Geophysical Processes Research Articles

Dissipative Seismicity for Hydrocarbon Reservoir Parameter Evaluation

The natural seismic background of the Earth and its deep emission component are a form of dissipation of energy of geodynamic processes. The methods of studying the seismic background as a signal generated by an open complex non-linear system (the Earth’s crust) can be grouped under one branch—dissipative seismicity. In this paper, one of such methods, namely, the thermodynamic indicator of the state of rocks, is used for the remote evaluation of the local productivity of the reservoir on the hydrocarbon deposit site. The thermodynamic indicator was created using the Klimontovich entropy and yields quantitative estimates of the local disequilibrium of rocks associated with the activity of geophysical processes. We revealed monotonic, near-linear relationship between the thermodynamic indicator values calculated using the seismic background records and the cumulative thickness of productive layers in the wells in close proximity to recording points. The thermodynamic indicator is calculated assuming that there is a sliding time window threshold that must be taken empirically. The obtained results show that the thermodynamic indicator can be effectively used for outlining the deposit boundaries and choosing the potentially most productive well drilling points by extrema in the indicator value field.

Spatiotemporal analysis of the distribution of earthquake chains 
 in the Baikal rift system with the purpose of revealing migrating seismicity

The study of the phenomenon of migrating seismicity in the epicentral fields of various seismically active regions of the Earth is the subject of many works. Chains of "migrations" of earthquakes are identified using various methods and are often explained by the passage of deformation waves in the Earth's lithosphere. This paper presents the results of studying the spatiotemporal distribution of quasi-linear chains of earthquakes in the Baikal region using statistical approaches and a large amount of initial data on earthquakes of representative energy classes. It is shown that the chains are formed mainly within the Baikal Rift System (BRS) and are confined to zones of seismotectonic destruction of the lithosphere. When studying the lengths of earthquake chains, five maxima of the distribution of chains were revealed, three of which correspond to possible geological and geophysical processes in the BRS lithosphere.

The Large Earthquakes and Deformation Waves as Possible Triggers of Climate Warming in the Arctic and Glacier Destruction in the Antarctic

According to the modern climate paradigm, anomalous phenomena occurring in the polar regions of the Earth, such as rapid warming in the Arctic and intensive destruction of glaciers in the Antarctic, are a serious danger and challenge for civilization since they can potentially lead to global climate warming by several degrees and a rise in the level of the World Ocean by several tens of centimeters as soon as the 21st century. It is presumed that the main cause of these processes, which have strongly accelerated since the second half of the 1970s, was the anthropogenic factor of carbon dioxide emissions into the atmosphere, leading to the greenhouse effect. This statement, taken for granted in most developed countries, has led to several international agreements to limit carbon emissions and ideas about the need for a rapid transition to a low-carbon green economy. As for the influence of natural factors on the development of the mentioned dangerous processes, no one denies such a possibility since the facts of climatic changes in preindustrial eras are well known in the geological history of the Earth. However, the geological time scales are so large that most climatologists implicitly proceed from the assumption that short-term climate changes observed over the past and present centuries with a characteristic time of tens of years are mainly determined by rapidly changing atmospheric and oceanic processes. However, one should bear in mind the influence of rapid geophysical processes, such as cycles of earthquakes or volcanic eruptions, which are comparable in time scales with modern climate changes. If an analysis is based on the large megathrust earthquakes with a magnitude greater than 8 and the large-scale deformation waves caused by them in the lithosphere, then, considering physically based trigger mechanisms, it is possible to construct a geodynamic scheme that explains the observed climatic changes in the Arctic and the glacier destruction processes in the Antarctic. This article describes this new geodynamic concept.

