ALBERT

Description: Strike-slip faults are classically associated with pull-apart basins where continental crust is thinned between two laterally offset fault segments. We propose a subsidence mechanism to explain the formation of a new type of basin where no substantial segment offset or syn-strike-slip thinning is observed. Such “flexural strike-slip basins” form due to a sediment load creating accommodation space by bending the lithosphere. We use a two-way coupling between the geodynamic code ASPECT and surface-processes code FastScape to show that flexural strike-slip basins emerge if sediment is deposited on thin lithosphere close to a strike-slip fault. These conditions were met at the Andaman Basin Central fault (Andaman Sea, Indian Ocean), where seismic reflection data provide evidence of a laterally extensive flexural basin with a depocenter located parallel to the strike-slip fault trace.

Description: Carbonatites host some unique ore deposits, especially REE, and fractional crystallization might be a potentially powerful mechanism for control enrichment of carbonatitic magmas by these metals to economically significant levels. At present, data on distribution coefficients of REE during fractional crystallization of carbonatitic melts at volcanic conditions are extremely scarce. Here we present an experimental study of REE partitioning between carbonatitic melts and calcite in the system CaCO3-Na2CO3 with varying amounts of P2O5, F, Cl, SiO2, SO3 at 650–900 °C and 100 MPa using cold-seal pressure vessels and LA-ICP-MS. The presence of phosphorus in the system generally increases the distribution coefficients but its effect decreases with increasing concentration. The temperature factor is high: at 770–900 °C DREE ≥ 1, while at lower temperatures DREE become below unity. Silicon also promotes the fractionation of REE into calcite, while sulfur contributes to retention of REE in the melt. Our results imply that calcite may impose significant control upon REE fractionation at the early stages of crystallization of carbonatitic magmas and might be a closest proxy for monitoring the REE content in initial melt.

Description: Deep hydrothermal Mo, W and base metal mineralization found in the Detroit City portal of the Sweet Home mine in the Alma district (Colorado Mineral Belt) was deposited in response to magmatic activity and the formation of Climax-type Mo deposits during the Oligocene. This study presents extensive geochemical analyses of fluid inclusions inminerals from early greisen-like vein mineralization to better understand the fluid system responsible for ore formation. Quartz and fluorite, which are associated with molybdenite, huebnerite and/or pyrite mineralization, precipitated from low- to medium-salinity (1.5-11.5 wt.% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415°C and probably under a fluctuating pressure regime at depths of at least 3.5 km. The formation of greisen-like and base metal mineralization at the Detroit City portal of the Sweet Home mine is related to fluids of different origin. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases) and mixed with significant amounts of heated meteoric water. Fluid mixing of magmatic fluids with meteoric water is constrained by δ 2H-δ 18O relationships of fluid inclusion water in different minerals (Fig. 1). Whether molybdenum was derived from magmatic fluids remains unclear. Fluid inclusions in huebnerite suggest that W originated from source rocks that are enriched in organic matter rather than from magmatic fluids. The deep hydrothermal mineralization at the Detroit City portal of the Sweet Home mine shows features similar to deep hydrothermal vein mineralization found in Climax-type Mo deposits and their periphery, suggesting that fluid migration and the deposition of ore and gangue minerals in the Sweet Home mine was triggered by a deep-seated magmatic intrusion. The findings of this study are in good agreement with the results of previous fluid inclusion studies of the mineralization of the Sweet Home mine (Lüders et al., 2009) and from Climaxtype Mo porphyry deposits in the Colorado Mineral Belt (Hall et al., 1974).

Description: The birth and expansion of continental plateaus exert a strong control on our planet's climate and the distribution and evolution of its biodiversity. It has been proposed that the Tibetan Plateau has been steadily growing by southward expansion. Here we demonstrate that the shape of the southeastern margin of the plateau has remained unchanged for the last 10 Myr despite vast amounts of exhumation. Our finding is based on a new, high-resolution thermochronological dataset from the deep gorges of the Salween and Mekong rivers, which we interpret using a physics-based model combined with an optimization method. We show that our scenario also agrees with a wide range of other, independent geological and geophysical data. This finding demonstrates that plateau margins can reach large-scale topographic steady-state between outward growth and surface erosion, which has important implications for our understanding of the evolution of Earth's climate and biodiversity in the recent geological past.

Description: Sulfidated nanoscale zerovalent iron (S-nZVI) exhibits low anoxic oxidation and high reactivity towards many chlorinated hydrocarbons (CHCs). However, nothing is known about S-nZVI reactivity once exposed to complex CHC mixtures, a common feature of CHC plumes in the environment. Here, three S-nZVI materials with varying iron sulfide (mackinawite, FeSm) shell thickness and crystallinity were exposed to groundwater containing a complex mixture of chlorinated ethenes, ethanes, and methanes. CHC removal trends yielded pseudo-first order rate constants (kobs) that decreased in the order: trichloroethene 〉 trans-dicloroethene 〉 1,1-dichlorethene 〉 trichloromethane 〉 tetrachloroethene 〉 cis-dichloroethene 〉 1,1,2-trichloroethane, for all S-nZVI materials. These kobs trends showed no correlation with CHC reduction potentials based on their lowest unoccupied molecular orbital energies (ELUMO) but absolute values were affected by the FeSm shell thickness and crystallinity. In comparison, nZVI reacted with the same CHCs groundwater, yielded kobs that linearly correlated with CHC ELUMO values (R2 = 0.94) and that were lower than S-nZVI kobs. The CHC selectivity induced by sulfidation treatment is explained by FeSm surface sites having specific binding affinities towards some CHCs, while others require access to the metallic iron core. These new insights help advance S-nZVI synthesis strategies to fit specific CHC treatment scenarios.

Description: By means of 4 years of Challenging Minisatellite Payload (CHAMP) zonal wind observations and a Thermosphere-Ionosphere Electrodynamics General Circulation Model simulation, longitudinal and seasonal variations of thermospheric superrotation at magnetic equator are investigated first. The superrotation shows four- and three-peaked longitudinal patterns in March and September equinoxes, and a two-peaked variation during solstices. The superrotation is stronger in December than in June solstice, and stronger in March than in September equinox. The mean correlation between the zonal variation of superrotation and nighttime eastward wind is about 0.8, while it is 0.6 with daytime westward zonal wind. The interaction between the neutral wind and geomagnetic field plays a more important role in the superrotation, rather than the F-region electron density. The lower atmospheric tides tend to suppress the superrotation, but contribute to the longitudinal patterns of the superrotation. The viscous force is also important for the longitudinal modulation of the superrotation.

Description: We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.

Description: The LArge-scale Reservoir Simulator (LARS) has been previously developed to study hydrate dissociation in hydrate-bearing systems under in-situ conditions. In the present study, a numerical framework of equations of state describing hydrate formation at equilibrium conditions has been elaborated and integrated with a numerical flow and transport simulator to investigate a multi-stage hydrate formation experiment undertaken in LARS. A verification of the implemented modeling framework has been carried out by benchmarking it against another established numerical code. Three-dimensional (3D) model calibration has been performed based on laboratory data available from temperature sensors, fluid sampling, and electrical resistivity tomography. The simulation results demonstrate that temperature profiles, spatial hydrate distribution, and bulk hydrate saturation are consistent with the observations. Furthermore, our numerical framework can be applied to calibrate geophysical measurements, optimize post-processing workflows for monitoring data, improve the design of hydrate formation experiments, and investigate the temporal evolution of sub-permafrost methane hydrate reservoirs.

Description: Tropical forests store 40–50 per cent of terrestrial vegetation carbon1. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests2. Owing to climatic and soil changes with increasing elevation3, AGC stocks are lower in tropical montane forests compared with lowland forests2. Here we assemble and analyse a dataset of structurally intact old-growth forests (AfriMont) spanning 44 montane sites in 12 African countries. We find that montane sites in the AfriMont plot network have a mean AGC stock of 149.4 megagrams of carbon per hectare (95% confidence interval 137.1–164.2), which is comparable to lowland forests in the African Tropical Rainforest Observation Network4 and about 70 per cent and 32 per cent higher than averages from plot networks in montane2,5,6 and lowland7 forests in the Neotropics, respectively. Notably, our results are two-thirds higher than the Intergovernmental Panel on Climate Change default values for these forests in Africa8. We find that the low stem density and high abundance of large trees of African lowland forests4 is mirrored in the montane forests sampled. This carbon store is endangered: we estimate that 0.8 million hectares of old-growth African montane forest have been lost since 2000. We provide country-specific montane forest AGC stock estimates modelled from our plot network to help to guide forest conservation and reforestation interventions. Our findings highlight the need for conserving these biodiverse9,10 and carbon-rich ecosystems.

Description: The Huanghe once had a sediment flux of 〉1,000 Mt/yr, but this has decreased by ∼90% as its river sediment routing systems have undergone dramatic changes influenced by human activities such as dam construction. However, the way in which the sediment geochemistry of the river has responded to the altered sediment routing processes is not well known. This study investigates the sediment source-to-sink routing regime of the Huanghe River using Nd isotope fingerprinting. Four major source terranes, namely the Songpan-Ganzi (SG) Block, Ordos Desert (OD), Chinese Loess Plateau (CLP) and North China Craton (NCC) are recognized according to their distinct Nd isotopes. The gradual downstream decrease in εNd values in sediments of the upper Huanghe indicates a decreasing contribution of material from the SG Block and a corresponding increase contribution of local underlying basement rocks, which is inferred to be related to sediment capture by a cascade of hydroelectric dams. A gradual increase in εNd from Yinchuan to Tongguan suggests an increasing contribution from the CLP under intense erosion. Relatively low εNd in the downstream sediments suggest a contribution from proximal NCC basement, consistent with the shift from deposition to erosion in the lower channel in recent years. The marked heterogeneity in Nd isotopes in the Huanghe sediments corresponds well to sediment source-to-sink processes in response to increasing human impacts. In a setting of global rivers facing strong anthropogenic impacts, the ways in which altered sediment routing systems affect river sediment geochemistry deserve more research attention.

Description: In this study, the effect of disturbance dynamo electric field (DDEF) induced by subauroral polarization streams (SAPS) on the variations of the equatorial electrojet (EEJ) and its counter electrojet (CEJ) during the geomagnetic storm on June 1, 2013 is analyzed in detail for the first time. Observations from ground-based magnetometers showed that the SAPS-induced EEJ flows westward and eastward in the daytime and dawn/dusk sectors, respectively. The effects of SAPS on EEJ are mainly associated with the changes of zonal ionospheric electric field, while the changes in the ionospheric conductivity play a secondary role. By using Thermosphere Ionosphere Electrodynamic General Circulation Model simulations, the zonal electric field induced by SAPS associated with the DDEF is examined. The results of the simulations show that the DDEF has a significant impact on the EEJ variability. The daytime westward EEJ at the dip equator is mainly driven by disturbance zonal wind, with secondary contributions from disturbance meridional wind. A similar mechanism can be observed in the dawn/dusk sector when the eastward EEJ is produced; however, it has a much weaker intensity than that during the daytime.

Description: CO2 release from particulate organic carbon (POC) oxidation during fluvial transit can influence climate over a range of timescales. Identifying the mechanistic controls on such carbon fluxes requires determining where POC oxidation occurs in river systems. While field data show POC oxidation and replacement moving downstream in lowland rivers, flume studies show that oxidation during active fluvial transport is limited. This suggests that most fluvial POC oxidation occurs during transient floodplain storage, but this idea has yet to be tested. Here, we isolate the influence of floodplain storage time on POC oxidation by exploiting a chronosequence of floodplain deposits above the modern groundwater table in the Rio Bermejo, Argentina. Measurements from 15 floodplain cores with depositional ages from 1 y to 20 ky show a progressive POC concentration decrease and 13C-enrichment with increasing time spent in floodplain storage. These results from the Rio Bermejo indicate that over 80% of fluvially-deposited POC can be oxidized over millennial timescales in aerated floodplains. Furthermore, POC in the oldest floodplain cores is more 14C-enriched than expected based on the independently-dated floodplain ages, indicating that a portion of this oxidized POC is replaced by autochthonous POC produced primarily by floodplain vegetation. We suggest floodplain storage timescales control the extent of oxidation of fluvially-deposited POC, and may play a prominent role in determining if rivers are significant atmospheric CO2 sources.

