Subjects -> EARTH SCIENCES (Total: 771 journals)     - EARTH SCIENCES (527 journals)    - GEOLOGY (94 journals)    - GEOPHYSICS (33 journals)    - HYDROLOGY (29 journals)    - OCEANOGRAPHY (88 journals) EARTH SCIENCES (527 journals)            First | 1 2 3
 Showing 401 - 371 of 371 Journals sorted alphabetically Physical Science International Journal Physics in Medicine & Biology       (Followers: 15) Physics of Life Reviews       (Followers: 1) Physics of Metals and Metallography       (Followers: 18) Physics of Plasmas       (Followers: 10) Physics of the Earth and Planetary Interiors       (Followers: 34) Physics of the Solid State       (Followers: 5) Physics of Wave Phenomena Physics World       (Followers: 18) Physik in unserer Zeit       (Followers: 9) Pirineos Planet       (Followers: 4) Plasma Physics Reports       (Followers: 7) Polar Record       (Followers: 2) Positioning       (Followers: 4) Pramana       (Followers: 13) Precambrian Research       (Followers: 7) Preview Proceedings of the Geologists' Association       (Followers: 6) Proceedings of the Linnean Society of New South Wales       (Followers: 2) Proceedings of the Yorkshire Geological Society       (Followers: 1) Progress in Earth and Planetary Science       (Followers: 16) Pure and Applied Geophysics       (Followers: 12) Quarterly Journal of Engineering Geology and Hydrogeology       (Followers: 4) Quaternary Quaternary Australasia Quaternary Geochronology       (Followers: 8) Quaternary International       (Followers: 14) Quaternary Research       (Followers: 19) Quaternary Science Advances Quaternary Science Reviews       (Followers: 26) Radiocarbon       (Followers: 12) Remote Sensing       (Followers: 57) Remote Sensing Applications : Society and Environment       (Followers: 9) Remote Sensing in Earth Systems Sciences       (Followers: 5) Remote Sensing Letters       (Followers: 45) Remote Sensing Science       (Followers: 29) Rendiconti Lincei Reports on Geodesy and Geoinformatics       (Followers: 7) Reports on Mathematical Physics       (Followers: 2) Research & Reviews : Journal of Space Science & Technology       (Followers: 18) Resource Geology       (Followers: 6) Resources, Environment and Sustainability       (Followers: 2) Results in Geochemistry Results in Geophysical Sciences Reviews in Mineralogy and Geochemistry       (Followers: 4) Reviews of Modern Physics       (Followers: 31) Revista Cerrados Revista de Ciências Exatas Aplicadas e Tecnológicas da Universidade de Passo Fundo : CIATEC-UPF Revista de Ingenieria Sismica Revista de Investigaciones en Energía, Medio Ambiente y Tecnología Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales Revista de Teledetección Revista Geológica de Chile Revue Française de Géotechnique Rock Mechanics and Rock Engineering       (Followers: 7) Rocks & Minerals       (Followers: 3) Russian Geology and Geophysics       (Followers: 3) Russian Journal of Mathematical Physics Russian Journal of Pacific Geology Russian Physics Journal       (Followers: 1) Science China Earth Sciences       (Followers: 3) Science News       (Followers: 11) Science of Remote Sensing       (Followers: 7) Scientific Annals of Stefan cel Mare University of Suceava. Geography Series Scientific Journal of Earth Science       (Followers: 1) Scientific Reports       (Followers: 85) Sedimentary Geology       (Followers: 20) Sedimentology       (Followers: 15) Seismic Instruments       (Followers: 1) Seismological Research Letters       (Followers: 12) Soil Dynamics and Earthquake Engineering       (Followers: 14) Soil Security       (Followers: 1) Solid Earth       (Followers: 5) Solid Earth Discussions       (Followers: 1) Solid Earth Sciences       (Followers: 1) South African Journal of Geomatics       (Followers: 2) Standort - Zeitschrift für angewandte Geographie       (Followers: 2) Stratigraphy and Geological Correlation       (Followers: 2) Studia Geophysica et Geodaetica       (Followers: 1) Studia Geotechnica et Mechanica Studia Universitatis Babes-Bolyai, Geologia Survey Review       (Followers: 6) Surveys in Geophysics       (Followers: 3) Swiss Journal of Palaeontology       (Followers: 4) Tectonics       (Followers: 15) Tectonophysics       (Followers: 24) Tellus A       (Followers: 21) Tellus B       (Followers: 20) Terra Latinoamericana Terra Nova       (Followers: 5) The Compass : Earth Science Journal of Sigma Gamma Epsilon The Holocene       (Followers: 16) The Leading Edge       (Followers: 1) Transportation Infrastructure Geotechnology       (Followers: 8) Turkish Journal of Earth Sciences UD y la Geomática Unconventional Resources Underwater Technology: The International Journal of the Society for Underwater       (Followers: 1) Universal Journal of Geoscience Unoesc & Ciência - ACET Vadose Zone Journal       (Followers: 5) Volcanica Water       (Followers: 10) Water International       (Followers: 19) Water Resources       (Followers: 21) Water Resources Research       (Followers: 94) Watershed Ecology and the Environment Weather, Climate, and Society       (Followers: 15) Wiley Interdisciplinary Reviews - Climate Change       (Followers: 33) World Environment       (Followers: 1) Yearbook of the Association of Pacific Coast Geographers       (Followers: 2) Yugra State University Bulletin       (Followers: 1) Zeitschrift der Deutschen Gesellschaft für Geowissenschaften       (Followers: 3) Zeitschrift für Geomorphologie       (Followers: 5) Zitteliana Землеустрій, кадастр і моніторинг земель       (Followers: 1)

