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- 1A review on microtremor H/V spectral ratio method
- 2Machine learning and its application in seismology
- 3Numerical methods of geodynamics in big data era: Review and outlook
- 4Revisiting the cross-correlation and SPatial AutoCorrelation (SPAC) of the seismic ambient noise based on the plane wave model
- 5EikoNet traveltime calculation method and application based on deep neural network
- 6Progress and prospect of deformation theory in the viscoelastic earth
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Preliminary results of the ionospheric high-frequency Doppler shift monitor for the Phase II of Chinese Meridian Project
Hao Yongqiang, Dai Guofeng, Zhang Donghe et al.
Abstract：The Phase II of Chinese Meridian Project 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. 【details】
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】
PDF 10869KBMagnetic reconnection and plasma waves share a critical connection. On the one hand, quasi-steady wave structures (shock, KAW eigenmode) play a pivotal role in the formation and structure of magnetic reconnection. On the other hand, higher-frequency and small-scale waves may influence energy conversion, particle heating, and anomalous resistivity. Waves of various scales dictate the multi-scale coupling characteristics and energy conversion within the reconnection process. This review focuses on plasma waves during the Earth's magnetosphere magnetic reconnection, seeking to elucidate the characteristics and roles of kinetic Alfven waves (KAWs), low hybrid waves, whistler waves, electrostatic solitary waves (ESWs), ion acoustic waves, and electron-scale high-frequency electrostatic waves. The KAW eigenmode is capable of describing various phenomena in the diffusion region such as Hall magnetic fields and Hall electric fields, significantly impacting the reconnection rate. Lower hybrid waves are easily excited in the strong density gradient in the current layer and found to heat electrons in the parallel direction, while whistler waves are excited through Landau resonance and cyclotron resonance. Both whistler waves and lower hybrid waves are found to exhibit minimal influence on the reconnection rate through the anomalous resistivity. ESWs predominantly emerge within the magnetic reconnection boundary region, necessitating further investigation into their heating effects. Finally, the review delves into high-frequency electrostatic waves, emphasizing their importance in the magnetic reconnection diffusion region, specifically for electron diffusion and scattering processes. The insights gained from these research advancements serve as a foundation for future studies and advancements in the field of magnetic reconnection and plasma wave interactions.
Multi-stage sedimentation and diagenetic processes lead to complex in situ stresses in subsurface hydrocarbon reservoirs. The in situ stresses have a broad magnitude range and their distribution directions are complicated, significantly impacting the rock physics properties and seismic propagation response in reservoirs. Seismic reflection and transmission (R/T) coefficient equations can quantify the relationship between reservoir properties and observed geophysical data. Therefore, seismic R/T coefficient equations considering the effects of in situ stresses can help to better understand the characteristics of wave propagation on deep-strata stratigraphic interfaces, laying a theoretical foundation for exploring deep-strata hydrocarbon. This research topic is attracting the attention of international scholars. Most reported stress-dependent wave R/T coefficient equations consider the infinitesimal deformations induced by the in situ stress and wave perturbation based on the theory of acoustoelasticity; these approaches have been preliminarily applied in several theoretical and practical scenarios such as seismic inversion for stress-induced anisotropy parameters, in situ stress detection, and discrimination of oil and gas reservoirs. In this paper, we introduce the main body of solid acoustoelasticity theory and the stress-dependent seismic R/T coefficient equations based on acoustoelasticity theory, along with their basic assumptions, preliminary applications, limitations, and prospects in seismic exploration.
Meteoroids entering the Earth's atmosphere lose most of their mass during atmospheric passage and considerably disturb the background ionosphere. To elucidate better the effects of meteoroids on the near-Earth space environment, it is important to simultaneously observe various meteoroids and their related phenomena in the Earth's atmosphere. This study briefly describes a newly developed Meteor and ionospheric Irregularity Observation System (MIOS), which consists of a phased-array radar, a bi-static all-sky radar, and a multi-station optical imaging and spectroscopy subsystem. The MIOS can capture the processes of ablation and evaporation of meteoroids, creating luminous and ionization trails, and measure the properties of both the meteor trail and its corresponding meteoroid within a large field of view. Based on the MIOS, some observational modes and data processing methods have been developed, where the physical and chemical properties of meteoroids (including their velocity, mass, composition, and source region), meteor plasma head and trail irregularity and their structural evolution, and the instantaneous neutral wind can be obtained. Using the MIOS measurements, a preliminary study of some of the characteristics of meteoroids, meteor plasma head, meteor plasma trail field–aligned and non-field–aligned irregularities, meteor flare and dust trail irregularity, and ionospheric irregularity is presented.
