Geophysical Research Research Articles

Геолого-геофизические исследования Владимира Марковича Новоселицкого

The article is devoted to the memory of Doctor of Geological and Mineralogical Sciences,Professor, Honored Scientist of the Russian Federation Vladimir Markovich Novoselitsky (01.01.1935 – 29.10.2008). V.M. Novoselitsky is a well-known scientist in Russia and abroad in the field of fundamental and applied geophysics. The directions developed by him are related to complex geological and geophysical research and studies of the earth's subsoil – search and exploration of mineraldeposits, geoecological, geotechnical research, forecasting of natural and man-made emergencies. His works remain defining in the theory and practice of exploration geophysics, mining geophysics and ensuring the safety of the population and national economic objects.

An alternate representation of the geomagnetic core field obtained using machine learning

Machine learning (ML) as a tool is rapidly emerging in various branches of contemporary geophysical research. To date, however, rarely has it been applied specifically for the study of Earth’s internal magnetic field and the geodynamo. Prevailing methods currently used in inferring the characteristic properties and the probable time evolution of the geodynamo are mostly based on reduced representations of magnetohydrodynamics (MHD). This study introduces a new inference method, referred to as Current Loop-based UNet Model Segmentation Inference (CLUMSI). Its long-term goal focuses on uncovering concentrations of electric current densities inside the core as the direct sources of the magnetic field itself, rather than computing the fluid motion using MHD. CLUMSI relies on simplified models in which equivalent current loops represent electric current systems emerging in turbulent geodynamo simulations. Various configurations of such loop models are utilized to produce synthetic magnetic field and secular variation (SV) maps computed at the core–mantle boundary (CMB). The resulting maps are then presented as training samples to an image-processing neural network designed specifically for solving image segmentation problems. This network essentially learns to infer the parameters and configuration of the loops in each model based on the corresponding CMB maps. In addition, with the help of the Domain Adversarial Training of Neural Networks (DANN) method during training, historical geomagnetic field data could also be considered alongside the synthetic samples. This implementation can increase the likelihood that a network trained primarily on synthetic data will appropriately handle real inputs. Our results focus mainly on the method's feasibility when applied to synthetic data and the quality of these inferences. A single evaluation of the trained network can recover the overall distribution of loop parameters with reasonable accuracy. To better represent conditions in the outer core, the study also proposes a computationally feasible process to account for magnetic diffusion and the corresponding induced currents in the loop models. However, the quality of the reconstruction of magnetic field properties is compromised by occasional poor inferences, and an inability to recover realistic SV.Graphical

Thank You to Our 2023 Peer Reviewers

AbstractOn behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2023. The hours reading and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 4,512 submissions in 2023 and 5,112 reviewers contributed to their evaluation by providing 8,587 reviews in total. We deeply appreciate their contributions.

COMPARISON OF PLOT ANALYTICAL METHODS FOR DETERMINING EXCESSIVE WATER PRODUCTION MECHANISMS IN OIL WELLS

Watering of production wells is an important factor leading to a decrease in production profitability and an increase in costs. There are several main mechanisms of excess water inflow. These are a leak in the production casing; a violation of contact between the production casing and the rock; a formation of a bottom water cone; a raising the WOC surface to the perforation interval; a breakthrough through a layer with high permeability. Mechanisms can complement each other, forming a complex integrated system. To identify them, there are three groups of diagnostic methods — geophysical research, hydrodynamic well testing and plot analytical studies. Each of these fundamentally different groups can be supplemented by field research. Specifically in this work, we considered the latter. The analysis is carried out using the example of wells in one of the deposits of an oil field of the Arkhangelsk region. In which the causes of unwanted water production have already been studied by other methods and can be considered known. The studied reservoir is massive, with carbonate hydrophobic rocks and the reserves of the entire field are predominantly concentrated in it (97 %); the oil field (in terms of reserves) is small. There are no injection wells, operation is carried out in a natural elastic water drive mode. In the article, in total, three plot analytical methods are analyzed, which are among the main ones and have different application algorithms. Both the physical principles of their application and their effectiveness in relation to specific oil field are considered. These are the methods of K. Chan; L.I. Merkulova and A.A. Ginzburg; R. Novotny. The first studies the dependence of the water-oil ratio and its derivative on time (WOR and WOR’(t)), is the most widely known and has a large number of modifications (however, here they are not considered in detail). The second is based on the study of the so-called «water-cut characteristics» (representing the dependence of the accumulated oil production vs accumulated liquid production during the water period of operation). It has more restrictions, but is also more comprehensive. The third is based on a comparison of the permeability properties of reservoirs that change during operation.