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Similar Journals
 Surveys in GeophysicsJournal Prestige (SJR): 1.813 Citation Impact (citeScore): 4Number of Followers: 3      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1573-0956 - ISSN (Online) 0169-3298 Published by Springer-Verlag  [2469 journals]
• Short-Term Polar Motion Forecast Based on the Holt-Winters Algorithm and
Angular Momenta of Global Surficial Geophysical Fluids

Abstract: By taking into account the variable free polar motion (PM) known as the Chandler wobble (CW) and irregular forced PM excited by quasi-periodic changes in atmosphere, oceans and land water (described by the data of effective angular momenta EAM), we propose a short-term PM forecast method based on the Holt-Winters (HW) additive algorithm (termed as the HW-VCW method, with VCW denoting variable CW). In this method, the variable CW period is determined by minimizing the differences between PM observations and EAM-derived PM for every 8-year sliding timespan. Compared to the X- and Y-pole forecast errors (ΔPMX and ΔPMY) of the International Earth Rotation and Reference Systems Service (IERS) Bulletin A, our results derived from operational EAM can reduce ΔPMX by up to 38.4% and ΔPMY by up to 34.3% for forecasts ranging from 1 to 30 days. Further, we prove that using EAM forecast instead of operational EAM in the HW-VCW method can achieve similar accuracies.
PubDate: 2022-08-16

• A Review on Applications of Time-Lapse Electrical Resistivity Tomography
Over the Last 30 Years : Perspectives for Mining Waste Monitoring

Abstract: Abstract Mining operations generate large amounts of wastes which are usually stored into large-scale storage facilities which pose major environmental concerns and must be properly monitored to manage the risk of catastrophic failures and also to control the generation of contaminated mine drainage. In this context, non-invasive monitoring techniques such as time-lapse electrical resistivity tomography (TL-ERT) are promising since they provide large-scale subsurface information that complements surface observations (walkover, aerial photogrammetry or remote sensing) and traditional monitoring tools, which often sample a tiny proportion of the mining waste storage facilities. The purposes of this review are as follows: (i) to understand the current state of research on TL-ERT for various applications; (ii) to create a reference library for future research on TL-ERT and geoelectrical monitoring mining waste; and (iii) to identify promising areas of development and future research needs on this issue according to our experience. This review describes the theoretical basis of geoelectrical monitoring and provides an overview of TL-ERT applications and developments over the last 30 years from a database of over 650 case studies, not limited to mining operations (e.g., landslide, permafrost). In particular, the review focuses on the applications of ERT for mining waste characterization and monitoring and a database of 150 case studies is used to identify promising applications for long-term autonomous geoelectrical monitoring of the geotechnical and geochemical stability of mining wastes. Potential challenges that could emerge from a broader adoption of TL-ERT monitoring for mining wastes are discussed. The review also considers recent advances in instrumentation, data acquisition, processing and interpretation for long-term monitoring and draws future research perspectives and promising avenues which could help improve the design and accuracy of future geoelectric monitoring programs in mining wastes.
PubDate: 2022-08-12

• Acoustic and Electrical Properties of Tight Rocks: A Comparative Study
Between Experiment and Theory

