Recent advances in acquisition design and fibre composition have led to an increasing number of fibre-optic sensing applications for both distributed and point sensor systems. In Earth sciences, these fibre-optic technologies are used to sample strain, temperature or chemicals in a great variety of environments such as boreholes, deep seas, at the surface and also in densely populated areas. In recent years, we have observed an explosion of pilot experiments leading to new applications and technological breakthroughs in many fields of Earth sciences.

The aim of this special issue is to gather and highlight different techniques, methods and applications these fibre-optic technologies offer to Earth sciences and to provide a broad perspective on recent and further developments (technical, numerical and methodological) in these new research fields. Contributions from all areas of applied geosciences (geochemistry, geophysics, geodesy, natural hazards, oceanography, soil science, geo-energy, civil and environmental engineering, volcanology, hydrology, glaciology, and many others) using fibre-optical cable sensing are welcome. We encourage including qualitative and quantitative case studies, embracing laboratory studies, large-scale field tests and modelling.

This special issue looks at inversion tectonics 3 decades after a late 1980s peak in interest that is documented, for instance, by a 1987 Tectonophysics special issue and a 1989 Geol. Soc. London book that soon became classics. Today inversion tectonics is well established as a basic concept, but by far not all aspects of it are well understood. Even the enormous variety of associated structures has probably not been exhaustively described and explained. The kinematics of inversion structures is particularly complex, and their mechanics a matter of debate. The special issue is meant to illustrate the advances made over the past 30 years but also to point out open questions. It has its roots in a session on inversion tectonics at the 2019 EGU General Assembly. Announced contributions already cover many aspects including the importance of inversion concepts in petroleum exploration, the role of plate-wide stress changes and plate rigidity, improved kinematic and timing constraints for well-studied examples, inversion interfering with regional uplift, and inversion of salt-bearing basins. Case studies, often based on high-resolution seismic data, cover diverse areas from Australia to Scandinavia and inversion events from the Paleoproterozoic to the Paleogene. We invite additional contributions dealing with all aspects of inversion tectonics from architecture over kinematics to dynamics and from field- or seismics-based case studies to analogue and numerical simulations, also including responses of depositional systems to active inversion tectonics. The focus will be on "positive inversion", i.e. a change from normal faulting to thrusting or transpression. However, papers on other cases of fault reactivation would also fit our envisaged frame. We particularly welcome new hypotheses challenging common wisdom!

The special issue welcomes studies in all aspects of bedforms, these being their formation and evolution, the associated sedimentary structures, or relations to parent flow dynamics. This issue spans the dynamic processes from the grain scale to the largest organizational patterns across temporal scales. We would like to embrace the variety of approaches that apply to sediment bedforms, including the following.

1. Field quantification of natural flows and bedforms in different environments
2. Description and interpretation of ancient sedimentary structures
3. Numerical/analogue experiments, models and predictions
4. Reviews of specific aspects.

Questions related to morphodynamics, feedback mechanisms and quantitative interpretations related to bedforms are especially encouraged. Depending on the article collection, sections will be organized into terms of depositional environments, namely marine, fluvial, aeolian, pyroclastic and extra-terrestrial.

The special issue is dedicated to state-of-the art research on the Alps and the adjacent orogens. It will improve our understanding of mountain-building processes and the past and ongoing tectonic evolution in the region. This multi- and interdisciplinary effort integrates geophysics, tectonics, petrology, geochronology, and basin and surface studies. The contributions highlight recent efforts to image deep structures, track motion and deformation of the crust and mantle through time, and investigate the surface response to deep-seated processes. Thus, the volume will highlight recent results from the European AlpArray project, which has featured an unprecedentedly dense seismic station network in the Alpine region. We invite researchers from inside and outside the AlpArray project and from all fields to contribute to this volume.

In the last months, there has been a storm both in traditional and social media about the observation that the Covid-19 lockdown measures cause an unprecedented seismic urban “silence”, which is observed globally on many urban seismic stations. It is the first time that such a protracted noise reduction has been observed on a global scale at the same time. To gather all seismological analyses that arise from this unique period, we are organising a Solid Earth special issue on the effects of the Covid-19 lockdown measures on global seismic noise. Any papers fitting the following thematics/topics are welcomed:

• key elements of anthropogenic ambient noise data processing
• anthropogenic noise source characterisation and detection
• influence of sensor types, self-noise, etc., on anthropogenic ambient seismic noise
• improvement of network performance and seismicity studies
• improved magnitude completeness
• “new” event detections during lockdown periods
• improved volcano monitoring
• noise reduction comparison with other observables
• mobility data
• other environmental physical data, like “audible noise”
• new ideas of comparison
• advantages of lockdown “silence” on felt earthquake report data.

