failure mechanism of engineering structures in near-fault areas and to carry out seismic fortification and seismic design. The key step is the effective identification of strong pulse-like ground motions. The strong pulse-like ground motions identified in previous studies have typically been selected by subjective judgment, because the velocity-time history of the ground motion is dominated by a large pulse. The selection of pulse-like ground motions using these approaches requires a certain level of judgment. However, the classification may not be obvious for many ground motions. Numerous researchers have attempted to capture pulse-like features using different approaches, of which simple pulse models, known as semi-quantitative methods, are commonly used. However, one limitation of semi-quantitative approaches is that most do not provide a quantitative pulse-detection scheme; that is, the classification of pulse-like ground motions may not be easily reproducible. Many quantitative classification methods for pulse-like ground motions have been developed. These quantitative classifications provide electronic libraries of recorded ground motions, list statistics indicating whether a given ground motion contains a velocity pulse, and help the science and engineering communities to access these ground motions and study their effects for research or practical applications. In brief, the identification methods for strong velocity pulse-like ground motions have undergone qualitative, semi-quantitative, and quantitative development processes. Among these methods, the quantitative identification method has the advantages of repeatability and batch processing and is increasingly recognized and applied. However, there is no uniform and definite classification principle for quantitative velocity pulse recognition methods. In this paper, three types of quantitative identification methods commonly used for velocity pulses are systematically summarized and introduced in detail from the aspects of recognition conditions, basic principles, key steps, and application scope. Representatives of these three methods are recommended, including a quantitative classification method using wavelet analysis, a quantitative identification method based on energy, and an efficient algorithm based on significant velocity half-cycles. In addition, their advantages and disadvantages were analyzed. Because of the instability of the velocity pulse recording waveform, no method can achieve a pulse recognition rate of 100%. In addition, although quantitative methods have made great progress in pulse recognition, period determination, and pulse recording direction determination, they are all based on the basic principles of signal processing methods and pulse characteristics without considering the mechanism of velocity pulse generation. Thus, it is necessary to include the above mentioned three points to synthetically identify the strong ground motions of the velocity pulse and form an optimal pulse-discriminant system. Finally, the key problems affecting the further improvement of the quantitative velocity pulse recognition method are discussed, and the research emphasis for its future development is highlighted. This provides a basic reference for beginners in the field.
Strong pulse-like ground motions have caused extensive damage to many engineering structures and are one of the main factors influencing earthquake damage in near-fault regions. Therefore, it is necessary to study near-fault velocity pulse-like ground motions to reveal the seismic failure mechanism of engineering structures in near-fault areas and to carry out seismic fortification and seismic design. The key step is the effective identification of strong pulse-like ground motions. The strong pulse-like ground motions identified in previous studies have typically been selected by subjective judgment, because the velocity-time history of the ground motion is dominated by a large pulse. The selection of pulse-like ground motions using these approaches requires a certain level of judgment. However, the classification may not be obvious for many ground motions. Numerous researchers have attempted to capture pulse-like features using different approaches, of which simple pulse models, known as semi-quantitative methods, are commonly used. However, one limitation of semi-quantitative approaches is that most do not provide a quantitative pulse-detection scheme; that is, the classification of pulse-like ground motions may not be easily reproducible. Many quantitative classification methods for pulse-like ground motions have been developed. These quantitative classifications provide electronic libraries of recorded ground motions, list statistics indicating whether a given ground motion contains a velocity pulse, and help the science and engineering communities to access these ground motions and study their effects for research or practical applications. In brief, the identification methods for strong velocity pulse-like ground motions have undergone qualitative, semi-quantitative, and quantitative development processes. Among these methods, the quantitative identification method has the advantages of repeatability and batch processing and is increasingly recognized and applied. However, there is no uniform and definite classification principle for quantitative velocity pulse recognition methods. In this paper, three types of quantitative identification methods commonly used for velocity pulses are systematically summarized and introduced in detail from the aspects of recognition conditions, basic principles, key steps, and application scope. Representatives of these three methods are recommended, including a quantitative classification method using wavelet analysis, a quantitative identification method based on energy, and an efficient algorithm based on significant velocity half-cycles. In addition, their advantages and disadvantages were analyzed. Because of the instability of the velocity pulse recording waveform, no method can achieve a pulse recognition rate of 100%. In addition, although quantitative methods have made great progress in pulse recognition, period determination, and pulse recording direction determination, they are all based on the basic principles of signal processing methods and pulse characteristics without considering the mechanism of velocity pulse generation. Thus, it is necessary to include the above mentioned three points to synthetically identify the strong ground motions of the velocity pulse and form an optimal pulse-discriminant system. Finally, the key problems affecting the further improvement of the quantitative velocity pulse recognition method are discussed, and the research emphasis for its future development is highlighted. This provides a basic reference for beginners in the field.