Abstract: Abstract The acoustic-electrical (AE) response of subsurface hydrocarbon reservoirs is highly affected by rock heterogeneity. In particular, the characterization of the microstructure of tight (low-permeability) rocks can be aided by a joint interpretation of AE data. To this purpose, we evaluate cores from a tight-oil reservoir to obtain the rock mineralogy and pore structure by X-ray diffraction and casting thin sections. Then, ultrasonic and resistivity experiments are performed under different confining pressures to analyze the effects of pores, microcracks and mineralogy on the AE properties. We have developed acoustic and electrical models based on effective-medium theories, and the Cole–Cole and triple-porosity equations, to simulate the response to total and soft (crack) porosities and clay content. The results show that these properties play a significant role. Then, a 3D rock-physical template is built and calibrated by using the core samples and well-log data. The template is applied to tight-oil reservoirs to estimate the rock properties, which are validated with log data. The good match between the predictions and these data indicates that the model can effectively explain the effects of the heterogeneous microstructure on the AE data.
PubDate: 2022-08-12

• Hydrocarbon Identification and Bedding Fracture Detection in Shale Gas

Abstract: Prediction of hydrocarbon enrichment and natural fractures is significant for sweet spot characterization in shale gas reservoirs. However, it is difficult to estimate reservoir properties using conventional seismic techniques based on elastic and isotropic assumptions. Considering that the viscoelastic anisotropic model better represents organic shale, we propose a new seismic inversion method to improve shale gas characterization by incorporating the anisotropic reflectivity theory in the frequency-dependent inversion scheme. The computed P-wave velocity dispersion attribute DP evaluates the hydrocarbon enrichment by estimating the inelastic properties of shale associated with organic materials. The inverted anisotropic dispersion attribute Dε detects the development intensity of bedding fractures using frequency-dependent anisotropy owing to wave-induced fluid flow in parallel fractures. Synthetic tests indicate that DP can robustly estimate shale attenuation and Dε is sensitive to the frequency-dependent anisotropy of shale. The results are validated by reservoir properties measured in gas-producing boreholes and rock physical modeling analysis, supporting the applicability of the dispersion attributes for hydrocarbon identification and bedding fracture detection. The predicted hydrocarbon enrichment and the development of bedding fractures correlate with the structural characteristics of the shale formation. The depth-related shale properties can be described by improving the geological understanding of the study area. Finally, favorable areas with high hydrocarbon enrichment and extensive development of bedding fractures are identified by simultaneously considering high DP and Dε anomalies, providing essential information for predicting potential shale gas reservoirs. Article Highlights A novel seismic inversion method for anisotropy dispersion attributes is proposed P-wave velocity dispersion attribute is used to identify hydrocarbon enrichment in shale Anisotropic dispersion attribute is used to detect bedding fractures in shale
PubDate: 2022-08-10

• Anisotropic Anelastic Impedance Inversion for Attenuation Factor and
Weaknesses Combining Newton and Bayesian Markov Chain Monte Carlo
Algorithms

Abstract: Abstract The problem of frequency-dependent seismic inversion for estimating attenuation and anisotropy based on rock physics effective model is reviewed and analyzed. Based on an extended periodically layered medium model, frequency-dependent stiffness parameters of anisotropic anelastic media as a function of attenuation factor and weaknesses are presented. For the case of an interface separating two anisotropic anelastic media, a new parameterized P-to-P reflection coefficient and anisotropic anelastic impedance $${\mathcal {A}}_\mathrm{EI}$$ are proposed. Based on the anisotropic $${\mathcal {A}}_\mathrm{EI}$$ , an inversion workflow of employing frequency components of seismic amplitudes to estimate attenuation factor and weaknesses for anisotropic anelastic media is presented. In the first stage inversion, the anisotropic $${\mathcal {A}}_\mathrm{EI}$$ is calculated using frequency components of partially incidence-angle-stacked seismic data; and the second-stage inversion for unknown attenuation factor and weaknesses is implemented combining a Newton method and Bayesian Markov chain Monte Carlo algorithm by calculating first- and second-order derivatives of anisotropic $${\mathcal {A}}_\mathrm{EI}$$ with respect to unknown parameters. Tests on synthetic seismic gathers confirm the accuracy of new parameterized reflection coefficient, and the unknown parameters are estimated reliably even in the case of seismic data of signal-to-noise ratio of 2 being employed. Applying the inversion approach and workflow to a field data set acquired over a shale reservoir, reliable attenuation factors and weaknesses that match well log curves are obtained, which are preserved as indicators for identifying potential hydrocarbon-bearing cracked reservoirs.
PubDate: 2022-08-09

