bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty Propagation and Stochastic Interpretation of Shear Motion Generation due to Underground Chemical Explosions in Jointed Rock
Authors: Ezzedine Souheil , Vorobiev Oleg , Antoun Tarabay , Walter William
Published: March 2020

We have performed 3D simulations of underground chemical explosions conducted recently in granitic outcrop as part of the Source Physics Experiment (SPE) campaign. The main goal of these simulations is to understand the nature of the shear motions recorded in the near field considering uncertainties in a) the geological characterization of the joints, such as density, orientation and persistency and b) the geomechanical material properties, such as, friction angle, bulk sonic speed, poroelasticity etc. The approach is probabilistic; joints are depicted using a Boolean stochastic representation of inclusions conditional to observations and their probability density functions inferred from borehole data. Then, using a novel continuum approach, joints and faults are painted into the continuum host material, granite. To ensure the fidelity of the painted joints we have conducted a sensitivity study of continuum vs. discrete representation of joints. Simulating wave propagation in heterogeneous discontinuous rock mass is a highly non-linear problem and uncertainty propagation via intrusive methods is practically forbidden. Therefore, using a series of nested Monte Carlo simulations, we have explored and propagated both the geological and the geomechanical uncertainty parameters. We have probabilistically shown that significant shear motions can be generated by sliding on the joints caused by spherical wave propagation. Polarity of the shear motion may change during unloading when the stress state may favor joint sliding on a different joint set. Although this study focuses on understanding shear wave generation in the near field, the overall goal of our investigation is to understand the far field seismic signatures associated with shear waves generated in the immediate vicinity of an underground explosion. Therefore, we have abstracted the near field behavior into a probabilistic source-zone model which is used in the far field wave propagation.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Budyko’s framework to estimate Runoff sensitivity for the Indian sub-continental river basins
Authors: Bharat Shalinee , Mishra Vimal
Published: March 2020

Indian rivers are an inevitable part of the nation’s economy and society due to which it is necessary to understand the water budget for Indian sub-continental river basins. The available water and energy both play a prominent role in the runoff generation. However, the sensitivity of precipitation and temperature in runoff estimates are not well-explored. Here, we estimate the total runoff using  Budyko’s original water balance model for 220 sub-basins that are selected based on the major discharge stations in India. The Budyko’s total runoff is well correlated with the Variable Infiltration Capacity (VIC) simulated total runoff. Further, we estimate the precipitation elasticity and potential evaporation (PET) sensitivity of total annual runoff using the second-degree linear relation. We find that runoff is more sensitive towards the change in precipitation rather than the change in temperature in Cauvery, South Coast, Pennar, East Coast and Krishna basins. However, Indus and Brahmaputra basins show the contrasting pattern.  
Modelling of seismicity-induced cracking of stone columns using discrete-element-method (DEM), a case study of Eufrasius cathedral, Porec, Croatia
Authors: Besharatinezhad Ali , Török Ákos , Al-Tawalbeh Mohammad , Kázmér Miklós
Published: March 2020

The Eufrasius Cathedral of Poreč in Istria Peninsula, Croatia, was built in the 6th century, The nave collapsed in parts due to the AD 1440 earthquake. Nave and aisles are supported by 18 monolithic columns of Proconnesian marble. Seventeen of the columns bear various fractures, forming two groups: (1) axis-parallel fractures and (2) oblique fractures. Azimuths of dip directions of oblique fractures indicate N-S shaking.

In this study, the fracture development and cracking of a stone column was modelled using computer code. To model the current fracture pattern and to link it to seismic activity a Lagrangian analysis of continua in three dimensions (FLAC3D) is employed to reveal the non-linear behaviour of the stone column. A 3-Dimensional model based on discrete-element-method (DEM) has been created to study the failure process of the ancient stone column under static and dynamic loads. A combination of vertical and horizontal loads with a dynamic load due to the earthquake has been imposed horizontally. The influence of different parameters such as mechanical properties of rock, the magnitude of the earthquake were also assessed to observe their influence on the failure mechanism of rock. The DEM model was able to describe the observed crack pattern and it has proved the applicability of FLAC3D to describe failure mechanism of stone columns.
Potential linkage between the atmospheric summer circulation over Eurasia and preceding sea ice anomalies southwest of Greenland
Authors: Sauer Jerome , Baehr Johanna , Žagar Nedjeljka
Published: March 2020

