bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal changes of seismic velocity associated with a magmatic unrest of Changbaishan volcano, northeast China
Authors: Liu Zhikun
Published: March 2020

The observations of seismicity, ground deformation, and volcanic gas geochemistry indicate a magmatic unrest of the Changbaishan volcano, northeast China between July 2002 and July 2005. In this study, we collected the continuous waveform data from more than 10 stations of permanent and portable networks around Changbaishan volcano area from 2000 to 2018, and studied the temporal velocity changes beneath the volcano based on both the cross-correlation of station pairs and auto-correlation of singe station method. We adopted the time-frequency domain phase weighted technique to speed up the convergence process of the noise-based Green's function, and improved the time resolution of monitoring from several tens of days to several days. We measured the temporal seismic velocity of the Changbaishan volcano in various frequency bands. The results shown that there were obvious seasonal changes of the seismic velocity for most frequency bands, and for 0.5-1 Hz frequency band a sudden velocity drop was observed starting on June 10, 2002 and the amplitude of velocity changes was up to 0.5%. After that, the number of volcanic events increased significantly. Our results suggest that there may be a precursory velocity drop phenomenon before the magma unrest, which is of great scientific significance for the studies of magma unrest and possible volcanic eruption in the future.
Linking glacial lake expansion with glacier dynamics: An assessment of the South Lhonak lake, Sikkim Himalaya
Authors: Kaushik Saurabh , Joshi Pawan Kumar , Singh Tejpal , Bhardwaj Anshuman
Published: March 2020

The Himalayan Cryosphere is imperative to the people of south and central Asia owing to its water availability, hydropower generation, environmental services, eco-tourism, and influences on overall economic development of the region. Additionally, this influences the energy balance of the earth and contributes significantly to the sea level rise. Therefore Himalayan Cryosphere remains center of attraction for scientific community.  Glacier dynamics, seasonal snow and glacial lakes are studied at various scales using a combination of remote sensing and field observations. The existing literature reveals heterogeneous behavior of Himalayan glaciers which is largely influenced by climate change, debris cover and presence of glacial lake at the terminus. There are very limited studies that attempt to comprehend glacier dynamics and lake expansion in the Eastern Himalayan region. Therefore the present study aims to demonstrate link between glacier dynamics and lake expansion of South Lhonak glacier which is situated in the northern Sikkim. Multitemporal remote sensing data (Landsat, 1979-2019) and climate data (1990-2017) observed at Gangtok meteorological station are used in the study. The results reveal that the lake has expanded with a rate of 0.026 km2 yr-1 during the last four decades. The preliminary results show strongly imbalanced state of glacier, as glacier has deglaciated (area and length), and surface flow velocity and ice thickness have reduced significantly. The statistical analysis (Mann Kendall and Sens slope) of climate data measured at Gangtok meteorological station shows an accelerated trend of mean maximum (0.031°C yr-1) and mean minimum (0.043°C yr-1) temperatures (95% confidence interval). Whereas, no significant trend in total annual precipitation was observed. Inference can be drawn from study that glacier slow down and retreat contribute significantly to the glacial lake expansion under the influence of climate change, such lake expansion pose anticipated risk of glacial lake outburst in the region.
The decadal decline of CO2 emissions from a large ephemeral lake in China
Authors: Zhao Xiaosong
Published: March 2020

The influence of natural hydrological factors on CO2 evasion from lakes has been widely studied. However, the long-term effects of man-made hydraulic infrastructures are not yet well understood. Here, we examined the multi-year (1961 - 2016) trend of the CO2 budget for Poyang Lake, a large ephemeral lake in China. Poyang Lake is situated downstream of the Three Gorges Dam (TGD), the world’s largest human-made hydraulic infrastructure. Using a combination of eddy covariance observations and artificial neural network modeling, we show that following the development of TGD in 2003, CO2 emissions of Poyang Lake significantly decreased by 77% (0.18 Tg C) compared with the pre-TGD period. The TGD can explained 21% of the CO2 flux decrease during impoundment period. The results imply that the TGD and other hydropower infrastructures potentially decrease the CO2 emission of lakes naturally connected or surrounded with Yangtze River in the middle and lower reaches.
Joint Bayesian spatial inversion of lithology/fluid classes, petrophysical properties and elastic attributes – A Norwegian Sea gas discovery
Authors: Fjeldstad Torstein , Omre Henning
Published: March 2020

A Bayesian model for prediction and uncertainty quantification of subsurface lithology/fluid classes, petrophysical properties and elastic material properties conditional on seismic amplitude-versus-offset measurements is defined. We demonstrate the proposed methodology  on a real Norwegian Sea gas discovery in 3D in a seismic inversion framework.

The likelihood model is assumed to be Gaussian, and it is constructed in two steps. First, the reflectivity coefficients of the elastic material properties are computed based on the linear Aki Richards approximation valid for weak contrasts. The reflectivity coefficients are then convolved in depth with a wavelet.  We assume a Markov random field prior model for the lithology/fluid classes with a first order neighborhood system to ensure spatial coupling. Conditional on the lithology/fluid classes we define a Gauss-linear petrophysical and rock physics model. The marginal prior spatial model for the petrophysical properties and elastic attributes is then a multivariate Gaussian mixture random field.