Improvement of the device’s design for increasing the efficiency of geophysical research using the Earth’s natural pulsed electromagnetic field method

Long-term field studies have shown the high efficiency of the geophysical method of the earth’s natural pulsed electromagnetic field (NPEMFE). It is a modern and experimentally substantiated tool for studying geodynamic processes in the geological environment. Disadvantages of the known device are the low efficiency of recording the intensity level of the NPEMFE, low productivity and high costs of manual labor when performing complex registration. The application of the proposed improvements will make it possible to increase the efficiency of registration of the intensity level of the NPEMFE with an increase in productivity and a decrease in costs and the level of manual labor. The technical result is achieved due to the mobility of the structure and the provision of the possibility of simultaneous registration of the intensity level of the NPEMFE both in the frequency band and in its spatial position.

Fundamental principles and results of deep well lining

The review of the theory and practice of the special technological fluids application is analyzed. On the example of a specific borehole, with an actual vertical depth of 3287 m, intended for opening horizons B-17v, B-17n and project B-21, measures to clarify the filtration and capacity properties of reservoir rocks, increase production volumes are considered of hydrocarbons and accelerating the rate of selection of mining reserves. Testing in the interval 3364 - 3337.6 m of the B-21 horizon by using a set of test tools KVI-95, objectively proved that the specified object is characterized as penetrating, gas-saturated, the activity of which is reduced by contamination of the near-outbreak zone of the seam. As a method of determining clogging, a cut of the working end of the core with a length of 1 mm was applied. According to the results of the interpretation of the materials of the geophysical research of the specified borehole, it was established that the seam fluid comes from the interval 3339 - 3344 m. The paper determined that a promising way to solve the issue of high-quality cementing is the application of composite tamponage systems in combination with advanced preparation methods of borehole shaft.

Challenges in Evaluating Climate Sensitivity from Climate Models

In recognition of the 50th anniversary of Geophysical Research Letters, the editors showcase an exceptional study published in the journal that investigates the climate sensitivity in CMIP6 models.

Thank You to Our 2023 Peer Reviewers

AbstractEditors of the Journal of Geophysical Research—Earth Surface express their appreciation to those who served as peer reviewers for the journal in 2023.

RETRACTION: Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling

RETRACTIOND. Qi, Y. Wu, L. Chen, W.‐J. Cai, Z. Ouyang, Y. Zhang, L. G. Anderson, R. A. Feely, Y. Zhuang, H. Lin, R. Lei, H. Bi. (2022). Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling. Geophysical Research Letters, 49, e2021GL097246. https://doi.org/10.1029/2021GL097246.The above article, published online on 21 February 2022 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the journal Editor‐in‐Chief, Harihar Rajaram; American Geophysical Union; and John Wiley & Sons LLC. The retraction has been agreed as it was discovered that the 2019 pCO2 data collected on the 10th Chinese National Arctic Research Expedition and analyzed along with other data in this paper was used without proper permission. AGU Publications and Wiley evaluated all information submitted by the authors and scientific agencies and carefully considered Committee on Publication Ethics (COPE) guidelines before making this decision. The authors have revised their statistical analyses by excluding the 2019 Chinese National Arctic Research Expedition data and have stated they intend to submit the revised manuscript to the journal. D. Qi acknowledges that the data ownership is disputed, and therefore accepts the retraction. L. Chen and W.‐J. Cai disagree with the retraction. Z. Ouyang, Y. Zhang, L. G. Anderson, R. A. Feely, Y. Zhuang, H. Lin, R. Lei, and H. Bi did not respond to our notice of retraction.