Sea ice alters the surface albedo and modulates the heat, moisture and momentum exchange between the ocean and the atmosphere. Various studies suggest an influence of the sea ice on the atmospheric circulation, whereby the focus is often on simultaneous connections and Arctic-wide sea ice conditions. Sea ice has a strong memory and we thus hypothesize a potential feedback on the atmosphere also at higher lags. Using ERA5 reanalysis data between 1983 and 2017, the present work investigates a potential connection of the summer atmospheric circulation over Eurasia to winter sea ice anomalies southwest of Greenland. Composites of the June-July geopotential height pattern show a wave-train structure throughout the troposphere and the resulting circulation anomalies are found to influence the two metre temperatures over northeastern Europe and northern Russia. These anomalies are significantly correlated with December-January sea ice anomalies. Persistent sea surface temperature (SST) anomalies associated with the strong ice memory indicates that the winter signal is partly stored in the Labrador Sea. The observations indicate a response in the June-July 500 hPa vertical velocity in proximity of the strongest SST anomalies that is dynamically consistent with the lower-level and upper-level divergence pattern. The result suggests that the vertical velocity potentially connects a vorticity forcing in the upper troposphere to near-surface conditions over the Labrador Sea that originate from the preceeding winter.
A further analysis shows a particularly pronounced wave-train signal when the December-January ice anomalies appear in phase with a strong North Atlantic Oscillation (NAO) index. Those years are characterized by extensive and persistent SST anomalies in the North Atlantic bearing similarities with the tripole pattern that is known to be associated with the NAO. The SST signal is accompanied by widespread heat flux anomalies hinting at a further influence coming from the central North Atlantic. The study provides a first analysis of two possible factors that potentially contribute to the linkage between winter sea ice and the summer atmospheric circulation.
Assessment of regional atmospheric transport model performance using 222Radon observations
Authors: Karstens Ute , Levin Ingeborg , Ramonet Michel , Gerbig Christoph , Arnold Sabrina , Conil Sebastién , Della Coletta Julian , Frumau Arnoud , Gheusi François , Kazan Victor , Kubistin Dagmar , Lindauer Matthias , Lopez Morgan , Maurer Lars , Mihalopoulos Nikos , Pichon Jean-Marc , Spain Gerard
Published: March 2020

The rather short life time of 222Radon of 5.5 days makes this radioactive noble gas an almost ideal tracer of atmospheric transport processes. 222Radon, the gaseous progeny of 226Radium, which is a trace constituent of all soils, can escape the soil grains and make its way from the unsaturated soil zone into the atmosphere. The exhalation rate of 222Radon from continental surfaces depends on soil type and permeability, but is orders of magnitude larger than that from ocean surfaces. Therefore, the atmospheric 222Radon activity concentration can be used as a measure of the residence time of air over continental surfaces or to distinguish continental from marine air masses. At continental sites, the short-term variability of 222Radon is mainly determined by diurnal or synoptic-scale boundary layer mixing processes. If its continental exhalation rate is known, 222Radon can even be applied as a quantitative tracer for evaluating regional scale transport model performance. In the present study we use 222Radon activity concentration measurements from the ICOS atmospheric station network and STILT transport model results to assess the ability of this routinely used model to correctly simulate the (diurnal) variation of boundary layer transport. This uncertainty assessment is an important step towards reliable estimates of the contribution of transport model error in GHGs inversion studies that aim at providing accurate fluxes from inversion of atmospheric GHGs observations in ICOS.  
Large wood hydraulics - a fluvial process of growing interest
Authors: Schnauder Ingo
Published: March 2020

In the last decade, the perception of large wood in rivers has shifted from a hazard perspective towards a valuable and required component of the river ecosystem. Consequently, there is a demand to quantify and predict the effects of large wood on flow, morphology and retention.

The research programme ‘Large Wood Hydraulics’ investigates the flow and turbulence characteristics of instream large wood. Within the programme, field measurements and lab experiments are conducted and cover different wood types (tree morphology, branching pattern), their position / orientation in the cross-section and single or multiple elements (wake interference). Field measurements were carried out in river Mulde, Germany within the BMBF-project ‘Wilde Mulde’ and flume experiments in the hydraulics lab of  TU Vienna.

The aim of the study is to predict the effects of different wood configurations to promote the use of wood in river restoration schemes.
Fast Airborne Extractive Electrospray Mass Spectrometry (EESI) Measurements of the Chemical Composition of Biomass Burning Organic Aerosol
Authors: Pagonis Demetrios , Campuzano-Jost Pedro , Guo Hongyu , Day Douglas , Brown Wyatt , Schueneman Melinda , Nault Benjamin , Piel Felix , Mikoviny Tomas , Tomsche Laura , Wisthaler Armin , Jimenez Jose
Published: March 2020

Fast measurements of the chemical composition of organic aerosol (OA) at the molecular level are essential to furthering the understanding of the sources and evolution of ambient particulate matter. To that end, we carried out airborne in-situ extractive electrospray time-of-flight mass spectrometry (EESI) measurements of aerosol in a large set of wildland and agricultural fire smoke plumes during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in summer 2019. We present the methodology that allowed for stable, quantitative measurements of targeted analytes up to altitudes of 7 km. Optimization of electrospray solvent, fine control of electrospray capillary position, pre- and post-flight calibrations, and tightly regulated inlet pressure all contributed to extending airborne EESI measurements to these altitudes.