Attenuation is an essential reservoir property, and understanding its mechanism in gas hydrate-bearing sediments is important for predicting gas hydrate saturation. Natural gas hydrates mainly accumulate in coarse-grained sands or fine-grained clays with different morphologies, and the attenuation characteristics of these gas hydrate-bearing sediments are inconsistent. Many rock-physics models have been proposed in recent years to elucidate the attenuation mechanisms of gas hydrate occurrence. There are two types of attenuation models for gas hydrates in sands. One of these models is based on the three-phase Biot theory and contains multiple mechanisms that describe the contact effects between hydrate and sediment grains, such as grain cementation and squirt flows caused by microcracks. This model can reasonably reproduce the enhanced attenuation observed with increasing hydrate saturation in sonic-logging data. Attenuation described in the effective grain model is dominated by the viscous flow between the water in hydrate pores and free water. These types of models agree with the seismic attenuation observed in gas hydrates in sands. Moreover, the attenuation model of gas hydrates in clay is formulated by first establishing an attenuation model for background sediments, which employs the effective grain model to characterize attenuation in clay minerals; then, the properties of pure gas hydrate and the effects of hydrate occurrence on sediments are quantified. This model has also been successfully applied to seismic reflection data in the seismic frequency band. The above models have achieved significant progress in attenuation studies on gas hydrate-bearing sediments, and they have aided the quantitative interpretation of observed attenuation in field data and attenuation-related constraints for gas hydrate saturation. However, the application of these models is limited to certain extents: the attenuation predicted by the gas hydrate-bearing sands model failed to match that observed in the field data. Additionally, the gas hydrate-bearing clays model does not consider fracture shapes, and its performance has not been verified at the ultrasonic frequency band. To improve the accuracy and applicability of these models, the relationship between hydrate morphology and attenuation must be elucidated, and further rock-physics studies based on field data must be conducted.
A tight sandstone gas reservoir is characterized by low porosity and permeability. The existence of fractures can improve the permeability of the reservoir, and fractures are a vital storage space and migration channel of oil and gas. The development of fractures is also conducive to forming a fracture network during hydraulic fracturing. The prediction of fractures can provide an essential basis for developing tight sandstone gas reservoirs. The variation of seismic amplitude with azimuth can provide information on vertical fractures in the reservoir. This study proposed an improved inversion method of azimuth amplitude difference for the HTI (transversely isotropy with a horizontal axis) medium and combined with the rock physical theory, predicted fracture weakness parameter, characterizing the fracture properties. Conventional inversion methods invert elastic and fracture parameters simultaneously. The improved azimuth amplitude difference method introduces a reference azimuth, builds the track set of azimuth amplitude difference to eliminate the isotropic background, and inverts only the fracture weakness parameters related to the anisotropic terms. Using the only azimuth anisotropic response, the sensitivity of fracture identification and the accuracy of fracture parameter inversion are improved. The application of the field data shows that the sensitivity of the proposed inversion method to the prediction of fracture parameters is improved compared with the conventional inversion method, and the predicted fracture weakness is consistent with the permeability well logs and has a significant correlation with the gas production of tight sandstone gas reservoirs. Therefore, the prediction of fracture distribution and development degree based on the proposed method can provide a reliable indicator for the identification and development of gas-bearing favorable areas in tight sandstone reservoirs.
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.