• Probabilistic Estimation of Seismically Thin-Layer Thicknesses with
Application to Evaporite Formations

Abstract: Abstract The identification of potassium (K) and magnesium (Mg) salts prior to the well drilling is a key factor to avoid washouts, closing pipes, fluid loss damage, and borehole collapse. The Bayesian classification combines the outcomes from statistical rock physics and seismic inversion, providing the spatial occurrence of the most-probable salt types. It serves as a facies identifier of Mg–K-rich salts (bittern salts) before drilling. Nevertheless, the most-probable classification is limited to the seismic resolution which may underestimate seismically thin-layer thicknesses. Along with the most-probable facies, the Bayesian classification renders the facies probability volume. We demonstrate that the facies probability and facies-specific total thickness highly correlate to each other even under the threshold of seismic resolution. Thus, we employ the bittern-salts probability volume to predict thin-bed bittern-salts thickness in undrilled locations. To capture the variability of the seismic estimation, we resort to Monte Carlo-assisted simulations of wells that emulate the layering patterns of a site-specific deposition environment. These simulations are crucial to assist the estimation of the joint probability density function between the facies volume and the total thickness. Therefore, given the facies probability, the joint probability density function enables us to derive the conditional expectation and percentiles of thin-bed thicknesses. Furthermore, this paper proposes a method to quantify the negative influence of seismic noise in the estimation of thin-bed thicknesses. The blind well confirms the consistency of this technique to unfold the uncertainty in the seismic predictability of thin layers. We argue that this procedure is extendable to other facies.
PubDate: 2022-08-01

• Earthquake Genesis and Earthquake Early Warning Systems: Challenges and a
Way Forward

Abstract: Several natural hazards, including earthquakes, may trigger disasters and the presence of disaster drivers further lead to the massive loss of life and property, every year around the world. The earthquakes are unavoidable, as exact earthquake prediction in terms of date, and time is difficult. However, with the advancement in technology, earthquake early warning (EEW) has emerged as a life-saving guard in many earthquake-prone countries. Unlike other warning systems (where hours of warning are possible), only a few seconds of warning is possible in the EEW system, but this warning may be very helpful in saving human lives by taking the proper action. The concept of EEW relies on using the initial few seconds of information from nearby instruments, performing basic calculations, and issuing the warning to the farther areas. A dense network or enough network coverage is the backbone of an EEW system. Because of insufficient station coverage, the estimated earthquake location is error-prone, which in turn may cause problems for EEW in terms of estimating strong shaking for the affected areas. Seismic instrumentation for EEW has improved significantly in the last few years considering the station coverage, data quality, and related applications. Many countries including the USA, Mexico, Japan, Taiwan, and South Korea have developed EEW systems and are issuing a warning to the public and authorities. Several other countries, namely China, Turkey, Italy, and India are in process of developing and testing the EEW system. This article discusses the challenges and future EEW systems developed around the world along with different parameters used for EEW. Article Highlights This article aims to provide a comprehensive review related to the development The explicit emphasis is on the scientific development of EEW parameters The challenges and future scopes for the effective implementation of EEWS are discussed in terms of the correct location, the magnitude estimation, the region-specific use of ground motion prediction equations, communication technologies, and general public awareness
PubDate: 2022-08-01

• Residual Terrain Modelling: The Harmonic Correction for Geoid Heights

Abstract: Abstract The harmonic correction (HC) is one of the key quantities when using residual terrain modelling (RTM) for high-frequency gravity field modelling. In the RTM technique, high-frequency topographic gravitational signals are obtained through removing gravitational effects of a long-wavelength reference surface, e.g., MERIT2160. There might be points located below the reference surface. In such cases, the RTM gravity field is calculated in the non-harmonic condition, HC is therefore required. Over past decades, though various methods have been proposed to handle the HC issue for the RTM technique, most of them were focused on the HC for RTM gravity anomaly rather than for other gravity functionals, such as RTM geoid height. In practice, the HC for RTM geoid height was generally assumed to be negligible, but a detailed quantification was missing for present-day RTM computations. This might cause large errors in the regional geoid determination over rugged areas. In this study, we derive HC expressions for the RTM geoid height in the framework of the classical condensation method. The HC terms are derived under four different assumptions separately: residual masses approximated by an unlimited Bouguer plate, residual masses approximated by a limited Bouguer plate which overcomes the mass inconsistency effect, residual masses approximated by a Bouguer shell which overcomes the effect of planar approximation, and residual masses approximated by a limited Bouguer shell which overcomes the errors induced by both planar approximation and mass-inconsistency. The errors due to various approximations in HC terms are investigated through comparison among various terms. Besides, HC terms are computed using an expansion up to degree and order 2159. Our results show that HC for RTM geoid height is less 1 mm and could be ignored over $$\sim 99$$ % of continental areas, but be of great significance for regional geoid determination over mountain areas, e.g., more than 10 cm effect over very rugged areas. The validation through comparison with terrestrial measurements and a baseline solution of the RTM technique proves that the HC terms provided in this study can improve the accuracy of RTM geoid heights and are expected to be useful for applications of the RTM technique in regional and global gravity field modelling.
PubDate: 2022-08-01

