A Velocity-Based Approach to Visco-Elastic Flow of Rock     

Wouter Zijl  Max Hendriks  Marcelt Hart 《Mathematical Geology》2005,37(2):141-162

In structural geology, viscous creep is generally recognized as the major deformation mechanism in the folding of rock layers through geological time scales of hundreds of thousands of years. Moreover, since deformation of rock salt by creep takes already place on relatively small time scales—weeks to months, say—creep is a relevant phenomenon when studying salt mining, notably the convergence of mine cavities and the land subsidence caused by it. While creep is the dominant process on relatively long time scales, elasticity plays a dominant role in processes that take place on relatively short time scales. The elastic response to a stress is a displacement; the shape of the rock is deformed instantaneously with respect to its initial shape. However, the viscous response of a rock to a stress is a relatively low velocity in the order of millimeters per months or years, say. In this paper we consider the two deformation phenomena creep and elasticity. In general, elasticity is a compressible phenomenon, while creep is incompressible. Here we approximate creep by the introduction of a negligibly small amount of compressibility, which makes creep velocity calculations similar to conventional elastic displacement calculations. Using this procedure, a standard finite element package for elasticity can be applied to viscous problems, also in combination with elasticity. The method has been demonstrated to upscaling of creep viscosities.  相似文献   

Erratum to “The identification of an active fault by a multidisciplinary study at the archaeological site of Sagalassos (SW Turkey)” [Tectonophysics Volume 420 (2006) 371–387]     

Dominique Similox-Tohon  Manuel Sintubin  Philippe Muchez  Griet Verhaert  Kris Vanneste  Max Fernandez  Sara Vandycke  Hannelore Vanhaverbeke  Marc Waelkens   《Tectonophysics》2007,435(1-4):55-62

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Thérèse Mound: a case study of coral bank development in the Belgica Mound Province,Porcupine Seabight     

Ben De Mol  Max Kozachenko  Andy Wheeler  Hugo Alvares  Jean-Pierre Henriet  Karine Olu-Le Roy 《International Journal of Earth Sciences》2007,96(1):103-120

High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime.  相似文献   

The identification of an active fault by a multidisciplinary study at the archaeological site of Sagalassos (SW Turkey)     

Dominique Similox-Tohon  Manuel Sintubin  Philippe Muchez  Griet Verhaert  Kris Vanneste  Max Fernandez  Sara Vandycke  Hannelore Vanhaverbeke  Marc Waelkens   《Tectonophysics》2006,420(3-4):371-387

The archaeological site of Sagalassos (SW Turkey) is located in a region characterized by the absence of any significant recent seismic activity, contrary to adjacent regions. However, the assessment of earthquake-related damage at the site suggests that the earthquakes that have been demonstrated to have struck this Pisidian city in ca. AD 500 and in the middle or second half of the 7th century AD are characterized by an MSK intensity of at least VIII and occurred on a fault very close to the city. Different investigation techniques (archaeoseismology, remote sensing and geomorphology, surface geology and structural data, 2D resistivity imaging and palaeoseismological trenching) have been applied at the archaeological site and its direct surroundings in search for the causative fault of these earthquakes. This multidisciplinary approach shows that each of the different approaches independently provides only partial, non-conclusive information with respect to the fault identification. Integration is imperative to give a conclusive answer in the search for the causative fault. This study has, indeed, revealed the existence of a to date unknown active normal fault system passing underneath ancient Sagalassos, i.e. the Sagalassos fault. A historical coseismic surface rupture event on this fault could be identified. This event possibly corresponds to the devastating Sagalassos earthquakes of ca. AD 500 and the middle or second half of the 7th century AD. Finally, this study demonstrates that in the particular geodynamic setting of SW Turkey archaeological sites with extensive earthquake-related damage form an important tool in any attempt to asses the seismic hazard.  相似文献   

VHF radar observations of surface currents off the northern Opal coast in the eastern English Channel     