Description: Wuhan (China) is facing severe consolidation subsidence of soft soil and karst collapse hazards. To quantitatively explore the extent and causes of land subsidence in Wuhan, we performed multitemporal interferometry (MTI) analysis using synthetic aperture radar (SAR) data from the TerraSAR-X satellite from 2013 to 2017 and the Sentinel-1A satellite from 2015 to 2017. MTI results reveal four major subsidence zones in Wuhan, namely, Hankou (exceeding −6 cm/yr), Xudong-Qingshan (−3 cm/yr), Baishazhou-Jiangdi (−3 cm/yr), and Jianshe-Yangluo (−2 cm/yr). Accuracy assessment using 106 levelling benchmarks and cross-validation between the two InSAR-based results indicate an overall root-mean-square error (RMSE) of 2.5 and 3.1 mm/yr, respectively. Geophysical and geological analyses suggest that among the four major subsiding zones, Hankou, Xudong-Qingshan, and Jianshe-Yangluo are located in non-karstic soft soil areas, where shallow groundwater (〈 30 m) declines driven by engineering dewatering and industrial water depletion contribute directly to soft soil compaction. Subsidence in the Baishazhou-Jiangdi zone develops in the karst terrain with abundant underground caves and fissures, which are major natural factors for gradual subsidence and karst collapse. Spatial variation analysis of the geological conditions indicates that the stage of karst development plays the most important role in influencing kart subsidence, followed by municipal construction, proximity to major rivers, and overlying soil structure. Moreover, land subsidence in this zone is affected more via coupling effects from multiple factors. Risk zoning analysis integrating subsidence horizontal gradient, InSAR deformation rates, and municipal construction density show that the high-risk areas in Wuhan are mainly distributed in the Tianxingzhou and Baishazhou-Jiangdi zone, and generally spread along the metro lines.

Description: Climate change and rapid expansion of urban areas are expected to increase pluvial flood hazard and risk in the near future, and particularly so in large developed areas and cities. Therefore, large-scale and high-resolution pluvial flood hazard mapping is required to identify hotspots where mitigation measures may be applied to reduce flood risk. Depressions or low points in urban areas where runoff volumes can be stored are prone to pluvial flooding. The standard approach based on estimating synthetic design hyetographs assumes, in a given depression, that the T-year design storm generates the T-year pluvial flood. In addition, urban areas usually include several depressions even linked or nested that would require distinct design hyetographs instead of using a unique synthetic design storm. In this paper, a stochastic methodology is proposed to address the limitations of this standard approach, developing large-scale ∼ 2 m-resolution pluvial flood hazard maps in urban areas with multiple depressions. The authors present an application of the proposed approach to the city of Pamplona in Spain (68.26 km2). The Safer_RAIN fast-processing algorithm based on digital elevation models (DEMs) is compared with the IBER 2D hydrodynamic model in four real storms by using 10-min precipitation fields. Precipitation recorded at rainfall-gauging stations was merged with continuous fields obtained from a meteorological radar station. Given the hydrostatic limitations of Safer_RAIN, the benchmarking results are adequate in terms of water depths in depressions. A long set of 10 000 synthetic storms that maintain the statistical properties of observations in Pamplona is generated. Safer_RAIN is used to simulate runoff response, and filling and spilling processes, in depressions for the 10 000 synthetic storms, obtaining the probability distribution of water depths in each cell. Maps of pluvial flood hazards are developed in the Pamplona metropolitan area for 10 return periods in the range from two to 500 years from such pixel-based series of simulated water depths. Bivariate return-period curves are estimated in a set of cells, showing that several storms can generate a given T-year pluvial flood with an increasing precipitation with storm duration that depends on the draining catchment soil characteristics. The methodology proposed is useful to develop maps of pluvial flood hazards in large multi-depression urban areas in reasonable computation times, identifying the main pluvial flood hotspots.

Description: Geochemical processes such as mineral dissolution and precipitation alter the microstructure of rocks, and thereby affect their hydraulic and mechanical behaviour. Quantifying these property changes and considering them in reservoir simulations is essential for a sustainable utilisation of the geological subsurface. Due to the lack of alternatives, analytical methods and empirical relations are currently applied to estimate evolving hydraulic and mechanical rock properties associated with chemical reactions. However, the predictive capabilities of analytical approaches remain limited, since they assume idealised microstructures, and thus are not able to reflect property evolution for dynamic processes. Hence, aim of the present thesis is to improve the prediction of permeability and stiffness changes resulting from pore space alterations of reservoir sandstones. A detailed representation of rock microstructure, including the morphology and connectivity of pores, is essential to accurately determine physical rock properties. For that purpose, three-dimensional pore-scale models of typical reservoir sandstones, obtained from highly resolved micro-computed tomography (micro-CT), are used to numerically calculate permeability and stiffness. In order to adequately depict characteristic distributions of secondary minerals, the virtual samples are systematically altered and resulting trends among the geometric, hydraulic, and mechanical rock properties are quantified. It is demonstrated that the geochemical reaction regime controls the location of mineral precipitation within the pore space, and thereby crucially affects the permeability evolution. This emphasises the requirement of determining distinctive porosity-permeability relationships by means of digital pore-scale models. By contrast, a substantial impact of spatial alterations patterns on the stiffness evolution of reservoir sandstones are only observed in case of certain microstructures, such as highly porous granular rocks or sandstones comprising framework-supporting cementations. In order to construct synthetic granular samples a process-based approach is proposed including grain deposition and diagenetic cementation. It is demonstrated that the generated samples reliably represent the microstructural complexity of natural sandstones. Thereby, general limitations of imaging techniques can be overcome and various realisations of granular rocks can be flexibly produced. These can be further altered by virtual experiments, offering a fast and cost-effective way to examine the impact of precipitation, dissolution or fracturing on various petrophysical correlations. The presented research work provides methodological principles to quantify trends in permeability and stiffness resulting from geochemical processes. The calculated physical property relations are directly linked to pore-scale alterations, and thus have a higher accuracy than commonly applied analytical approaches. This will considerably improve the predictive capabilities of reservoir models, and is further relevant to assess and reduce potential risks, such as productivity or injectivity losses as well as reservoir compaction or fault reactivation. Hence, the proposed method is of paramount importance for a wide range of natural and engineered subsurface applications, including geothermal energy systems, hydrocarbon reservoirs, CO2 and energy storage as well as hydrothermal deposit exploration

Description: Geochemische Lösungs- und Fällungsprozesse verändern die Struktur des Porenraums und können dadurch die hydraulischen und mechanischen Gesteinseigenschaften erheblich beeinflussen. Die Quantifizierung dieser Parameteränderung und ihre Berücksichtigung in Reservoirmodellen ist entscheidend für eine nachhaltige Nutzung des geologischen Untergrunds. Aufgrund fehlender Alternativen werden dafür bisher analytische Methoden genutzt. Da diese Ansätze eine idealisierte Mikrostruktur annehmen, können insbesondere Änderungen der Gesteinseigenschaften infolge von dynamischen Prozessen nicht zuverlässig abgebildet werden. Ziel der vorliegenden Doktorarbeit ist es deshalb, die Entwicklung von Gesteinspermeabilitäten und -steifigkeiten aufgrund von Porenraumveränderungen genauer vorherzusagen. Für die möglichst exakte Bestimmung physikalischer Gesteinsparameter ist eine detaillierte Darstellung der Mikrostruktur notwendig. Basierend auf mikro-computertomographischen Scans werden daher hochaufgelöste, dreidimensionale Modelle typischer Reservoirsandsteine erstellt und Gesteinspermeabilität und -steifigkeit numerisch berechnet. Um charakteristische Verteilungen von Sekundärmineralen abzubilden, wird der Porenraum dieser virtuellen Sandsteinproben systematisch verändert und die resultierenden Auswirkungen auf die granulometrischen, hydraulischen und elastischen Gesteinseigenschaften bestimmt. Die Ergebnisse zeigen deutlich, dass charakteristische Fällungsmuster unterschiedlicher geochemischer Reaktionsregime die Permeabilität erheblich beeinflussen. Folglich ist die Nutzung von porenskaligen Modellen zur Bestimmung der Porosität-Permeabilitätsbeziehungen unbedingt notwendig. Im Gegensatz dazu ist die Verteilung von Sekundärmineralen für die Gesteinssteifigkeit nur bei bestimmten Mikrostrukturen von Bedeutung, hierzu zählen hochporöse Sandsteine oder solche mit Korngerüst-stützenden Zementierungen. In der Arbeit wird außerdem ein Ansatz zur Konstruktion granularer Gesteine vorgestellt, welcher sowohl die Kornsedimentation als auch die diagenetische Verfestigung umfasst. Es wird gezeigt, dass die synthetischen Proben die mikrostrukturelle Komplexität natürlicher Reservoirsandsteine gut abbilden. Dadurch können generelle Limitationen von bildgebenden Verfahren überwunden und unterschiedlichste virtuelle Repräsentationen von granularen Gesteinen generiert werden. Die synthetischen Proben können zukünftig in virtuellen Experimenten verwendet werden, um die Auswirkungen von Lösungs- und Fällungsreaktionen auf verschiedene petrophysikalische Korrelationen zu untersuchen. Die vorgestellte Arbeit liefert methodische Grundlagen zur Quantifizierung von Permeabilitäts- und Steifigkeitsänderungen infolge geochemischer Prozesse. Die berechneten petrophysikalischen Beziehungen basieren direkt auf mikrostrukturellen Veränderungen des Porenraums. Daher bieten sie eine genauere Vorhersage der Gesteinseigenschaften als herkömmliche analytische Methoden, wodurch sich die Aussagekraft von Reservoirmodellen erheblich verbessert. Somit können Risiken, wie Produktivitäts- oder Injektivitätsverluste sowie Reservoirkompaktion oder Störungsreaktivierung, verringert werden. Die präsentierten Ergebnisse sind daher relevant für verschiedenste Bereiche der geologischen Untergrundnutzung wie CO2- oder Energiespeicherung, Geothermie, Kohlenwasserstoffgewinnung sowie die Erkundung hydrothermaler Lagerstätten.

Description: The real-time Earth orientation parameters (EOP) estimation is needed for many applications, including precise tracking and navigation of interplanetary spacecraft, climate forecasting, and disaster prevention. However, the complexity and time-consuming data processing always lead to time delays. Accordingly, several methods were developed and applied for the EOP prediction. However, the accuracy of EOP prediction is still not satisfactory even for prediction of just a few days in the future. Therefore, new methods or a combination of the existing approaches can be investigated to improve the predicted EOP. To assess the various EOP prediction capabilities, the international Earth rotation and reference systems service (IERS) established the working group on the 2nd Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC). Our EOP prediction team provides the full set of EOP predictions weekly for one year ahead. In this campaign, we used the SSA+Copula method and the empirical free core nutation (FCN) model (named B16) for Earth rotation parameters and celestial pole offsets (CPO) prediction, respectively. Additionally, we investigated new prediction techniques and different input data set; as an example, the Convolutional Neural Networks (CNN) is introduced to model and predict the short-term EOP. Our preliminary results illustrate an improvement in EOP prediction compared to the current EOP prediction methods, especially on CPO.

