Finite Difference Simulations of Seismic Wave Propagation for the 2007 Mw 6.6 Niigata-ken Chuetsu-Oki Earthquake: Validity of Models and Reliable Input Ground Motion in the Near-Field

Finite difference simulations of seismic wave propagation are performed in the Niigata area, Japan, for the 2007 Mw 6.6 Niigata-ken Chuetsu-Oki earthquake at low frequencies. We test three 3D structural models built independently in various studies. First aftershock simulations are carried out. The model based on 3D tomography yields correct body waves in the near field, but later phases are imperfectly reproduced due to the lack of shallow sediment layers; other models based on various 1D/2D profiles and geological interpretation provide good site responses but generate seismic phases that may be shifted from those actually observed. Next, for the mainshock simulations, we adopt two different finite source models that differ in the near-field ground motion, especially above the fault plane (but under the sea) and then along the coastline. Each model is found to be calibrated differently for the given stations. For engineering purposes, the variations observed in simulated ground motion are significant, but for seismological purposes, additional parameter calibrations would be possible for such a complex 3D case.     

A new amber deposit from the Cretaceous (uppermost Albian-lowermost Cenomanian) of southwestern France

A Cretaceous amber deposit has recently been discovered in a quarry of Charente-Maritime (southwestern France), at Cadeuil. This paper presents the sedimentary and palaeoenvironmental settings of the uppermost Albian-lowermost Cenomanian series including the amber deposit. A preliminary analysis of the amber samples reveals diverse fossil arthropods (a few mites and at least 20 insect families within 9 orders), as well as numerous micro-organisms, mainly algae and mycelia. A myceloid colony of bacteria, a flagellate algae and four especially well preserved insects are illustrated (Diptera Dolichopodidae, Diptera Chironomidae, Hymenoptera Parasitica, and Heteroptera Tingidae). The abundance of the limnic micro-organisms is discussed in terms of bloom events. Their relative scarcity in almost all the amber pieces containing fossil arthropods is attributed to differences in the origin of resin: production along trunk and branches for amber with arthropods; production by aquatic roots for amber rich in algae. The absence of pollen and spores in amber is attributed to differences in the respective periods of resin and palynomorph production, which may be related to a seasonal climate during the Albian-Cenomanian transition in Western Europe.     

Analysis of snow-vegetation interactions in the low Arctic-Subarctic transition zone (northeastern Canada)

Abstract

Recent studies have shown that northern vegetation has been growing in relation to a warming climate over the last four decades, especially across the transition zone between tundra and taiga. Shrub growth affects snow properties and the surface energy budget, which must be better studied to quantify shrub-snow-climate feedbacks. The objective of this research is to improve the characterization of the impact of shrubs on snow evolution, from its accumulation to its melt, using in-situ and satellite measurements. The research is presented for the Umiujaq site, Nunavik, representative of the low Arctic–Subarctic transition zone. Snow depth, measured along numerous transects spanning different land cover types is found to increase by a factor 2.5–3 between tundra and forest, while snow density decreases. This illustrates the trapping effect of vegetation well. Complementary, continuous snow depth measurements using weather stations from two sites (tundra with low shrubs and a small clearing with shrubs within the forest) show different site-dependent behaviors. Spatial analysis from high-resolution Pleiades images combined with Landsat (Normalized Difference Snow Index) and MODIS (Fractional Snow Cover) images suggest a slight delay in melt over open and dense forest areas compared to tundra and dense high shrubs.     

Bioconcentration of the anionic surfactant linear alkylbenzene sulfonate (LAS) in the marine shrimp Palaemonetes varians: A radiotracer study

Uptake and depuration kinetics of dissolved [¹⁴C]C₁₂-6-linear alkylbenzene sulfonate (LAS) were determined in the shrimp Palaemonetes varians using environmentally relevant exposure concentration. The shrimp concentrated LAS from seawater with a mean BCF value of 120 L kg⁻¹ after a 7-day exposure. Uptake biokinetics were best described by a saturation model, with an estimated BCF_ss, of 159 ± 34 L kg⁻¹, reached after 11.5 days. Shrimp weight influenced significantly BCF value with smaller individuals presenting higher affinity to LAS. To the light of a whole body autoradiography, major accumulation of LAS occurred in the cephalothorax circulatory system (gills, heart, hepatopancreas) and ocular peduncle, but not in the flesh, limiting potential transfer to human consumers. LAS depuration rate constant value of the shrimp was 1.18 ± 0.08 d⁻¹ leading to less than 1% of remaining LAS in its tissues after 8 days of depuration.     