The convolution kernel in the likelihood model restricts analytic assessment of the posterior model since the neighborhood system of the lithology/fluid classes is no longer a simple first order neighborhood. We propose a recursive algorithm that translates the Gibbs formulation into a set of vertical Markov chains. The vertical posterior model is approximated by a higher order Markov chain, which is computationally tractable. Finally, the approximate posterior model is used as a proposal model in a Markov chain Monte Carlo algorithm. It can be verified that the Gaussian mixture model is a conjugate prior with respect to the Gauss-linear likelihood model; thus, the posterior density for petrophysical properties and elastic attributes is also a Gaussian mixture random field.

We compare the proposed spatially coupled 3D model to a set of independent vertical 1D inversions. We obtain an increase of the average acceptance rate of 13.6 percentage points in the Markov chain Monte Carlo algorithm compared to a simpler model without lateral spatial coupling. At a blind well location we obtain a reduction of at most 60 % in mean absolute error and root mean square error for the proposed spatially coupled 3D model.
Correlation between wave activities in different layers of the atmosphere
Authors: Ratovsky Konstantin , Medvedeva Irina , Yasyukevich Anna , Shpynev Boris , Khabituev Denis
Published: March 2020

We study the correlation between wave activities in different layers of the atmosphere. The variability of the measured characteristic in the range of internal gravity wave periods is used as a proxy of wave activity. In the case of ground-based measurements, we consider temporal variations with periods less than ~ 6 hours; while in the case of satellite measurements we take into account spatial variations with periods less than ~ 1000 km. The wave activity is calculated as the standard deviation of variations in the indicated period range with averaging over one day. The aim of the study is to detect a correlation between day-to-day variations of wave activity in different layers of the atmosphere. Correlation coefficients are calculated for various intervals from one month to one year. Correlation analysis reveals the potential relationship between wave phenomena in the stratosphere, mesosphere and ionosphere. The study uses the following characteristics. The ionospheric characteristics are the peak electron density from the Irkutsk ionosonde (52.3 N, 104.3 E) and the total electron content from the Irkutsk GPS receiver. The characteristic of the mesosphere is the mesopause temperature from spectrometric measurements of the OH emission (834.0 nm, band (6-2)) near Irkutsk (51.8 N, 103.1 E, Tory). The stratospheric characteristic is the vertical gas velocity at 1 hPa from the ERA-Interim reanalysis (apps.ecmwf.int/datasets/data/).

This study was supported by the Grant of the Russian Science Foundation (Project N 18-17-00042). The observational results were obtained using the equipment of Center for Common Use «Angara» http: //ckp-rf.ru/ckp/3056/ within budgetary funding of Basic Research program II.12.
Future Arctic soil nutrient availability and microbial community structure
Authors: Stimmler Peter
Published: March 2020

The Arctic permafrost soils are very diverse in regard to parent material, geobiological composition and genesis. There is sparse knowledge about nutrient availability in Arctic soil and it was found that the permafrost layer differs in nutrient availability compared to the active layer. Recently, it was shown that elements like Si, Ca and P are potentially affecting the greenhouse gas from Arctic soil. However, it is not known how those elements are distributed in Arctic soils for a larger dataset. Furthermore, it is unclear whether regional differences in the availability of those elements or a change in availability due to permafrost thaw is changing microbial decomposer community. Therefore, we analyzed 445 soil depth profiles around the Arctic regarding different element availabilities.

Furthermore, we conducted an incubation experiment to measure the effect of different Si, Ca and P availabilities on the structure of the microbial decomposer community. We found large differences in the availability of Si, Ca, Al, Fe and P in the layers of the panarctic permafrost soils from Canada, Alaska, Russia, Scandinavia, Greenland and Svalbard. There are differences in the distribution of Ca and Si pools over the panarctic permafrost soils. Especially the availability of P is directly linked to the concentration of Ca and Si and the presence of Al and Fe based minerals. With rising temperatures, the thaw depth of the upper horizon may increase and elements stored in deeper layers become potentially mobilized. These processes modify the nutrient availability for microorganisms and by this the production of greenhouse gases like CO2 and CH4.

The community structure of bacteria and fungi is related to the availability of Ca and Si. With modified availabilities of Si and Ca, we found direct linear correlations in the changes of the microbial structure at the phylum level for Greenlandic soils. These changes depend on the origin of the soil and the original availability of Ca and Si. We found direct links between the share of gram-positive bacteria and the Ca concentration in both soils and the production of greenhouse gases. The availabilities of these elements may be helpful for better predicting greenhouse gases fluxes in the Arctic as well as element transfer to marine systems.
The 2018-2019 European drought sets a new benchmark over 250 years
Authors: Rakovec Oldrich , Hari Vittal , Markonis Yannis , Samaniego Luis , Hanel Martin , Thober Stephan , Maca Petr , Kumar Rohini
Published: March 2020

The 21st-century droughts in Europe are regarded as exceptionally severe
and negatively affecting a wide range of socio-economic sectors due to
increases in temperature together with a lack of precipitation during
the spring/summer months [1]. In this study, we synthesize a space-time
evolution of soil moisture droughts in the period of 1766-2019
to better understand the evolution of large-domain multi-year droughts
reflecting the long-term historical changes in hydroclimate variability across Europe.