Description: Despite its high seismogenic potential, the details of the seismogenic processes of Zagros Simply Folded Belt (SFB) remains debated. Three large earthquakes (Mw 7.3, 5.9, and 6.3) struck in the Lurestan arc of the Zagros SFB in 2017 and 2018. The sequence was recorded by seismic stations at regional, and teleseismic distances. Coseismic surface displacements, measured by Sentinel-1A/B satellites, provide additional data and a unique opportunity to study these earthquakes in detail. Here, we complement previous studies of the coseismic slip distribution of the 12 November 2017 Mw 7.3 Ezgeleh earthquake by a detailed analysis of its aftershocks, and we analyzed the rupture process of the two interrelated earthquakes (25 August 2018 Mw 5.9 Tazehabad and the 25 November 2018 Mw 6.3 Sarpol-e Zahab earthquakes). We model the surface displacements obtained from Interferometric Synthetic Aperture Radar (InSAR) measurements and seismic records. We conduct non-linear probabilistic optimizations based on joint InSAR and seismic data to obtain finite-fault rupture of these earthquakes. The Lurestan arc earthquakes were followed by a sustained aftershock activity, with 133 aftershocks exceeding Mn 4.0 until December 30, 2019. We rely on the permanent seismic networks of Iran and Iraq to relocate ∼700 Mn 3 + events and estimate moment tensor solutions for 85 aftershocks down to Mw 4.0. The 2017 Ezgeleh earthquake has been considered to activate a low-angle (∼17°) dextral-thrust fault at the depth of 10–20 km. However, most of its aftershocks have shallow centroid depths (8–12 km). The joint interpretation of finite source models, moment tensor, and hypocentral location indicate that the 2018 Tazehabad and Sarpol-e Zahab earthquakes ruptured different strike-slip structures, providing evidence for the activation of the sinistral and dextral strike-slip faults, respectively. The deformation in the Lurestan arc is seismically accommodated by a complex fault system involving both thrust and strike-slip faults. Knowledge about the deformation characteristics is important for the understanding of crustal shortening, faulting, and hazard and risk assessment in this region.

Description: Monitoring and controlling of mineral precipitation is a major challenge in several industry segments such as oil and gas or geothermal energy. Especially at elevated pressures, temperatures, and salinities, these reactions are poorly understood and difficult to predict. Real-time monitoring under such conditions, however, is crucial for reduction or prevention of scaling as well as for process modelling. In this study, a novel fibre-optical method for monitoring the barite precipitation process at high pressures and high temperatures was developed and tested. The applicability of a fibre-optical sensor was demonstrated and kinetic data derived from experiments using synthetic fluids that were oversaturated with barite. The ionic strength was varied between 0 and 5 mol/l NaCl to simulate geothermal brines typically found in deep sedimentary reservoirs. Experiments were performed at 25 and 150 °C. For the studied variations it was found that the ionic strength had a strong impact on the barite precipitation rate whereas temperature had only a minor influence. The kinetic rate constants were decreasing with increasing salinity ranging from 9 to 0.4 l‧mol−1‧s−1 at 25 °C and from 8.6 to 0.66 l‧mol−1‧s−1 at 150 °C.

Description: New data acquisition techniques are generating data at much finer temporal and spatial resolution, compared to traditional seismic experiments. This is a challenge for data centers and users. As the amount of data potentially flowing into data centers increases by one or two orders of magnitude, data management challenges are found throughout all stages of the data flow. The Incorporated Research Institutions for Seismology—Réseau sismologique et géodésique français and GEOForschungsNetz data centers—carried out a survey and conducted interviews of users working with very large datasets to understand their needs and expectations. One of the conclusions is that existing data formats and services are not well suited for users of large datasets. Data centers are exploring storage solutions, data formats, and data delivery options to meet large dataset user needs. New approaches will need to be discussed within the community, to establish large dataset standards and best practices, perhaps through participation of stakeholders and users in discussion groups and forums.

Description: Earth’s lowermost mantle displays complex geological phenomena that likely result from its heterogeneous physical interaction with the core. Geophysical models of core-mantle interaction rely on the thermal and electrical conductivities of appropriate geomaterials which, however, have never been probed at representative pressure and temperature (P-T) conditions. Here we report on the opacity of single crystalline bridgmanite and ferropericlase and link it to their radiative and electrical conductivities. Our results show that light absorption in the visible spectral range is enhanced upon heating in both minerals but the rate of change in opacity with temperature is a factor of six higher in ferropericlase. As a result, bridgmanite in the lowermost mantle is moderately transparent while ferropericlase is highly opaque. Our measurements support previous indirect estimates of low (〈 1 W/m/K) and largely temperature-independent radiative conductivity in the lowermost mantle. This implies that the radiative mechanism has not contributed significantly to cooling the Earth’s core throughout the geologic time. Opaque ferropericlase is electrically conducting and mediates strong core-mantle electromagnetic coupling, explaining the intradecadal oscillations in the length of day, low secular geomagnetic variations in Central Pacific, and the preferred paths of geomagnetic pole reversals.

Description: Elliptical sulfate-rich features, stained red by the presence of iron oxides, are set within permafrost and carbonate rock at Borup Fiord Pass in the Canadian High Arctic. These features, which vary in diameter from ∼0.5 to 3 m, exhibit the co-localization of sulfur (S) and iron (Fe) minerals, with S and Fe both preserved in multiple oxidation states. Through application of x-ray diffraction (XRD) and Raman microspectroscopy, we find that these features appear to encapsulate central cores with abundant pyrite while S0, gypsum, and iron-bearing secondary minerals such as jarosite, goethite, and hematite have formed from oxidative weathering of the pyrite. These features appear similar to terrestrial gossans, mineral features representative of weathered sulfide ores in the near-surface. We use Raman microspectroscopy and scanning transmission x-ray microscopy (STXM) to show that organic carbon is associated with the minerals within these features. The origin of this carbon remains enigmatic; however, we consider the possibility that this carbon, along with etching of the pyrite grains and accumulation of encrusted filaments detected in the features, may be indicative of preserved biological activity during alteration of the pyrite. We also consider how such geological sulfide emplacements and their weathered surface expressions may provide a target for future surface and remote sensing studies of Mars and in the search for extraterrestrial life.

Description: The SWATH‐D experiment involved the deployment of a dense temporary broadband seismic network in the Eastern Alps. Its primary purpose was enhanced seismic imaging of the crust and crust–mantle transition, as well as improved constraints on local event locations and focal mechanisms in a complex part of the Alpine orogen. The study region is a key area of the Alps, where European crust in the north is juxtaposed and partially interwoven with Adriatic crust in the south, and a significant jump in the Moho depth was observed by the 2002 TRANSALP north–south profile. Here, a flip in subduction polarity has been suggested to occur. This dense network encompasses 163 stations and complements the larger‐scale sparser AlpArray seismic network. The nominal station spacing in SWATH‐D is 15 km in a high alpine, yet densely populated and industrialized region. We present here the challenges resulting from operating a large broadband network under these conditions and summarize how we addressed them, including the way we planned, deployed, maintained, and operated the stations in the field. Finally, we present some recommendations based on our experiences.

Description: Potassium feldspars (KAlSi3O8) are ubiquitous minerals in the Earth's upper crust. This family of minerals has been the subject of numerous experimental and theoretical investigations concerning their dissolution kinetics and the mechanisms controlling chemical alteration at acid and neutral pH, and at temperatures ranging from ambient to hydrothermal conditions. On the other hand, considerably less research on the dissolution behavior of K-feldspars has been carried out at alkaline conditions, in particular at pH 〉 9 and elevated temperatures. Filling in this gap in knowledge is the major motivation for this study. More specifically, we wanted to document and understand how the K-feldspar interface structurally and chemically evolves during alteration in order to determine the mechanism of dissolution. In this study we examined interfaces of orthoclase samples that were altered in separate experiments in a Ca(OH)2-H2O solution (pH25°C 12.4) at 190 °C for 24 h. We used a combination of focused ion beam (FIB) milling and advanced analytical transmission electron microscopy (TEM) techniques to investigate the structure and chemistry of the near surface region of post-reaction grains, with particular attention being given to the fluid-solid interface. Even though each grain diminishes in volume due to dissolution, high-resolution TEM imaging indicates that the feldspar structure itself remains completely intact and crystalline, as evidenced by lattice fringes that abruptly terminate at the grain edge. Nanometer-scale chemical composition measurements and mapping by TEM-EDXS (energy dispersive X-ray spectroscopy) and EFTEM (energy filtered TEM) show that the chemistry of the parent feldspar also remains unchanged at the interface. In particular, there is no evidence for the incursion of Ca from the fluid solvent into the structure, either by interdiffusion or by a replacement process. Taken together, the TEM observations point to a sharp chemical reaction front characterized by the congruent (i.e. stoichiometric) release of all elements from the feldspar structure. Nanometer-scale measurements by high resolution analytical TEM also reveal that a surface alteration layer (SAL) of amorphous material forms in situ at the expense of the feldspar structure. The interface demarcates a spatially coincident and nm-sharp chemical and structural discontinuity between the parent feldspar and the amorphous phase. The amorphous SAL has a variable thickness, from under 10 nm up to ~200 nm. This is likely one of the first observed occurrences of a significant surface amorphous layer on feldspar due to alteration in an alkaline solvent. The lack of a gap between the two phases points to an interfacial dissolution-reprecipitation process that continuously operates during hydrothermal alteration, and mostly likely right from the onset of contact with the fluid. After the initial formation of the amorphous layer, a 1–2 μm-thick porous amalgam of secondary crystalline phases comprised of calcite, tobermorite, and hydrogrossular, as well as other minor phases, precipitated over the SAL. These authigenic crystalline minerals formed during the experiment (hydrothermal alteration, followed by fluid loss due to evaporation) by a classical thermodynamically-controlled precipitation process as the reactor bulk fluid became increasingly concentrated. We propose that a coupled interfacial dissolution-reprecipitation (CIDR) mechanism best explains the chemical and structural properties of the interface and the formation of an amorphous surface layer. In fact, many recent studies postulate that a CIDR process controls feldspar dissolution and the formation of SALs at acid and circumneutral pH over a wide range of temperatures. Combining these previous results with our new observations supports the idea that a unique and unifying mechanism likely controls chemical alteration of feldspars in all aqueous fluids.

Description: The Pan-Eurasian Experiment (PEEX) Science Plan, released in 2015, addressed a need for a holistic system understanding and outlined the most urgent research needs for the rapidly changing Arctic-boreal region. Air quality in China, together with the long-range transport of atmospheric pollutants, was also indicated as one of the most crucial topics of the research agenda. These two geographical regions, the northern Eurasian Arctic-boreal region and China, especially the megacities in China, were identified as a “PEEX region”. It is also important to recognize that the PEEX geographical region is an area where science-based policy actions would have significant impacts on the global climate. This paper summarizes results obtained during the last 5 years in the northern Eurasian region, together with recent observations of the air quality in the urban environments in China, in the context of the PEEX programme. The main regions of interest are the Russian Arctic, northern Eurasian boreal forests (Siberia) and peatlands, and the megacities in China. We frame our analysis against research themes introduced in the PEEX Science Plan in 2015. We summarize recent progress towards an enhanced holistic understanding of the land–atmosphere–ocean systems feedbacks. We conclude that although the scientific knowledge in these regions has increased, the new results are in many cases insufficient, and there are still gaps in our understanding of large-scale climate–Earth surface interactions and feedbacks. This arises from limitations in research infrastructures, especially the lack of coordinated, continuous and comprehensive in situ observations of the study region as well as integrative data analyses, hindering a comprehensive system analysis. The fast-changing environment and ecosystem changes driven by climate change, socio-economic activities like the China Silk Road Initiative, and the global trends like urbanization further complicate such analyses. We recognize new topics with an increasing importance in the near future, especially “the enhancing biological sequestration capacity of greenhouse gases into forests and soils to mitigate climate change” and the “socio-economic development to tackle air quality issues”.

Description: Glacial isostatic adjustment is largely governed by the rheological properties of the Earth's mantle. Large mass redistributions in the ocean–cryosphere system and the subsequent response of the viscoelastic Earth have led to dramatic sea level changes in the past. This process is ongoing, and in order to understand and predict current and future sea level changes, the knowledge of mantle properties such as viscosity is essential. In this study, we present a method to obtain estimates of mantle viscosities by the assimilation of relative sea level rates of change into a viscoelastic model of the lithosphere and mantle. We set up a particle filter with probabilistic resampling. In an identical twin experiment, we show that mantle viscosities can be recovered in a glacial isostatic adjustment model of a simple three-layer Earth structure consisting of an elastic lithosphere and two mantle layers of different viscosity. We investigate the ensemble behaviour on different parameters in the following three set-ups: (1) global observations data set since last glacial maximum with different ensemble initialisations and observation uncertainties, (2) regional observations from Fennoscandia or Laurentide/Greenland only, and (3) limiting the observation period to 10 ka until the present. We show that the recovery is successful in all cases if the target parameter values are properly sampled by the initial ensemble probability distribution. This even includes cases in which the target viscosity values are located far in the tail of the initial ensemble probability distribution. Experiments show that the method is successful if enough near-field observations are available. This makes it work best for a period after substantial deglaciation until the present when the number of sea level indicators is relatively high.