Do not hesitate to contact the special issue editors prior to submission to discuss the eligibility of your ideas.

This issue is derived from the EGU Sharing Geosciences Online 2020’s session ERE5.4, entitled “State-of-the-art in mineral exploration”. The rationale behind this proposal is to bring together a number of articles aimed at exploring the current state and future prospects of mineral exploration, from different perspectives (e.g. remote sensing, geochemistry, geology, geophysics, modelling, mineralogy, structural geology).

Mineral resources are used in larger quantities than ever before in history, and are the basis of our modern society. The safe and sustainable supply of mineral resources is fostering a demand for innovative actions to cover the foreseeable future industry and human demands. Exploration is the first step in the mineral resources cycle. On the one hand, most of the giant deposits at shallow depths have been already explored and mined out and the industry is moving towards deeper and more complex mineral systems, which brings significant exploration challenges. On the other hand, the exploration sector needs time-saving, cost-effective, and, particularly in Europe, environmentally friendly and socially acceptable techniques to ensure sustainable access to mineral resources.

This special issue aims to bring together a meaningful collection of articles that will shape the mineral exploration for the 21st century. Articles can include, but are not limited to, the following topics: new methods of exploration; imaging; conceptual modelling and quantification of deposits and mineral systems; cost reduction in exploration; non-invasive exploration; environmentally sustainable exploration; integration of multidisciplinary methodologies and datasets; scale-up and replicability; industry–academia synergies; and FAIR data repositories.

The orogenic processes leading to the construction of major mountain chains are of great importance for the resulting features of the crust. Accurate knowledge of these traits is significant for the human life in different ways as it will help improve the green exploitation of natural resources, minimize the damage of natural hazards, back the sustainability of urban development (including the water cycle management), and support the building of communication links.

The Variscan Belt, including the related American orogens, is one of the best known orogenic chains in the world, mainly due to its location in countries with a long research history. However, fresh data are continuously becoming available and the geotectonic models are unceasingly being refined. In the westernmost segment of the Variscan Belt in Europe (the Iberian Massif), new research outcomes are resulting in interesting proposals for the structure of this part of the chain and allowing the proposal of improved genetic models for the complete Variscan orogen.

It is becoming increasingly apparent that the majority of rifts contain a component of obliquity. As such, a spectrum of obliquity can be recognised from orthogonal rifts through to pure strike-slip tectonics. At one end of the spectrum, continental strike-slip and deep oceanic transform faults form major active plate boundaries and are intrinsic features of plate tectonics. Both types of faults are still poorly known in terms of structure, rheology and deformation. Recent works have shown that fracture zones, supposedly inactive features, can be reactivated and be the site of large earthquakes and deformation. The tectonic and magmatic response of large offset transform faults, particularly, is still largely unknown. The cause of rift obliquity and transform tectonics has been attributed to a range of driving mechanisms, including: oblique crustal and mantle inheritance, a reduced force required for plastic yielding, changes in far-field forces, asthenospheric dynamics, and grain size changes in the lower crust and mantle. The effects of obliquity on rift and transform evolution are extensive, often leading to unique structural settings dominated by transtensional and transpressional processes. The spatio-temporal overlap of distinctive rifting events (governed by transtensional, transpressional or orthogonal kinematics) can result in strongly segmented 3D rift architectures that may influence subsequent reactivation. Rift obliquity and transforms have been linked to a diverse array of phenomena including rift and breakup-related magmatism, subduction initiation, supercontinent dispersal, microcontinent cleaving, structural inheritance, relative plate motion, hydrocarbon systems, geothermal energy potential, lithosphere–hydrosphere interaction, and hazardous seismic activity.