Following steps are taken to quantify the prolonged (multi-year) soil
moisture droughts: (1) simulate soil moisture (SM) with
the mesoscale Hydrologic Model (mHM, [2]) forced using several bias-corrected
meteorological merged products [3-5]; (2) estimate
quantile-based soil moisture index (SMI) based on a 254-year long
monthly dataset, which is estimated with a kernel density approach [6];
(3) perform a spatio-temporal clustering algorithm to track droughts
through space and time along their evolution, for a given threshold of
SMI<0.2 [6]; (4) estimate drought statistics such as areal extent,
duration, intensity for all identified soil moisture drought events. 

The results from the period 1766-2019 show that total drought intensity
over Europe has an increasing trend, while the average
drought area remains unchanged.  In terms of total drought magnitude,
the ongoing recent 2018-2019 drought is ranked as the most extreme,
followed by 1920-1922, 1947-1948, 1857-1860, and 1988-1991
events. All these exceptional summer droughts were initiated in spring
primarily as a result of compounding effects of low precipitation and
high temperatures leading to extreme soil water
deficits. The 2018-2019 event exhibits average drought area covering
50% of the study domain, which is same as in 1947-1948. Our analysis
suggests that the 2018-2019 event is a new European drought benchmark,
replacing the well-documented 2003 drought event.

References:

[1] https://doi.org/10.1038/s41598-018-27464-4
[2] https://www.ufz.de/mhm
[3] https://doi.org/10.1007/s00382-007-0257-6
[4] https://doi.org/10.1002/joc.3711
[5] https://doi.org/10.1029/2009JD011799
[6] https://doi.org/10.1175/JHM-D-12-075.1
Explicit solution of the scattering problem involving a vertical flexible membrane
Authors: Manam Srinivasa Rao , Kumar Ashok , Chandrasekar Gunasundari
Published: March 2020

The problem of normally incident water wave scattering by a flexible membrane is completely solved. The physical problem in a half-plane is reduced to a couple of equivalent quarter-plane problems by allowing incident waves from either direction of the membrane. In the same way, quarter-plane boundary value problems are posed for solid wave potentials that are solutions of the scattering problem involving a rigid structure of the same geometric configuration. Then, two novel integral relations are introduced to establish a link between the required solution wave potentials and few resolvable solid wave potentials. Explicit expressions for the scattering quantities such as the reflection and the transmission wave amplitudes are obtained. Also, the deflection of the flexible vertical membrane and the solution potentials are determined analytically. Numerical results for the scattering quantities and the membrane deflection are presented.
Simulation of Downstream Effects of Urbanization on Cloud and Precipitation with WRF Model in Yangtze River Delta, China
Authors: Han Xiaomen , Sun Jianning
Published: March 2020

Urbanization, one of the extreme cases of land-use change, plays an important role in modifying precipitation and urban hydrology. In this study, urbanization effect on cloud and precipitation in the Yangtze River Delta of China is simulated using Weather Research and Forecasting (WRF) model coupled with a single-layer Urban Canopy Model(SLUCM). Based on the 4-summer simulation results from 2011 to 2014, we find that the influence of cities on clouds and precipitation is obviously affected by wind field. During the day, more cloud on higher level and precipitation occurs in urban area and downwind region of urban, induced by more unstable urban air transported downstream, which enhances vertical mixing and updraft moisture transport. At night, the urban dry island become the dominant factor, resulting in the decrease of cloud occurrence in the urban and downstream areas. The downstream effects of urbanization on cloud and precipitation turn out to be strongly related to the moisture and convective conditions.

 
Towards near-realtime computation of tsunami inundation as part of the LEXIS project
Authors: Rakowsky Natalja , Sven Harig , Alexey Androsov , Thierry Goubier , Hannah Neuwirth , Lucas Kersten
Published: March 2020

State of the art tsunami warning systems employ a combined approach of pre-computed scenarios and on the fly tsunami simulation in case of an event. The on the fly simulations are performed on rather coarse meshes (approx. 1km resolution), usually neglect e.g., the non-linear advection in the shallow water equations, and can deliver a reasonable estimate of the wave height at the coast within a few seconds of computation time. As in the early warning situation, the earthquake source is the major unknown, they can improve the hazard assessment compared to pre-computed scenarios based on idealized sources.

On the other hand, it requires a resolution of approximately 10m on land and the non-linear shallow water equations augmented by terms like the bottom roughness to simulate the inundation in the quality needed to derive risk maps for civil protection measures. With the simulation code TsunAWI, which employs an unstructured triangular mesh to seamlessly change the spatial resolution from a few meters in an area of interest to a few kilometers in the deep ocean, such simulations can be performed with a regional focus in less than 20min computation time.

Hence, with a coarsened resolution, a first estimate of the inundation could be provided within a few minutes, improving the near-realtime assessment of the hazard. We investigate which quality of inundation result can be achieved within a limited computation time, regarding computing platforms based on various generations of Intel Xeon from Broadwell to Cascade Lake.