• Complex Frequency-Shifted Perfectly Matched Layers for 2.5D
Frequency-Domain Marine Controlled-Source EM Field Simulations

Abstract: Abstract For geophysical electromagnetic (EM) forward modeling problems, the accuracy of solutions mainly depends on the numerical modeling method used and the corresponding boundary conditions. Most multi-dimensional EM studies deal with numerical methods for discretisation (e.g., finite-difference, finite-element, integral equation, etc.) and pay less attention to the boundaries. This review presents the recent research on optimizing boundary conditions for the frequency-domain marine controlled-source EM (CSEM) forward modeling algorithm. Current geophysical EM field simulation techniques usually utilize the truncated Dirichlet boundary condition, which requires the modeling domain boundaries to be far away from the area of interest and field values to be zero at the boundaries to mitigate artificial reflections/refractions resulting from truncated boundaries. The perfectly matched layer (PML) approach with few additional absorbing layers can serve as an alternative boundary to supress these truncated boundary effects. In this review, the application of the PML boundary condition to marine CSEM using a staggered finite-difference scheme for the 2.5D problem in vertical transverse isotropic (VTI) conductivity structures is introduced. This new algorithm utilizes the complex frequency-shifted PML (CFS-PML) boundary condition. The selection of optimal PML parameters are also further investigated for numerical stability. Numerical tests for several Earth conductivity models show that the CFS-PML approach is of similar high accuracy compared to using traditional Dirichlet boundary condition and exhibits additional advantages in terms of computational time and memory usage. Furthermore, the numerical tests indicate that the proposed forward modeling algorithm using CFS-PML boundary condition works well for both shallow and deep water cases, including the application to real field example from the Troll Field in Norway. The detectability of subsurface-related EM fields in airwave dominated shallow waters can be enhanced by using the weighted difference fields for mitigating the effect of airwaves on the models.
PubDate: 2022-08-01

• First-Order Derivatives of Principal and Main Invariants of Magnetic
Gradient Tensor of a Uniformly Magnetized Tesseroid and Spherical Shell

Abstract: Abstract Similar to the gravitational curvatures in the gravity field, the magnetic curvatures (i.e., third-order derivatives of the magnetic potential) have been recently proposed in the magnetic field. The components of the magnetic curvatures are all involved in the expressions for the first-order derivatives of invariants of the magnetic gradient tensor (MGT), whose physical meaning is the change rate of invariants of the MGT and their theoretical models have not yet been fully developed. In this contribution, the general expressions for the First-order derivatives of Principal and Main Invariants of the Magnetic Gradient Tensor (i.e., FPIMGT and FMIMGT) with combined components of the MGT and magnetic curvatures are presented. Specifically, the expressions for the FPIMGT and FMIMGT of a uniformly magnetized tesseroid and spherical shell are derived as examples for basic mass bodies in the spherical coordinate system in the spatial domain for the magnetic field modeling. The near zone and polar singularity problems are numerically investigated for these newly derived expressions. Numerical experiments show that the near zone problem has been found for the FPIMGT and principal invariants of the magnetic gradient tensor (PIMGT), whereas the polar singularity problem does not occur for the FPIMGT and PIMGT when using the Cartesian integral kernels for different heights and grid resolutions. This study shows that the calculation strategy by substituting the calculated values of the MGT and magnetic curvatures into the general formulae of the PIMGT and FPIMGT can provide proper numerical precision measured by relative approximation errors dependent on the computation point’s height and latitude for the FPIMGT and PIMGT. For instance, using the grid size of $$1^{\circ }\times 1^{\circ }$$ at a satellite height of 260 km, relative approximation errors in $$Log_{10}$$ scale have been reduced at a level lower than − 1 for the evaluation of the FPIMGT and PIMGT. The first-order derivatives of principal and main invariants of the MGT will be applied in related magnetic field studies (e.g., magnetic detection, inversion, location, position, characterization, navigation, and exploration) to present additional information (i.e., more detailed geophysical features in terms of change rates) compared to the principal and main invariants of the magnetic gradient tensor.
PubDate: 2022-08-01