Description: Mantle metasomatism is an important process in subduction zones in which fluids from the dehydrating oceanic slab interact with the overlying upper mantle resulting in a chemical alteration of the mantle. Consequently, this fluid-rock interaction may influence the mantle rock's physical properties such as the deformation behavior. In order to study element redistribution during mantle metasomatism in the laboratory, we used the simplified model reaction olivine + quartz = orthopyroxene, where olivine acts as representative for the upper mantle and quartz as proxy for the metasomatizing agent. We conducted piston-cylinder experiments at 1.5 GPa and 950 to 1400 °C, lasting between 48 and 288 h, on samples containing a mixture of quartz and one set of synthesized forsterite samples doped with either Co, Ni, Mn, or Zn. Additionally, we tested the influence of either nominally anhydrous or hydrous experimental conditions on the chemical distribution of the respective dopant element by using either crushable alumina or natural CaF2 as pressure medium. Results of the chemical analyses of the recovered samples show dopant specific partitioning between doped forsterite and orthopyroxene independent of the confining pressure medium; except for the runs in which Ni-doped forsterite samples were used. The observed Ni- and Co-enrichment in forsterite samples may be used to identify mantle rocks that underwent mantle metasomatism in nature.

Description: To mark the 20th anniversary of Natural Hazards and Earth System Sciences (NHESS), an interdisciplinary and international journal dedicated to the public discussion and open-access publication of high-quality studies and original research on natural hazards and their consequences, we highlight 11 key publications covering major subject areas of NHESS that stood out within the past 20 years. The papers cover all the topics contemplated in the European Geosciences Union (EGU) Division on Natural Hazards including dissemination, education, outreach and teaching. The selected articles thus represent excellent scientific contributions in the major areas of natural hazards and risks and helped NHESS to become an exceptionally strong journal representing interdisciplinary areas of natural hazards and risks. At its 20th anniversary, we are proud that NHESS is not only used by scientists to disseminate research results and novel ideas but also by practitioners and decision-makers to present effective solutions and strategies for sustainable disaster risk reduction.

Description: With the completion of Chinese BeiDou Navigation Satellite System (BDS), the world has begun to enjoy the Positioning, Navigation, and Timing (PNT) services of four Global Navigation Satellite Systems (GNSS). In order to improve the GNSS performance and expand its applications, Low Earth Orbit (LEO) Enhanced Global Navigation Satellite System (LeGNSS) is being vigorously advocated. Combined with high-, medium-, and low- earth orbit satellites, it can improve GNSS performance in terms of orbit determination, Precise Point Positioning (PPP) convergence time, etc. This paper comprehensively reviews the current status of LeGNSS, focusing on analyzing its advantages and challenges for precise orbit and clock determination, PPP convergence, earth rotation parameter estimation, and global ionosphere modeling. Thanks to the fast geometric change brought by LEO satellites, LeGNSS is expected to fundamentally solve the problem of the long convergence time of PPP without any augmentation. The convergence time can be shortened within 1 minute if appropriate LEO constellations are deployed. However, there are still some issues to overcome, such as the optimization of LEO constellation as well as the real time LEO precise orbit and clock determination.

Description: Precise point positioning with ambiguity resolution (PPP-AR) is a powerful tool for geodetic and time-constrained applications that require high precision. The performance of PPP-AR highly depends on the reliability of the correct integer carrier-phase ambiguity estimation. In this study, the performance of narrow-lane ambiguity resolution of PPP using the Least-squares AMBiguity Decorrelation (LAMBDA) and bootstrapping methods is extensively investigated using real data from 55 IGS stations over one-month in 2020. Static PPP with 24-, 12-, 8-, 4-, 2-, 1- and ½-h sessions using two different cutoff angles (7° and 30°) was conducted with three PPP modes: i.e. ambiguity-float and two kinds of ambiguity-fixed PPP using the LAMBDA and bootstrapping methods for narrow-lane AR, respectively. The results show that the LAMBDA method can produce more reliable results for 2 hour and shorter observation sessions compared with the bootstrapping method using a 7° cutoff angle. For a 30° cutoff angle, the LAMBDA method outperforms the bootstrapping method for observation sessions of 4 h and less. For long observation times, the bootstrapping method produced much more accurate coordinates compared with the LAMBDA method without considering the wrong fixes cases. The results also show that occurrences of fixing the wrong integer ambiguities using the bootstrapping method are higher than that of the LAMBDA method.

Description: The project DARE proposes an integrated study of seismic site effects on the deep and elongated Messinian Rhône Canyon (French Rhône Valley). Lithological information from boreholes reaching the bedrock and preliminary geophysical campaigns indicate that the canyon can reach locally 〉500 m and may be deeply incised. The strong material contrast between the sedimentary filling and the substratum, as well as its expected confined geometry make this canyon a good candidate for generating various kinds of multi-dimensional site effects. Waveform data are available from the GEOFON data centre, under network code Y7.

Description: The temporary seismic array of MySCOLAR in northern Myanmar consists of 30 broadband stations. The overall scientific goals are to understand the transition from continental collision to oceanic subduction, to quantify the partitioning of deformation in the accretionary prism, in the Burma Plate and along the strike-slip Sagaing fault system and to image the subducting Indian Plate beneath Myanmar and southwest China. The seismological analysis methods applied to this dataset will include location of local earthquakes and determining their focal mechanisms, surface wave tomography from ambient noise and earthquake data, body wave tomography from local and teleseismic earthquakes, full waveform inversion for Earth structure, receiver functions, and shear wave splitting. A subset of the stations was transmitting data in real time, and these stations contributed to real-time earthquake analysis by the Department of Meteorology and Hydrology (DMH) in Myanmar and the GEOFON earthquake monitoring service. Waveform data are available from the GEOFON data centre, under network code 6C.

Description: Near Reykjavik/Iceland, a "soft stimulation” geothermal experiment was performed in the frame of the DESTRESS project in 2019. The installed seismic stations consist of short period, and borehole stations in and around Geldinganes, NE of Reykjavik. The task of this network is the monitoring of the seismic events in the area around the stimulation site. The installation started in late 2018 with 6 short period stations (Reykjavik Energy). Since July 2019 additional seismic stations were integrated as a small scale array on the island Geldinganes and additional short period stations. A borehole geophone chain was installed with 17 short period 3-component geophones with a vertical spacing of 10 meter in the depth interval 1040m to 1200 m. Waveform data are available from the GEOFON data centre, under network code YG, and are embargoed until January 2025.

Description: The Villarrica Volcano is one of the most active volcanoes in South America and is located in a major tourism region. A dense seismological network is used to investigate the seismic characteristics of the volcano and its seismic structure tomographically with high spatial resolution. The network was in operation for 2 week from 01.03.2012 to 14.03.2012. It consisted of 30 3-component and 45 1-component short period seismographs covering an area of 2000 km*2. The covered area has a diameter of 45 km and includes the volcanic building.

Description: The Bransfield Strait is a seismically active extensional rift located between the Antarctic Peninsula and the South Shetland Islands. The Strait is partly located on continental crust including areas within the transition to seafloor spreading. The amphibious seismic network BRAVOSEIS is an international effort focused on the seismological research of submarine volcanoes and rift dynamics in the Bransfield Strait. This network is the onshore component of the entire network consisting of 15 broadband land stations deployed in the South Shetland Islands and Antarctic Peninsula between January 2018 and February 2020. The offshore components (network code ZX) include 9 broadband ocean bottom seismometers (OBS) across the Central Bransfield Basin and a group of 6 hydrophone moorings spanning the rift area of 200 x 100 km2, with inter-station distance of ~30 km. Additionally, a smaller offshore array consisting of 15 short-period OBSs with an aperture of 20 km and a narrow inter-station distance of ~4 km was deployed around the Orca submarine volcanic edifice south of King George Island. The data will be used to study the geodynamics of the Bransfield Strait and the evolution of the incipient rifting zone in the domain where extension has been suggested. Seismological methods will include earthquake location, source mechanism, surface wave analysis with ambient noise and earthquake data, receiver function and shear wave splitting. The results may shed light on the crustal structure and tectonic regime in the region and image the location and extent of magma accumulations related to submarine volcanic structures. Finally, the results should provide clues to assess the internal processes that occur in the submarine volcanoes of the area undergoing rifting. Waveform data are available from the GEOFON data centre, under network code 5M and are embargoed until Mar 2024. Acknowledgments: We thank all participants in the BRAVOSEIS 2018, 2019, and 2020 cruises, with a special acknowledgement to Capt. Jose Emilio Regodon and his crew at R/V Hesperides; Capt. Juan Carlos Hernandez and his crew at Sarmiento de Gamboa; Miki Ojeda, Ezequiel Gonzalez, and all the UTM staff involved in the planification and realization of the surveys. We also thank the Spanish Polar Committee and institutions involved in the management of the Spanish Antarctic campaigns and the development of the Spanish Polar Program. We are grateful for the help and support that we always find in the personnel of the Antarctic Bases, especially the Spanish Bases Juan Carlos I and Gabriel de Castilla.

Description: The main aim of this project is to investigate the crustal and mantle structure beneath the Longmenshan fault zone in China, based on a very dense passive seismology profile. The Longmenshan fault zone hosted the Wenchuan earthquake of May 2008 with a magnitude (Mw) of 7.9 and the Lushan earthquake of June 2013 with a magnitude (Mw) of 6.6. It is planned to mainly use the receiver-function method, to investigate the crustal and mantle structure beneath the Longmenshan fault zone. Waveform data are available from the GEOFON data center, under network code 4O under license CC BY-NC-ND 4.0, and are embargoed until February 2024.

Description: Oldoinyo Lengai in the North Tanzanian Divergence is the only active natrocarbonatite volcano world-wide and presents an important endmember magmatic system in a young rift segment of the East African Rift System. This volcano typically experiences long-duration episodes of natrocarbonatitic effusions with intermittent short-duration explosive eruptions. To better understand the role of the stress interactions and magma plumbing on the eruptions dynamics, this study aims to constrain the subsurface magmatic architecture of Oldoinyo Lengai, and a zone of ongoing seismicity and intrusive activity below the extinct 1 Ma-old Gelai shield volcano and active Naibor Soito monogenetic cone field. Waveform data are available from the GEOFON data centre, under network code 9J, and are embargoed until November 2025.

Description: On 26th of November 2019 an Mw 6.4 earthquake ruptured near the port town of Durres, only 25 km from Tirana, the capital of Albania. The earthquake caused major damage and killed 51 people, making it the deadliest earthquake in 2019 worldwide. The mainshock was relatively deep (~25 km) and of thrust type. In December 2019, a Hazard and Risk team (HART) from German Center for Geosciences (GFZ), Karslruhe Institute of Technology (KIT) in cooperation with the Institute of Geosciences, Energy, Water and Environment (IGEWE) of the Polytechnic University of Tirana, Albania installed a 30-station seismic network in the epicentral region to record aftershocks. Stations were equipped with short-period (1 Hz or 4.5 Hz) 3-component seismometers and CUBE data loggers recording continuously 100 sps. Waveform data are available from the GEOFON data centre, under network code 9K under CC-BY 4.0 license and are embargoed until January 2024.

Description: Irpinia seismic Array is part of the DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging (DETECT) project focused on the acquisition of a unique multiparametric dataset and fosters collaboration among various institutions. The University of Naples Federico II (UniNa) and the German Research Centre for Geosciences (GFZ) are leading this effort carried out in collaboration with various local institutions and supported by the local municipalities. The DETECT project aims at exploiting very dense seismic networks deployed across a segmented fault system (Irpinia and Pergola-Melandro) to foster the development of scientific integrated methodologies for monitoring and imaging the fault behavior during the inter-seismic phase. The Irpinia seismic Array consists of a dense constellation of seismic antennas using more than 200 seismic stations deployed for one year. Each seismic antenna, with maximum aperture of ~2 km, uses one broad-band sensor, one short period sensor with 1 Hz and 8 with 4.5 Hz natural frequency. The antennas are deployed above and near the fault segments that generated during the last centuries many strong earthquakes in the southern Apennines. Waveform data are available from the GEOFON data centre, under network code ZK.