In this special issue we welcome papers that explore the formation, the evolution, the physical properties, the extinction and the reactivation of orthogonal, oblique and transform extensional systems and large deep oceanic transform–fracture systems. We seek contributions that address these topics from all geoscience disciplines using both geological and geophysical data, numerical and analogue modelling, and/or direct rock studies from different settings and natural examples, at all scales. Special emphasis will be given to multidisciplinary studies.

As urban populations grow, destructive natural earthquakes pose an increasing threat in tectonically active regions. At the same time, seismicity caused by geo-resource extraction, geological storage and other subsurface activities is becoming increasingly widespread. The need to improve our understanding of faulting and seismogenesis is therefore reaching new levels of urgency. Yet these phenomena involve some of the most complex and highly coupled thermo–hydro–mechanical–chemical (THMC) processes imaginable. The initiation, propagation and cessation of slip instabilities on faults, for example, embody damage accumulation, frictional deformation, heat production, pore fluid pressurization, phase changes, chemical reactions, creep and reactive fluid flow at multiple temporal and spatial scales. Advances that contribute to earthquake hazard assessment and mitigation depend on integrating different research fields and disciplines to address such processes and their coupling.

This special issue aims to collect studies that consider THMC processes in earthquake and faulting mechanics building on insights from laboratory and computational experiments and from induced and natural seismicity.

The special issue arises out of an international workshop on “Tools, data and models for 3D seismotectonics: the Italian laboratory over time” that was held in Perugia on 9–10 July 2019. The workshop was organized by the Inter-University CENTRE for 3D Seismotectonics (CRUST, Italy) to commemorate Professor Giampaolo Pialli, who died suddenly 20 years ago, at the age of 59. Giampaolo was an open-minded and inclusive researcher of the University of Perugia, especially keen on the use of multidisciplinary and multi-scale approaches in active and sustained geological processes of deformation. The main aim of the workshop was to promote new research and interdisciplinary collaborations among structural geologists and geophysicists who operate in the field of seismotectonics, at local and regional scales, with the common goal to reach a deep understanding of earthquake–fault interactions and to build realistic 3-D structural–seismotectonic fault models for better evaluation of seismic hazards with consequent seismic risk reduction.

This special issue has the purpose of collecting high-quality papers presented at the workshop but is not restricted to these. The main goal is to put together a reference volume that contains the most innovative and as complete as possible knowledge on Italian seismotectonics and seismogenesis, analysed at various spatial and temporal scales and taken as a methodological example for multidisciplinary and interdisciplinary studies in other areas of high seismic hazard.

The main topics of interest include

• observational seismology for seismotectonics and earthquake mechanics;
• active tectonics and surface faulting;
• geophysical data and modelling for seismotectonics;
• 3-D geometric–kinematic and dynamic active and evolutionary fault models.

The last 50 years have enabled significant progress in our ability to describe and model both the oceanic and atmospheric environments of the Indian Ocean and their interactions with the sea floor and coastal regimes. However, our understanding of the major processes of the Indian Ocean is still far from complete and is rudimentary in many respects. This SI compiles various synthesis articles about the recent results of the 2nd International Indian Ocean Expedition Program (IIOE-2: https://iioe-2.incois.gov.in/). The synthesis articles will review and highlight results of physical, biogeochemical, ecological, geological, coastal and atmospheric studies from all parts of the Indian Ocean. Moreover, the SI will serve to illustrate some of the key questions that are relevant for future research on the grand challenges in the Indian Ocean system.

Volcanology has made great advances in the last 3 decades, becoming a modern interdisciplinary science that has learned how to quantify volcanic processes, their associated hazards and resources, as well as the impact of volcanic activity on society and the environment. Numerical models are developed in order to better understand volcanic processes and aid in hazard prediction. At the same time, an accurate forecasting of future volcanic events requires detailed understanding of past trends. Because models can describe only a simplified version of complex natural processes, geologic and field data are critical for constraining model input, necessary for model validation, and will ultimately improve model accuracy. The aim of this special issue is to present studies in which traditional field-based methods are conceived and used for constraining, improving, and validating numerical models describing volcanic processes. We collect contributions describing field data and the role of volcano geology in model validation for a wide range of volcanic phenomena, including tephra fall, pyroclastic density currents, and lava flows. The contributions listed below arise out of both an IAVCEI COV10 session in 2018 and an open call for contributions. The volume is under aegis of IAVCEI Volcano Geology commission.