Characterizing the automatic radon flux transfer standard system Autoflux: laboratory calibration and field experiments

Abstract. High-quality, long-term measurements of terrestrial trace gas emissions are important for investigations of atmospheric, geophysical and biological processes to help mitigate climate change and protect the environment and the health of citizens. High-frequency terrestrial fluxes of the radioactive noble gas 222Rn, in particular, are useful for validating radon flux maps and used to evaluate the performance of regional atmospheric models, to improve greenhouse gas emission inventories (by the radon tracer method) and to determine radon priority areas for radiation protection goals. A new automatic radon flux system (Autoflux) was developed as a transfer standard (TS) to assist with establishing a traceability chain for field-based radon flux measurements. The operational characteristics and features of the system were optimized based on a literature review of existing flux measurement systems. To characterize and calibrate Autoflux, a bespoke radon exhalation bed (EB) facility was also constructed with the intended purpose of providing a constant radon exhalation under a specific set of controlled laboratory conditions. The calibrated Autoflux was then used to transfer the derived calibration to a second continuous radon flux system under laboratory conditions; both instruments were then tested in the field and compared with modeled fluxes. This paper presents (i) a literature review of state-of-the-art radon flux systems and EB facilities; (ii) the design, characterization and calibration of a reference radon EB facility; (iii) the design, characterization and calibration of the Autoflux system; (iv) the calibration of a second radon flux system (INTE_Flux) using the EB and Autoflux, with a total uncertainty of 9 % (k = 1) for an average radon flux of ∼ 1800 mBq m−2 s−1 under controlled laboratory conditions; and (v)​​​​​​​ an example application of the calibrated TS and INTE_Flux systems for in situ radon flux measurements, which are then compared with simulated radon fluxes. Calibration of the TS under different environmental conditions and at lower reference fluxes will be the subject of a separate future investigation.

New horizons for hydrography

Compared to the complexity required to measure other physical quantities, the continuous monitoring globally of water levels, current directions, and velocities, as well as the measurement of underwater topography, do not appear ambitious tasks for modern technologies. The challenges lie in the sheer size of the area to be measured, which makes up about 70% of the Earth’s total surface, in its constant variability due to natural processes, the inaccessibility of the seabed, and the still inadequate mathematical modelling of global geophysical processes at the oceanic scale. Since most of the world’s population lives on, from and with the oceans, a demand-oriented provision of hydrographic information is of fundamental importance. Hydrography is called upon to serve this need for information in support of informed decision-making. Starting from the present status and the discernible trends in technical development, this article aims to provide a glimpse into the expected future development up to the end of the current decade.

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

The interactions between the geophysical processes and geodynamics of the lithosphere play a crucial role in the geologic structure of the Earth’s crust. The Bangui magnetic anomaly is a notable feature in the lithospheric structure of the Central African Republic (CAR) resulting from a complex tectonic evolution. This study reports on the coherence in the geophysical data and magnetic anomaly field analysed from a series of maps. The data used here include raster grids on free-air altimetric gravity, magnetic EMAG2 maps, geoid EGM2008 model and topographic SRTM/ETOPO1 relief. The data were processed to analyse the correspondence between the geophysical and geologic setting in the CAR region. Histogram equalization of the topographic grids was implemented by partition of the raster grids into equal-area patches of data ranged by the segments with relative highs and lows of the relief. The original data were compared with the equalized, normalized and quadratic models. The scripts used for cartographic data processing are presented and commented. The consistency and equalization of topography, gravity and geoid data were based using GMT modules ‘grdfft’ and ‘grdhisteq’ modules. Using GMT scripts for mapping the geophysical and gravity data over CAR shows an advanced approach to multi-source data visualization to reveal the relationships in the geophysical and topographic processes in central Africa. The results highlighted the correlation between the distribution of rocks with high magnetism in the central part of the Bangui anomaly, and distribution of granites, greenstone belts, and metamorphosed basalts as rock exposure. The correspondence between the negative Bouguer anomaly (<−80 mGal), low geoid values (<−12 m) and the extent of the magnetic anomaly with extreme negative values ranging from −1000 to −200 nT is identified. The integration of the multi-source data provides new insights into the analysis of crustal thicknesses and the average density of the Earth in CAR, as well as the magnitude of the magnetic fields with notable deviations caused by the magnetic flux density in the Bangui area related to the distribution of mineral resources in CAR.

