Post-drilling destabilization of temperature profile in borehole Yaxcopoil-1, Mexico     

Jan Šafanda  Philipp Heidinger  Helmut Wilhelm  Vladimír Čermák 《Hydrogeology Journal》2007,15(2):423-428

As part of the International Continental Scientific Drilling Program (ICDP), the 1.5-km-deep borehole Yaxcopoil-1, located in the Chixculub meteor impact structure in Mexico, has undergone further study after drilling operations ceased. Temperature logs were repeated ten times at intervals 0.3–0.8, 15, 24 and 34 months after borehole shut-in. The logs bear a distinct signature of transient heat transfer by groundwater flow manifested by a gradual distortion of the linear temperature profile when a cold wave of 0.8–1.6°C amplitude was detected propagating downward from 145 to 312 m at a rate of 4–6 m/month. To understand the nature of this moving anomaly, a 20-day monitoring of the cold wave was carried out at a depth of 307 m that showed further cooling of 0.6°C during the first 16 days of the passage followed by temperature stabilisation. As an explanation of this unusual phenomenon, a theory is proposed, whereby the drilling mud has accumulated within the overlying and cooler highly porous and permeable karstic rocks during the drilling and migrates downward. The observed migration rate suggests a permeability higher than 10^?11 m². This indicates a high vulnerability to contamination of the only freshwater aquifer in the Yucatan region.  相似文献   

Mineralogical,geochemical and microfabric evidences of gypsum crusts: a case study from Budapest     

Siegfried Siegesmund  Akos Török  Andre Hüpers  Christian Müller  Werner Klemm 《Environmental Geology》2007,52(2):385-397

High levels of SO₂ and particulate pollution enable the rapid development of gypsum-rich weathering crusts in Budapest. Two types of white crusts, thin and thick ones, and two forms of black crusts, laminar and framboidal ones, were studied in limestone buildings of the parliament and Citadella. The percentage of crust cover and damage categories were documented on selected walls. Petrographic, XRD, XRF and sulphur isotope analyses were performed under laboratory conditions to understand the mechanism of crust formation. White crusts found both on exposed and sheltered walls display a calcite-rich layer with gypsum, while black crusts are enriched with gypsum. The sulphur isotopic composition of white and black crusts overlaps, but the crusts are slightly enriched in heavy isotopes compared to rainwater. S content, Si/Al ratios and particulates in black crusts suggest that air pollution (SO₂, dust) contributes to black crust formation. The accumulation of sulphur and Zn enrichment of white crusts were also documented indicating that under high pollution levels, even these compound can accumulate on exposed facades.  相似文献   

An Estimate of Global Mean Sea-level Rise Inferred from Tide-gauge Measurements Using Glacial-isostatic Models Consistent with the Relative Sea-level Record   总被引：1，自引：0，他引：1  

J. M. Hagedoorn  D. Wolf  Z. Martinec 《Pure and Applied Geophysics》2007,164(4):791-818

This study is concerned with the influence of the glacial-isostatic adjustment caused by the last Pleistocene deglaciation on the present-day sea level. The viscoelastic deformation caused by the time-variable ice and ocean loads is simulated by computing the resulting perturbations for a spherical, self-gravitating, incompressible, Maxwell-viscoelastic earth model. The associated variation of the earth rotation is described in terms of the Liouville equation, which is solved by means of the MacCullagh formulae. This allows the determination of the vertical displacement and geoid height and, thus, the solution of the sea-level equation. We test several viscosity and ice models and evaluate them by comparison of the computed response with the Holocene relative sea-level record. Using the optimum combination of viscosity and ice models, we then estimate the influence of the last Pleistocene deglaciation on the tide-gauge measurements. A comparison between the observational and residual linear trends for the tide-gauge measurements shows a significant reduction of the variance and geographical variability for the latter, in particular for the formerly ice-covered regions of North America and Scandinavia. The favoured value determined for the global mean sea-level rise is (1.46±0.2) mm a⁻¹.  相似文献   