Description: Raw, SEGY and other supplementary data are presented from the seismic refraction / wide-angle reflection profile, TTZ-South, in Poland and Ukraine. The purpose of this 550 km long seismic profile was to reveal the lithospheric structure along the Teisseyre-Tornquist Zone (TTZ), a major geophysical boundary in Europe.

Description: The Villarrica Volcano is one of the most active volcanoes in South America and is located in a major tourism region. A dense temporal seismological network was installed to investigate the volcanic seismicity and the seismic structure of the edifice with seismic traveltime tomography at high spatial resolution. The network was in operation for 2 weeks from 01.03.2012 to 14.03.2012. It consisted of 30 three-component and 45 one-component short period seismographs covering an area of about 2000 km2. The covered area has a diameter of 45 km and includes the volcanic building.

Description: Study Region Vietnamese Mekong Delta. Study focus This study investigates the trends of groundwater levels (GWLs), the memory effect of alluvial aquifers, and the response times between surface water and groundwater across the Vietnamese Mekong Delta (VMD). Trend analysis, auto- and cross-correlation, and time-series decomposition were applied within a moving window approach to examine non-stationary behavior. New hydrological insights Our study revealed an effective connection between the shallowest aquifer unit (Holocene) and surface water, and a high potential for shallow groundwater recharge. However, low-permeable aquicludes separating the aquifers behave as low-pass filters that reduce the high‐frequency signals in the GWL variations, and limit the recharge to the deep groundwater. Declining GWLs (0.01−0.55 m/year) were detected for all aquifers throughout the 22 years of observation, indicating that the groundwater abstraction exceeds groundwater recharge. Stronger declining trends were detected for deeper groundwater. The dynamic trend analysis indicates that the decrease of GWLs accelerated continuously. The groundwater memory effect varied according to the geographical location, being shorter in shallow aquifers and flood-prone areas and longer in deep aquifers and coastal areas. Variation of the response time between the river and alluvial aquifers was controlled by groundwater depth and season. The response time was shorter during the flood season, indicating that the bulk of groundwater recharge occurred in the late flood season, particularly in the deep aquifers.

Description: Important aspects of geothermal exploration and exploitation are the assessment and mitigation of natural and/or induced seismicity, the imaging and resource assessment of a geothermal reservoir and the monitoring of the effects of the exploitation activities. With this thesis the analysis and application of various seismological tools for the planning, exploration, and monitoring of geothermal fields are given. The methods explored and further developed include survey design for microseismic network construction and assessment, local earthquake tomography, ambient noise tomography, and coda wave interferometry. These techniques were applied to study Los Humeros (Mexico), Theistareykir (Iceland) and Reykjanes (Iceland) geothermal fields. The geometry of seismological arrays is essential for high quality seismic event retrieval and minimal location errors. A sequential survey design algorithm that uses a quality measure based on the D-criterion was applied to extend the seismic network at Theistareykir and to qualify the geometry of the Reykjanes network. Assuming mean picking errors of tp =0.2 s and ts = 0.4 s, the extended Theistareykir network presented an improvement of ∼0.2 km for the computed hypocentral components of seismic events located within the new network. Conversely, we estimated that the Reykjanes network could spare up to 18 of its station locations and obtain comparable location errors nonetheless. This study showed thei mportance of prior survey design experiments to optimize the expenses for a geothermal project (required number of sensors) while obtaining good location estimates of expected seismic events (benefit/cost relations). To characterize the seismic structures at Los Humeros and Theistareykir geothermal fields, a local earthquake tomography and an ambient noise tomography were computed at both locations, respectively. A local earthquake tomography is feasible in areas with high seismicity and good ray coverage (earthquake/station geometries). On the other hand, an ambient noise tomography depends on a good and sufficiently dense station distribution. With the results of these studies, the seismic structures and the dynamics of these two producing fields were obtained for the first time. The seismicity distribution at Los Humeros was used to characterize structures and potential permeability enhancements in some of the existing faults. The retrieved Vp model was combined with available well log data and ultrasonic pulse measurements of collected rock samples to estimate the boundaries of different geologic units. The Vp/Vs model was then used in combination with resistivity data and surface CO2 measurements to deduce the geometry of the conductive clay cap (Vp/Vs ≤ 1.65 and resistivities ≤ 10 Ωm), to identify fluid (Vp reduction, Vp/Vs ≥ 1.71, and resistivities between ∼ 10-60 Ωm), and to locate gas bearing regions (Vp/Vs ≤ 1.55 and high surface CO2 concentrations). A similar study was carried out at Theistareykir, where the Vs model was combined with resistivity data to identify magmatic and/or hydrothermal bodies (Vs ≤ -7 %, resistivities ≤ 30 Ωm). An important conclusion from these studies is that the combination of seismic properties with additional geological and/or geophysical data avoids ambiguities and provides robust interpretations of the dynamics and structure of a geothermal reservoir. Finally, a coda wave interferometry technique (stretching method) was applied to two years of ambient noise records at the Theistareykir geothermal field with the aim to monitor possible velocity changes due to the exploitation activities. Here, the effects of the injection and production changes were very small on the computed Δv/v ratio and only a small long-term velocity reduction (possibly due to production) was detected (-0.05 %/year at the producing field compared to a regional -0.04 %/year). Such observations are also very relevant for the safe long-term continuation of exploitation activities. Although not yet a standard practice, the computation of these changes is very useful to control aseismic processes prior to potentially triggered/induced large seismic events and is complementary to microseismic monitoring. With these results, this thesis contributes to the efforts of the International Energy Agency to develop and increase the use of geothermal energy.

Description: Wichtige Aspekte der geothermischen Exploration und Nutzung sind die Bewertung und Reduzierung der natürlichen und/oder induzierten Seismizität, die Abbildung und Ressourcenbewertung eines geothermischen Reservoirs, sowie die Überwachung der Auswirkungen der Explorationsaktivitäten. In dieser Arbeit werden die Analysen und Anwendungen verschiedener seismologischer Methoden zur Planung, Erkundung und Überwachung geothermischer Felder vorgestellt. Die untersuchten und hier weiterentwickelten Methoden umfassen das Design für den Aufbau und die Bewertung mikroseismischer Netzwerke, die lokale Erdbebentomographie, die Ambient-Noise-Tomographie und die Coda-Wellen-Interferometrie. Diese Techniken werden angewendet, um die geothermischen Felder Los Humeros (Mexiko), Theistareykir (Island) und Reykjanes (Island) zu untersuchen. Die Geometrie seismologischer Arrays ist essentiell für eine gute Bestimmung seismischer Ereignisse mit kleinen Lokationsungenauigkeiten. Ein sequenzieller Algorithmus zum Design des Arrays, der eine Qualitätskennzahl auf der Grundlage des D-Kriteriums verwendet, wurde benutzt, um das seismische Netzwerk in Theistareykir zu erweitern und die Geometrie des Reykjanes-Netzwerks zu testen. Unter der Annahme von mittleren Ablesefehlern von tp = 0.2 s und ts = 0.4 s für P- und S- Wellen verbessert das erweiterte Theistareykir-Netzwerk die berechneten Hypo-Zentren um 0.2 km innerhalb des neuen Netzes. Das Reykjanes-Netz könnte andererseits um bis zu 18 Stationsstandorte reduziert werden und dennoch vergleichbare Lokationsgenauigkeiten erzielen. Diese Studie zeigte die Wichtigkeit vor den eigentlichen Feld-Experimenten Tests möglicher Array-Designs durchzuführen um die Kosten für ein geothermisches Projekt (erforderliche Anzahl von Sensoren) zu optimieren und gleichzeitig gute Lokationen für erwartete seismische Ereignisse zu erhalten (Nutzen/Kostenverhältniss). Um die seismischen Strukturen der geothermischen Felder Los Humeros und Theistareykir zu charakterisieren, wurden an beiden Standorten eine lokale Erdbebentomographie und eine Ambient-Noise-Tomographie berechnet. Eine lokale Erdbebentomographie ist in Gebieten mit hoher Seismizität und guter Strahlenabdeckung (Erdbeben/Stationsgeometrie) möglich. Eine Ambient-Noise-Tomographie hängt nur von einer guten und ausreichend dichten Stationsverteilung ab. Mit den Ergebnissen dieser Studien wurden dann erstmals die seismischen Strukturen und die Dynamik dieser beiden produzierenden Felder ermittelt. Die Seismizitätsverteilung in Los Humeros wurde verwendet, um Strukturen und potenzielle Verbesserungen in der Durchlässigkeit einiger Störungszonen zu charakterisieren. Das abgeleitete Vp-Modell wurde mit Bohrloch-Daten und Ultraschall-Messungen an Gesteinsproben kombiniert, um die Grenzen verschiedener geologischer Einheiten abzuschätzen. Das Vp/Vs-Modell wurde dann in Kombination mit Widerstandsdaten und Oberflächen-CO2-Messungen verwendet, um die Geometrie der leitfähigen Tonkappe abzuleiten (Vp/Vs ≤ 1.65 und Widerstand ≤ 10 Ωm), um Fluide zu identifizieren (reduzierte Vp Werte, Vp/Vs ≥ 1.71 und Widerstände zwischen 10-60 Ωm) und um gasführende Bereiche zu lokalisieren (Vp/Vs ≤ 1.55 und hohe CO2-Konzentrationen). Eine ähnliche Studie wurde in Theistareykir durchgeführt, wo das Vs-Modell mit Widerstandsdaten kombiniert wurde, um magmatische und/oder hydrothermale Körper zu identifizieren (Vs ≤ -7 %, Widerstände ≤ 30 Ωm). Eine wichtige Schlussfolgerung aus diesen Studien ist, dass die Kombination von seismischen Eigenschaften mit zusätzlichen geologischen und/oder geophysikalischen Daten Mehrdeutigkeiten vermeidet und robuste Interpretationen der Dynamik und Struktur eines geothermischen Reservoirs liefert. Weiterhin wurde eine Coda-Wellen-Interferometrie-Technik (Dehnungsmethode) auf zwei Jahre Ambient-Noise-Daten im Geothermiefeld Theistareykir angewendet, um mögliche Geschwindigkeitsänderungen aufgrund der Nutzung des Feldes zu überwachen. Hier waren die Auswirkungen der Injektions- und Produktionsveränderungen auf das Δv/v-Verhältnis sehr gering und nur eine kleine, möglicherweise produktionsbedingte, langfristige Geschwindigkeitsreduktion wurde festgestellt (-0.05 %/Jahr innerhalb des Produktionsbereichs im Vergleich zum regionalen Wert von -0.04 %/Jahr). Solche Beobachtungen sind für die sichere langfristige Ausbeutung von geothermischen Feldern von großer Bedeutung. Obwohl es noch keine Standardpraxis ist, ist die Berechnung dieser Änderungen weiterhin sehr nützlich, um aseismische Prozesse vor potenziell ausgelösten/induzierten großen seismischen Ereignissen zu steuern, sie ergänzen weiterhin die mikroseismische Überwachung. Mit diesen Ergebnissen trägt die vorgelegte Arbeit zu den Bemühungen der Internationalen Energieagentur bei, die Nutzung von Geothermie zu entwickeln und zu erhöhen.