Alexei Sentchev  Max Yaremchuk 《Continental Shelf Research》2007

Two very high-frequency radars (VHFR) operating on the Opal coast of eastern English Channel provided a nearly continuous 35-day long dataset of surface currents over a 500 km² area at 0.6–1.8 km resolution. Argo drifter tracking and CTD soundings complemented the VHFR observations, which extended approximately 25 km offshore. The radar data resolve three basic modes of the surface velocity variation in the area, that are driven by tides, winds and freshwater fluxes associated with seasonal river discharge. The first mode, accounting for 90% of variability, is characterized by an along-shore flow pattern, whereas the second and third modes exhibit cross-shore, and eddy-like structures in the current velocity field. All the three modes show the dominant semi-diurnal variability and low-frequency modulation by the neap-spring tidal cycle. Although tidal forcing provides the major contribution to variability of local currents, baroclinicity plays an important role in shaping the 3D velocity field averaged over the tidal cycle and may strongly affect tracer dynamics on larger time scales. An empirical orthogonal function (EOF) decomposition and a spectral rotary analysis of the VHFR data reveal a discontinuity in the velocity field occurring approximately 10 km offshore which was caused by the reversal in the sign of rotation of the current vector. This feature of local circulation is responsible for surface current convergence on ebb, divergence on flood and strong oscillatory vertical motion. Spectral analysis of the observed currents and the results of the Agro drifter tracking indicate that the line of convergence approximately follows the 30-m isobath. The most pronounced feature of the radar-derived residual circulation is the along-coast intensification of surface currents with velocity magnitude of 0.25 m/s typical for the Regions of Freshwater Influence (ROFI). The analysis has provided a useful, exploratory examination of surface currents, suggesting that the circulation off the Opal coast is governed by ROFI dynamics on the hypertidal background.  相似文献   

Primary petrology,mineralogy and age of the Letšeng-la-Terae kimberlite (Lesotho,Southern Africa) and parental magmas of Group-I kimberlites     

Natalia?StammEmail authorView author&#;s OrcID profile  Max?W.?Schmidt  Dawid?Szymanowski  Albrecht?von?Quadt  Thabang?Mohapi  Andre?Fourie 《Contributions to Mineralogy and Petrology》2018,173(9):76

The Let?eng-la-Terae kimberlite (Lesotho), famous for its large high-value diamonds, has five distinct phases that are mined in a Main and a Satellite pipe. These diatreme phases are heavily altered but parts of a directly adjacent kimberlite blow are exceptionally fresh. The blow groundmass consists of preserved primary olivine with Fo_86?88, chromite, magnesio-ulvöspinel and magnetite, perovskite, monticellite, occasional Sr-rich carbonate, phlogopite, apatite, calcite and serpentine. The bulk composition of the groundmass, extracted by micro-drilling, yields 24–26 wt% SiO₂, 20–21 wt% MgO, 16–19 wt% CaO and 1.9–2.1 wt% K₂O, the latter being retained in phlogopite. Without a proper mineral host, groundmass Na₂O is only 0.09–0.16 wt%. However, Na-rich K-richterite observed in orthopyroxene coronae allows to reconstruct a parent melt Na₂O content of 3.5–5 wt%, an amount similar to that of highly undersaturated primitive ocean island basanites. The groundmass contains 10–12 wt% CO₂, H₂O is estimated to 4–5 wt%, but volatiles and alkalis were considerably reduced by degassing. Mg# of 77.9 and 530 ppm Ni are in equilibrium with olivine phenocrysts, characterize the parent melt and are not due to olivine fractionation. ⁸⁷Sr/⁸⁶Sr_(i)?=?0.703602–0.703656, ¹⁴³Nd/¹⁴⁴Nd_(i)?=?0.512660 and ¹⁷⁶Hf/¹⁷⁷Hf_(i)?=?0.282677–0.282679 indicate that the Let?eng kimberlite originates from the convective upper mantle. U–Pb dating of groundmass perovskite reveals an emplacement age of 85.5?±?0.3 (2σ) Ma, which is significantly younger than previously proposed for the Let?eng kimberlite.  相似文献   

Windfalls for whom? The evolving notion of ‘community’ in community benefit provisions from wind farms     

Gillian Bristow  Richard Cowell  Max Munday 《Geoforum》2012,43(6):1108-1120

This paper investigates the increasing provision of ‘community benefits’ – i.e. financial or material benefits to communities affected by wind energy development – with a focus on on-shore wind projects in Wales. The paper argues that as community benefits are becoming more significant in scale, so pressures are mounting on what have hitherto been largely ad hoc arrangements for their disbursement. The paper finds that previously dominant definitions of communities as places directly affected by and within close proximity to wind farm development, are being challenged by the tendency to define ‘affected’ communities as broader entities characterised by more indirect and widely dispersed claims to benefit entitlement. This redefinition of the recipient community is causing conflict, much of it focused on debates about how community benefits should be governed. Evidence suggests that any re-scaling of relations around community benefits – from local compensation towards wider development goals – may be more consensually achieved in communities with previous experience in handling these funds, and where growing income streams allow multiple constituencies to be satisfied.  相似文献   