2023, 54(5): 541-557.
doi: 10.19975/j.dqyxx.2022-070
Abstract:
The coupling between solar wind and the magnetosphere and the dynamic processes in geo-space are the basic driving factors of space weather. Understanding these processes on the system level is essential to the studies of space physics and space weather. Recent solar wind charge exchange (SWCX) X-ray emission discoveries provide a novel approach to detect the large-scale magnetosphere through soft X-ray imaging. SWCX occurs when high-charge heavy ions such as C6+, N7+, O7+, and O8+ in the solar wind interact with neutral atoms or molecules, such as neutral hydrogen atoms in near-Earth space, neutral hydrogen and helium atoms in the heliosphere, and H2O and CO2 molecules on comets and other planets. Solar wind ions become excited by receiving one or more electrons, and then return to the ground state by releasing one or more photons in the soft X-ray band. The characteristics of the SWCX emissions include the X-ray spectrum showing line emissions corresponding to different species of solar wind particles and neutrons, and fast time variations closely related to solar wind variations. The SWCX soft X-ray emission of the Earth's magnetosphere mainly occurs in the magnetosheath on the dayside and the cusp regions. Therefore, the magnetosphere can be remotely imaged using large-scale soft X-ray imaging technology, allowing the fundamental modes of the interaction between the solar wind and magnetosphere to be recognized on a systematic scale. In this context, the European Space Agency (ESA) and Chinese Academy of Sciences (CAS) jointly proposed the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE). SMILE was approved in 2016 and implemented thereafter. SMILE aims to provide remote sensing measurements of the magnetopause and bow shock around the subsolar region, part of the cusp regions, and the aurora, as well as simultaneous in situ observations of the solar wind plasma and magnetic field. SMILE is planned to be launched in 2024–2025. Other missions have also been proposed to image the Earth's magnetosphere, such as the GEOspace X-ray imager (GEO-X) in Japan, Lunar Environment heliospherics X-ray Imager (LEXI) in the United States, and Lunar-based soft X-ray imager (LSXI) in China. With the advent of soft X-ray imaging missions to detect the magnetopause, evaluating the expected soft X-ray images and developing appropriate techniques to extract 3-dimentional boundary information from the 2-dimentional images is essential. Global magnetohydrodynamic (MHD) and instrument simulations are used to generate expected X-ray images under different solar wind conditions with different viewing geometries. Based on these images, several approaches have been developed to analyze the signals, composing the 'arsenal' or 'toolkit' for magnetopause reconstruction. Each approach has its own advantages and disadvantages, applicable to different situations. This paper introduces the mechanism of magnetospheric X-ray emission, reviews the research on the observational evidence and characteristics of SWCX X-ray emissions, summarizes the progress of simulation studies, presents the missions (or concept) of the magnetospheric X-ray detection, and discusses the possibility of future implementation of X-ray imaging for detecting other planets.