Projecting future drought in Mediterranean forests: bias correction of climate models matters!

Global and regional climate models (GCM and RCM) are generally biased and cannot be used as forcing variables in ecological impact models without some form of prior bias correction. In this study, we investigated the influence of the bias correction method on drought projections in Mediterranean forests in southern France for the end of the twenty-first century (2071–2100). We used a water balance model with two different atmospheric climate forcings built from the same RCM simulations but using two different correction methods (quantile mapping or anomaly method). Drought, defined here as periods when vegetation functioning is affected by water deficit, was described in terms of intensity, duration and timing. Our results showed that the choice of the bias correction method had little effects on temperature and global radiation projections. However, although both methods led to similar predictions of precipitation amount, they induced strong differences in their temporal distribution, especially during summer. These differences were amplified when the climatic data were used to force the water balance model. On average, the choice of bias correction leads to 45 % uncertainty in the predicted anomalies in drought intensity along with discrepancies in the spatial pattern of the predicted changes and changes in the year-to-year variability in drought characteristics. We conclude that the choice of a bias correction method might have a significant impact on the projections of forest response to climate change.     

Reducing Uncertainties in Climate Projections with Emergent Constraints:Concepts,Examples and Prospects

Models disagree on a significant number of responses to climate change,such as climate feedback,regional changes,or the strength of equilibrium climate sensitivity.Emergent constraints aim to reduce these uncertainties by finding links between the inter-model spread in an observable predictor and climate projections.In this paper,the concepts underlying this framework are recalled with an emphasis on the statistical inference used for narrowing uncertainties,and a review of emergent constraints found in the last two decades.Potential links between highlighted predictors are explored,especially those targeting uncertainty reductions in climate sensitivity,cloud feedback,and changes of the hydrological cycle.Yet the disagreement across emergent constraints suggests that the spread in climate sensitivity can not be significantly narrowed.This calls for weighting the realism of emergent constraints by quantifying the level of physical understanding explaining the relationship.This would also permit more efficient model evaluation and better targeted model development.In the context of the upcoming CMIP6 model intercomparison a growing number of new predictors and uncertainty reductions is expected,which call for robust statistical inferences that allow cross-validation of more likely estimates.     

Numerical modeling to predict the spread of landslide of schist’s area under climatic event of Ain El Hammam (Algeria)

The several reactivations of the landslide of Ain El Hammam (AEH) after each important weather event compel us to look closely at its triggering factors and predict its mechanisms and its evolution at the longer term. In this sense, the prediction of the slope behavior becomes necessary. This paper presents a numerical model of the AEH landslide using Plaxis® software. This model considers hydraulic effects such as precipitation and pore pressure even in the unsaturated parts. Soil and rock behaviors are described with proper elasto-plastic models named Hardening Soils and Jointed Rocks. The first model takes into account hardening on isotropic and deviatoric mechanism as well as a non-associated flow rule. The second model considers a non-isotropic elasticity with perfect plasticity along with given sliding directions. The hydraulic and mechanical models are coupled with an effective stress concept. To detect unstable areas in the landslide, we developed a Matlab® program to take into account the Hill’s bifurcation criterion, which is based on sign of the second-order work. It has been proved that this criterion allows detecting all failure modes that can appear in rate-independent materials and especially the ones that develop before the plasticity limit criterion. From such computations, we can predict the shape and position of slip surface responsible of the actual ground movement of the slope. To validate the numerical results, analysis of field measurement is included. We use high resolution of electrical tomography to delineate the geometry and position of failure surface and approve our results.