A Temporal Variant‐Invariant Validation Approach for Agent‐based Models of Landscape Dynamics     

Christopher Bone  Bart Johnson  Max Nielsen‐Pincus  Eric Sproles  John Bolte 《Transactions in GIS》2014,18(2):161-182

Agent‐based modeling provides a means for addressing the way human and natural systems interact to change landscapes over time. Until recently, evaluation of simulation models has focused on map comparison techniques that evaluate the degree to which predictions match real‐world observations. However, methods that change the focus of evaluation from patterns to processes have begun to surface; that is, rather than asking if a model simulates a correct pattern, models are evaluated on their ability to simulate a process of interest. We build on an existing agent‐based modeling validation method in order to present a temporal variant‐invariant analysis (TVIA). The enhanced method, which focuses on analyzing the uncertainty in simulation results, examines the degree to which outcomes from multiple model runs match some reference to how land use parcels make the transition from one land use class to another over time. We apply TVIA to results from an agent‐based model that simulates the relationships between landowner decisions and wildfire risk in the wildland‐urban interface of the southern Willamette Valley, Oregon, USA. The TVIA approach demonstrates a novel ability to examine uncertainty across time to provide an understanding of how the model emulates the system of interest.  相似文献   

Ra-partitioning between phlogopite and silicate melt and 226Ra/Ba–230Th/Ba isochrons     

Alessandro Fabbrizio  Max W. Schmidt  Detlef Günther  Jost Eikenberg 《Lithos》2010,114(1-2):121-131

In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). D_Ra^{phlogopite/melt} was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio D_Ra/D_Ba is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of D_Ra and D_Ra/D_Ba for magmatic minerals containing appreciable Ra, yields D_Ra^mineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 ? 10^? 5 for pyroxenes, and D_Ra/D_Ba^mineral/melt from ~ 4 for leucite to 2 ? 10^? 2 for orthopyroxene. The influence of melt composition on D_Ra/D_Ba is less than 10%. All investigated minerals have different D_Ra/D_Ba, strongly fractionating Ra from Ba. Thus, for magmatic systems, (²²⁶Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (²²⁶Ra)/Ba–(²³⁰Th)/Ba system at the time of crystallization and thus, there is no (²²⁶Ra)/Ba–(²³⁰Th)/Ba isochron at t₀. ²²⁶Ra–²³⁰Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known D_Ra.  相似文献   

On Rates and Acceleration Trends of Global Glacier Mass Changes   总被引：4，自引：0，他引：4  

Wilfried Haeberli  Regula Frauenfelder  Martin Hoelzle  & Max Maisch 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):585-591

Worldwide glacier mass changes are considered to represent natural key variables within global climate-related monitoring programmes, especially with respect to strategies concerning early detection of enhanced greenhouse effects on climate. This is due to the fact that glacier mass changes provide important quantitative information on rates of change, acceleration tendencies and pre-industrial variability relating to energy exchange at the earth/athmosphere interface. During the coming decades, excess radiation income and sensible heat (a few watts per square metre) as calculated with numerical climate models are both estimated to increase by a factor of about two to four as compared to the mean of the 20th century. The rate of average annual mass loss (a few decimetres per year) measured today on mountain glaciers in various parts of the world now appears to accelerate accordingly, even though detailed interpretation of the complex processes involved remains difficult. Within the framework of secular glacier retreat and Holocene glacier fluctuations, similar rates of change and acceleration must have taken place before, i.e. during times of weak anthropogenic forcing. However, the anthropogenic influences on the atmosphere could now and for the first time represent a major contributing factor to the observed glacier shrinkage at a global scale. Problems with such assessments mainly concern aspects of statistical averaging, regional climate variability, strong differences in glacier sensitivity and relations between mass balance and cumulative glacier length change over decadal to secular time scales. Considerable progress has recently been achieved in these fields of research.  相似文献