• Revisiting Force Model Error Modeling in GRACE Gravity Field Recovery

Abstract: Abstract The gravity field recovery from GRACE (Gravity Recovery and Climate Experiment) mission data is contaminated by both observation noise and dynamic force errors, especially the temporal aliasing errors. To reduce their influence, four approaches are widely adopted, namely the estimation of empirical accelerations (ACC approach), the estimation of K-band range-rate parameters (KBR approach), the incorporation of the full variance–covariance matrix of observations into the least-squares adjustment (COV approach), and the time series model-based filtering (FILT approach). Essentially, the ACC and KBR approaches can be grouped into the method of functional model compensation, while the COV and FILT approaches belong to the method of stochastic model compensation. The four approaches are systematically revisited in this paper concerning their connections and differences from both theoretical perspectives and numerical simulations. Results show that all of them can significantly reduce errors in the recovered monthly gravity field models compared to the nominal approach not applying any of the four approaches. Moreover, their performances are quite consistent in the simulation case where only white observation noise is included. When both colored observation noise and temporal aliasing effects are considered, however, their performances are different. The noise reduction ratio can reach up to 87% by the ACC, COV and FILT approaches, while it is 79% in the KBR approach. The discrepancy can be explained by the compromise between noise reduction and signal absorption in the KBR approach due to the lack of constraints on empirical parameters. Moreover, in the spectral domain, ACC and KBR approaches function as high-pass filters, whereas the stochastic method, COV or FILT approach, can competently cope with colored noise in a full-spectrum manner.
PubDate: 2022-08-01

• Multi-Objective Petrophysical Seismic Inversion Based on the
Double-Porosity Biot–Rayleigh Model

Abstract: Petrophysical seismic inversion, aided by rock physics, aims at estimating reservoir properties based on reflection events, but it is generally based on the Gassmann equation, which precludes its applicability to complex reservoirs. To overcome this problem, we present a methodology based on the double-porosity Biot–Rayleigh (BR) model, which takes into account the rock heterogeneities. The volume ratio of inclusions in the BR model is treated as a spatially varying parameter, facilitating a better description of the pore microstructure. The method includes the Zoeppritz equations to extract reservoir properties from prestack data. To handle the ill-posedness of the inversion and achieve a stable solution, the algorithm is formulated as a multi-objective optimization based on the Bayes theorem, where the reservoir-property estimation is jointly conditioned to seismic and elastic data with multiple prior terms. The method is validated with field data of a tight gas sandstone reservoir, illustrating its effectiveness compared to the Gassmann-based estimation, reducing uncertainties and improving the accuracy of identifying gas zones. Article Highlights The petrophysical seismic inversion is based on the double-porosity Biot–Rayleigh model Spatially varying inclusion volumes are used to describe complex pore structures A multi-objective optimization with joint data misfit enables stable results
PubDate: 2022-08-01

• Review of Acquisition and Signal Processing Methods for Electromagnetic
Noise Reduction and Retrieval of Surface Nuclear Magnetic Resonance
Parameters

Abstract: Surface nuclear magnetic resonance (sNMR) is an electromagnetic hydrogeophysical method directly sensitive to liquid phase water in the upper $$\approx$$ 100 m of the subsurface. For this reason, sNMR is a uniquely capable of unambiguous exploration and quantitative characterization of groundwater and its structural environment in the near-surface. In spite of these physical attributes, the method suffers from notoriously low signal-to-noise ratio (SNR) which can limit its application. A large span of research has therefore been dedicated to sNMR developments including instrument innovations, acquisition methodologies and signal processing techniques which improve the SNR of the method and expand its scope of application outside the research world. Towards this goal, we include a description of community-developed best practice techniques and strategies that can be relied upon to successfully gather and analyse sNMR data sets in a production setting. Complementing this, we provide a comprehensive review of past, recent, and on-going approaches that—while not currently widely adopted—present promising features should further research be dedicated to their development. As such, the objective of this paper is to provide both newcomers and specialists of the sNMR method a clear view of the existing signal processing techniques and strategies along with a structured proposition of promising research leads and future perspectives to be explored.
PubDate: 2022-08-01