This investigation is part of the EU funded LEXIS project lead by It4Innovations, Ostrava, Czech Republic. The overall aim is to build an advanced engineering platform at the confluence of HPC, Cloud and Big Data. Of particular interest is the development of time constrained workflows over HPC and cloud resources, with a pilot combining tsunami simulations and earthquake damage assessment. Fast tsunami inundation estimates are a key element of that pilot.

 

 
Response/feedback of the Arctic Ocean in the Northern Hemisphere climate system: the sea-level joker
Authors: Hillaire-Marcel Claude , de Vernal Anne , Liu Yanguang
Published: March 2020

The Arctic Ocean is a major player in the climate system of the Northern Hemisphere due to its role vs albedo, atmospheric pressure regimes, and thermohaline circulation. It shows large amplitude variability from millennial, to decadal and seasonal time scales. At millennial time scales, two drastically distinct regimes prevail primarily in relation with ocean volume and sea level (SL) changes: A modern like system, with a high SL when the Arctic Ocean shelves are submerged and Bering Strait is opened vs a glacial one, with a low SL, when shelves are emerged and partly glaciated and Bering Strait is closed. In the modern system, large submerged shelves result in high productivity, high sea-ice production rates and sea ice-rafting deposition in the Central Arctic. Moreover, a fully open Bering Strait, with SL at the present elevation, contributes about 40% of the freshwater budget of the Arctic Ocean (Woodgate & Aagaard, 2005, doi:10.1029/2004GL021747), and supports Si fluxes of about 20 kmol.s-1 towards the Western Arctic (Torres-Valdés et al., 2013, doi:10.1002/jgrc.20063), thus impacting primary productivity. Under low SL conditions, the Arctic Ocean is linked exclusively to the North Atlantic, through practically a single gateway, that of Fram Strait. Sedimentation in the Central Arctic is then dominated ice-rafting deposition from icebergs, thus controlled by streaming and calving processes along surrounding ice sheets. Due to its shallowness (< 50 m), the Bering Strait gateway becomes effective at a very late stage of glacial to interglacial transitions but closes early during reverse climate trends. Sedimentary records from shelves North of Strait may provide information on the status of the gateway, so far, for the present interglacial. Clay minerals in cores from the northern Alaskan shelf (Ortiz et al., 2009, doi:10.1016/j.gloplacha.2009.03.020) and micropaleontological tracers from the Chukchi Sea southern shelf (present study) can be used to document the status of the gateway. Here, North Pacific microfossils transported by currents through the gateway demonstrate its full effectiveness at ca 6 ka BP, well after the insolation maximum of the early Holocene but when SL had reached its maximum postglacial elevation, with significant impacts on Arctic Ocean salinity, sea-ice cover and productivity.. This out-of-phase behavior of the Arctic Ocean may have impacted the North Atlantic and Northern Hemisphere climate system, as the openings and closings of Bering Strait constitute critical tipping points on this system, off out of phase with other parameters controlling more globally the climate of the Northern Hemisphere.
Reproduction and projection of sea level around Korean Peninsula using regional climate ocean model with dynamical downscaling method
Authors: Jeong Kwang-Young , Lee Eunil , Byun Do-Seong , Seo Gwang-Ho , Lee Hwa-Young , Cho Yang-Ki , Kim Yong-Yub
Published: March 2020

Recently, the rate of sea level rise in accelerating with time, and many studies have reported that sea level will increase rapidly in the near future. Also, various global ocean climate models are used to predict sea level rise due to global warming. However, most global ocean climate models have low resolutions, so it is hard to explain detailed the ocean phenomena such as sea level and currents around Korean Peninsula. This study aims to past 30-year reproduce and future 100-year predict for rising trend of sea level using Regional Climate Ocean Model (RCOM) with ROMS according to IPCC climate change scenario (RCP 4.5).

The RCOM with high resolution of 1/20° horizontally and 40 layers vertically has been established for reproduction and long term forecast of sea-level rise in the Northwest Pacific, including marginal seas around Korea. Dynamic downscaling processes using result of the global climate models were applied to the open boundary conditions of our RCOM. To prepare the optimal boundary data for RCOM, the CMIP5 climate model was evaluated to select 4 climate models: IPSL-CM5A-LR, and -MR, NorESM1-M, MPI-ESM-LR.

Based on the RCOM results of 4 experiments, the rate of sea level rise for IPCC climate change scenario (RCP4.5) around Korean peninsula were 2.52, 2.21, 3.11, 3.36 mm/yr for the last 30 years (1976~2005), and 5.17, 4.99, 5.62, 5.42 mm/yr for the next 100 years (2006~2100), respectively. Ensemble mean value of next 100 years for 4 model results was 5.30 mm/yr. The sea level rise of 4 models for RCP 4.5 were 48, 48, 58, 48 cm for next 100 years, respectively, and ensemble mean value of 4 models was 50 cm during 2006~2100.

Future studies will focus on predicting the next 100 years of sea level change based on IPCC climate change scenario (RCP2.6, 8.5).

