A state-dependent hyperelastic-plastic constitutive model considering shear-induced particle breakage in granular soils     

Irani  Nazanin  Lashkari  Ali  Tafili  Merita  Wichtmann  Torsten 《Acta Geotechnica》2022,17(11):5275-5298

Acta Geotechnica - An elastic–plastic constitutive model considering particle breakage for simulation of crushable granular soils behavior is proposed. In the model, elastic strain rates are...  相似文献   

Late Pleistocene dust deposition in the Patagonian steppe - extending and refining the paleoenvironmental and tephrochronological record from Laguna Potrok Aike back to 55 ka     

Torsten Haberzettl  Flavio S. Anselmetti  Sabine W. Bowen  Michael Fey  Christoph Mayr  Bernd Zolitschka  Daniel Ariztegui  Barbara Mauz  Christian Ohlendorf  Stephanie Kastner  Andreas Lücke  Frank Schäbitz  Michael Wille 《Quaternary Science Reviews》2009,28(25-26):2927-2939

Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3.  相似文献   

Discrimination of induced seismicity by full moment tensor inversion and decomposition   总被引：3，自引：1，他引：2  

Simone Cesca  Alexander Rohr  Torsten Dahm 《Journal of Seismology》2013,17(1):147-163

Human activities, including operations related to mining and reservoir exploitation, may induce seismicity and pose a risk for population and infrastructures. While different observations are commonly used to assess the origin of earthquakes, there is a lack of rules and methods for the discrimination between natural and induced seismicity. The inversion and decomposition of the full moment tensor and the observation of relevant deviation from a pure double couple (DC) model may be an indicator for induced seismicity. We establish here a common procedure to analyse a set of natural and induced events of similar magnitude, which occurred in Germany and neighbouring regions. The procedure is based on an inversion method and on a consistent velocity model and recording network. Induced seismicity is recorded during different mining and/or reservoir exploitations. Moment tensors are inverted using a multi-step inversion approach. This method, which was successfully applied in previous studies at regional and teleseismic distances, is further developed here to account for full moment tensor analysis. We first find a best DC solution and then perform a full moment tensor inversion, fitting full waveforms amplitude spectra at regional distances. The moment tensor solution is decomposed into DC, compensated linear vector dipole and isotropic terms. The discrimination problem is then investigated through the evaluation of distributions of non-DC source components for natural and induced data sets. Results illustrate the potential of the inversion and discrimination approach. Additional detailed analyses are carried out for the two most significant induced earthquakes, and rupture models are compared with the full moment tensor solutions.  相似文献   

A probabilistic approach for the classification of earthquakes as ��triggered�� or ��not triggered��     

Luigi Passarelli  Francesco Maccaferri  Eleonora Rivalta  Torsten Dahm  Elias Abebe Boku 《Journal of Seismology》2013,17(1):165-187

The occurrence time of earthquakes can be anticipated or delayed by external phenomena that induce strain energy changes on the faults. ??Anticipated?? earthquakes are generally called ??triggered??; however, it can be controversial to label a specific earthquake as such, mostly because of the stochastic nature of earthquake occurrence and of the large uncertainties usually associated to stress modelling. Here we introduce a combined statistical and physical approach to quantify the probability that a given earthquake was triggered by a given stress-inducing phenomenon. As an example, we consider an earthquake that was likely triggered by a natural event: the M?=?6.2 13 Jan 1976 Kópasker earthquake on the Grímsey lineament (Tj?rnes Fracture Zone, Iceland), which occurred about 3?weeks after a large dike injection in the nearby Krafla fissure swarm. By using Coulomb stress calculations and the rate-and-state earthquake nucleation theory, we calculate the likelihood of the earthquake in a scenario that contains only the tectonic background and excludes the dike and in a scenario that includes the dike but excludes the background. Applying the Bayes?? theorem, we obtain that the probability that the earthquake was indeed triggered by the dike, rather than purely due to the accumulation of tectonic strain, is about 60 to 90?%. This methodology allows us to assign quantitative probabilities to different scenarios and can help in classifying earthquakes as triggered or not triggered by natural or human-induced changes of stress in the crust.  相似文献   

Fully coupled generalised hybrid-mixed finite element approximation of two-phase two-component flow in porous media. Part II: numerical scheme and numerical results     

Estelle Marchand  Torsten Müller  Peter Knabner 《Computational Geosciences》2012,16(3):691-708

We consider the modeling and simulation of compositional two-phase flow in a porous medium, where one phase is allowed to vanish or appear. The modeling of Marchand et al. (in review) leads to a nonlinear system of two conservation equations. Each conservation equation contains several nonlinear diffusion terms, which in general cannot be written as a function of the gradients of the two principal unknowns. Also the diffusion coefficients are not necessarily explicit local functions of them. For the generalised mixed finite elements approximation, Lagrange multipliers associated to each principal unknown are introduced, the sum of the diffusive fluxes of each component is explicitly eliminated and the static condensation leads to a “global” nonlinear system of equations only in the Lagrange multipliers also including complementarity conditions to cope with vanishing or appearing phases. After time discretisation, this system can be solved at each time step using a semi-smooth Newton method. The static condensation involves “local” nonlinear systems of equations associated to each element, solved also by a semismooth Newton method. The algorithm is successfully applied to 1D and 2D examples of water–hydrogen flow involving gas phase appearance and disappearance.  相似文献   