Time and mechanism of formation of mud volcanoes in the South Caspian basin according to seismic data

There are 277 mud volcanoes located in the South Caspian basin and the Apsheron-Gobustan periclinal trough and the Lower Kura depression that open to it. On land there are 177 mud volcanic structures, from which steam, water, mud, gas and oil are constantly erupting at approximately 500 points. Mud volcanoes located in the Caspian Sea (about 100) also play an important role in the degassing (mainly methane) of the sedimentary layer of the earth’s crust. Based on the results of geological and geophysical research, it has been established that almost all mud volcanoes discovered on the territory of Azerbaijan are associated with hydrocarbon deposits. In the Oligocene – Lower Miocene, mainly in the Maikop time, a thick clayey stratum (Maikop) - source rocks – accumulated in the South Caspian depression. At the end of the Miocene, there was a sharp drop in erosion levels in this basin. As a result of the activity of several river systems (Pleo-Volga, Paleo-Kura, Paleo-Pirsagat, Paleo-Amu Darya) over the Maikop clay deposits, a system of alternating layers of low and high density was formed with a total thickness of sediments of eight kilometers or more. The Maikop clay formations buried under this multilayer system, possessing the properties of a non-Newtonian fluid, created intrusions in the overlying environment, which at subsequent stages of development of the sedimentation basin became eruptive channels of mud volcanoes. The results of research using 3D seismic data made it possible to identify the mechanism of formation of mud volcanism, which, according to the authors, is associated with the migration of hydrocarbons from oil and gas source rocks to reservoir rocks, with the channels of mud volcanoes being considered as the main migration routes. Geological interpretation of seismic data shows that the formation of mud volcanoes in the South Caspian basin supposedly began from the beginning of the Miocene and continued in parallel during subsequent periods of development of the sedimentation basin. As the thickness of the sedimentary cover increased, mud volcanoes periodically became active.

Assess the Effectiveness of Multichannel Analysis of Surface Waves Method in Mapping Ancient Structures in Ultrashallow Aquatic Environments: The Case of Agioi Theodoroi, Greece

ABSTRACTThe present geophysical research aims to evaluate the applicability of multichannel analysis of surface waves (MASW) on mapping ultrashallow underwater ancient masonry remnants. The work presents the analysis from a single seismic line using MASW and seismic refraction tomography (SRT) methods and its corresponding electrical resistivity tomography (ERT) section surveyed at the submerged prehistoric site of Agioi Theodoroi area located 10 km eastern of Heraklion, Crete, Greece. The 2D MASW velocity model exhibits significant correspondence with the resistivity structure extracted from the ERT data, showing lateral S‐wave velocity (Vs) variations at the positions where the high resistivity anomalies exist. The analysis of synthetic seismic data calculated from a respective model reproduced a comparable S‐wave velocity pseudo‐section with the real data. However, the investigated targets (submerged buried masonry) appear shallower and wider in MASW sections than in the real world and the corresponding synthetic models, due to insufficient vertical and horizontal resolution of this method. Surface waves travelling through the seafloor sediments (Scholte‐waves) demonstrate very low velocity values. This makes them suitable for the detection of shallow and relatively large (> 0.5 m) underwater manmade structures, providing the enhancement of MASW method resolution, by utilizing a high frequency (> 100 Hz) seismic source, recording short Scholte wavelengths (≤ 1 m) and using shorter (≤ 0.5 m) receiver spacing and array length. Consequently, the results of this work demonstrate the potential in employing conventional seismic techniques in the delineation of underwater antiquities and the revealing of the cultural dynamics in very shallow off‐shore archaeological sites.

Assessment of Near-Surface Geophysical Methods Used to Discover Karst Bauxite Deposits in the Dinarides Using the Example of Posušje Area, Bosnia and Herzegovina