 
Tsunami Generation due to Supershear Earthquakes: A Case Study
Authors: Amlani Faisal , Bhat Harsha
Published: March 2020

The 28 September 2018 Mw 7.5 Sulawesi strike-slip earthquake generated an unexpected tsunami with devastating consequences. Since such strike-slip earthquakes are not expected to generate large tsunamis, the latter’s origin remains much debated. A key notable feature of this earthquake is that it ruptured at supershear speed, i.e., with a rupture speed greater than the shear wave speed of the host medium. Dunham and Bhat (2008) showed that such supershear ruptures, in half-space, produce two shock fronts (or Mach fronts) corresponding to an exceedance of shear and Rayleigh wave speeds. The Rayleigh Mach front carries significant vertical velocity along its front. We couple the ground motion produced by such a supershear earthquake to a 1D non-linear shallow water wave equation that accounts for both the time-dependent bathymetric displacement as well its velocity. We use an extension of Fourier-based PDE solvers called the Fourier Continuation (FC) method to numerically solve the system. The FC method enables high-order convergence of Fourier series approximations of non-periodic functions by resolving the well-known Gibbs “ringing” effect.  FC-based solvers offer limited numerical dispersion, high-order accuracy and mild CFL conditions—making them ideal to solve this system. Using the local bathymetric profile of Palu bay around the Pantoloan harbor tidal gauge, we have been able to clearly reproduce the observed tsunami with minimal tuning of parameters. We conclude that the Rayleigh Mach front, generated by a supershear earthquake combined with the Palu bay geometry, caused the tsunami.
Towards 3D multiscale adjoint waveform tomography of the crust and upper mantle beneath Southeast Asia
Authors: Wehner Deborah , Blom Nienke , Rawlinson Nick
Published: March 2020

Southeast Asia is one of the most complex tectonic regions on Earth. This is mainly a result of its location within the triple junction of the Australian, Eurasian and Philippine Sea plates which has created a complicated configuration of active plate tectonic boundaries. High plate velocities have generated thousands of kilometers of subducted material and ongoing subduction along the Sunda Arc represents a significant natural hazard (such as the 2004 Sumatra-Andaman earthquake, 2012 Indian Ocean earthquakes and 2018 Anak Krakatoa eruption). However, recent tectonic activity around Borneo may be related to postsubduction processes which could be the key to understanding how the tectonic subduction cycle terminates. Further east, the region is dominated by several minor tectonic plates and the spectacular 180-degree curvature of the Banda Arc. Our work aims to further improve the understanding of this area by providing detailed images of the upper mantle.

Adjoint waveform tomography is especially suitable for imaging such complex regions. By simulating the 3D wavefield, it is possible to directly compare observed and simulated seismograms, thereby taking into account both body and surface waves. The method can account for the effects of anisotropy, anelasticity, wavefront healing, interference and (de)focusing that can hamper other seismological methods, and is thus especially suitable for strongly heterogenous areas such as Southeast Asia.

To date, sparse instrument coverage in the region has contributed to a heterogeneous path coverage. In this project, we make use of publicly available data as well as our recently deployed networks of broadband seismometers on Borneo and Sulawesi. This, in addition to access to national permanent networks promises a significant improvement in data coverage around the Banda Arc, Borneo and Sulawesi, thereby providing new opportunities to untangle the region’s complexity.

We compiled a catalogue of well-constrained earthquakes, optimising for coverage, signal-to-noise ratio and data availability across a wide frequency band, and compared our observed data to synthetics generated from an initial model. In the first part of the inversion, we use long periods of 100 - 150 s to update our initial model using a gradient-based optimisation scheme. We use adjoint methods to obtain sensitivity kernels as the corresponding gradients and initial results will be documented in this presentation. In subsequent iterations, we permit increasingly shorter periods in order to progressively recover finer scales structure and avoid cycle skipping issues.
The lithologic composition of Earth’s emerged lands reconstructed from the chemistry of terrigenous sediments
Authors: Greber Nicolas D. , Dauphas Nicolas , Ptàček Matous P.
Published: March 2020

Despite its importance for the biological and atmospheric evolution of our planet, the question how the lithological composition of Earth’s landmasses evolved from around 3.5 Ga to present is still a matter of considerable debate. Furthermore, the type of rocks that build the continents are an expression of the prevailing rock forming mechanisms and thus the geodynamic regime that was at work. Therefore, a good understanding of the lithological and chemical composition of Archean continents is crucial to gain a comprehensive picture of Earth’s evolution.

Lately, the view that Earth’s continents were dominated by basaltic rocks until around 3.0 Ga became increasingly popular. The subsequent rapid transformation from mafic to felsic continents has been used to argue for the onset of plate tectonics at 3.0 Ga and to suggest that the change in the chemical composition of the emerged continents initiated the Great Oxidation Event. Here we present a summary of our work over the past three years (Greber et al., 2017, Greber and Dauphas 2019, Ptáček et al., accepted) that challenges this view. Reconstructing the composition of past continents is difficult because erosion and crustal reworking may have modified the geologic record in deep time, so direct examination of the nature of igneous rocks could provide a biased perspective on the nature of the continents through time. A less biased record is provided by terrigenous sediments that average the composition of rocks exposed to weathering on emerged lands. We use the Ti isotopic, major and trace element composition of fine grained terrigenous sediments (shales) as a proxy for the average composition of the emerged continents in the past. Our model shows that since 3.5 Ga, the landmasses that were subjected to erosion were dominated by felsic rocks. Furthermore, our reconstructed relative abundance of felsic, mafic and komatiitic rocks in the Archean is close to that currently observed in Archean terrains. The combination of Ti isotopes and element abundances also indicates that the rocks exposed to weathering in the Archean resemble that of modern type calc-alkaline rocks and that tholeiitic rocks (e.g. Icelandites) were of subordinate importance.

