Contrasting radon background levels in volcanic settings: clues from 220Rn activity concentrations measured during long-term deformation experiments     

Piergiorgio Scarlato  Paola Tuccimei  Silvio Mollo  Michele Soligo  Mauro Castelluccio 《Bulletin of Volcanology》2013,75(9):1-8

To better understand the mechanisms leading to different radon background levels in volcanic settings, we have performed two long-term deformation experiments of 16 days using a real-time setup that enables us to monitor any variation of radon activity concentration during rock compression. Our measurements demonstrate that, in the case of highly porous volcanic rocks, the emanating power of the substrate changes as a function of the volcanic stress conditions. Constant magmatic pressures, such as those observed during dike intrusions and hydrothermal fluid injections, can result in pervasive pore collapse that is mirrored by a significant radon decrease until a constant emanation is achieved. Conversely, repeated cycles of stress due to, for example, volcano inflation/deflation cycles, cause a progressive radon increase a few days (but even weeks and months) before rupture. After rock failure, however, the formation of new emanation surfaces leads to a substantial increase of the radon signal. Our results suggest that surface deformation in tectonic and volcanic settings, such as inflation/deflation or constant magmatic pressures, have important repercussions on the emanating power of volcanic substrates.  相似文献   

Modeling the sediment yield and the impact of vegetated filters using an event‐based soil erosion model—a case study of a small Canadian watershed          下载免费PDF全文

Gabriel Hould‐Gosselin  Alain N. Rousseau  Silvio J. Gumiere  Dennis W. Hallema  Claudie Ratté‐Fortin  Georges Thériault  Eric van Bochove 《水文研究》2016,30(16):2835-2850

This paper presents the first application of the event‐based MHYDAS‐Erosion model to a small agricultural watershed under temperate climate conditions (Quebec, Canada). Simulation results based on observed and synthetic rainfall events revealed a bimodal behaviour of sediment yield. During high‐intensity rainfall events, most of the sediments reaching the watershed outlet originate from cropland. Meanwhile, during low‐intensity events, most of the sediments come from the drainage network. Furthermore, simulation results show that implementation of 5‐m and 20‐m wide vegetated filters throughout the watershed or at the edge of the most problematic fields (4% of the total fields) could reduce soil loss by 52% and 31%, respectively. The modeling framework could be used for the design and location of beneficial management practices such as grass strips and riparian zones Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Decadal climate predictions with a coupled OAGCM initialized with oceanic reanalyses   总被引：2，自引：1，他引：1  

A. Bellucci  S. Gualdi  S. Masina  A. Storto  E. Scoccimarro  C. Cagnazzo  P. Fogli  E. Manzini  A. Navarra 《Climate Dynamics》2013,40(5-6):1483-1497

We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmosphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using historical radiative forcing conditions for the 1960–2005 period, followed by RCP4.5 scenario settings for the 2006–2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full-value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2–5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturning circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions.  相似文献   

Holocene sea-surface temperature variability in the Chilean fjord region     

Magaly Caniupán  Frank Lamy  Carina B. Lange  Jérôme Kaiser  Rolf Kilian  Helge W. Arz  Tania León  Gesine Mollenhauer  Susana Sandoval  Ricardo De Pol-Holz  Silvio Pantoja  Julia Wellner  Ralf Tiedemann 《Quaternary Research》2014

Here we provide three new Holocene (11–0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50–53°S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past ~ 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During the mid-Holocene, pronounced short-term variations of up to 2.5°C and a cooling centered at ~ 5 cal ka BP, which coincides with the first Neoglacial glacier advance in the Southern Andes, are recorded. The latest Holocene is characterized by two pronounced cold events centered at ~ 0.6 and 0.25 cal ka BP, i.e., during the Little Ice Age. These cold events have lower amplitudes in the offshore records, suggesting an amplification of the SST signal in the inner fjords.  相似文献   

Kinematic evolution of thrusts wedge and erratic line length balancing: insights from deformed sandbox models     

Mohammad Irfan Ahmad  A. K. Dubey  Giovanni Toscani  Lorenzo Bonini  Silvio Seno 《International Journal of Earth Sciences》2014,103(1):329-347

Kinematic evolution of fold-thrust structures has been investigated by analogue models that include syntectonic sedimentation. Different decollement dips and basement thicknesses produced different wedge geometries and propagating characteristics. A model with one decollement level was characterized by a closely spaced thrust system during early stages of shortening as compared to the late stages. The frequency of fault nucleation was rapid during the early stages of deformation. Conversely, the frequency of fault nucleation was low and thrust spacing was significantly wider in a model with two decollement levels. Individual faults became locked at steep dips and deformation stepped forward as a new fault nucleated in-sequence in front of the older locked structure. Once the thrust system was established up to 27 % overall shortening, an overlying bed was introduced to simulate syntectonic deformation. Model sand wedge did not grow self similarly but rather its length and height increased episodically with deformation. Restoration of deformed models show that layer parallel shortening accommodated for approximately half of the total model shortening across the multilayers. Calculated error in apparent layer shortening from the restored layers revealed a direct relation with depth of the layers in the models. The experimental results are comparable to a natural example from the Northern Apennines fold-and-thrust belts.  相似文献   

Fuzzy parameters analysis of time‐dependent fracture of concrete dam models     

Fabrizio Barpi  Silvio Valente 《国际地质力学数值与分析法杂志》2002,26(10):1005-1027

In order to apply the mechanical properties (measured on material specimens or laboratory‐sized models) to large structures (such as concrete dams), a non‐linear theory able to predict the size‐scale effect has to be used. One of these theories was first proposed by Hillerborg and co‐workers (fictitious crack model) and is based on the earlier works by Barenblatt and Dugdale for metals (cohesive crack model). It is based on the existence of a fracture process zone (FPZ), where the material undergoes strain softening. The behaviour of the material outside the FPZ is linear elastic. A large number of short‐time laboratory tests were executed, by varying the load, under crack mouth opening displacement control. Since concrete exhibits a time‐dependent behaviour, an interaction between creep and micro‐crack growth occurs in the FPZ. Therefore, different testing conditions can be applied: rupture can be achieved by keeping the load constant before peak value (pre‐peak tests), or after peak value and after an unloading and reloading procedure (post‐peak tests). The crack propagation rate is shown to be small enough to neglect inertial forces and large enough to keep the time‐dependent behaviour of the process zone as dominant compared to the behaviour of the undamaged and viscoelastic zone. Due to the variability in material microstructure from one specimen to another, experimental data show large ranges of scatter. Well established methods in probability theory require sufficient experimental data in order to assume a probability density distribution. The objective of this study is to investigate the ranges of variation of the time response under constant load in simple structural elements associated with pre‐selected variation (fuzziness) in the main material parameters. For situations where the values of the material parameters are of a non‐stochastic nature, the fuzzy set approach to modelling variability has been proposed as a better and more natural approach. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献