Geophysical exploration of bauxite deposits has been carried out in the area of Posušje in Bosnia and Herzegovina, which were formed on an Upper Cretaceous carbonate substrate, whereas the hanging wall rocks can be Paleogene limestones and sedimentary clastic rocks. Karst terrains are demanding for geophysical exploration due to the relatively complex geological relationships and exceptional near-surface inhomogeneities that generate large noises and challenging conditions for taking field measurements. The fundamental question is whether geophysical research can detect exceptionally irregular karst bauxite deposits with relatively small dimensions. The basic idea is to combine several geophysical methods and a joint interpretation of several data sets to increase the efficiency of geophysical surveying in detecting complex bauxite deposits in karst terrains. Therefore, fundamental near-surface research methods, electrical tomography and seismic refraction are used. In addition, magnetometry was used to examine whether bauxite deposits yield potential magnetic anomalies that could help in detecting them. Research undertaken in the area of Posušje was carried out in the first step on already discovered and known bauxite deposits to determine whether geophysical responses correlate with the occurrence of bauxite deposits and to evaluate the effectiveness of each of the applied surface geophysical methods. Measurements were taken at several locations, and results for two micro-locations, Krstače and Mratnjača, are shown. Geophysical measurements were firstly performed on discovered bauxite deposits in order to reliably determine the possibility of identifying deposits in geophysical inverse models. Bauxite deposits were clearly recognised as characteristic geophysical responses in inversion models using both methods, electrical tomography and seismic refraction. Although the response of bauxite deposits is expressed in both models, resistivity and velocity, it is much more evident in resistivity models. The characteristic resistivity response was confirmed by the discovery of a new deposit. Therefore, the conclusion is that electrical resistivity tomography should be considered a basic method for exploring karst bauxite deposits. Seismic refraction provides a better characterisation of deposits and reduces the interpretation ambiguity. This solution can generally be applied to the problem of researching bauxite deposits in the Dinarides and similar geological models in the Mediterranean. Magnetometric measurements have shown that no magnetic anomalies could be associated with bauxite deposits, and only magnetometry was not successful in discovering bauxite deposits.

Thank You to Our 2023 Reviewers

AbstractThe Editors and Staff of Earth and Space Science thank the reviewers whose selfless work has significantly contributed to the publication process of papers highlighting the best research in geophysics, planetary, and space science in 2023. Peer‐reviewing is a demanding and thankless job. It is however an essential component of the scientific process, requiring the highest standards of integrity and rigor. Reviewers check data and procedures and test reproducibility of methods and results; they share their expertise to verify that the interpretations and conclusions of a paper are consistent with assumptions and existing knowledge. Without this essential work it would not be possible to trust in the scientific process. Publication of papers in a multidisciplinary journal such as Earth and Space Science, that highlights methods, instruments, data and algorithms, relies directly on the expertise of its reviewers to verify and vouch for the quality of the papers that are published. We are indebted to all our reviewers and are delighted to acknowledge them publicly in this Editorial.

The use of non-invasive ERT method to diagnose karst in roadengineering in the Lublin Upland (Poland)

Appropriate design in linear construction depends on many factors, including detailed geological conditions. One of the biggest problems are unrecognized erosion forms, in particular karst ones, which have a huge impact on the design and subsequent operation of roads. For this purpose, in addition to conventional methods such as drilling or geotechnical probing, which are point-based, non-invasive spatial geophysical methods are used. This article presents an example of the use of geoelectrical surveys, Electrical Resistivity Tomography (ERT) for the recognition of karst zones for linear investments. The article describes ERT investigations, which to some extent allows to identify dangerous karst phenomena occurring in the Lublin Upland (Poland), which are of great importance at the design stage of roads and in their further safe operation. Non-invasive geophysical research has been verified and confirmed by traditional geotechnical research, which confirms the effectiveness of their use. The Electrical Resistivity Tomography was used as a method providing a broader spectrum of knowledge on the spatial arrangement of soil layers in the subgrade of the planned road investments. It also enabled a more accurate, more detailed interpretation of geotechnical studies. The described geophysical investigations opens wide possibilities for their application to researchers. In the future, non-invasive methods have a chance to become as reliable as geotechnical methods, but this requires a lot of research to improve the effectiveness and accuracy of the interpretation of the obtained results.