To summarize, the lithological composition of the Paleoarchean continents should no longer be used as argument against the existence of subduction zones at that time. Instead, their nature rather supports that some form of subduction process was already operating since the early Archean.

References:  Greber N.D., et al (2017), Science 357, 1271–1274; Greber N.D. and Dauphas N. (2019), GCA 255, 247–264; Ptáček M.P., Dauphas N. and Greber N.D. (accepted), EPSL.
Partitioning of chalcophile and siderophile elements during partial melting of serpentinized peridotite in subduction settings
Authors: Merkulova Margarita , Triantafyllou Antoine , Charlier Bernard
Published: March 2020

Enrichment of subduction derived magmas in chalcophile and siderophile elements plays a key role in the formation of economically important ore deposits. Melting of mantle wedge peridotite induced by fluxing slab-derived fluids is the first step in the chemical transfer from the slab to melts (Spandler and Pirard, 2013). Changes in redox conditions, sulfur content, amount of fluid, and P-T conditions affect the elements partitioning between melts and residual phases (Dale et al., 2009; Li and Audetat, 2012; Perchuk et al., 2018; Rielli et al., 2018). However, to date there is a few systematic data on mineral-melt partitioning for economically important elements during partial melting of peridotite in mantle wedge conditions.

We determined experimentally mineral-melt partition coefficients for a range of chalcophile and siderophile elements (V, Co, Cu, Zn, As, Se, Mo, Ru, Rh, Pd, Ag, Cd, Sb, Re, Os, Ir, Pt, Au, Tl, Bi) at different P-T conditions. Slightly serpentinized peridotite (3 wt.% H2O; Debret et al., 2013) was used as a starting material for all experiments. A set of experiments with 1 wt.% of FeS added to the peridotite was also performed in order to study the effect of S on element partitioning. Starting materials were doped with 100-200 ppm of targeted elements. The experiments were performed at pressures of 1-2 GPa and at temperatures between 1100 and 1300°C in end-loaded 0.5” piston-cylinder apparatus in the newly established high-pressure laboratory at the University of Liege (Belgium). In order to avoid Fe-loss, chemical reduction and volatile loss of experimental charges, double Au80Pd20 capsules pre-saturated with Fe were used. Major and trace element composition in synthesized experimental products were measured by electron microprobe and LA-ICP-MS respectively.

In this study, we report a wide range of partition coefficients determined between coexisting silicate, oxide, sulfide minerals and melt as a function of P-T and S content. The results provide further insights into mobility of economically important elements during genesis of ore-forming magmas in subduction settings.

References:

Spandler and Pirard (2013) Lithos, 170-171, 208-223

Dale et al. (2009) GCA, 73 (5), 1394-1416

Li and Audetat (2012) EPSL, 355-356, 327-340

Perchuk et al. (2018) Lithos, 302-303, 203-223

Rielli et al. (2018) EPSL, 497, 181-192

Debret et al. (2013) Chem. Geol., 357, 117-133
Development of the stochastic approach to groundwater hydrology: a personal account of G. de Marsily contributions.
Authors: Carrera Jesús
Published: March 2020

I review early developments of the stochastic modeling approach. It is generally believed that it is an American contribution. Indeed, North-Americans (notably Lynn Gelhar and Allan Freeze, but also Eduardo Alonso) pointed to the importance of spatial variability of hydraulic conductivity in controlling large scale water flow and solute transport in the mid 1970’s (Matheron’s much earlier 1967 solution did not become broadly known until much later). However, the formulation of an approach to solve the problem was the result of work by French mining engineers at Fontainebleau. They had developed the field of Geostatistics, initially for the assessment of mineral reserves. It was natural to apply these concepts to groundwater. It was Ghislain de Marsily who framed the basic concepts of the geostatistical approach to address spatial variability, which remains essentially unchanged to this day.
Post-Seismic Shallow Landslide Triggering: Stress States and Hydrology
Authors: Leshchinsky Ben , Lehmann Peter , Or Dani
Published: March 2020