Glacial dynamics and transport of debris during the final phases of the Weichselian Glaciation,southwest Skåne,Sweden     

Krstin Malmberg Persson  Erik Lagerlund 《第四纪科学杂志》1994,9(3):245-256

Late Weichselian glacial sediments were studied in three sections west of Lund, southwest Sweden. The lowermost sedimentary unit is a lodgement till containing rock fragments derived from the northeast-east. Fabric analyses indicate successive ice flow directions: from the northeast, east-northeast, south-southeast and then east. The last active ice movement in the area was from the east. Above the lodgement till are deglaciation sediments consisting of meltout till, flow till and glaciofluvial sand and gravel deposited in a subaerial stagnant-ice environment. The uppermost unit consists of glaciolacustrine clay and silt, containing abundant ice-rafted debris, deposited during a short-lived transgression phase when stagnant ice was still present in the area. At the westernmost site investigated, the petrographical composition of the deglaciation deposits displays a gradual change, with upwards increasing components of Cretaceous chalky limestone. The presence of this rock type requires a period of glacial transport from the south. This stratigraphy cannot be explained with traditional glaciodynamic models. A possible scenario can, however, be constructed using a previously published model (Lagerlund, 1987) where marginal ice domes in the southwestern Baltic area interact with the main Scandinavian Ice Sheet.  相似文献   

Regional gravity modeling in terms of spherical base functions     

Michael Schmidt  Martin Fengler  Torsten Mayer-Gürr  Annette Eicker  Jürgen Kusche  Laura Sánchez  Shin-Chan Han 《Journal of Geodesy》2007,81(1):17-38

This article provides a survey on modern methods of regional gravity field modeling on the sphere. Starting with the classical theory of spherical harmonics, we outline the transition towards space-localizing methods such as spherical splines and wavelets. Special emphasis is given to the relations among these methods, which all involve radial base functions. Moreover, we provide extensive applications of these methods and numerical results from real space-borne data of recent satellite gravity missions, namely the Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE). We also derive high-resolution gravity field models by effectively combining space-borne and surface measurements using a new weighted level-combination concept. In addition, we outline and apply a strategy for constructing spatio-temporal fields from regional data sets spanning different observation periods.  相似文献   

Discharge and transport processes along the German Baltic Sea Coast     

Herbert Siegel  Torsten Seifert  Gerald Schernewski  Monika Gerth  Thomas Ohde  Jan Reißmann  Victor Podsetchine 《Ocean Dynamics》2005,55(1):47-66

The western Baltic Sea infront of the German coast is a highly variable dynamical system, dominated by a complex and small-scale morphometry, the water exchange between the Baltic and North Seas, and driven by local wind. Neither data collection, nor satellite images or model simulations alone were able to explain the observed spatial patterns and transport processes. Therefore, all these methods were combined to explain the dynamical features and to systematise them according to the typical local wind pattern and time series. The aim was to develop an instrument for regional authorities which supports the interpretation of coastal water monitoring data and forms a basis for an improved monitoring strategy. Satellite data of sea surface temperature and ocean colour from the sensors NOAA-AVHRR and SeaWiFS were applied for synoptic investigations in the entire region and Landsat-7-ETM+ for regional studies. Model simulations were performed for the western Baltic using a 3D model MOM-3 and for the Szczecin Lagoon using 2D model FEMFLOW. For the first time, regional particularities in the coastal dynamical features and processes are derived for the main wind directions and for transitions between dominant wind situations west and east as derived from wind statistics. The simulated transport of particles released from different coastal and open sea sources indicate the affected areas during changing forcing conditions. The results support the interpretation of acquired coastal monitoring data as well as the assessment and optimisation of the monitoring programme.  相似文献   

有机组分土-水分配系数的确定(英文)     

Erping BI　 Torsten SCHMIDT 《地学前缘》2005,12(Z1):199-208

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi  相似文献   

Erosion and Flooding—Threats to Coastal Infrastructure in the Arctic: A Case Study from Herschel Island,Yukon Territory,Canada     

Boris Radosavljevic  Hugues Lantuit  Wayne Pollard  Paul Overduin  Nicole Couture  Torsten Sachs  Veit Helm  Michael Fritz 《Estuaries and Coasts》2016,39(4):900-915

Arctic coastal infrastructure and cultural and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this paper are to provide such a tool by assessing potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site. This study focused on Simpson Point and the adjacent coastal sections because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost path analysis based on a high-resolution light detection and ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from ?5.5 to 2.7 m·a^?1 (mean ?0.6 m·a^?1). Mean coastal retreat decreased from ?0.6 m·a^?1 to ?0.5 m·a^?1, for 1952–1970 and 1970–2000, respectively, and increased to ?1.3 m·a^?1 in the period 2000–2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion. This study demonstrates that transgressive forcing may provide ample sediment for the expansion of depositional landforms, while growing more susceptible to overwash and flooding.  相似文献