The EESI was operated with both positive and negative ion polarity during the study, and we report 1-Hz aerosol concentrations of levoglucosan for EESI(+) and nitrocatechol for EESI(-). Campaign-averaged 1-second detection limits for each compound were 720 and 17 ng m-3 during low-altitude sampling. Intercomparison of EESI with an Aerodyne high-resolution Aerosol Mass Spectrometer (AMS) flown during FIREX-AQ shows the fast response time of EESI in concentrated aerosol plumes. Total EESI signal was well correlated with AMS OA for both EESI(+) and EESI(-) measurements, and we present bulk EESI OA sensitivities. We also compare EESI measurements of levoglucosan to a CHemical Analysis of aeRosol ONline Proton-Transfer Reaction Mass Spectrometer (CHARON PTR-MS) flown during FIREX-AQ, demonstrating quantitative agreement between the two instruments. We also compare compounds detected in-situ by EESI with offline electrospray ionization (ESI) of filter samples collected during FIREX-AQ, showing overlap in the detected spectra of the two techniques.

Positive matrix factorization (PMF) of EESI data shows that the chemical composition of biomass burning OA evolves as it is transported downwind, with production of some species and loss of others. This evolution occurs while dilution-corrected OA concentrations remain roughly constant, suggesting that there is a balance between processes that increase and reduce OA concentrations. 
Sensitivity analysis of an integrated numerical flow model output to key parameters used in common qualitative vulnerability assessment methods
Authors: Doummar Joanna , Kassem Assaad H.
Published: March 2020

Qualitative vulnerability assessment methods applied in karst aquifers rely on key factors in the hydrological compartments usually assigned different weights according to their estimated impact on groundwater vulnerability. Based on an integrated numerical groundwater model on a snow-governed karst catchment area (Assal Spring- Lebanon), the aim of this work is to quantify the importance of the most influential parameters on recharge and spring discharge and outline potential parameters that are not accounted for in standard methods, when in fact they do play a role in the intrinsic vulnerability of a system. The assessment of the model sensitivity and the ranking of parameters are conducted using an automatic calibration tool for local sensitivity analysis in addition to a variance-based local sensitivity assessment of model output time series (recharge and discharge)  for two consecutive years (2016-2017) to various model parameters. The impact of each parameter was normalized to estimate standardized weights for each of the process based key-controlling parameters. Parameters to which model was sensitive were factors related to soil, 2) fast infiltration (bypass function) typical of karst aquifers, 3) climatic parameters (melting temperature and degree day coefficient) and 4) aquifer hydraulic properties that play a major role in groundwater vulnerability inducing a temporal effect and varied recession. Other less important parameters play different roles according to different assigned weights proportional to their ranking. Additionally, the effect of slope/geomorphology (e.g., dolines) was further investigated.  In general, this study shows that the weighting coefficients assigned to key vulnerability factors in the qualitative assessment methods can be reevaluated based on this process-based approach.

 

 

 
The identification and assessment of asbestos exposure from mineral raw materials in Germany - definitions, conventions, analytical methods, exposure situation and protective measures
Authors: Mattenklott Markus
Published: March 2020

In Germany, there has been an exemption for the use of mineral raw materials containing asbestos since 1993 on the basis of the Hazardous Substances Ordinance. While activities involving asbestos or materials containing asbestos are generally prohibited since that time, demolition/maintenance work and working involving asbestos containing mineral raw materials (maximum permissible asbestos content: 0.1 mass%) are permitted, subject to compliance with defined protective measures. Activities involving mineral raw materials containing asbestos (e.g. talcum, gravel) NOA are usually released from tremolite / actinolite or anthophyllite, in a few cases also chrysotile / antigorite. The occurrence of grunerite or riebeckite is the exception. In occupational health and safety, analytical methods for determining exposure are limited to the detection of fibres with critical dimensions (L > 5 µm, D < 3 µm, L:D > 3:1; so-called WHO fibres). For this purpose, an extended definition of asbestos has been laid down in the Special Technical Rules for Hazardous Substances ("TRGS" 517), which concerns the chemical composition and morphology of the NOAs to be determined. It was also necessary to establish a convention by means of which asbestos minerals can be distinguished from other chemically similar minerals. In Germany, the determination of asbestos fibre concentrations is usually carried out by means of SEM-EDX analysis. The convention therefore refers to a distinction based on certain element contents and their ratios. This catalogue of criteria is freely available in the form of an EXCEL sheet. This ensures that different laboratories achieve comparable results. On this basis, exposure measurements have been carried out by the measurement services of the accident insurance institutions since about 1998. Measurement results are presented from the extraction of rocks in quarries, the cold milling of road pavings, the use of talcum and from asphalt mixing plants, among others. Depending on the determined exposure level, protective measures have to be taken for the activities concerned. In addition to general protective measures, special protective measures have been defined for specific industries. For the determination of the asbestos content in mineral raw materials, the TRGS 517 defines four specific determination procedures, including a procedure based on a dustiness test.
Using tree rings to estimate the annual carbon sequestration of hardwood floodplain forests along the Middle Elbe
Authors: Shupe Heather , Jensen Kai , Ludewig Kristin
Published: March 2020