• Ground Penetrating Radar Applied to Monumental Stone Conservation:

Abstract: This paper deals with the application of the Ground Penetrating Radar (GPR) method in the assessment of stone monuments. Compilation of published works and a discussion of their main findings are first addressed. Next, to show the potential of the method, a case study is presented aiming to assess the state of conservation of the rock necropolis of San Vítor de Barxacova (Ourense, Spain) consisting of 56 anthropomorphic graves carved into the natural rock. Fieldwork was carried out using a GPR system equipped with a 2.3 GHz central frequency antenna. The main goal of this study is to provide an effective approach for the detection and localization of internal damages such as fractures and voids. New amplitude-based 2D and 3D imaging strategies are presented aiming to improve damage detection. A new approach was also developed to digitize the extracted information into a point cloud format, thus improving the possibilities for 3D visualization with the surrounding environment. Although a total of 39 graves were surveyed, only 13 graves are included in this paper due to their singularity and relevant results. The potential of using GPR tests for the assessment of the conservation state of monumental stone structures is also discussed. Article Highlights A case study is presented aiming to assess the state of conservation of a rock necropolis (cemetery) in Spain New amplitude-based imaging strategies allowed us to detect inner voids and fractures A new approach was developed to digitize the extracted information into a point cloud format
PubDate: 2022-07-27

• Natural and Anthropogenic Sources of Seismic, Hydroacoustic, and
Infrasonic Waves: Waveforms and Spectral Characteristics (and Their
Applicability for Sensor Calibration)

Abstract: Abstract The record of seismic, hydroacoustic, and infrasonic waves is essential to detect, identify, and localize sources of both natural and anthropogenic origin. To guarantee traceability and inter-station comparability, as well as an estimation of the measurement uncertainties leading to a better monitoring of natural disasters and environmental aspects, suitable measurement standards and reliable calibration procedures of sensors, especially in the low-frequency range down to 0.01 Hz, are required. Most of all with regard to the design goal of the Comprehensive Nuclear-Test-Ban Treaty Organisation’s International Monitoring System, which requires the stations to be operational nearly 100% of the time, the on-site calibration during operation is of special importance. The purpose of this paper is to identify suitable excitation sources and elaborate necessary requirements for on-site calibrations. We give an extensive literature review of a large variety of anthropogenic and natural sources of seismic, hydroacoustic, and infrasonic waves, describe their most prominent features regarding signal and spectral characteristics, explicitly highlight some source examples, and evaluate the reviewed sources with respect to requirements for on-site calibrations such as frequency bandwidth, signal properties as well as the applicability in terms of cost–benefit. According to our assessment, earthquakes stand out across all three waveform technologies as a good natural excitation signal meeting the majority of the requirements. Furthermore, microseisms and microbaroms allow a calibration at very low frequencies. We also find that in each waveform technique man-made controlled sources such as drop weights or air guns are in good agreement with the required properties, although limitations may arise regarding the practicability. Using these sources, procedures will be established allowing calibration without record interrupting, thereby improving data quality and the identification of treaty-related events.
PubDate: 2022-07-25

• Anisotropic Attenuation Compensated Reverse Time Migration of Pure qP-Wave
in Transversely Isotropic Attenuating Media

Abstract: Abstract The absorption (anelastic attenuation) and anisotropy properties of subsurface media jointly affect the seismic wave propagation and the quality of migration imaging. Anisotropic viscoelastic model can effectively describe seismic velocity and attenuation anisotropy effects. To reduce the computational cost and complexity of elastic wave modes decoupling for seismic imaging in anisotropic attenuating media, we have developed a pure-viscoacoustic transversely isotropic (TI) wave equation starting from the complex-valued velocity dispersion relation of quasi-compressional (qP) wave. The wave equation involving fractional Laplacians has advantages of being able to describe the constant-Q (frequency-independent quality factor) attenuation, arbitrary TI velocity and attenuation, decoupled amplitude loss and velocity dispersion effects. Numerical analyses showed that the simplified equation can accurately hold the velocity and attenuation anisotropy of qP-wave in viscoelastic anisotropic media in the range of moderate anisotropy. Compared to previous pseudo-viscoacoustic equations, the pure-viscoacoustic equation can be completely free from undesirable S-wave artifacts and behaves good numerical stability in tilted transversely isotropic (TTI) attenuating media. There are obvious wavefield differences between isotropic attenuation and anisotropic attenuation cases especially in the direction perpendicular to the axis of symmetry. Furthermore, to mitigate the influences of velocity and attenuation anisotropy on migrated seismic images, we have developed an anisotropic attenuation (Q) compensated reverse time migration (AQ-RTM) approach based on the new propagator. The compensation can be implemented by reversing the sign of the dissipation terms and keeping the dispersion terms unchanged during wavefields extrapolation. Synthetic example from a Graben model illustrated that the anisotropic Q-compensated RTM scheme can produce images with more balanced amplitude and accurate position of reflecters compared with conventional RTM methods under assumptions of acoustic anisotropic (uncompensated) and isotropic attenuating media. Results from a Marmousi-II model demonstrated that the new methodology is applicable for complicated geological model to significantly improve imaging resolution of the target area and deep layers.
PubDate: 2022-07-20