Jupiter-Trojan asteroids, as fossils of planet formation, orbiting the Sun in Jupiter's stable Lagrange points, provide a unique and critical insight into planetary origins, the sources of volatiles and organics on the terrestrial planets, and the evolution of the planetary system as a whole. To present, Jupiter-Trojan asteroids have only been observed through remote spectroscopic measurements using ground-based telescopes or space telescopes, and they remain one of the most enigmatic groups of celestial bodies. In the past decade, significant advances in understanding their physical and spectral properties have been made, and there has been a revolution in thinking about the origin and evolution of Trojans. Fine-grained silicates that appear to be similar to cometary silicates have gradually replaced water ice and organics as a significant component of the surface composition of Trojan asteroids, and a color bimodality may indicate distinct compositional groups among the Trojans. Whereas Trojans had traditionally been thought to have formed near 5 AU, a new paradigm in which the Trojans formed in the proto-Kuiper Belt, were scattered inward, and then captured in the Trojan swarms as a result of resonant interactions of the giant planets has developed. There are significant differences between the currently determined physical properties of Trojans and Kuiper Belt objects. These differences may be indicative of surface modification attributable to the inward migration of the objects that became the Trojans. The upcoming Lucy mission will provide a unique opportunity to conduct close-up exploration of these enigmatic small celestial bodies, potentially yielding evidence important for unraveling the mysteries surrounding the origin and evolution of Jupiter-Trojan asteroids. This paper provides a comprehensive overview of the observational history, physical and spectral properties, material composition, and formation and evolution of Jupiter-Trojan asteroids, as well as an introduction to the goals and objectives of the Lucy mission. This study provides support for potential future deep space exploration missions that may have the capacity of exploring asteroids.
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.
Tropospheric ozone, mainly produced by chemical reactions that involve the photo-chemical oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxide (NOx), is an air pollutant that adversely impacts human health and natural vegetation. Due to rapid industrialization and urbanization over the last three decades, tropospheric ozone concentrations are rising at a rate of ~0.5%–2% per year. By 2040, ozone concentrations are projected to reach 35–48 ppb (currently ~31 ppb). Thus, the assessment of the effects of this increase on plant physiology is important for ensuring global food security and human health. In this paper, we review the effects of tropospheric ozone pollution on plant physiology, including the visible damage to leaves and roots, changes in photosynthetic rate, carbon sequestration capacity, and the structure of pollen grains. The results show that continuous exposure to high ozone concentrations cause: (1) visible foliar injury, and reduction in the photosynthetic rate and carbon sequestration capacity, which in turn affect the accumulation and distribution of dry matter and consequently reduces crop yields; and (2) damage to cell membranes, protein of pollen grains, and lipid peroxidation in cells, which may increase the risk of respiratory allergies in humans. The response of plants to ozone varies with species, plant growth stage and climatic conditions. Damaged fossil pollen grains have been observed in the sediments of the end-Devonian and the end-Permian, coeval with mass extinction events, which was attributed to increased ozone concentrations resulting from either volcanic eruptions or rapid global warming. These findings highlight the urgent need for research on the impacts of ozone on plant ecological habits in the natural environment, especially on below-ground ecological processes, as well as on measures to mitigate the impacts of ozone on crops and the selection of ozone-resistant crops.
The Tibetan Plateau, known as the "Roof of the World" , is one of the most tectonically complex areas on Earth. Its deep tectonics and dynamical mechanisms have been the focus of intense research in the fields of deep geophysics and continental dynamics. The eastern Tibetan Plateau is characterized by strong topographic fluctuations, frequent seismic activities, and abundant metal deposits, which reveal the extremely complex crust–mantle structure, deep deformation, and intense deep material movement. In recent years, with the rapid development of comprehensive geophysical observation techniques, deep structure imaging methods, and geodynamic simulations, significant progress has been made in deep tectonics, block motions, deep dynamic models, strong seismic activity, deep seismic mechanisms, as well as the deep structure of metal mineralization in the eastern Tibetan Plateau. The Workshop on Tectonics and Geophysics in the east part of Tibetan Plateau (WTGTP) is an annual academic exchange symposium for the eastern part of the Tibetan Plateau. The 9th and 10th conferences were held in Xichang, China, in 2021 and online in 2022, respectively. Based on the reports of these conferences, in combination with the relevant research results in recent years, this paper focuses on the India–Eurasian plate collision, tectonic deformation and dynamic mechanisms, and strong earthquake activity and deep seismic mechanisms in the eastern Tibetan Plateau. The paper describes the research progress pertaining to the tectonic structure, deep structural deformation, and dynamic mechanisms of the eastern Tibetan Plateau. The research prospects of further delineating the deep structure and geophysics of the Tibetan Plateau are preliminarily addressed, with the goal of providing a useful reference for interested researchers. The research in this field has great significance because it enhances our understanding of the deep tectonic processes that shape the Tibetan Plateau. Such knowledge could have implications for predicting and mitigating seismic hazards in the region. Additionally, research into the metallogenic tectonics of the eastern Tibetan Plateau may provide insights into the formation of mineral deposits in other parts of the world. Overall, research into the deep tectonics and dynamical mechanisms of the Tibetan Plateau is a complex and challenging field that requires the use of advanced technology and multidisciplinary approaches. The WTGTP provides a valuable forum for researchers to share their findings and collaborate on solutions to these geologically complex problems.