Description: The Caribbean and South American tectonic plates bound the north-eastwards expulsion of the North Andean Block in western Venezuela. This complicated geodynamic setting resulted in the formation of major strike-slip fault systems and sizeable mountain chains. The 100 km wide Mérida Andes extend from the Colombian/Venezuelan border to the Coastal Cordillera. To the north and south, the Mérida Andes are bound by hydrocarbon-rich sedimentary basins. Knowledge of lithospheric structures, related to the formation of the Mérida Andes, is limited though, due to a lack of deep geophysical data. This thesis presents the results of the first broadband magnetotelluric profile crossing the Mérida Andes and the Maracaibo and Barinas-Apure foreland basins spanning a distance of 240 km. The MT dataset consists of 72 stations installed during March and April 2015 with a minimum recording period of 3 days per station. Geoelectrical strike and dimensionality analyses are consistent with one- or two- dimensional subsurface structures for the sedimentary basins yet also indicate a strong three- dimensional setting for the Mérida Andes. Even more significantly, these analyses showed the presence of off-profile features that influenced the data considerably, particularly at long periods. Therefore, a combination of 2D and 3D modelling was necessary for analysing the geoelectrical structures associated with this dataset. Off-profile structures can significantly affect the outcome of a 2D inversion. Thus, the systematic examination of the influence of 3D structures on 2D inversions was necessary to support the obtained result. Synthetic data sets derived from 3D modelling allowed identification and quantification of spurious off-profile features as well as smoothing artefacts due to limited areal station coverage of data collected along a profile. In general, structures in the 2D inversion are affected by the projection and rotation of the data resulting in sub-horizontal anomalies to reproduce the oblique extent of the fault systems and sedimentary basins. Moreover, a profile distributed dataset can limit the lateral resolution of a 3D inversion considerably. Hence, the effect of data distribution on a 3D inversion was carefully studied to determine the areas of the models that can be confidently explained by the data. To this end, several synthetic datasets were derived from 3D models with varying levels of complexity. The analysis of the synthetic datasets allows determination of the lateral resolution of the 3D models and identification of spurious shallow and deep features considered artefacts related to off-profile features. Furthermore, the inversion of synthetic models provided support to the geological interpretation of the recovered anomalies for the 2D and 3D modelling. The 2D and 3D inversion models were similar above the sedimentary basins and showed marked differences above the Mérida Andes, due to the 3D nature of this section. The inversion models show electrically conductive basins with depths of 2 to 5 km for the Barinas-Apure and 2 to 9 km for the Maracaibo basins. Many resistive bodies within the Maracaibo basin could be related to active deformation causing juxtaposition of older geological formations and younger basin sediments. A conductive zone under the Maracaibo Basin correlates spatially with the location of a Bouguer anomaly low and seem to describe the SE tilt of the Maracaibo Triangular Block under the Mérida Andes. This conductive zone is limited towards the mountain by the north-western thrust system, whose fault plane may function as a detachment surface reaching depth larger than 30 km in the 3D inversion models. The most prominent fault systems of the area, the Boconó and Valera Faults, cross-cut the Mérida Andes in NE-SW direction along its strike with a length 400 km and N-S direction at its centre with a length 60 km, respectively. Both faults are associated with sub-vertical zones of high electrical conductivity and sensitivity tests suggest that the Valera fault reach depths of up to 12 km. The Boconó fault can be considered a crustal structure with a depth up to 35 km. The observed anomalies seem to show a deep connection of the fault planes, possibly related to the formation of the fault systems in a transpressive regime. Conductive anomalies to the south of the Boconó Fault seem to represent a considerable back thrust structure well constrained between 3 and 10 km depth. The high conductivity of these structures is possibly related to weathering water from the surface and the accumulation of clay minerals in the fault gauges. However, fluids related to the flat and shallow subduction of the Caribbean Plate in north-western Venezuela could better explain the low resistivity of the deep structures (〉 15 km). A sizeable conductor at 50 km depth, which appears consistently in the 2D sections, could be identified as an inversion artefact caused by a conductor east of the profile. The 3D inversion places this structure 10 km to the east at 15 km deep. This model also shows depth connection (12 km depth) of the anomalies related to the Valera and Boconó faults with the off-profile conductor. The observed anomalies in the 2D and 3D inversion related to these conductors were tested and reproduced employing synthetic datasets, leading to the speculation that the high conductivity associated with the off-profile conductor may be related to the detachment of the Trujillo Block. The models obtained confirm the shape and distribution of the known geological structures related to the complicated geodynamic settings responsible for the formation of the Mérida Andes. These results partially support the "floating orogen hypothesis" developed to explain the geodynamic evolution of western Venezuela, and they highlight the relevance of the Trujillo Block in this process. However, they also show that features of known structures such as the Boconó fault system maximum depth, the back-thrusting in the Mérida Andes, and the relevance of the escape of the Trujillo Block in the tectonic processes need to be adjusted to the current knowledge.

Description: Die Karibische und Südamerikanische tektonischen Platten begrenzten die nordöstliche Abschiebung des Nord-Anden-Blocks im Westen Venezuelas. Diese komplizierte geodynamische Umgebung führte zur Bildung großer Blattverschiebungen-Verwerfungssysteme und beträchtlicher Gebirgsketten. Die 100 km breiten Mérida-Andes erstrecken sich von der Grenze zwischen Kolumbien und Venezuela bis zum Coastal Cordillera. Im Norden und Süden sind die Mérida-Anden von kohlenwasserstoffreichen Sedimentbecken umgeben. Das Wissen über lithosphärische Strukturen im Zusammenhang mit der Bildung der Mérida-Anden ist jedoch aufgrund des Mangels an tiefen geophysikalischen Daten begrenzt. Diese Arbeit präsentiert die Ergebnisse des ersten breitbandigen magnetotellurischen Profils, das die Mérida-Anden und die Vorlandbecken Maracaibo und Barinas-Apure über eine Entfernung von 240 km quert. Der MT-Datensatz besteht aus 72 Stationen, die im März und April 2015 mit einer Mindestaufzeichnungsdauer von 3 Tagen pro Station installiert wurden. Geoelektrische Streich- und Dimensionalitätsanalysen stimmen mit ein- oder zweidimensionalen Untergrundstrukturen für die Sedimentbecken überein, weisen jedoch auch auf eine starke dreidimensionale Strukturen in der Umgebung der Mérida-Andes hin.. Noch wichtiger ist, dass diese Analysen das Vorhandensein von Merkmalen außerhalb des Profils zeigten, die die Daten insbesondere für lange Perioden erheblich beeinflussen. Daher war eine Kombination aus 2D- und 3D-Modellierung erforderlich, um Störungssysteme und Sedimentbecken quer zum Profil zu reproduzieren. Off-Profile-Strukturen können das Ergebnis einer 2D-Inversion erheblich beeinflussen. Daher war die systematische Untersuchung des Einflusses von 3D-Strukturen auf 2D-Inversionen erforderlich, um das erhaltene Ergebnis zu verifizieren. Synthetische Datensätze, die aus der 3D-Modellierung abgeleitet wurden, ermöglichten die Identifizierung und Quantifizierung von störenden Strukturen außerhalb des Profils sowie die Glättung von Artefakten aufgrund der begrenzten Stationsüberdeckung der entlang eines Profils gesammelten Daten. Im Allgemeinen werden Strukturen in der 2D-Inversion durch die Projektion und Rotation der Daten beeinflusst, was zu flach stehenden Anomalien führt, um die schräge Ausdehnung der Verwerfungssysteme und Sedimentbecken zu reproduzieren. Darüber hinaus kann ein Datensatz entlang eines Profils die laterale Auflösung einer 3D-Inversion erheblich einschränken. Daher wurde die Auswirkung der Datenverteilung auf eine 3D-Inversion sorgfältig untersucht, um die Bereiche der Modelle zu bestimmen, die durch die Daten sicher erklärt werden können. Zu diesem Zweck wurden mehrere synthetische Datensätze aus 3D-Modellen mit unterschiedlicher Komplexität abgeleitet. Die Analyse der synthetischen Datensätze ermöglicht die Bestimmung der lateralen Auflösung der 3D-Modelle und die Identifizierung von störenden oberflächennahen und tiefen Merkmalen, die als Artefakte im Zusammenhang mit Strukturen außerhalb des Profils betrachtet werden. Darüber hinaus unterstützte die Inversion synthetischer Modelle die geologische Interpretation der reproduzierten Anomalien für die 2D- und 3D-Modellierung. Die 2D- und 3D-Inversionsmodelle stimmen über den Sedimentbecken überein. Aufgrund der 3D Strukturen über den MA ergaben sich jedoch deutliche unterschiede. Die Inversionsmodelle zeigen elektrisch leitende Becken mit Tiefen von 2 bis 5 km für das Barinas-Apure und 2 bis 9 km für das Maracaibo-Becken. Viele Gebiete höheren Widerstands im Maracaibo-Becken könnten mit einer aktiven Deformation zusammenhängen, die ein Nebeneinander älterer geologischer Formationen und jüngerer Beckensedimente verursacht. Eine besserleitende Zone unter dem Maracaibo-Becken korreliert räumlich mit der Lage einer Bouguer-Anomalie und scheint die SE-Neigung des Maracaibo-Dreiecksblocks unter den Mérida-Anden zu markieren. Diese leitende Zone ist in Richtung des Gebirges durch das nordwestliche Schubsystem begrenzt, dessen Störungsebene als Ablösefläche fungieren kann, die in den 3D-Inversionsmodellen eine Tiefe von mehr als 30 km erreicht. Die bekanntesten Störungssysteme des Gebiets, die Verwerfungen Boconó und Valera, kreuzen die Mérida-Anden in Nordost-Südwest-Richtung entlang ihres Streichens mit einer Länge von 400 km und die N-S-Richtung in ihrer Mitte mit einer Länge von 60 km. Beide Störungen sind durch steil stehende Zonen hoher elektrischer Leitfähigkeit verbunden. Sensitivitätsstudien legen nahe, dass die Valera-Störung Tiefen von bis zu 12 km erreicht. Die Boconó-Verwerfung kann als Krustenstruktur mit einer Tiefe von bis zu 35 km angesehen werden. Die beobachteten Anomalien scheinen eine tiefe Verbindung der Verwerfungsebenen zu zeigen, möglicherweise im Zusammenhang mit der Bildung der Verwerfungssysteme in einem transpressiven Regime. Leitfähige Anomalien südlich der Boconó-Verwerfung scheinen eine beträchtliche Rückschubstruktur darzustellen, die zwischen 3 und 10 km Tiefe gut lokalisiert ist. Die hohe Leitfähigkeit dieser Strukturen hängt möglicherweise mitWasser aus Verwitterungsprozessen nahe der Erdoberfläche und der Ansammlung von Tonmineralien in den Störungszonen zusammen. Alte Fluide im Zusammenhang mit flach stehenden und oberflächenahen Subduktion der Karibikplatte im Nordwesten Venezuelas könnten jedoch den geringen spezifischen Widerstand der tiefen Strukturen (〉 15 km) besser erklären. Ein beträchtlicher Leiter in einer Tiefe von 50 km, der in den 2D-Schnitten konsistent erscheint, konnte als Inversionsartefakt identifiziert werden, der durch einen Leiter östlich des Profils verursacht wird. Durch die 3D-Inversion wird diese Struktur 10 km östlich in 15 km Tiefe platziert. Dieses Modell zeigt auch die Tiefenverbindung (12 km Tiefe) der Anomalien im Zusammenhang mit den Störungen von Valera und Boconó mit dem Leiter außerhalb des Profils. Die beobachteten Anomalien in der 2D- und 3D-Inversion in Bezug auf diese Leiter wurden unter Verwendung synthetischer Datensätze getestet und reproduziert. Daher kann man annehmen das die mit dem Leiter abseits des Profils verbundene Leitfähigkeit mit der Ablösung des Trujilo Blocks zusammenhängt. Die erhaltenen Modelle bestätigen die Form und Verteilung der bekannten geologischen Strukturen im Zusammenhang mit dem komplizierten geodynamischen Millieu, welches für die Bildung der Mérida-Andes verantwortlich ist. Diese Ergebnisse stützen teilweise die "schwimmende Orogenhypothese", die entwickelt wurde, um die geodynamische Entwicklung West-Venezuelas zu erklären, und sie unterstreichen die Relevanz des Trujillo-Blocks in diesem Prozess. Sie zeigen jedoch auch, dass Merkmale bekannter Strukturen wie die maximale Tiefe des Boconó-Verwerfungssystems, das Zurückschieben in den Mérida-Anden und die Relevanz des Entweichens des Trujillo-Blocks in den tektonischen Prozessen an den aktuellen Kenntnisstand angepasst werden müssen.