This issue is derived from the EGU Sharing Geosciences Online 2020’s session ERE5.4, entitled “State-of-the-art in mineral exploration”. The rationale behind this proposal is to bring together a number of articles aimed at exploring the current state and future prospects of mineral exploration, from different perspectives (e.g. remote sensing, geochemistry, geology, geophysics, modelling, mineralogy, structural geology).

Mineral resources are used in larger quantities than ever before in history, and are the basis of our modern society. The safe and sustainable supply of mineral resources is fostering a demand for innovative actions to cover the foreseeable future industry and human demands. Exploration is the first step in the mineral resources cycle. On the one hand, most of the giant deposits at shallow depths have been already explored and mined out and the industry is moving towards deeper and more complex mineral systems, which brings significant exploration challenges. On the other hand, the exploration sector needs time-saving, cost-effective, and, particularly in Europe, environmentally friendly and socially acceptable techniques to ensure sustainable access to mineral resources.

This special issue aims to bring together a meaningful collection of articles that will shape the mineral exploration for the 21st century. Articles can include, but are not limited to, the following topics: new methods of exploration; imaging; conceptual modelling and quantification of deposits and mineral systems; cost reduction in exploration; non-invasive exploration; environmentally sustainable exploration; integration of multidisciplinary methodologies and datasets; scale-up and replicability; industry–academia synergies; and FAIR data repositories.

In the last months, there has been a storm both in traditional and social media about the observation that the Covid-19 lockdown measures cause an unprecedented seismic urban “silence”, which is observed globally on many urban seismic stations. It is the first time that such a protracted noise reduction has been observed on a global scale at the same time. To gather all seismological analyses that arise from this unique period, we are organising a Solid Earth special issue on the effects of the Covid-19 lockdown measures on global seismic noise. Any papers fitting the following thematics/topics are welcomed:

• key elements of anthropogenic ambient noise data processing
• anthropogenic noise source characterisation and detection
• influence of sensor types, self-noise, etc., on anthropogenic ambient seismic noise
• improvement of network performance and seismicity studies
• improved magnitude completeness
• “new” event detections during lockdown periods
• improved volcano monitoring
• noise reduction comparison with other observables
• mobility data
• other environmental physical data, like “audible noise”
• new ideas of comparison
• advantages of lockdown “silence” on felt earthquake report data.

Do not hesitate to contact the special issue editors prior to submission to discuss the eligibility of your ideas.

It is becoming increasingly apparent that the majority of rifts contain a component of obliquity. As such, a spectrum of obliquity can be recognised from orthogonal rifts through to pure strike-slip tectonics. At one end of the spectrum, continental strike-slip and deep oceanic transform faults form major active plate boundaries and are intrinsic features of plate tectonics. Both types of faults are still poorly known in terms of structure, rheology and deformation. Recent works have shown that fracture zones, supposedly inactive features, can be reactivated and be the site of large earthquakes and deformation. The tectonic and magmatic response of large offset transform faults, particularly, is still largely unknown. The cause of rift obliquity and transform tectonics has been attributed to a range of driving mechanisms, including: oblique crustal and mantle inheritance, a reduced force required for plastic yielding, changes in far-field forces, asthenospheric dynamics, and grain size changes in the lower crust and mantle. The effects of obliquity on rift and transform evolution are extensive, often leading to unique structural settings dominated by transtensional and transpressional processes. The spatio-temporal overlap of distinctive rifting events (governed by transtensional, transpressional or orthogonal kinematics) can result in strongly segmented 3D rift architectures that may influence subsequent reactivation. Rift obliquity and transforms have been linked to a diverse array of phenomena including rift and breakup-related magmatism, subduction initiation, supercontinent dispersal, microcontinent cleaving, structural inheritance, relative plate motion, hydrocarbon systems, geothermal energy potential, lithosphere–hydrosphere interaction, and hazardous seismic activity.

In this special issue we welcome papers that explore the formation, the evolution, the physical properties, the extinction and the reactivation of orthogonal, oblique and transform extensional systems and large deep oceanic transform–fracture systems. We seek contributions that address these topics from all geoscience disciplines using both geological and geophysical data, numerical and analogue modelling, and/or direct rock studies from different settings and natural examples, at all scales. Special emphasis will be given to multidisciplinary studies.