Named Landforms of the World: A Geomorphological and Physiographic Compilation

Prior to the current era of digital geomorphological mapping, global and regional-scale land surface characterization was advanced by qualitative interpretations that relied on human visualization aided by disciplinary knowledge of geophysical processes combined with extensive field study. In the early twentieth century, Fenneman proposed to devise systematic physiographic divisions of the United States and in 1916 produced what is still regarded as an authoritative map of these divisions. His physiographic regions were developed to provide context when describing land surface characteristics of smaller areas using well-known regional characteristics and descriptors. In 1968, geographer Richard E. Murphy published a large-format map of the “Landforms of the World” to fill a gap in the suite of standard classroom maps. In 1990, the British geomorphologist E. M. Bridges published World Geomorphology, providing the first global treatment and description of divisions, provinces, and sections—the same hierarchical land partitioning concepts that Fenneman used decades earlier. In the twenty-first century, geographic information systems (GIS) technologies are nearly ubiquitous, yet neither Murphy’s nor Bridges’s work existed as GIS data. To further illuminate their pioneering work, we (1) recompiled Murphy’s landforms as a spatial combination of modern existing data layers, and (2) used the recompiled Murphy’s landforms as a basis for the boundaries of the divisions, provinces, and sections described by Bridges. Our aggregation yields a new resource, Named Landforms of the World, version 2.0, which provides a reference-level, basemap-quality data layer that can significantly facilitate mapping, assessing, and understanding Earth surface features.

Satellite-Derived Land Surface Temperature Dynamics in the Context of Global Change—A Review

Satellite-derived Land Surface Temperature (LST) dynamics have been increasingly used to study various geophysical processes. This review provides an extensive overview of the applications of LST in the context of global change. By filtering a selection of relevant keywords, a total of 164 articles from 14 international journals published during the last two decades were analyzed based on study location, research topic, applied sensor, spatio-temporal resolution and scale and employed analysis methods. It was revealed that China and the USA were the most studied countries and those that had the most first author affiliations. The most prominent research topic was the Surface Urban Heat Island (SUHI), while the research topics related to climate change were underrepresented. MODIS was by far the most used sensor system, followed by Landsat. A relatively small number of studies analyzed LST dynamics on a global or continental scale. The extensive use of MODIS highly determined the study periods: A majority of the studies started around the year 2000 and thus had a study period shorter than 25 years. The following suggestions were made to increase the utilization of LST time series in climate research: The prolongation of the time series by, e.g., using AVHRR LST, the better representation of LST under clouds, the comparison of LST to traditional climate change measures, such as air temperature and reanalysis variables, and the extension of the validation to heterogenous sites.

Capturing seismic velocity changes in receiver functions with optimal transport

SUMMARY Temporal changes in seismic velocities are an important tool for tracking structural changes within the crust during transient deformation. Although many geophysical processes span the crust, including volcanic unrest and large-magnitude earthquakes, existing methods for seismic monitoring are limited to the shallow subsurface. We present an approach for deep seismic monitoring based on teleseismic receiver functions, which illuminate the crustal velocity structure from the bottom-up. Using synthetic waveform modelling, we show that receiver functions are uniformly sensitive to velocity changes throughout the crust and can locate the depth of the perturbation. We introduce a novel method based on optimal transport for measuring the non-linear time–amplitude signal variations characteristic of receiver function monitoring. We show that optimal transport enables comparison of full waveform distributions rather than relying on representative stacked waveforms. We further study a linearized version of optimal transport that renders time-warping signal variations into simple Euclidean perturbations, and use this capability to perform blind source separation in the space of waveform variations. This disentangles the effects of changes in the source–receiver path from changes in subsurface velocities. Collectively, these methods extend the reach of seismic monitoring to deep geophysical processes, and provide a tool that can be used to study heterogeneous velocity changes with different spatial extents and temporal dynamics.

Electrical conductivity of iron in Earth's core from microscopic Ohm's law

Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties under conditions prevalent in the Earth's core calls for first-principles methods that can support diagnostics. We present results on the electrical conductivity obtained by simulating the microscopic Ohm's law using time-dependent density functional theory and place them in the context of recent experimental measurements.