Anthropogenic land use and landscape change has dramatically decreased the presence of hardwood floodplain forests (HFF) globally. In Germany, it is estimated that only 1% of the former HFFs still exist today. Natural HFFs provide an abundance of ecosystem services such as the mitigation of climate change through the sequestration of atmospheric carbon. In order to confidently quantify global carbon fluxes, local in-situ investigations are required. This research aims to quantify and compare carbon sequestration rates (CSRs) of temperate HFFs at a local scale. Traditional dendrochronological methods are applied to tree cores collected from oak (Quercus robur) and elm (Ulmus laevis) trees located within 35 HFF plots differing in age classes and hydrological situations along 100 km of the Middle Elbe river. Tree ring widths (TRW) from both tree species are measured and used to estimate basal area increments (BAI) and CSRs. Preliminary results show that CSRs are higher in oaks than in elms. While CSRs seem not to differ between hydrological situations in trees with ages between 60 and 150 years, we found pronounced effects of hydrological conditions on CSRs in the oldest trees (> 180 years). Interestingly, highest mean CSRs were found for old trees in regularly flooded HFF with a dense canopy cover. These results are in agreement with recent research that have overturned the old paradigm that old forests are less productive than young forests. We conclude that HFFs remain active carbon sinks as they age and that the preservation or even expansion of HFFs can contribute to other global strategies for climate change mitigation.
Evaluation of the retention capacity of Pb and Cu in technosoils of Sustainable Urban Drainage Systems (SUDs) in Bogota, Colombia
Authors: Sanchez Hernandez Karel Aldrin , Santos Granados Germán Ricardo , Angulo-Jaramillo Rafael , González Murillo Carlos Alberto , Lozada Lopez Catalina
Published: March 2020

Recently, cities growth has enhanced economic development but also generates different problems that affect the population such as stormwater drainage. It is known that the area available for water infiltration decrease in these urban centers generating scenarios of high vulnerability and risk of flooding associated with extreme weather events of precipitation. Therefore, an alternative is the implementation of Sustainable Urban Drainage systems (SUDs) that allows high efficiency in the control and local infiltration of rainwater. SUDs are often built with technosoils from the recycling of materials from different industries, for which it is necessary to study their hydraulic and solute retention properties. Indeed, one of the functions of SUDs must therefore be the retention of pollutants before they reach the groundwater. Therefore, this research aimed to evaluate the retention capacity of metallic solutes Pb and Cu in technosoils (compacted mixture of sand, loam and rice husk ash) proposed for SUDs in Bogota, Colombia. A research work was conducted by combining adsorption isotherms measurements, unsaturated column breakthrough flow experiments and numerical modeling with RETC, STANMOD and HYDRUS 1D models. Adsorption isotherm can be described satisfactorily using the Freundlich and Langmuir models. Additionally, unsaturated soil column leaching tests (ISO/TS S1268-3) allows estimation of solute diffusion through the soil profile. A multi-reaction model (MRM) and convection dispersion flow model reveal non-linear and non-equilibrium in the movement of solute in soil. Moreover, there is a competition for adsorption of metal ions in the technosoil profile; the order of selectivity of heavy metals in the active sites of the microporal network will be Pb+2> Cu+2, so that these technosoil is a favorable material in heavy metals retention.

 

 
Isotopic and elemental mapping of bamboo corals – reference to calcification mechanism and proxy applications
Authors: Flöter Sebastian , Fietzke Jan , Gutjahr Marcus , Farmer Jesse , Hönisch Bärbel , Nehrke Gernot , Eisenhauer Anton
Published: March 2020

Bamboo corals are calcitic octocorals dwelling in a broad range of water depths and in all ocean basins. Their skeletons could give insight into the temporal variability of environmental parameters at their growth locations, in areas where long-time observations are often lacking. A thorough understanding of calcification mechanisms is essential to interpret the chemical composition of their high-magnesium calcite skeleton regarding environmental fluctuations of the deeper ocean. To address this issue, we employed electron microprobe analysis, confocal Raman spectroscopy, laser ablation-ICPMS and solution based multi collector-ICPMS that together provide insights into the fine-scale spatial heterogeneity of the coral chemical composition. We investigate the spatial distribution of Na, S, and Ca, as well as organic matter in skeletal sections of specimens of Keratoisis grayi (family Isididae) from the Atlantic Ocean. Two bamboo coral samples from the Atlantic and Pacific Ocean were further used to create laser ablation-based maps of δ11B and boron to carbon ratios (B/C) over the sample radii. These maps are compared with results obtained via solution based δ11B analyses on drilled samples.