Earthquakes are major drivers of landslides. After shaking has passed, landslide activity remains elevated, eventually returning to baseline landslide activity dictated by climactic forcing. While this phenomenon has been observed worldwide, there has been limited quantitative insight towards describing some of the physical drivers behind this occurrence. We describe the role of shear band propagation and permanent changes in the stress state of the soil mantle in post-seismic landslide activity. This this described through a coupled seismic-hydro-mechanical slope failure model, which quantitatively describes the damaged state of the hillslope from shaking. This model enables quantification of the influence of alterations in the stress-states caused by shaking, decreased triggering precipitation, and shear-induced weakening of soil on post-seismic landslide activity. The results provide new insights on the roles of soil depth, hillslope characteristics as well as climate on increased landslide susceptibility and gradual return to baseline conditions.
The Influence of Dynamic Topography on the Great Escarpments
Authors: Holdt Megan , White Nicky , Stephenson Simon
Published: March 2020
Constraining dynamic models in North America using the static gravity field
Authors: Reusen Jesse , Root Bart , Fullea Javier , Martinec Zdenek , van der Wal Wouter
Published: March 2020

The negative anomaly present in the static gravity field near Hudson Bay bears striking resemblance to the area depressed by the Laurentide ice sheet during the Last Glacial Maximum, suggesting that it is at least partly due to Glacial Isostatic Adjustment (GIA), but mantle convection and density anomalies in the crust and the upper mantle are also expected to contribute. At the moment, the contribution of GIA to this anomaly is still disputed. Estimates, which strongly depend on the viscosity of the mantle, range from 25 percent to more than 80 percent. Our objective is to find the contributions from GIA and mantle convection, after correcting for density anomalies in the topography, crust and upper mantle. The static gravity field has the potential to constrain the viscosity profile which is the most uncertain parameter in GIA and mantle convection models. A spectral method is used to transform 3D spherical density models of the crust into gravity anomalies. Density anomalies in the lithosphere are estimated so that isostatic compensation is reached at a depth of 300 km. The dynamic processes of mantle flow are corrected for before isostasy is assumed. Upper and lower mantle viscosities are varied so that the gravity anomaly predicted from the dynamic models matches the residual gravity anomaly. We consider uncertainties due to the crustal model, the lithosphere-asthenosphere boundary (LAB), the conversion from seismic velocities to density and the ice history used in the GIA model. The best fit is found for lower mantle viscosities >1022 Pa s.
Don't blame the rain: Explaining sociohydrological (in)security in Cape Town, South Africa
Authors: Savelli Elisa , Rusca Maria , Di Baldassarre Giuliano , Cloke Hannah
Published: March 2020

While depicted as a major global threat, water insecurity usually affects the most disadvantaged and marginalized people. Current definitions of water insecurity still fail to address this injustice as they either over-simplify and disconnect human-water dynamics or disregard the politics thereof. In light of this critique, this paper aims to contribute to reconceptualise water insecurity by integrating examinations of socio-political processes in analyses of chronic water insecurity and extreme drought events. To this end, we draw on sociohydrology and critical political ecology as a way to retrace the mutual shaping of hydrological flows and power dynamics that over time produce uneven geographies of water insecurity. We do so in the face of extreme droughts to understand to what extent these events intersect with the production and distribution of water insecurity. This paper draws on empirical work on the severe drought which affected Cape Town in 2015-17 and escalated into a water crisis also known as Day Zero. Despite being portrayed as a middle-class crisis, our study found that the marginalized people were the most affected while the wealthier elite were able to water secure themselves. This unequal picture sharply reflects the same water insecurities which existed long before Day Zero. We, thus, argue that they are a legacy of the spatial and economic segregation which has shaped Cape Town since colonial times. More than producing it, the drought has accelerated a pre-existing water crisis and exacerbated the level of water insecurity of every Capetonian. Proving that water insecurity is a sociohydrological phenomenon, we believe that such politically aware conceptualization is key to address its root causes and prevent the resulting injustices. Our analysis contributes to advance understanding of water insecurity by incorporating questions of uneven distribution and sociohydrological justice.
Investigation of ancient mass movements by seismic noise analysis: application to the Romanian Carpathian Mountains
Authors: Cauchie Léna , Mreyen Anne-Sophie , Cerfontaine Philippe , Micu Mihai , Havenith Hans-Balder
Published: March 2020

Assessing the geometry and volume of mass movements is essential for the appraisal of slope stability and for the understanding of slope failure trigger mechanisms. For the latter, we developed seismic ambient noise measurement techniques in order to better characterize the sub-surface of ancient deep-seated landslides in seismic regions as the Carpathian Mountains in Romania.
In particular, we conducted thorough seismological and geophysical campaigns on the landslides of Eagle’s Lake, Paltineni, and Varlaam, in the Buzau-Vrancea region, Romania. This region, marked by a high seismicity with intermediate-depth earthquakes, hosts very large and generally old (i.e. >1000 years) mass movements with morphologies which might be due to seismically induced failure.

On the three study sites, we performed abundant horizontal-to-vertical noise spectral ratio (HVSR) measurements and installed several seismic arrays. The HVSR technique, based on the analysis of three component seismic signals, is commonly used to identify the resonance frequency of a given site. Polarization of the seismic wavefield is also investigated over the landslides. Through the installation of seismic arrays, we analyse the dispersive properties of the surface waves. By jointly inverting the information through a non-linear approach, we retrieve the shear-wave velocity profiles beneath the arrays and identify velocity contrasts with depth.
On Eagle’s Lake and Paltineni rockslides, the results have also been integrated with seismic refraction tomography profiles, evidencing lateral contrasts in soil properties, and multichannel analysis of surface waves providing the subsurface shear-wave velocities. At Varlaam, the extensive measurements performed over the landslide allowed us to identify a major impedance contrast at depth highlighting the base of the failed body. We also performed UAV flights to establish a 3D model of the investigated sites. All these investigations contributed to assess the landslide geometries and estimate the volumes of the failed bodies.