The special issue welcomes studies in all aspects of bedforms, these being their formation and evolution, the associated sedimentary structures, or relations to parent flow dynamics. This issue spans the dynamic processes from the grain scale to the largest organizational patterns across temporal scales. We would like to embrace the variety of approaches that apply to sediment bedforms, including the following.

1. Field quantification of natural flows and bedforms in different environments
2. Description and interpretation of ancient sedimentary structures
3. Numerical/analogue experiments, models and predictions
4. Reviews of specific aspects.

Questions related to morphodynamics, feedback mechanisms and quantitative interpretations related to bedforms are especially encouraged. Depending on the article collection, sections will be organized into terms of depositional environments, namely marine, fluvial, aeolian, pyroclastic and extra-terrestrial.

The special issue is dedicated to state-of-the art research on the Alps and the adjacent orogens. It will improve our understanding of mountain-building processes and the past and ongoing tectonic evolution in the region. This multi- and interdisciplinary effort integrates geophysics, tectonics, petrology, geochronology, and basin and surface studies. The contributions highlight recent efforts to image deep structures, track motion and deformation of the crust and mantle through time, and investigate the surface response to deep-seated processes. Thus, the volume will highlight recent results from the European AlpArray project, which has featured an unprecedentedly dense seismic station network in the Alpine region. We invite researchers from inside and outside the AlpArray project and from all fields to contribute to this volume.

Recent advances in acquisition design and fibre composition have led to an increasing number of fibre-optic sensing applications for both distributed and point sensor systems. In Earth sciences, these fibre-optic technologies are used to sample strain, temperature or chemicals in a great variety of environments such as boreholes, deep seas, at the surface and also in densely populated areas. In recent years, we have observed an explosion of pilot experiments leading to new applications and technological breakthroughs in many fields of Earth sciences.

The aim of this special issue is to gather and highlight different techniques, methods and applications these fibre-optic technologies offer to Earth sciences and to provide a broad perspective on recent and further developments (technical, numerical and methodological) in these new research fields. Contributions from all areas of applied geosciences (geochemistry, geophysics, geodesy, natural hazards, oceanography, soil science, geo-energy, civil and environmental engineering, volcanology, hydrology, glaciology, and many others) using fibre-optical cable sensing are welcome. We encourage including qualitative and quantitative case studies, embracing laboratory studies, large-scale field tests and modelling.

Volcanology has made great advances in the last 3 decades, becoming a modern interdisciplinary science that has learned how to quantify volcanic processes, their associated hazards and resources, as well as the impact of volcanic activity on society and the environment. Numerical models are developed in order to better understand volcanic processes and aid in hazard prediction. At the same time, an accurate forecasting of future volcanic events requires detailed understanding of past trends. Because models can describe only a simplified version of complex natural processes, geologic and field data are critical for constraining model input, necessary for model validation, and will ultimately improve model accuracy. The aim of this special issue is to present studies in which traditional field-based methods are conceived and used for constraining, improving, and validating numerical models describing volcanic processes. We collect contributions describing field data and the role of volcano geology in model validation for a wide range of volcanic phenomena, including tephra fall, pyroclastic density currents, and lava flows. The contributions listed below arise out of both an IAVCEI COV10 session in 2018 and an open call for contributions. The volume is under aegis of IAVCEI Volcano Geology commission.

The special issue arises out of an international workshop on “Tools, data and models for 3D seismotectonics: the Italian laboratory over time” that was held in Perugia on 9–10 July 2019. The workshop was organized by the Inter-University CENTRE for 3D Seismotectonics (CRUST, Italy) to commemorate Professor Giampaolo Pialli, who died suddenly 20 years ago, at the age of 59. Giampaolo was an open-minded and inclusive researcher of the University of Perugia, especially keen on the use of multidisciplinary and multi-scale approaches in active and sustained geological processes of deformation. The main aim of the workshop was to promote new research and interdisciplinary collaborations among structural geologists and geophysicists who operate in the field of seismotectonics, at local and regional scales, with the common goal to reach a deep understanding of earthquake–fault interactions and to build realistic 3-D structural–seismotectonic fault models for better evaluation of seismic hazards with consequent seismic risk reduction.