An inverse correlation between Na and S is observed while S seems to be positively correlated with organic matter. We will discuss the ability of a qualitative physicochemical model to explain the observed Na and S distribution and the potential role of organic matter and amorphous calcium carbonate. Our results indicate that skeletal Na/Ca in bamboo corals is largely driven by physiological processes rather than environmental salinity variability. The spatial distribution of δ11B shows a positive correlation with B/C. The observed range of bulk δ11B - partly falling below the theoretical borate fractionation curve in seawater - is larger than the conventional measured δ11B of the calcite fraction alone. The latter cannot be explained with a spatial smoothing of the distribution during sample drilling but is rather associated with a loss of an isotopically highly variable B fraction during sample bleaching. Potential reasons for the observed differences in B isotopic range and their implications will be presented. We conclude that skeletal δ11B as a proxy for pHSW is dependent on the applied technique and investigated material fraction.
Variations in The Frequency of Sudden Stratospheric Warmings in CMIP5 and CMIP6
Authors: Wu Zheng , Reichler Thomas
Published: March 2020

The frequency of sudden stratospheric warming events (SSWs) is an essential characteristic of the coupled stratosphere-troposphere system. This study is motivated by the fact that many of the CMIP5 and CMIP6 climate models considerably over- or underestimate the observed SSW frequency. The goal is to understand the causes for the large intermodel spread in the number of SSWs and relate it to specific model configurations. To this end, various dynamical quantities associated with the simulation of SSWs are investigated. It is found that variations in the SSW frequency are closely related to the strength of the polar vortex and the stratospheric wave activity. While it is difficult to explain the variations in the strength of the polar vortex, the stratospheric wave activity is strongly influenced by the background state (i.e., zonal wind and index of refraction) of the lower stratosphere. An important regulator for the background is the extratropical tropopause temperature, which in turn is associated with the vertical model resolution. Low-resolution models tend to have large biases in simulating the location and temperature of the extratropical tropopause. The results indicate that the simulated SSW frequency is a useful metric for model performance, as the frequency is highly sensitive to a number of stratospheric and tropospheric factors.
Hele-Shaw Cell of Varying Thickness for Modeling of Leakage Pathways
Authors: Trudel Elizabeth , Frigaard Ian
Published: March 2020

Canada is an important player in the global oil and gas industry and is ranked fourth largest producer of natural gas and crude oil. Alberta and British Columbia are the two largest producing provinces of natural gas with a combined 98% of the national production. Recent development of the Montney formation, a low permeability unit, has led to a rise in the number of unconventional (horizontal and hydraulically fractured) wells drilled in Western Canada. Recent studies have shown that 28.5% of wells drilled starting in 2010 in British Columbia have reported an instance of wellbore leakage, and 4.0% of the wells drilled in Alberta during the same time period have also reported an instance of wellbore leakage resulting in several thousand wells with known leakage issues in these two provinces. Wellbore leakage is the unwanted flow of hydrocarbons from the reservoir, or a formation intersected by the well, through leakage pathways found along the wellbore and discharging to the atmosphere through either the surface casing assembly, surface casing vent flow (SCVF) or a surrounding permeable formation, gas migration (GM). In addition to the greenhouse gas emissions produced by wellbore, groundwater contamination may occur. Provincial regulations state that the remediation of cases of non-serious wellbore leakage, which represents 85.5% of the cases of wellbore leakage in Alberta and over 94% of the cases in British Columbia, can be delayed until the time of well abandonment. Less than 30% of the gas wells in these provinces have been abandoned and both provinces are seeing an alarming number of suspended wells which can be considered ready for abandonment. At which point, wells experiencing wellbore leakage will need to be remediated. Understanding of wellbore leakage, which occurs through leakage pathways such as radial cracks and microannulus, is limited. The model presented in this study relies on flow through a Hele-Shaw cell of varying thickness representing a microannulus. Microannulus thickness data is obtained through experimental data available in the literature. The aim of the model is to determine the flow rate of natural gas through a microannulus of varying thickness and the resulting permeability of the leakage pathways.
Numerical solution of the mass continuity equation for snowpack modeling on moving meshes: Coupling between mechanical settling and water vapor transport
Authors: Simson Anna , Kowalski Julia , Löwe Henning
Published: March 2020

The snowpack continuously evolves due to metamorphic and mechanical processes. Understanding and quantifying these processes and in particular their complex interplay and impact on the snowpack's strength is challenging, yet of large interest to the snowpack modeling community. Due to the layer representation and the absence of an explicit numerical solution of the mass continuity equation in common snowpack models, competing effects of mechanical settling and phase changes (e.g. due to vapor transport) can hardly be assessed faithfully. Towards a remedy, we investigate the potential of a numerical scheme that treats the vapor recrystallization term on a moving mesh as imposed by the settling term of the continuity equation.
First, we introduce a continuum mechanical snowpack model that explicitly accounts for both water vapor transport induced by temperature gradients, and settling processes. Next, we describe a computational approach to solve the coupled snowpack model. Water vapor transport as a result of temperature and condensation rate evolution are solved by means of a finite difference scheme. Accounting for settling processes requires to solve an additional ice volume balance, which is done based on the method of characteristics. Its advantage is that it can exactly account for the moving upper free surface of the snowpack. Unstructured meshes enable us to track (potentially densifying) snow layers at high spatial resolution. A closure for the settling velocity is formulated in terms of stresses from the overburdened snow mass and snow viscosity. The proposed continuum-mechanical snowpack model enables us for the first time to investigate the coupled interplay and relative importance of water vapor transport and snowpack settling on time scales from minutes to several hours. 
In a series of numerical examples, we present simulation results for varying snow heights (0.02 - 1 m), snow densities (100 - 917 kgm-3) and temperature gradients (20, 100, 1000 Km-1) to assess the effect of simultaneous snowpack settling and water vapor transport. The proposed model allows us to observe the downward propagation of a snow layer interface coupled to water vapor deposition and sublimation, at high spatial resolution. One of our major findings is that while settling might strongly increase ice densities, it also has an additional (weaker) impact on the condensation rate. Finally, we will discuss to which extent the proposed novel computational approach could be used to study and quantify the interplay of coupled mechanical and metamorphic processes in future community snowpack models, for instance while identifying regimes that require to account for process coupling.
Yearly land cover mapping between 1984 and 2018 in the Haouz plain (Marrakech, Morocco) using robust decision trees approaches.
Authors: Simonneaux Vincent , Baby Paul , Kharrou Mohamed Hakim
Published: March 2020