An introduction to the Bowland Shale Formation, UK: processes and resources

Abstract This volume showcases recent geological, geophysical and geochemical research on the Carboniferous Bowland Shale Formation. The Bowland Shale is a relatively thick and extensive Palaeozoic black shale unit with a long history of debate and controversy in the UK. The Bowland Shale is proven in many of the key Carboniferous basins in the Midlands, northern England and North Wales, and represents a significant, near-continuous temporal record spanning 16 Myr including the important mid-Carboniferous boundary (Mississippian–Pennsylvanian). Since the first geological surveys in the late nineteenth century, the Bowland Shale has been of interest for a variety of reasons, including the search for Irish-type Pb–Zn base metal mineral deposits, and as a source rock in conventional hydrocarbon systems. In the mid-2000s, attention turned to the Bowland Shale as a target for unconventional hydrocarbon extraction, shale gas, following success in the USA. This placed the Bowland Shale at the centre of a series of interconnected controversies and debates from the local to national scale. The geological credibility of the purported shale gas resource in the UK was – and continues to be – highly contentious. This volume contributes to a more updated view of the Bowland Shale, covering topics such as sedimentary, geochemical and physical properties and processes, basin-forming events, hydrocarbon prospectivity, mineralization and heat and fluid flow in the subsurface. The volume also includes a field guide to some of the key localities in the UK. With the benefit of hindsight offered by the latest generation of research, the early regional shale gas assessments failed to attach sufficient weight to the compositional heterogeneity, structural complexity, compartmentalization and highly variable exhumation, erosion and palaeo-heat flow history of the Bowland Shale. The following topics are identified as promising avenues for future research beyond shale gas: (1) the role of the Bowland Shale in the context of mineral systems; (2) the role of the Bowland Shale as a cap rock in the Lower Carboniferous limestone geothermal play and potentially as an analogue of CO 2 or radioactive waste storage in the UK; and (3) pathways and mechanisms for weathering, alteration and trace element release from the Bowland Shale into the surface and/or subsurface environment.

Near-Surface Geophysical Characterization of a Marble Deposit to Promote a Sustainable Small-Scale Mining

Small-scale mining (SSM) is responsible for almost all the production of non-metallic minerals in the world and represents around 80% of the mining in Brazil. The lack of direct geological information increases the level of uncertainty associated with the exploratory process, compromises mine planning, limits mineral extraction, and contributes to maximizing environmental issues. In this research, near-surface geophysical methods, including Electrical Resistivity, Capacitive Resistivity, Ground Penetrating Radar (GPR), and Transient Electromagnetic (TEM), were applied to characterize a marble deposit in an SSM located in the Campos do Jordão region, São Paulo state, southeast Brazil. The geophysical methods used provide indirect information about the subsurface geology based on the contrast in electrical and electromagnetic properties. Resistivity results show the efficiency of locating marble deposits, as well as fracture zones. GPR profiles allowed for the investigation of the structural heterogeneities in the subsurface. Geophysical data and lithological information from drill holes were integrated into Micromine software and guided the development of a geological model and a conceptual pit model. The information inferred from the pit modeling allowed us to analyze the potential of the deposit and should be used to assist in developing sustainable mining planning. The results of this work demonstrate that the investment in geophysical research can support the modernization of an SSM and contribute to more sustainable and productive mining.

Comment on “Comparison of the Efficiencies of the Prognostic Generalized Complementary Functions on Evaporation Estimation” by Wang, L., et al., Published in Journal of Geophysical Research: Atmospheres

AbstractSurprising significant underperformance of the polynomial complementary relationship (PCR) of evaporation (Szilagyi et al., 2017, https://doi.org/10.1002/2016jd025611) by Wang et al. (2023, https://doi.org/10.1029/2023jd038683) is caused by the (a) station‐by‐station application of a grid‐based estimation procedure of the Priestley‐Taylor parameter (α) value, and (b) choice of the wind function. Application of the Rome wind function in the Penman equation together with either a well‐chosen single (constant) α or α as a function of the wet‐environment air temperature, should result in much improved evaporation estimates by the PCR in line with previous studies.