Global Trends and Prospects of Nepheloid Layers: A Comprehensive Bibliometric Review

Nepheloid layers are widely distributed in the marine environment, and their formation and evolution pose many challenges to the current understanding of ocean dynamics and marine sedimentology. In sediment transport processes, nepheloid layers significantly contribute to the exchange of sediment between the continental shelf and the slope. In this paper, we summarize the global research trends on nepheloid layers. In total, 689 publications from 1990 to 2022 were collected from the Web of Science and analyzed using bibliographic software, including Bibliometrix, VOSviewer, CiteSpace, and CorText. Based on these publications, past and present popular research on nepheloid layers is examined and evaluated. The trends in nepheloid layer research are summarized by analyzing keywords, article references, countries, institutions, and authors. Finally, prospects and several key questions related to nepheloid layers are concluded, which can potentially guide future studies. The bibliographic analysis can provide new insights into the history of nepheloid layers. The results also provide valuable information for other researchers and programs investigating geological, geophysical, and biogeochemical processes.

Geometry‐Based Prediction of Solute Transport Process in Single 3D Rock Fractures Under Laminar Flow Regime

AbstractSubsurface substance migration in the fractured rock aquifer is mainly controlled by fractures, and prediction of solute transport in fractures is important to many geophysical processes and engineering activities. This study explores the possibility of predicting transport process in single rock fractures from measurable physical properties. For this purpose, we conducted a large number of pore‐scale simulations of solute transport in single 3D rock fractures with different apertures and various degrees of roughness. The numerically‐obtained breakthrough curves under laminar flow regime were reproduced with high fidelity by the classic analytical solution within the framework of macroscopic advection‐dispersion theory. The fitted transport coefficients (hydrodynamic dispersion coefficient and transport velocity) were normalized by the parallel‐plate model's values, and were further parameterized by aperture b and roughness parameter σ/b in form of ωeb/ψ + λ(mσ/b − 1)/bn and 1 − α(σ/b)/βb, respectively. By incorporating these parameterized transport coefficients and the modified cubic law into the classic analytical solution, we proposed a new transport predictive model. This model was adaptively degenerated into the classic analytical solution of parallel‐plate model, and was proved to be capable of predicting macroscopic solute transport only relying on arithmetic‐mean mechanical aperture and its standard deviation, without solving the velocity and concentration fields. By the established model, we quantitatively revealed the impacts of aperture and roughness on the breakthrough curve under laminar flow regime. This study puts a step toward predicting solute transport process in fractured rock aquifers with measurable geometric properties.

Liquid Cohesion Induced Particle Agglomeration Enhances Clogging in Rock Fractures

AbstractSuspended particle transport is frequently involved in many geophysical processes and subsurface engineering applications. Although common and important, the effect of liquid cohesion on particle clogging has been overlooked in previous studies. We conduct visualized experiments of dilute suspension flow in a rough fracture and find a dramatic enhancement of clogging by a tiny amount of additional immiscible wetting liquid, even at weight percentage ω ≤ 0.5%. An experimental phase diagram of clogging patterns is obtained in the space of secondary liquid content and flow rate. The combined effect of suspension composition and hydrodynamic condition on the clogging behavior is analyzed to explain transitions of clogging regimes. A theoretical model of agglomerate size is proposed to quantify the capillary cohesion effect. This work improves the understanding of fines migration and particle‐clogging behaviors in the subsurface and paves the way for possibility of controlling particle transport and clogging in various applications.

Evaluating Differences between Ground-Based and Satellite-Derived Measurements of Urban Heat: The Role of Land Cover Classes in Portland, Oregon and Washington, D.C.

The distinction between satellite-based land surface temperature (LST) and air temperature has become an increasingly important part of managing urban heat islands. While the preponderance of urban heat research relies on LST, the emergence of a growing infrastructure of publicly available consumer oriented, ground-based sensor networks has offered an alternative for characterizing microscale differences in temperatures. Recent evidence suggests large differences between LST and air temperatures, yet discerning the reason for these differences between satellite-derived measurements of urban heat islands (UHI) and ground-based measurements of air temperature remains largely unresolved. In this study, we draw on an unusually robust and spatially exhaustive dataset of air temperature in two distinct bioclimates—Portland, Oregon, USA and Washington, D.C., USA—to evaluate the role of land cover on temperature. Our findings suggest that LST in highly built environments is consistently higher than recorded air temperatures, at times varying upwards of 15-degree Celsius, while forested areas contain between 2.5 and 3.5-degree Celsius lower temperatures than LST would otherwise indicate. Furthermore, our analyses points to the effects of land use and land cover features and other geophysical processes may have in determining differences in heat measurements across the two locations. The strength of the present analyses also highlights the importance of hyperlocal scales of data used in conjunction with coarser grain satellite derived data to inform urban heat assessments. Our results suggest a consistent pattern in both study areas, which can further our capacity to develop predictive models of air temperature using freely available descriptions of LST.