The R-2 rotary seismograph can record rotating three components, MEMS acceleration, and tilt angle. In this study, the difference between ground acceleration and tilted background noise were analyzed using two phases of continuous observation data implemented in the ground and deep underground of the Huainan Deep Earth Laboratory. It was found that the deep earth environmental background interference was weaker, with background noise differences on the spectrum of up to 10 dB, showing that the Deep Earth Laboratory has superior conditions regarding low vibration and noise. The contrast before and after the skew correction of the MEMS acceleration using the tilt data revealed that the tilt had a non-negligible influence. The time-frequency analysis showed that the deep earth environment was favorable relative to the surface environment. The precision requirements of solid tide signal observations and shortcomings of existing instruments were also analyzed, proving the necessity of high precision observations in the deep earth environment.
In recent years, the risk of disasters on Earth caused by space issues has increased gradually. Future planetary exploration is of great significance to enhance the ability to monitor space disaster risks. In 2018, underground media structures at different scales were explored beneath Mars stations through the InSight mission; however, there remain significant limitations to large-scale Mars exploration. Therefore, in this study, a single-station observation system was designed by combining a single receiving station and a mobile source as a novel method for collecting planetary seismic data, thereby enabling the collection of more reliable seismic signals in early extraterrestrial explorations. To obtain a one-dimensional underground medium structure, high-order dispersion curve imaging methods were applied, and a high-resolution frequency Hankel function dispersion curve extraction method was proposed to eliminate artifacts in the dispersion curve and improve the extracted dispersion curves. The system was then extended to a multicomponent case to demonstrate the complementarity between the multicomponent and single-component results. The proposed data acquisition system provides a foundation for two-dimensional and three-dimensional underground media imaging systems. Furthermore, the feasibility of developing automotive seismic technology based on this system to address the widespread issue of viaduct collapse caused by overweight vehicles was discussed, demonstrating the importance of single-station systems in seismic imaging and source monitoring.
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.
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.
Applications of neural network algorithms in rock physics have developed rapidly developed, mainly due to the neural network's powerful abilities in data modeling, signal processing, and image recognition. However, mathematical and physical explanations of neural networks remain limited, which makes it difficult to understand the behavior and mechanism of neural networks and limits their further development. Using mathematical and physical methods to explain the behavior of neural networks remains a challenging task. The goal of this study was to design a sound wave neural network (SWNN) structure based on sound wave partial differential equations and finite difference methods. The method transforms the first-order sound equations into the frequency domain and discretizes them using a central difference scheme. The differential formula takes the same form as the propagation function of a neural network, enabling the construction of a sound wave neural network. The main features of the SWNN are (1) a neural network with explicitly coupled pressure-velocity streams and inter-layer connections and (2) an adjoint variable method to improve the vanishing gradient problem in network training. The sound wave neural network established from the sound wave partial differential equation and finite difference algorithm has a solid mathematical modeling process and a clear physical explanation. This makes improving network performance within the framework of the mathematical and physical methods feasible. The numerical results showed that SWNN outperforms residual neural networks in image classification on CIFAR-10 and CIFAR-100 datasets. The partial differential equation neural network modeling method proposed in this paper can be applied to many other types of mathematical physics equations, providing a deep mathematical explanation for neural networks.
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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