Land Cover is a major variable required for agricultural management and biophysical modelling. Remote sensing is the more efficient manner to map this information although robust method are still hardly available especially in semi-arid areas where the development of crops is very heterogeneous, where crops often have low vegetation coverage (e.g. tree plantations) and where several crops are sometimes associated on the same plot (e.g. trees with understory of annuals). Besides, the major problem of classical land cover classification approaches is that they require ground data every year for calibration.

To solve both land cover complexity and ground data availability problems, we propose decision tree approaches based on phenological criteria assumed to remain true for any year. The present work was achieved in the Haouz plain (Marrakech, Morocco) where land cover belongs to six main classes, namely: bare soil, evergreen trees (olive and citrus), deciduous trees (apricot, apple, pomegranate…), winter crops (wheat), summer crops (melon and watermelons), fall crops (peas and broadbean). A decision tree is build based on phonological criteria supposed to be independent of the year, related either to the dynamic of NDVI (min, max and range of NDVI as compared to thresholds) and the period in which the peak or the minimum of NDVI happen (linked respectively to the max of vegetation of annual crops and to the leave fall for trees). This decision tree was applied to map the irrigated areas in the Haouz plain between 1984 and 2018 at yearly time scale using the Landsat archive downloaded from USGS. Only five years with not enough clear images were discarded. The time series obtained are consistent with the known changes that took place in the Haouz plain since 1984, namely a strong development of tree plantations, and of summer crops in some areas. The advantage of processing each year instead of only some key dates (e.g. 3 or 4 images as often encountered in studies when Landsat archive was not so easily available as now) is that it gives a better idea of uncertainties and provides a more robust trend. This work will be continued with estimates of the irrigation water consumption linked with these land cover changes.
Comparing permanent deformation and seismic asperities in the 2015 Illapel earthquake rupture zone
Authors: Freisleben Roland , Jara-Muñoz Julius , Melnick Daniel , Strecker Manfred
Published: March 2020

Abstract:

Giant subduction earthquakes (MW 8 to 9) are usually characterized by heterogeneous slip distributions, including regions of very pronounced slip that are commonly known as asperities. However, it is a matter of ongoing debate whether asperities constitute persistent geologic features or if they rather represent transient features related to the release of elastic strain accumulated in areas of seismic gaps. Recent giant earthquakes along the coast of north-central Chile, such as the 2010 Maule (M8.8), 2015 Illapel (M8.3), and 2014 Iquique (M8.2) events, were all associated with the rupture of single or multiple seismic asperities. Here we compare permanent deformation and seismic-cycle deformation patterns and rates along the 2015 Illapel earthquake rupture zone (~30° to 32°S) spanning orbital to decadal time scales. To decipher permanent deformation features manifested in the upper plate of the subduction system we identified and correlated the elevations of Late Pleistocene marine terraces using TanDEM-X digital topography and previously published terrace ages. We focused on terraces related to the Marine Isotope Stages (MIS) 5 and 9 (~124 ka and ~320 ka) due to their excellent preservation and lateral continuity. We furthermore compared deformation rates based on these uplifted terraces and compared them with published co-seismic slip and interseismic locking models of the Illapel earthquake. Uplift rates derived from the MIS-5 marine terraces range between 0.08 and 0.35 m/ka, while uplift rates based on MIS-9 terraces range between 0.38 to 0.96 m/ka. The higher uplift rates are found at the northern part of the Illapel rupture and these areas correlate to crustal structures (e.g. Puerto Aldea Fault). We observed a direct correlation between MIS-5 and MIS-9 uplift rates and co-seismic slip in the northern parts of the rupture while there was no clear correlation in the south at the central and southern parts of the rupture zone. The comparison between the spatial distribution of locked areas and uplift rates provided only a weak correlation for the MIS-9 terraces at the southern part of the rupture. Our results suggest that the northern part of the IIIapel rupture zone may accumulate permanent deformation during megathrust earthquakes. In contrast, accumulation of deformation at the southern part of the rupture may be controlled by activity in the neighboring seismotectonic segment. Broad warping patterns of marine terraces might reflect changes in boundary conditions at interplate depths, such as subduction of seamounts or other oceanic bathymetric features. This analysis highlights the temporal and spatial variability of deformation at convergent plate margins over multiple time scales.
Geotourism – practices, challenges and potentialities in Algarve
Authors: Azevedo Rodrigues Luis , Bamberger Axel , Blum Astrid
Published: March 2020

Algarve is one Portugal regions’ in where the tourism activities are most relevant both socially and economically. Although Algarve’s most important touristic products are beaches resorts and summer weather conditions, as well as golf and gastronomy, this region still preserve a wide variety of topographies and geographical features that could constitute the basis for Geotourism activities.