This special issue has the purpose of collecting high-quality papers presented at the workshop but is not restricted to these. The main goal is to put together a reference volume that contains the most innovative and as complete as possible knowledge on Italian seismotectonics and seismogenesis, analysed at various spatial and temporal scales and taken as a methodological example for multidisciplinary and interdisciplinary studies in other areas of high seismic hazard.

The main topics of interest include

• observational seismology for seismotectonics and earthquake mechanics;
• active tectonics and surface faulting;
• geophysical data and modelling for seismotectonics;
• 3-D geometric–kinematic and dynamic active and evolutionary fault models.

As urban populations grow, destructive natural earthquakes pose an increasing threat in tectonically active regions. At the same time, seismicity caused by geo-resource extraction, geological storage and other subsurface activities is becoming increasingly widespread. The need to improve our understanding of faulting and seismogenesis is therefore reaching new levels of urgency. Yet these phenomena involve some of the most complex and highly coupled thermo–hydro–mechanical–chemical (THMC) processes imaginable. The initiation, propagation and cessation of slip instabilities on faults, for example, embody damage accumulation, frictional deformation, heat production, pore fluid pressurization, phase changes, chemical reactions, creep and reactive fluid flow at multiple temporal and spatial scales. Advances that contribute to earthquake hazard assessment and mitigation depend on integrating different research fields and disciplines to address such processes and their coupling.

This special issue aims to collect studies that consider THMC processes in earthquake and faulting mechanics building on insights from laboratory and computational experiments and from induced and natural seismicity.

The orogenic processes leading to the construction of major mountain chains are of great importance for the resulting features of the crust. Accurate knowledge of these traits is significant for the human life in different ways as it will help improve the green exploitation of natural resources, minimize the damage of natural hazards, back the sustainability of urban development (including the water cycle management), and support the building of communication links.

The Variscan Belt, including the related American orogens, is one of the best known orogenic chains in the world, mainly due to its location in countries with a long research history. However, fresh data are continuously becoming available and the geotectonic models are unceasingly being refined. In the westernmost segment of the Variscan Belt in Europe (the Iberian Massif), new research outcomes are resulting in interesting proposals for the structure of this part of the chain and allowing the proposal of improved genetic models for the complete Variscan orogen.

This special issue looks at inversion tectonics 3 decades after a late 1980s peak in interest that is documented, for instance, by a 1987 Tectonophysics special issue and a 1989 Geol. Soc. London book that soon became classics. Today inversion tectonics is well established as a basic concept, but by far not all aspects of it are well understood. Even the enormous variety of associated structures has probably not been exhaustively described and explained. The kinematics of inversion structures is particularly complex, and their mechanics a matter of debate. The special issue is meant to illustrate the advances made over the past 30 years but also to point out open questions. It has its roots in a session on inversion tectonics at the 2019 EGU General Assembly. Announced contributions already cover many aspects including the importance of inversion concepts in petroleum exploration, the role of plate-wide stress changes and plate rigidity, improved kinematic and timing constraints for well-studied examples, inversion interfering with regional uplift, and inversion of salt-bearing basins. Case studies, often based on high-resolution seismic data, cover diverse areas from Australia to Scandinavia and inversion events from the Paleoproterozoic to the Paleogene. We invite additional contributions dealing with all aspects of inversion tectonics from architecture over kinematics to dynamics and from field- or seismics-based case studies to analogue and numerical simulations, also including responses of depositional systems to active inversion tectonics. The focus will be on "positive inversion", i.e. a change from normal faulting to thrusting or transpression. However, papers on other cases of fault reactivation would also fit our envisaged frame. We particularly welcome new hypotheses challenging common wisdom!

The last 50 years have enabled significant progress in our ability to describe and model both the oceanic and atmospheric environments of the Indian Ocean and their interactions with the sea floor and coastal regimes. However, our understanding of the major processes of the Indian Ocean is still far from complete and is rudimentary in many respects. This SI compiles various synthesis articles about the recent results of the 2nd International Indian Ocean Expedition Program (IIOE-2: https://iioe-2.incois.gov.in/). The synthesis articles will review and highlight results of physical, biogeochemical, ecological, geological, coastal and atmospheric studies from all parts of the Indian Ocean. Moreover, the SI will serve to illustrate some of the key questions that are relevant for future research on the grand challenges in the Indian Ocean system.