Application of supervised machine learning to predict the enhanced gas recovery by CO2 injection in shale gas reservoirs

The technique of Enhanced Gas Recovery by CO2 injection (CO2-EGR) into shale reservoirs has brought increasing attention in the recent decade. CO2-EGR is a complex geophysical process that is controlled by several parameters of shale properties and engineering design. Nevertheless, more challenges arise when simulating and predicting CO2/CH4 displacement within the complex pore systems of shales. Therefore, the petroleum industry is in need of developing a cost-effective tool/approach to evaluate the potential of applying CO2 injection to shale reservoirs. In recent years, machine learning applications have gained enormous interest due to their high-speed performance in handling complex data and efficiently solving practical problems. Thus, this work proposes a solution by developing a supervised machine learning (ML) based model to preliminary evaluate CO2-EGR efficiency. Data used for this work was drawn across a wide range of simulation sensitivity studies and experimental investigations. In this work, linear regression and artificial neural networks (ANNs) implementations were considered for predicting the incremental enhanced CH4. Based on the model performance in training and validation sets, our accuracy comparison showed that (ANNs) algorithms gave 15% higher accuracy in predicting the enhanced CH4 compared to the linear regression model. To ensure the model is more generalizable, the size of hidden layers of ANNs was adjusted to improve the generalization ability of ANNs model. Among ANNs models presented, ANNs of 100 hidden layer size gave the best predictive performance with the coefficient of determination (R2) of 0.78 compared to the linear regression model with R2 of 0.68. Our developed ML-based model presents a powerful, reliable and cost-effective tool which can accurately predict the incremental enhanced CH4 by CO2 injection in shale gas reservoirs.

Atmospheric Electricity Measurements in the Pacific Northwest, Russia

A complex for measuring the electrical parameters of the surface layer of the atmosphere, which has been successfully operating in Kamchatka since 1997, is described. The basic principles of organization of such measurements and methods for their implementation under specific conditions are given. The main reactions of the electric field to meteorological phenomena, as well as to seismic and space events, are shown. A feature of the observatory is that it is located at mid-latitudes with a temperate maritime climate with a very small number of thunderstorms and in a region with high seismic activity. The paper presents the main results of studies of geophysical processes obtained at an observatory with such features. The measurement results of this complex are broadcast on the Internet and are available through a shared use center.

The radial slump of a gravity current in a confined porous layer

The flow of a gravity current widely occurs in many geophysical, environmental and industrial processes. We focus on the overlooked process of radial slump of a gravity current in confined porous layers, which is related to the post-injection flow dynamics of many subsurface displacement processes, initiated by fluid injection through vertical wells. Specifically, we describe the time evolution of the interface shape and location of the propagating front, governed by a second-order nonlinear partial differential equation (PDE). By solving a nonlinear eigenvalue problem, we identify a self-similar solution to describe the dynamics of confined flows at early times, when the interface attaches to both the top and bottom boundaries of the porous layer. As time progresses, the flow gradually becomes unconfined, as gravity-driven slump causes the interface to detach from one boundary; the interface evolution at late times is then described by a self-similar solution of a nonlinear diffusion equation. Time transition from the early-time confined towards late-time unconfined self-similar solutions is also verified by comparing the self-similar solutions and numerical solutions of the governing PDE for both the interface shape and the frontal location. Interestingly, two special vertical locations have also been identified where the best agreement appears between the PDE numerical solutions and the early-time self-similar solutions for the interface shape, which is a novel feature of the radial flow, and the degree of agreement is not impacted by the time evolution.