Here we present some examples of how Science Communication (SC) and a Science Museum/Centre (SCM) are the ideal intermediates between the tourists and the tourist site or scenic resource. We also disclose how SCM’s could act independently or with less obvious partners, private and public, in developing or complementing Geoutourism activities.

Geoutourism activities’ and intervention areas of the Lagos Ciência Viva Science Centre and its partners could be grouped and will detailed in:

a) Scientific advice and training of tour operators or visit co-guiding; b) scientific residencies programs and field trips; c) production of materials - exs. thematic guides, 3D reconstructions, and printed and mobile interpretative information; d) SCM partners participation in research projects (Citizen Science).

Finally, we present examples of how SC and SCM could adapt the informal education techniques into tourist operators training contributing this way to an increase and diversity of the tourist professionals that work in Algarve and enrich the tourist experience further than the landscape appreciation.

Here we use and adopt the following definition: “Geotourism is sustainable tourism with a primary focus on experiencing the earth’s geological features in a way that fosters environmental and cultural understanding, appreciation and conservation, and is locally beneficial” (Dowling & Newsome, 2006).
A qualitative approach to evaluating the impact of human interventions on the middle Charente River (West France)
Authors: Duquesne Amélie , Plumejeaud-Perreau Christine , Carozza Jean-Michel
Published: March 2020

Although many studies have analyzed the impact of human interventions on European rivers over decades or centuries, researchers have rarely evaluated the geomorphological effects of these anthropogenic pressures on fluvial systems. However, quantifying anthropogenic impacts is fundamental to understanding how rivers are affected by human interventions and to improving the river management and restoration. The aim of this study is to propose a new and original qualitative method to estimate the importance of human impacts on rivers over the last three centuries using the middle Charente River as a test case. The study area is an anastomosing, low-energy and little mobile river of the lowlands of Western France. It extends from the city of Angoulême (Charente) to the city of Saintes (Charente-Maritime), with a length of approximately 100 km. The study segment has been subjected to high anthropogenic pressure since the High Middle Ages, and it was enhanced during the 19th century to facilitate navigation and terrestrial transportation, to ensure the exploitation of the water's driving force (water mills and paper mills), to maintain the local people (fishing dams and agro-pastoral uses) and to allow for flood protection. To understand and estimate the anthropogenic heritage of the Charente River, this study employed a two-stage method: 1) an inventory of the human interventions on the fluvial system through the consultation of geo-historical data (textual archives, historical maps and iconography) dating from the end of the 17th century to the 2010s and 2) an evaluation of the human impact of each human intervention, sub-category and category of intervention based on the calculation of the Cumulative Human Impact Index. The Cumulative Human Impact Index is composed of several qualitative attributes graded by an evaluator. The results allow one 1) to generate a database and typology of the human interventions affecting the middle Charente River over the long term; 2) to map the cumulative impacts of human interventions on the study area; and 3) to analyze the unitary and overall impact of each human intervention, sub-category and category of intervention on the river landscape's heritage. Finally, this study concludes with 1) a discussion of the advantages of using a qualitative methodology for the estimation of anthropogenic impacts and 2) a reflection on the use of the maps of cumulative human impacts for Charente River management and restoration.
Origin of the temporal evolution of elastic properties during laboratory seismic cycle.
Authors: Paglialunga Federica , Passelègue François X. , Acosta Mateo , Violay Marie
Published: March 2020

Recent seismological observations highlighted that earthquakes are associated to drops in elastic properties around the fault zone (Brenguier et al., 2008). This drop is often attributed to co-seismic damage produced at the rupture tip, and can mostly be observed at shallow depths. However, it is known that in the upper crust, faults are surrounded by a zone of damage (Caine, Evans, & Forster, 1996). Because of this, the origin of the velocity change associated to earthquakes, as well as its recovery in the months following the rupture remains highly debated.

We conducted stick-slip experiments to explore the evolution of elastic waves velocities during the entire seismic cycle. The tests were run on saw-cut La Peyratte granite samples presenting different initial degrees of damage, obtained through thermal treatment. Three types of samples were studied: not thermally treated, thermally treated at 650 °C and thermally treated at 950 °C. Seismic events were induced in a triaxial configuration apparatus at different confining pressures ranging from 15 MPa to 120 MPa. Active acoustic measurements were carried through the whole duration of the tests and P-wave velocities were measured.