Description: The Pacific Northwest (PNW) has substantial earthquake risk, both due to the offshore Cascadia megathrust fault but also other fault systems that produce earthquakes under the region's population centers. Forecasts of aftershocks following large earthquakes are thus highly desirable and require statistical models of a catalog of the PNW’s past earthquakes and aftershock sequences. This is complicated by the fact that the PNW contains multiple tectonic regimes hypothesized to have different aftershock dynamics as well as two types of earthquake clustering (aftershock sequences and swarms). The Epidemic-Type Aftershock Sequence (ETAS) model is a top-performing spatiotemporal point process model which describes the dynamics of earthquakes and aftershocks in a seismic region using a set of parameters. Typically, maximum likelihood estimation is used to fit ETAS to an earthquake catalog; however, the ETAS likelihood suffers from flatness near its optima, parameter correlation and numerical instability, making likelihood-based estimates less reliable. We present a Bayesian procedure for ETAS estimation, such that parameter estimates and uncertainty can be robustly quantified, even for small and complex catalogs like the PNW. The procedure is conditional on knowing which earthquakes triggered which aftershocks; this latent structure and the ETAS parameters are estimated iteratively. The procedure uses a Gibbs sampler to conditionally estimate the posterior distributions of each part of the model. We simulate several synthetic catalogs and test the modelling procedure, showing well-mixed posterior distributions centered on true parameter values. We also use the procedure to model the continental PNW, using a new catalog formed by algorthmically combining US and Canadian data sources and then, identifying and removing earthquake swarms. While MLEs are unstable and depend on both the optimization procedure and its initial values, Bayesian estimates are insensitive to these choices. Bayesian estimates also fit the catalog better than do MLEs. We use the Bayesian method to quantify the uncertainty in ETAS estimates when including swarms in the model or modelling across different tectonic regimes, as well as from catalog measurement error. Seismicity rate estimates and the earthquake forecasts they yield vary spatially and are usually represented as heat maps. While the visualization literature suggests that displaying forecast uncertainty improves understanding in users of forecast maps, research on uncertainty visualization (UV) is missing from earthquake science. In a pre-registered online experiment, we test the effectiveness of three UV techniques for displaying uncertainty in aftershock forecasts. Participants completed two map-reading tasks and a comparative judgment task, which demonstrated how successful a visualization was in reaching two key communication goals: indicating where many aftershocks and no aftershocks are likely (sure bets) and where the forecast is low but the uncertainty is high enough to imply potential risk (surprises). All visualizations performed equally well in the goal of communicating sure bet situations. But the visualization mapping the lower and upper bounds of an uncertainty interval was substantially better than the other map designs at communicating potential surprises. We discuss the implications of these experimental results for the communication of uncertainty in aftershock forecast maps.

Description: Carbonate has often been identified in aqueous carbonic inclusions in spodumene-bearing and other pegmatites, but its origin remains unclear. Here, the conditions at which carbonate and hydrogen carbonate can be generated from spodumene, CO2 and H2O, were studied using a hydrothermal diamond-anvil cell (HDAC) and Raman spectroscopy. In all experiments, spodumene persisted in aqueous carbonic solution up to the maximum temperature (600 to 800 °C). Heating of hydrogen carbonate/oxalate solutions produced CO2- and HCO−3-rich peralkaline fluids, which resulted in strong corrosion of spodumene (and polylithionite-trilithionite) and, in one run, formation of zabuyelite [Li2(CO3)] crystals at low temperatures. The experiments indicate that the reaction of spodumene with CO2 and H2O requires a peralkaline fluid to proceed rapidly. In addition, they show that spodumene crystallizes upon the heating of quartz, muscovite, and aqueous lithium carbonate solution. We conclude that if the aqueous fluid was rich in alkali hydrogen carbonate, zabuyelite in fluid inclusions in pegmatites can form both via a subsolidus reaction of CO2-bearing fluid inclusion with the spodumene host or by trapping a peralkaline fluid early in the evolution of simple or complex pegmatites. The results of our experimental study strengthen the conclusion that, although counterintuitive, hydrogen carbonate-rich peralkaline fluids may be involved in the evolution of peraluminous granitic pegmatites, in which peralkaline minerals are normally absent or very rare.

Description: Knowledge of groundwater flow is of high relevance for groundwater management and the planning of different subsurface utilizations such as deep geothermal facilities. While numerical models can help to understand the hydrodynamics of the targeted reservoir, their predictive capabilities are limited by the assumptions made in their set up. Among others, the choice of appropriate hydraulic boundary conditions, adopted to represent the regional to local flow dynamics in the simulation run, is of crucial importance for the final modelling result. In this publication we present the hydrogeological models to obtain results to quantify how and to which degree different upper hydraulic boundary conditions and vertical cross boundary fluid movement influence the calculated deep fluid conditions Therefore, we take the central Upper Rhine Graben area as a natural laboratory. The presented three models are set up with different sets of boundary conditions. The Reference Model uses the topography as upper hydraulic pressure surface of 0 kPa. In model S1, a subdued replica of the topography, which was built on the base of hydraulic head measurements is applied as the upper hydraulic boundary condition and in model S2 vertical cross boundary flow is implemented. Based on our results, we illustrate in the landing paper that for the Upper Rhine Graben specific characteristics of the flow field are robust and insensitive to the choice of imposed hydraulic boundary conditions, while specific local characteristics are more sensitive. Accordingly, these robust features characterizing the first order groundwater flow dynamics in the Upper Rhine Graben include: (i) a regional groundwater flow component descending from the graben shoulders to rise at its centre; (ii) infiltration of fluids across the graben shoulders, which locally rise along the main border faults; (iii) the presence of heterogeneous hydraulic potentials at the rift shoulders. The configuration of the adopted boundary conditions influence primarily calculated flow velocities and the absolute position of the upflow axis within the graben sediments. In addition, the choice of upper hydraulic boundary conditions exerts a direct control on the evolving local flow dynamics, with the degree of influence gradually decreasing with increasing depth. With respect to regional flow modelling of basin hosted, deep water resources, the main conclusions derived from this study are: (i) the often considered water table as an exact replica of the model topography (Reference Model) likely introduces a source of error in the simulations in regional hydraulic modelling approaches. Here, we show that these errors can be minimized by making use of a water table as upper boundary condition derived from available hydraulic head measurements (model S1). If the study area is part of a supra-regional flow system - like the central Upper Rhine Graben is part of the whole Upper Rhine Graben - the in- and outflow across vertical boundaries need to be considered (model S2).

Description: This dataset provides friction and elasticity data from ring shear and axial tests, respectively, on rock analogue materials used at the University Roma Tre (Rome, IT) in “Foamquake”, a novel seismotectonic analog model mimicking the megathrust seismic cycle (Mastella et al., under review). Two granular materials (quartz sand and Jasmine rice) have been characterized by means of internal friction coefficients µ and cohesions C. An elastic material (foam rubber) have been characterized by means of Young’s modulus E and Poisson’s ratio v. According to our analysis the granular materials show Mohr-Coulomb behaviour characterized by linear failure envelopes in the shear stress vs. normal load Mohr space. Peak, dynamic and reactivation friction coefficients of the quartz sand are µP = 0.69, µD = 0.56 and µR = 0.64, respectively. Cohesion ranges between 50 and 100 Pa. Rate-dependency of friction in quartz sand seems insignificant. Peak, dynamic and reactivation friction coefficients of the Jasmine rice are µP = 0.70, µD = 0.59 and µR = 0.61, respectively. Cohesion ranges between 30 and 50 Pa. Rate-weakening of Jasmine rice is c. 6% per tenfold change in shear velocity v. The Young’s modulus of the foam rubber has been constrained to 30 kPa, its Poisson’s ratio is v=0.1.

Description: This dataset includes particle image correlation data from 26 experiments performed with Foamquake, a novel analog seismotectonic model reproducing the megathrust seismic cycle. The seismotectonic model has been monitored by the means of a high-resolution top-view monitoring camera. The dataset presented here represents the particle image velocimetry surface velocity field extracted during the experimental model through the cross-correlation between consecutive images. This dataset is supplementary to Mastella et al. (2021) where detailed descriptions of models and experimental results can be found.

Description: The Younger Dryas (YD) is a roughly 1,100-year cold period marking the end of the last glaciation. Climate modelling for northern Europe indicates high summer temperatures and strong continentality. In eastern Europe, the scale of temperature variation and its influence on ecosystems is weakly recognised. Here, we present a multi-proxy reconstruction of YD conditions from Lake Gościąż (central Poland). The decadal-resolution analysis of its annually varved sediments indicates an initial decrease in Chironomidae-inferred mean July air temperature followed by steady warming. The pollen-inferred winter-to-summer temperature amplitude and annual precipitation is highest at the Allerød/YD transition and the early YD (ca. 12.7–12.4 ky cal BP) and YD/Holocene (11.7–11.4 ka cal BP) transition. Temperature and precipitation were the main reasons for lake level fluctuations as reflected in the planktonic/littoral Cladocera ratio. The lake’s diatom-inferred total phosphorus decreased with increasing summer temperature from about mid YD. Windy conditions in the early YD until ∼12.3 ka cal BP caused water mixing and a short-lived/temporary increase in nutrient availability for phytoplankton. The Chironomidae-inferred summer temperature and pollen inferred summer temperature, winter temperature and annual precipitation herein are one of only a few in eastern Europe conducted with such high resolution.

Description: Fluid inclusions in pegmatite minerals were studied using Raman spectroscopy to determine the carbon species. Carbon dioxide is very abundant in the aqueous liquid and vapor phases. Occasionally, CH4 was found in the vapor. In the aqueous liquid, HCO−3 was detected in fluid inclusions in tantalite-(Mn) from the Morrua Mine and in late-stage quartz from the Muiâne pegmatite and the Naipa Mine, all in the Alto Ligonha District, Mozambique. Moreover, we observed a carbonate (calcite group) in fluid inclusions in garnet from the Naipa Mine and in beryl from the Morrua Mine, both in the Alto Ligonha District, Mozambique, and a calcite-group carbonate and whewellite [CaC2O4∙H2O] in fluid inclusions in topaz from Khoroshiv, Ukraine. The occurrence of oxalate is interpreted to be due to a reaction of some form of carbon (possibly CO or bitumen) with a peralkaline fluid. Our results support the hypothesis that, although counterintuitive, hydrogen carbonate-rich peralkaline fluids may locally be involved in the evolution of peraluminous granitic pegmatites, in which peralkaline minerals are normally absent or very rare.

Description: One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness.

Description: We report a new improvement in self-organized maps for geological interpretation of geophysical data. By using a multi-geophysical dataset recorded in the mining area of Thuringia, Germany, we show the results of replacing the typical feature analysis by a principal component analysis. By performing a transformation of the dataset according to a few of the principal components, we obtain a more detailed representation of the local geology than previous works. Results also show a significant improvement in processing time, while also minimizing influence of user´s interpretation.

Description: The Songliao Block is located in the eastern part of the Central Asian Orogenic Belt. Its creation and evolution are believed to be related to the closure of the Paleo-Asian and Mongol-Okhotsk oceans, and to the subduction of the Paleo-Pacific Ocean. The deep seismic reflection profiles showed that there are sloping mantle reflections below the Songliao Block, which are suspected to be the result of the convergence of three tectonic domains. However, it is still not clear the current structural form of the Songliao Block is caused by the direct action or not of the tectonic systems. This work used 138 broadband magnetotelluric stations to obtain a three-dimensional electrical structural model of the northern Songliao Block. The results showed there are orthogonal network fault systems, faulted basins, igneous rocks. And the Lindian fault depression is the center of the asthenospheric upwelling, the shallowest up to 45 km. Combined with evidence from seismic studies, we proposed that the superposition of tectonic systems may have produced weak tectonic zones. These zones provided channels for the later upward movement of fluids and melt, likely due to hydrous upwellings caused by the subduction of the Paleo-Pacific system.