This work aims, in prospect, at reconstructing the conditions and the energy needed for triggering these landslides in order to understand if a seismic component is applicable in the failure process.
Evidence and analysis of ion/electron foreshocks for a curved shock in Subcritical regime:   2D self-consistent PIC simulations 
Authors: Savoini Philippe , Lembege Bertrand
Published: March 2020

Since early 2D PIC full self-consistent quasi-perpendicular simulations of the foreshock region [Savoini et Lembege, 2001] performed for a supercritical regime, different efforts have been invested later on to analyze the foreshock region. Previous 2D PIC simulations have succeeded in recovering both the local electron distribution [Savoini and Lembege, 2001] and the ion distribution [Savoini et al., 2013] in good agreement with the in-situ experimental data. These studies have retrieved both kinds of distributions and have analyzed in detail how these local distributions vary versus (i) the local angle ΘBn to the curved shock (defined between the normal of the shock front and the upstream interplanetary magnetic field) and (ii) the distance from the shock front, in order to identify in detail the different acceleration mechanisms at work at the curved front and supporting these local ion and electron distributions within the foreshock region [Savoini and Lembege, 2001, 2015; Savoini et al, 2013]. This last point can only be accessible to a self-consistent approach (where ion and electron scales are fully included) as in 2D PIC simulations.  

Then, the present work is an extension of the previous analyses listed above for a curved (quasi-perpendicular) shock applied now in a subcritical regime. This work is performed thanks to a new 2D parallel PIC code (SMILEI) which is highly optimized and allows much higher statistics. The main characteristics of the curved front microstructures, its time dynamics, and preliminary results on local distribution functions obtained for both electrons and ions in this new Mach regime will be presented.      

Savoini, P. and B. Lembege, « Two-dimensional simulations of a curved shock: Self-consistent formation of the electron foreshock »,  J. Geophys. Res., Vol. 106, A7, 12975-12992, 2001

Savoini P., B. Lembege and J. Stienlet, « On the origin of the quasi-perpendicular ion foreshock: Full-particle simulations”, J. Geophys. Res., V. 118, 1–14, doi:10.1002/jgra.50158, 2013 

Savoini P. and B. Lembege, “Production of nongyrotropic and gyrotropic backstreaming ion distributions in the quasi-perpendicular ion foreshock region”, J. Geophys. Res., V. 120, 7154–7171, doi: 10.1002/2015JA021018, 2015.
Studies on soils condition on the area of the closed Babina mine in 2009-2019 using multispectral satellite images
Authors: Buczyńska Anna
Published: March 2020

Mining activity on the area of ​​the former open-pit and underground brown coal mine called Friendship of Nations - Shaft Babina, which is at this moment part of the UNESCO Geopark - the Muskau Arch, was finished in 1973 and reclamation works were started with a special dedication to the forestation. As a part of the reclamation works, a number of technical and biological operations were performed, the subjects were: adjustment of water conditions, relevant land forming, development of ​​the former mine area by plantings and improvement of soil condition. The last of mentioned factor is extremely significant element whose condition determines the proper growth of vegetation. Considering the mining-industrial history and current development of this area, it seems necessary to constantly monitor the components of the natural environment, in particular soils. Adequate and timely used remedies can limit the negative effects and degradation of flora. The purpose of this research was an analysis of the soils condition in 2009-2019 on the area of Babina mine on the basis of geological indices determined using multispectral images of Sentinel-2 and Landsat 5/8 satellite missions. The subjects of analysis were the following soil properties: humidity, overall condition, salinity, texture and chemical composition. It should be emphasized that the research was the first on this area in which remote sensing data was used. Obtained results allowed determining of the current condition of soils, describing their changes in the last 10 years and indicating spatial and temporal trends of changes in the future. In addition, the results of the analysis made it possible to identify areas that may still be under the influence of former mining activities that adversely affect the condition of soils.
Lightning, Evolution and Biology
Authors: Price Colin , Williams Earle , Elhalel Gal , Sentman Dave
Published: March 2020

Most electrical activity in vertebrates and invertebrates occurs at extremely low frequencies (ELF), with characteristic maxima below 50Hz.  The origin of these frequency maxima is unknown and remains a mystery.  We propose that over billions of years during the evolutionary history of living organisms on Earth, the natural electromagnetic resonant frequencies in the atmosphere, continuously generated by global lightning activity, provided the background electric fields for the development of cellular electrical activity.  In some animals the electrical spectrum is difficult to differentiate from the natural background atmospheric electric field produced by lightning.  In this paper we present evidence for the link between the natural ELF fields and those found in many living organisms, including humans.

Price, C., E. Williams, G., Elhalel and D. Sentman, 2020:  Natural ELF Fields in the Atmosphere and in Living Organisms, Int. J. Biometeorology, in press.