• Coastal Zone Changes in West Africa: Challenges and Opportunities for
Satellite Earth Observations

Abstract: Abstract The West African coastal population and ecosystems are increasingly exposed to a multitude of hazards. These are likely to be exacerbated by global climate change and direct impacts from local human activities. Our ability to understand coastal changes has been limited by an incomplete understanding of the processes and the difficulty of obtaining detailed data. Recent advances in satellite techniques have made it possible to obtain rich coastal data sets that provide a solid foundation for improving climate change adaptation strategies for humanity and increasing the resilience of ecosystems for sustainable development. In this article, we review West African coastal layout and current socio-environmental challenges together with key parameters that can be monitored and several coastal management programs that rely on satellite techniques to monitor indicators at the regional level. The social, technical and scientific problems and difficulties that hinder the interest of coastal practitioners and decision-makers to use the satellite data are identified. We provide a roadmap to precisely respond to these difficulties and on how an improved satellite earth observation strategy can better support future coastal zone management in West Africa.
PubDate: 2022-07-18

• Correction to: Water Resources in Africa under Global Change: Monitoring
Surface Waters from Space

PubDate: 2022-07-13

• Seismic Amplitude Inversion for Orthorhombic Media Based on a Modified
Reflection Coefficient Approximation

Abstract: Shales represent strongly intrinsic vertical transverse isotropy (VTI) property or polar anisotropy. The presence of vertically aligned fractures makes shale exhibit orthogonal anisotropy and the seismic responses have azimuthal variation. Conventional linearized PP-wave reflectivity expression for orthorhombic (ORT) media includes at least 8 parameters to be inverted, and the amplitude inversion based on such equations can be highly ill-posed. In this paper, we derive a modified PP-wave approximation of reflection coefficients in ORT media and propose a two-step strategy based on the Bayesian-framework inversion method. The new equation represents the seismic response of polar anisotropy and azimuthal anisotropy separately, and it consists of only 5 model parameters to be inverted. Three of these model parameters are azimuthal independent: A—acoustic impedance, B—anisotropic shear modulus and C—horizontal P-wave phase velocity (along the fracture strike), and two of them are azimuthal dependent: D—azimuthal anisotropic gradient and E—horizontal P-wave anisotropy parameter. Accuracy analysis demonstrates that the derived approximation has similar accuracy to the existing approximation. A stepwise inversion strategy is proposed to invert azimuthal-independent parameters and azimuthal-dependent parameters separately. Synthetic tests show that the proposed strategy is more stable and better conditioned than the existing multi-parameter simultaneous inversion. Field seismic data set of a fractured shale-gas reservoir is also used to demonstrate the stability and accuracy of the proposed inversion method. Article Highlights PP-wave reflection coefficient is derived in terms of only 5 model parameters for orthorhombic media. Three of them are azimuthal independent: A—acoustic impedance, B—anisotropic shear modulus, C—horizontal P-wave phase velocity (along the fracture strike), and the others are azimuthal dependent: D—azimuthal anisotropic gradient, and E—horizontal P-wave anisotropy parameter A stepwise inversion strategy for inverting azimuthal-independent parameters and azimuthal-dependent parameters is proposed Tests on synthetic and field seismic datasets imply that the proposed inversion method has the potential to generate reliable results of the model parameters for reservoir characterization
PubDate: 2022-07-04

• Correction to: A Dynamical Prospective on Interannual Geomagnetic Field
Changes

PubDate: 2022-06-28

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