Description: Earth angular momentum forecasts are naturally accompanied by forecast errors that typically grow with increasing forecast length. In contrast to this behavior, we have detected large quasi-periodic deviations between atmospheric angular momentum wind term forecasts and their subsequently available analysis. The respective errors are not random and have some hard to define yet clearly visible characteristics which may help to separate them from the true forecast information. These kinds of problems, which should be automated but involve some adaptation and decision-making in the process, are most suitable for machine learning methods. Consequently, we propose and apply a neural network to the task of removing the detected artificial forecast errors. We found, that a cascading forward neural network model performed best in this problem. A total error reduction with respect to the unaltered forecasts amounts to about 30% integrated over a 6 day forecast period. Integrated over the initial 3 day forecast period, in which the largest artificial errors are present, the improvements amount to about 50%. After the application of the neural network, the remaining error distribution shows the expected growth with forecast length. However, a 24 hourly modulation and an initial baseline error of 2*10−8 became evident that were hidden before under the larger forecast error.

Description: Understanding how resilient rangelands are to climatic disturbances such as drought is of major importance to land managers. The resilience of ecosystems can be reduced by livestock grazing and by environmental conditions. Most studies quantifying resilience are based on model simulations. However, natural time series from satellite data offer the possibility to infer aspects of resilience from real systems. The objective of this study was to investigate two aspects of ecological resilience, namely resistance to climate variability and recovery from drought, by applying a change detection method (Breaks For Additive Seasonal and Trend; BFAST) spatially on a 28-year Landsat NDVI time series in a dry rangeland in southern Cyprus. First, we used the number of breakpoints fitted by the BFAST model as an inverted proxy for long-term vegetation resistance to climate variability (the ability to withstand change during a disturbance reduces the likelihood to trigger a breakpoint in the time series). Second, we used the linear slope of the BFAST model after a known drought as a proxy of the recovery rate of the vegetation. This information was then used to analyse the spatial distribution of the total number of breakpoints and of the NDVI recovery trend in relation to grazing and environmental properties. Our results show that high NDVI and a northern orientation (i.e. favourable environmental conditions) were associated with a highly resilient system, due to high resistance to climate variability and fast recovery after drought. Intermediate conditions were associated with low resistance. Unfavourable conditions and high grazing intensities were associated with an unresponsive ecosystem state characterised by high resistance and slow recovery after a drought event. Low grazing intensities positively affected the NDVI recovery trend, but did not improve resistance. On northern slopes, terrain slope had a positive effect on the NDVI recovery trend, while on southern slopes it had a negative effect. Our satellite-driven approach has a strong potential for resilience monitoring, because it can be applied on broad spatial and temporal scales in areas with low availability of field data. Moreover, it allows to jointly extract two important components of resilience: resistance and recovery rate.

Description: The evolution of chemical bonding in ferropericlase, (Mg,Fe)O, with pressure may affect the physical and chemical properties of the Earth’s lower mantle. Here, we report highpressure optical absorption spectra of single-crystalline ferropericlase ((Mg0.87Fe0.13)O) up to 135 GPa. Combined with a re-evaluation of published partial fluorescence yield X-ray absorption spectroscopy data, we show that the covalency of the Fe−O bond increases with pressure, but the iron spin transition at 57−76.5 GPa reverses this trend. The qualitative crossover in chemical bonding suggests that the spin-pairing transition weakens the Fe−O bond in ferropericlase. We find, that the spin transition in ferropericlase is caused by both the increase of the ligand field-splitting energy and the decrease in the spin-pairing energy of high-spin Fe2+.

Description: he competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these ‘internal’ and ‘external’ factors remain poorly understood, especially in 3D. In this study, we used brittle-viscous analogue models to assess how multiphase rifting, that is changes in plate divergence rate or direction, and the presence and orientation of weaknesses in the competent mantle and crust, influences rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without any kinematic changes already creates complex rift structures. Divergence rates affect the strength of the weak lower crustal layer and hence the degree of mantle-crustal coupling; slow rifting decreases coupling, so that crustal weaknesses can dominate deformation localisation and surface structures, whereas fast rifting increases coupling and deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle-related deformation can overprint structures that previously formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle-controlled towards crust-controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are sufficiently well developed. We furthermore place our results in a larger framework of brittle-viscous rift modelling results from previous experimental studies, showing the importance of general lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can produce a variety of deformation styles that may, however, lead to comparable end products. Therefore, careful investigation of the distribution of strain localisation, and to an equal extent of basin depocenter locations over time is required to properly determine the evolution of complex rift systems, providing an incentive to revisit various natural examples.

Description: The Kiaka orogenic gold deposit (Burkina Faso), located in the Paleoproterozoic domain of the West African Craton, is characterized by a two-stage gold mineralization hosted in volcano-sedimentary metamorphic rocks that was formed during the Eoeburnean (2.20–2.13 Ga) and Eburnean (2.13–2.05 Ga) orogenic cycles. These two stages include an early disseminated low-grade gold mineralization and a late vein-hosted high-grade gold mineralization. Paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline. The aim of this paper is twofold: (i) to determine the processes responsible for deposition of the economic disseminated gold mineralization and (ii) to identify the source of the mineralizing fluids. For this purpose, we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes. Hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different δ11B values falling within the two intervals of − 25.1 to − 22.0‰ and − 19.6 to − 15.1‰, respectively. Our results suggest that tourmaline formed from a distal, high-temperature (ca. 400 °C), reduced, and low-salinity hydrothermal fluid that interacted with the local host rocks. Based on the modeling of tourmaline–fluid boron isotope fractionation, we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca. 2.13 Ga. This metamorphic fluid–rock interaction model may possibly extend to other orogenic gold deposits in the West African Craton.

Description: Fluvial deposits offer Earth’s best-preserved geomorphic record of past climate change over geological timescales. Quantitatively extracting this information remains challenging in part due to the complexity of erosion, sediment transport and deposition processes and how each of them responds to climate. Furthermore, sedimentary basins have the potential to temporarily store sediments, and rivers subsequently rework those sediments. This may introduce time lags into sedimentary signals and obscure any direct correlation with climate forcing. Here, using a numerical model that combines all three processes—and a new analytical solution—we show that the thickness of fluvial deposits at the outlet of a mountain river can be linked to the amplitude and period of rainfall oscillations but is modulated by the mountain uplift rate. For typical uplift rates of a few mm/yr, climate oscillations at Milankovitch periods lead to alluvial sediment thickness of tens of meters as observed in nature. We also explain the time lag of the order of 20–25% of the forcing period that is commonly observed between the timing of maximum rainfall and erosion. By comparing to field datasets, our predictions for the thickness and time lag of fluvial deposits are broadly consistent with observations despite the simplicity of our modeling approach. These findings provide a new theoretical framework for quantitatively extracting information on past rainfall variations from fluvial deposits.

Description: Nutrient supply to the coastal euphotic zone is critical in sustaining the productivity of ecosystems and provides an important feedback on the carbon cycle via stimulating the biological pump. The supply of coastal nutrients is typically thought to be dominated by terrestrial inputs and upwelling of deep ocean waters. Marine-terminating glaciers can provide nutrients via both mechanisms but the relative importance of each is dependent on complex physical–biogeochemical processes ranging from those in the glacier drainage system to the ice–ocean interface. Constraining these glacial nutrient supply processes in a remote part of the Canadian Arctic Archipelago (CAA) is the focus of a new study by Williams et al. (2021, https://doi.org/10.1029/2021JG006289). Their findings advance our understanding of the role glaciers play in polar nutrient cycling by highlighting significant shallow meltwater pumping of macronutrient-replete marine waters by CAA marine-terminating glaciers into the euphotic zone.

Description: Earthquakes are generally known to alter the stress field near seismogenic faults. Observations using YRY-four-gauge borehole strainmeters within Yushu (YSH) borehole near the Ganzi-Yushu fault in eastern Tibetan Plateau shows that the azimuth variation of maximum horizontal stress (SH) first decreased and then increased substantially when the earthquakes occurred during the measurement period from January 1, 2009 to December 31, 2018. In this period, 38 earthquakes (M ≥ 3) were detected near the fault and the SH orientation showed a drastic change after the 2010 Ms 7.3 Yushu mainshock. We present a discrete element modelling using Particle Flow Code 2D (PFC2D) to simulate a dynamic fault rupturing process and to use the modelling results for interpretation of the stress reorientation. The modelling reveals that dilatation and compression quadrants are formed around a fault rupturing in strike-slip model, resulting in different spatiotemporal changes of the orientation of maximum horizontal stress (Δθ). The value of Δθ in the compression quadrants shows a sharp drop at the time of coseismic slip, then approaches slowly to an asymptotic value. In the dilatation quadrants, Δθ drops by coseismic slip, then increases sharply and finally reaches a stable value. The modelled Δθ by coseismic fault slip agrees with in-situ observations at YSH borehole during 2010 Ms 7.3 Yushu mainshock. It is also found that, the value of Δθ decreases with increasing distance from the rupturing source. We modelled the effect of fault geometry and host rock properties on the Δθ, and found that structural complexity and off-fault damage by coseismic fault slip have significant impact on the stress field alteration near the rupturing source.

Description: Physical weathering in cold, steep bedrock hillslopes occurs at rates that are thought to depend on temperature, but our ability to quantify the temperature-dependence of erosion remains limited when integrating over geomorphic timescales. Here, we present results from a 1D numerical model of in-situ cosmogenic 10Be, 14C, and 3He concentrations that evolve as a function of erosion rate, erosion style, and ground surface temperature. We used the model to explore the suitability of these nuclides for quantifying erosion rates in areas undergoing non-steady state erosion, as well as the relationship between bedrock temperature, erosion rate, and erosional stochasticity. Our results suggest that even in stochastically-eroding settings, 10Be-derived erosion rates of amalgamated samples can be used to estimate long-term erosion rates, but infrequent large events can lead to bias. The ratio of 14C to 10Be can be used to evaluate erosional stochasticity, and to determine the offset between an apparent 10Be-derived erosion rate and the long-term rate. Finally, the concentration of 3He relative to that of 10Be, and the paleothermometric interpretations derived from it, are unaffected by erosional stochasticity. These findings, discussed in the context of bedrock hillslopes in mountainous regions, indicate that the 10Be-14C-3He system in quartz offers a method to evaluate the temperature-sensitivity of bedrock erosion rates in cold, high-alpine environments.

Description: Fluid-induced seismicity in tectonically inactive regions has been attributed to fluid overpressurization of rock fractures during natural resource extraction and storage. We conducted a series of triaxial shear-flow experiments on sawcut fractures in granite and showed that the fracture responses can be dissimilar under various fluid pressurization conditions. For pressure-controlled fluid pressurization, a uniform fluid pressure distribution can be promoted by lowering pressurization rate and enhancing fracture permeability. However, during volume-controlled fluid pressurization, a high pressurization rate causes a drastic increase in fluid pressure before fracture failure. In this case, our analytical model reveals that the fracture area and normal stiffness also influence fluid pressure variations. The maximum seismic moment predicted by this model is well validated by the experimental data for the cases with low pressurization rates. The discrepancy between the analytical and experimental data increases with higher fluid overpressure ratio owing to the assumption of uniform fluid pressure distribution in the model. The sensitivity analysis demonstrates the importance of fracture size estimation in the maximum seismic moment prediction. Our model can potentially be applied to control the fluid overpressurization of rock fractures and to mitigate the risks of fluid-induced seismicity.

Description: Combining in situ measurements of energetic electrons and remote sensing observations of hard X-rays and type III radio bursts, we examine the release times of energetic electrons in the July 23, 2016 event. We find that the releases of in situ energetic electrons from the Sun are delayed from those electrons that are responsible for the hard X-rays. We further find that the release time of in situ electrons is a function of electron energy. Under the assumption that the acceleration mechanism for the upward propagating electrons is of Fermi-type and is controlled by an energy-dependent diffusion coefficient, we fit these release times by a simple functional form, related to the turbulence spectral index. Implications of our study on the underlying electron acceleration mechanisms and the magnetic reconnection process in solar flares are discussed. Our results demonstrate the power of the recently developed fractional velocity dispersion analysis (FVDA) method in solar flare studies.