Integral inversion of SST data of type GRACE     

P. Novák 《Studia Geophysica et Geodaetica》2007,51(3):351-367

Satellite missions CHAMP and GRACE dedicated to global mapping of the Earth’s gravity field yield accurate satellite-to-satellite tracking (SST) data used for recovery of global geopotential models usually in a form of a finite set of Stokes’s coefficients. The US-German Gravity Recovery And Climate Experiment (GRACE) yields SST data in both the high-low and low-low mode. Observed satellite positions and changes in the intersatellite range can be inverted through the Newtonian equation of motion into values of the unknown geopotential. The geopotential is usually approximated in observation equations by a truncated harmonic series with unknown coefficients. An alternative approach based on integral inversion of the SST data of type GRACE into discrete values of the geopotential at a geocentric sphere is discussed in this article. In this approach, observation equations have a form of Green’s surface integrals with scalar-valued integral kernels. Despite their higher complexity, the kernel functions exhibit features typical for other integral kernels used in geodesy for inversion of gravity field data. The two approaches are discussed and compared based on their relative advantages and intended applications. The combination of heterogeneous gravity data through integral equations is also outlined in the article. panovak@kma.zcu.cz  相似文献   

Magmatic structures in the Krkonoše–Jizera Plutonic Complex,Bohemian Massif: evidence for localized multiphase flow and small-scale thermal–mechanical instabilities in a granitic magma chamber     

Jiří Žák  Josef Klomínský 《Journal of Volcanology and Geothermal Research》2007

The present paper examines magmatic structures in the Jizera and Liberec granites of the Krkonoše–Jizera Plutonic Complex, Bohemian Massif. The magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal-rich mushes, and to capture the evolution of physical processes in an ancient granitic magma chamber. We propose that after chamber-wide mixing and hybridization, as suggested by recent petrological studies, laminar magma flow became highly localized to weaker channel-like domains within the higher-strength crystal framework. Mafic schlieren formed at flow rims, and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape. Local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure. After the cessation or deceleration of channel flow, gravity-driven processes (settling of crystals and enclaves, gravitational differentiation, development of downward dripping instabilities), accompanied by compaction, filter pressing and melt segregation, dominated in the crystal mush within the flow channels. Subsequently, magmatic folds developed in schlieren layers and the magma chamber recorded complex, late magmatic strains at high magma crystallinities. Late-stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization. We emphasize that the most favorable environments for the formation and preservation of magmatic structures, such as those hosted in the Jizera and Liberec granites, are slowly cooling crystal-rich mushes. Therefore, where preserved in plutons, these structures may lend strong support for a “mush model” of magmatic systems.  相似文献   

Possibilities of GPS Kinematic Measurements for Geological Survey in East Slovakia     

Vladimir  Sedlak  Viera  Hurcikova 《地球空间信息科学学报》2002,5(4):21-25

This paper deals with transformation procedures for observed GPS data from the world geodetic system WGS-84 into the national geodetic grid datum S-UTCN(system of united trigonometric cadaster network) and Baa(the Baltic Sea after adjustment).Transformation from WGS-84 into SUTCN is performed most frequently by means of the 7-element Helmert transformation with three identical points.Geodetic network was adjusted by two ways.  相似文献   

Geoid, topography, and the Bouguer plate or shell   总被引：1，自引：1，他引：1  

P. Vaníc˘ek  P. Novák  Z. Martinec 《Journal of Geodesy》2001,75(4):210-215

 Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind. For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography. Received: 24 December 1999 / Accepted: 11 December 2000  相似文献   

Effects of the spherical terrain on gravity and the geoid   总被引：3，自引：0，他引：3  

P. Novák  P. Vaníček  Z. Martinec  M. Véronneau 《Journal of Geodesy》2001,75(9-10):491-504

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Determination of Geopotential Differences between Local Vertical Datums and Realization of a World Height System   总被引：2，自引：0，他引：2  

Burša  Milan  Kouba  Jan  Müller  Achim  Raděj  Karel  True  Scott A.  Vatrt  Viliam  Vojtíšková  Marie 《Studia Geophysica et Geodaetica》2001,45(2):127-132

The methodology developed for connecting Local Vertical Datums (LVD) was applied to the Australian Height Datum (AHD) and the North American Vertical Datum (NAVD88). The geopotential values at AHD and NAVD88 were computed and the corresponding vertical offset of 974 mm with rms 51 mm was obtained between the zero reference surfaces defined by AHD and NAVD88. The solution is based on the four primary geodetic parameters, the GPS/levelling sites and the geopotential model EGM96. The Global Height System (or the Major Vertical Datum) can be defined by a geoidal geopotential value used in the solution as the reference value, or by the geopotential value of the LVD, e.g. NAVD88.  相似文献   

Preface     

Ivan Pšenčík  Vlastislav Červený  Luděk Klimeš 《Pure and Applied Geophysics》1996,148(1-2):1-1

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