Hydroclimatic time series features at multiple time scales

A comprehensive understanding of the behaviours of the various geophysical processes and an effective evaluation of time series (else referred to as “stochastic”) simulation models require, among others, detailed investigations across temporal scales. In this work, we propose a novel and detailed methodological framework for advancing and enriching such investigations in a hydroclimatic context. This specific framework is primarily based on a new feature compilation for multi-scale hydroclimatic analyses, and can facilitate largely interpretable feature investigations and comparisons in terms of temporal dependence, temporal variation, “forecastability”, lumpiness, stability, nonlinearity (and linearity), trends, spikiness, curvature and seasonality. Multifaceted characterizations are herein obtained by computing the values of the proposed feature compilation across nine temporal resolutions (i.e., the 1-day, 2-day, 3-day, 7-day, 0.5-month, 1-month, 2-month, 3-month and 6-month ones) and three hydroclimatic time series types (i.e., temperature, precipitation and streamflow) for 34-year-long time series records originating from 511 geographical locations across the contiguous United States. Based on the acquired information and knowledge, similarities and differences between the examined time series types with respect to the evolution patterns characterizing their feature values with increasing (or decreasing) temporal resolution are identified. Moreover, the computed features are used as inputs to unsupervised random forests for detecting any meaningful clusters between the examined hydroclimatic time series. This clustering plays an illustrative role within this research, as it facilitates the identification of spatial patterns (with them consisting an important scientific target in hydroclimatic research) and their cross-scale comparison. We find that these specific patterns are largely analogous across temporal resolutions for the examined continental-scale region. We also apply explainable machine learning to compare the features with respect to their usefulness in clustering the time series at the various temporal resolutions. These latter investigations play a vital role within the proposed methodological framework, as they allow interpretation of hydroclimatic similarity at the various temporal resolutions. For most of the features, this usefulness can vary to a notable degree across temporal resolutions and time series types, thereby implying the need for conducting multifaceted time series characterizations for the study of hydroclimatic similarity.

Spatiotemporal evolution of global long-term patterns of soil moisture

Surface soil moisture (SM) is essential for existence of biotic lifeform and geophysical processes. However, with increasing global warming due to climatic changes, its spatiotemporal evolution is uncertain and largely unknown. In this study we detected long-term (40 years; 1981–2020) SM patterns of global vegetated areas through spatial timeseries clustering using the state-of-the-art ERA5-Land dataset. In addition, we also analyzed long-term patterns of precipitation (P), evapotranspiration (bare soil evaporation (BSe) and vegetation transpiration (VT)), and normalized difference vegetation index (NDVI). Our results indicate that surface SM (0–7 cm depth) of about 48 % and 9 % of the global vegetated area is showing drying and wetting pattern over the past 40 years, respectively. The detected soil drying, and wetting patterns were largely consistent across different soil depth, with 90 % and 80 % pattern similarity of surface soil layer with 2nd soil layer (7–28 cm) and 3rd soil layer (28–100 cm), respectively. About 80 % of areas with drying soil pattern also showed increasing evapotranspiration and/or decreasing precipitation. Specifically, decreasing P, increasing BSe and VT pattern were detected for 11 % of the soil drying pattern area. Similarly, increasing BSe and VT pattern, only decreasing P and only increasing VT pattern were detected for 17 %, 25 % and 12 % of soil drying areas, respectively. Both decreasing precipitation and increasing evapotranspiration patterns showed about 40 % similarity with decreasing soil moisture patterns. Across different landcover types, broadleaved forests, and cropland areas showed largest drying pattern. Under the future global warming scenario, the global soil water is expected to decrease as evapotranspiration would increase with inconsistent trend of global precipitation change. Our findings are of utmost importance for global soil water resource conservation and management.

Small-scale study of Debris-Flows Interactions with a Lateral Debris Basin and Crossings: The Manival Torrent case study

Small-scale models are useful tools to study the interactions between debris flows and structures and channels. Small-scale modelling of debris flows remains however complicated because of the complex rheology and scaling challenges of these geophysical processes. An on-going study of a debris basin and the downstream channel where two fords and a bridge are located is presented in this extended abstract. The studied torrent is the Manival catchment, located near Grenoble in France. We present the catchment features, the scientific questions studied, some preliminary calibration results describing the mixtures used to model debris flows as well as results from three debris-flood and two debris-flow runs. In essence, the model highlighted that the structure enable a large share of the bedload transport to pass downstream. Debris flows can be more or equally trapped depending on their rheology which controls the surges dynamics and the deposition slope in the debris basin.