2023, 54(5): 558-571.
doi: 10.19975/j.dqyxx.2022-045
Abstract:
Electron diffusion caused by plasmaspheric hiss is an important mechanism for the loss of electrons in Earth's inner magnetosphere; it has also been considered responsible for the formation of the slot region between inner and outer radiation belts. The cold plasma dispersion relation of plasmaspheric hiss is widely used to quantify the scattering effect of energetic electrons. However, the existence of hot plasma in a realistic magnetospheric plasma environment modifies the dispersion relation of plasmaspheric hiss, thereby affecting wave-induced energetic electron scattering. This paper presents the results of some recent studies on the influence of hot plasma on the dispersion relation and electron scattering effects of plasmaspheric hiss. Using statistical analysis results based on satellite wave observations, the modification of the hiss dispersion relation under the effects of hot plasma was verified. Furthermore, based on typical case analyses and numerical calculations using the quasi-linear diffusion theory, we investigated the dependence of the hiss-driven electron scattering rates on the geomagnetic activities and hot plasma parameters (i.e., temperature anisotropy, hot electron temperature, and hot electron abundance). The results revealed that the cold plasma dispersion relation overestimates the scattering rate of energetic electrons below 100 keV. For electrons above 100 keV, the differences between the cold plasma and hot plasma dispersion relations in terms of the induced scattering rates are somewhat smaller; this indicates that using the cold plasma dispersion relation can lead to the underestimation of the hiss-driven rates of electron pitch angle diffusion at smaller pitch angles and the overestimation of the rates at higher pitch angles. In addition, the cold plasma assumption can cause resonant diffusion down to lower electron energies; however, when the observed hiss wave dispersion curves are used, the resonant electron diffusion tends to extend to smaller pitch angles with a broader range. Notably, the differences in the scattering rates between the cold plasma and hot plasma dispersion relations increase with the hot plasma parameters. Therefore, our results are important for future simulations of the hiss wave-induced electron diffusion processes in the actual magnetospheric plasma environment and the dynamic variability of radiation belt electrons.
Electron diffusion caused by plasmaspheric hiss is an important mechanism for the loss of electrons in Earth's inner magnetosphere; it has also been considered responsible for the formation of the slot region between inner and outer radiation belts. The cold plasma dispersion relation of plasmaspheric hiss is widely used to quantify the scattering effect of energetic electrons. However, the existence of hot plasma in a realistic magnetospheric plasma environment modifies the dispersion relation of plasmaspheric hiss, thereby affecting wave-induced energetic electron scattering. This paper presents the results of some recent studies on the influence of hot plasma on the dispersion relation and electron scattering effects of plasmaspheric hiss. Using statistical analysis results based on satellite wave observations, the modification of the hiss dispersion relation under the effects of hot plasma was verified. Furthermore, based on typical case analyses and numerical calculations using the quasi-linear diffusion theory, we investigated the dependence of the hiss-driven electron scattering rates on the geomagnetic activities and hot plasma parameters (i.e., temperature anisotropy, hot electron temperature, and hot electron abundance). The results revealed that the cold plasma dispersion relation overestimates the scattering rate of energetic electrons below 100 keV. For electrons above 100 keV, the differences between the cold plasma and hot plasma dispersion relations in terms of the induced scattering rates are somewhat smaller; this indicates that using the cold plasma dispersion relation can lead to the underestimation of the hiss-driven rates of electron pitch angle diffusion at smaller pitch angles and the overestimation of the rates at higher pitch angles. In addition, the cold plasma assumption can cause resonant diffusion down to lower electron energies; however, when the observed hiss wave dispersion curves are used, the resonant electron diffusion tends to extend to smaller pitch angles with a broader range. Notably, the differences in the scattering rates between the cold plasma and hot plasma dispersion relations increase with the hot plasma parameters. Therefore, our results are important for future simulations of the hiss wave-induced electron diffusion processes in the actual magnetospheric plasma environment and the dynamic variability of radiation belt electrons.