 

The evolution of P-wave velocity follows the evolution of the shear stress acting on the fault, showing velocity drops during dynamic slip events. The evolution of the P-wave velocity drops with increasing confining pressure shows two different trends; the largest drops can be observed for low confining pressure (15 MPa) and decrease for intermediate confining pressures (up to 45 MPa), while for confining pressures of 60 MPa to 120 MPa, drops in velocity slightly increase with confining pressure.

Our results highlight that at low confining pressures (15-45 MPa), the change in elastic velocity is controlled by the sample bulk properites (damage of the medium surrounding the fault), while for higher confining pressures (60-120 MPa), it might be the result of co-seismic damage.

These preliminary results bring a different interpretation to the seismic velocity drops observed in nature, attributed to co-seismic damage. In our experiments co-seismic damage is not observed, except for high confining pressures (laboratory equivalent for large depths), while the change in P-wave velocity seems to be highly related to combined stress conditions and initial damage around the fault for low confining pressures (laboratory equivalent for shallow depths).
Determining tributary sources of increased sedimentation in East-African Rift Lakes using a combination of sediment tracing and radioactive dating.
Authors: Wynants Maarten , Millward Geoffrey , Patrick Aloyce , Taylor Alex , Munishi Linus , Mtei Kelvin , Brendonck Luc , Gilvear David , Boeckx Pascal , Ndakidemi Patrick , Blake William
Published: March 2020

Temporal and spatial sediment dynamics in an East-African Rift Lake (Lake Manyara, Tanzania), and its river inputs, have been evaluated via a combination of sediment tracing and radioactive dating. Changes in sedimentation rate were assessed using radioactive dating of sediment cores in combination with geochemical profile analysis of allogenic and autogenic elements. Geochemical fingerprinting of riverine and lake sediment was integrated within a Bayesian mixing model framework, including spatial factors, to establish which tributary sources were the main contributors to recent lake sedimentation. The novel application of Bayesian source attribution on sediment cores and subsequent integration with sedimentation data permitted the coupling of changes in the rate of lake sedimentation with variations in sediment delivery from the tributaries. These complimentary evidence bases demonstrated that Lake Manyara has experienced an overall upward trajectory in sedimentation rates over the last 120 years with distinct maxima in the 1960s and in 2010. Sedimentation rates are largely a result of a complex interaction between increased upstream sediment delivery following changes in land cover and natural rainfall fluctuations. Modelling results identified two specific tributaries as responsible for elevated sedimentation rates, contributing 58% and 38% of the recently deposited lake sediment. However, the effects of sedimentation were shown to be spatially distinct given the domination of different tributaries in various areas of Lake Manyara. The application of source-tracing techniques constrained sedimentation problems in Lake Manyara to specific tributary sources and established a link between upstream land degradation and downstream ecosystem health. This novel application provides a solid foundation for targeted land and water management strategies to safeguard water security and environmental health in Lake Manyara and has potential application to fill knowledge gaps on sediment dynamics in other East-African Rift Lakes.
Fossil Subduction Recorded By Quartz From The Coesite Stability Field
Authors: Alvaro Matteo , Mazzucchelli Mattia L. , Angel Ross J. , Murri Mara , Campomenosi Nicola , Scambelluri Marco , Nestola Fabrizio , Korsakov Andrey , Tomilenko Anatoly , Marone Federica , Morana Marta , Alabarse Frederico
Published: March 2020

Investigation of mantle xenoliths can provide information on the architecture and evolution of subcontinental lithospheric mantle through time. These reconstructions rely also on correct estimates of the pressures and temperatures (P-T) experienced by these rocks over time. Unlike chemical geothermobarometers, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on over-stepping of reaction boundaries and to identify other examples of non-equilibrium behaviour in rocks. Here we introduce a method that exploits the elastic anisotropy of minerals to determine the unique P and T of equilibration from a measurements of single-crystal mineral inclusions trapped in a crystalline host from an eclogite xenolith [1]. We apply it to perfectly preserved quartz inclusions in garnet from eclogite xenoliths in kimberlites. We show that the elastic strains of inclusions calculated from in-house Raman spectroscopy measurements of the inclusions are in perfect agreement with those determined from in-situ X-ray diffraction measurements performed both in-house and at the synchrotron. Calculations based on these measured strains demonstrate that quartz trapped in garnet can be preserved even when the rock passes into the stability field of coesite (high pressure and temperature polymorph of quartz). This supports a metamorphic origin for these xenoliths that provides constraints on mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that some key inclusion minerals do not always indicate the P and T attained during subduction and metamorphism.

 

This project has received funding from the European Research Council under the H2020 research and innovation programme (N. 714936 TRUE DEPTHS to M. Alvaro)

 

[1] M Alvaro, ML Mazzucchelli, RJ Angel, M Murri, N Campomenosi, M Scambelluri, F Nestola, A Korsakov, AA Tomilenko, F Marone, M Morana (2020) Fossil subduction recorded by quartz from the coesite stability field, Geology, 48, 24-28