Our Vision for JGR: Machine Learning and Computation

AbstractThis editorial introduces the inaugural issue of the Journal of Geophysical Research: Machine Learning and Computation to the scientific community, elucidating the motivations and vision behind its establishment. The landscape of computational tools for geoscientists has undergone a rapid transformation in the last decade, akin to a new scientific revolution challenging the traditional scientific method. The paradigm shift emphasizes the integration of data‐driven methods and the possibility of predicting and/or reproducing the evolution of natural phenomena with computers as the fourth pillar of scientific discovery, sparking debates on trustworthiness, and ethical implications. The data science revolution is fueled by the convergence of advancements, including the big‐data revolution, GPU market expansion, and significant investments in Artificial Intelligence and high performance computing by both institutional and private players. This transformation has given rise to a trans‐disciplinary community that has investigated a wide range of questions under the lens of machine learning (ML) approaches and has generally advanced the field of computational methods within the broader geosciences community, the core of the American Geophysical Union (AGU) membership. Responding to an unmet demand in the existing worldwide editorial offer, the Journal of Geophysical Research: Machine Learning and Computation aims to serve as an intellectual crucible, fostering collaborations across multiple geophysical disciplines and data scientists. The journal welcomes papers with strong methodological developments that allow for geoscience advancements grounded in specific computational and data‐driven methods, leveraging ML as well as innovative computational strategies, and leading to breakthrough discoveries and original scientific outcomes. Authors are encouraged to balance succinctness in introducing methods with a thorough exploration of the novelty of the work proposed and its future applications placing special emphasis on the connection between the data science approach and the scientific outcome, considering a broad readership. Emphasis on result reproducibility aligns with AGU guidance, inviting active participation from the community in shaping geophysical research in the era of machine learning and computation.

PROMISING DEVELOPMENTS AND SCIENTIFIC TECHNOLOGICAL ACHIEVEMENTS IN GEOLOGICAL EXPLORATION IN THE MIDDLE EAST REGION

Technological and economic trends in the development of the oil and gas industry form promising directions for the development of geological research, oil and gas fields development and hydrocarbons production. Currently, in the world oil and gas production practice, there is a tendency to increase the share of involvement in the hard-to-reach and hard-to-recover reserves development, which results in the cost of geological exploration increasing. It is important to minimize these costs by improving existing and developing new technological solutions. Increasing the efficiency and knowledge intensity of new technologies being introduced is the most promising strategy for exploration activities, oil and gas fields development and exploitation.The current conditions for the exit of most foreign companies from the Russian sector of the oil and gas industry, including the search for potential oil locations, require the development or maintenance at the proper level of own innovative and knowledge-intensive solutions that ensure the further systematic development of the geological exploration sector. A potential vector in this direction could be technology transfer from foreign countries, including most of the Middle East and North Africa countries. The innovative activities of up stream in these countries (including in terms of geological exploration) determine the trends in the development of international geological exploration technologies, as well as potential foreign companies for the systematic institutionalization of mutually beneficial relations between Russian and foreign oil businesses.Saudi Arabia, Israel and Iraq companies develop promising innovative solutions for the oil and gas industry exploration sector, including attracting foreign technologies to their market. Saudi Arabian companies are the most active companies with a significant increase in the number of innovative technologies. The main focus of the innovative solutions developed by these companies for the geological exploration sector is: improving methods of laboratory and geophysical research, improving the quality of seismic exploration, as well as introducing mathematical modeling modern trends in geological exploration.

Automating hyperparameter optimization in geophysics with Optuna: A comparative study

AbstractDeep learning has gained attraction amongst geophysicists for solving complex longstanding problems. Nevertheless, proper hyperparameter optimization methodologies remain critically underexplored in geophysical deep learning research. This paper attempts to first highlight the importance of hyperparameter optimization and then showcase two geophysics‐related deep learning examples where a grid search and Optuna framework (an automated optimization approach) were used for hyperparameter optimization. We consider two geophysical problems related to denoising seismic traces and the inversion of seismic traces for velocity information. In both cases, models created based on Optuna hyperparameter optimization were able to perform better than those created through grid search. The most significant advantage of Optuna, however, is having quantifiable results to justify the choice of a neural network architecture, depth and other hyperparameters rather than relying on inefficient methods of exploring the hyperparameter space such as a trial‐and‐error or grid search. This study aims to stimulate further exploration and adoption of these frameworks, pushing the boundaries of current deep learning based geophysical problem‐solving methodologies towards full automation.