2023, 54(5): 572-580.
doi: 10.19975/j.dqyxx.2022-062
Abstract:
The universal time (UT1-UTC) and length of day change (ΔLOD) are two parameters that describe the Earth's rotation rate variations. UT1-UTC is typically used in space projects, whereas ΔLOD is used for scientific investigations. Therefore, studying the variations between the two parameter sequences is very important. In this study, we reviewed the Earth's rotation rate over the last five decades and revealed an abnormal phenomenon in UT1-UTC. Since May 2020, the Earth's rotation has reversed from a deceleration trend to an acceleration trend. Besides, we used ΔLOD to find the possible geophysical contributors and focused on the climate-related contributions. Results revealed that the interannual LOD exhibited a notable degree of consistency with ENSO indices after using the Difference+FDSR method to remove the internally and externally induced signals. Notably, two La Nina with intermediate strength and the beginning of a closely followed third trough were detected in the last three years. The contributions of these events to the latest rotation acceleration are approximately 9%.
The universal time (UT1-UTC) and length of day change (ΔLOD) are two parameters that describe the Earth's rotation rate variations. UT1-UTC is typically used in space projects, whereas ΔLOD is used for scientific investigations. Therefore, studying the variations between the two parameter sequences is very important. In this study, we reviewed the Earth's rotation rate over the last five decades and revealed an abnormal phenomenon in UT1-UTC. Since May 2020, the Earth's rotation has reversed from a deceleration trend to an acceleration trend. Besides, we used ΔLOD to find the possible geophysical contributors and focused on the climate-related contributions. Results revealed that the interannual LOD exhibited a notable degree of consistency with ENSO indices after using the Difference+FDSR method to remove the internally and externally induced signals. Notably, two La Nina with intermediate strength and the beginning of a closely followed third trough were detected in the last three years. The contributions of these events to the latest rotation acceleration are approximately 9%.
2023, 54(5): 581-586.
doi: 10.19975/j.dqyxx.2022-061
Abstract:
Remote sensing satellite SiCH-2 from Ukraine was launched in 2011. At present, it has stopped working and is out of control, and it has been forecasted to become space debris by a two-line root (TLE) from the North American Air Defense Command (NORAD). Here, the "cat's eye" effect of the optical system is analyzed, and the satellite laser ranging (SLR) system at Shanghai Observatory is used to measure the echo intensity of satellite SiCH-2, which is very strong, and the ranging accuracy, which is better than 10 cm. The analysis of the measurement capability results shows that the laser reflection echo from satellite SiCH-2 reaches the laser ranging level of the satellite with the reflector, and is consistent with the detection ability of the photoelectric detection equipment "cat's eye" effect analysis. The measurement results also show that satellite SiCH-2 is in a state of rotation, with a period of 4.3 s. In this study, the laser ranging of on-orbit targets based on the "cat's eye" effect is realized for the first time, which provides a new method for analyzing long-distance space targets, promotes the application and development of high-precision laser ranging technology, and is beneficial to monitor the photoelectric detection series of satellites that fail or have abnormal orbits.
Remote sensing satellite SiCH-2 from Ukraine was launched in 2011. At present, it has stopped working and is out of control, and it has been forecasted to become space debris by a two-line root (TLE) from the North American Air Defense Command (NORAD). Here, the "cat's eye" effect of the optical system is analyzed, and the satellite laser ranging (SLR) system at Shanghai Observatory is used to measure the echo intensity of satellite SiCH-2, which is very strong, and the ranging accuracy, which is better than 10 cm. The analysis of the measurement capability results shows that the laser reflection echo from satellite SiCH-2 reaches the laser ranging level of the satellite with the reflector, and is consistent with the detection ability of the photoelectric detection equipment "cat's eye" effect analysis. The measurement results also show that satellite SiCH-2 is in a state of rotation, with a period of 4.3 s. In this study, the laser ranging of on-orbit targets based on the "cat's eye" effect is realized for the first time, which provides a new method for analyzing long-distance space targets, promotes the application and development of high-precision laser ranging technology, and is beneficial to monitor the photoelectric detection series of satellites that fail or have abnormal orbits.
Founded in 1970， bimonthly
Governed by：China Earthquake Administration
Sponsored by：Institute of Geophysics, China Earthquake Administration
Co-sponsored by：Chinese Geophysical Society Geophysical Exploration Center, China Earthquake Administration
Published by：Editorial Office of Reviews of Geophysics and Planetary Physics
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