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1.
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
2.
The paper presents a numerical solution of the oblique derivative boundary value problem on and above the Earth’s topography using the finite volume method (FVM). It introduces a novel method for constructing non-uniform hexahedron 3D grids above the Earth’s surface. It is based on an evolution of a surface, which approximates the Earth’s topography, by mean curvature. To obtain optimal shapes of non-uniform 3D grid, the proposed evolution is accompanied by a tangential redistribution of grid nodes. Afterwards, the Laplace equation is discretized using FVM developed for such a non-uniform grid. The oblique derivative boundary condition is treated as a stationary advection equation, and we derive a new upwind type discretization suitable for non-uniform 3D grids. The discretization of the Laplace equation together with the discretization of the oblique derivative boundary condition leads to a linear system of equations. The solution of this system gives the disturbing potential in the whole computational domain including the Earth’s surface. Numerical experiments aim to show properties and demonstrate efficiency of the developed FVM approach. The first experiments study an experimental order of convergence of the method. Then, a reconstruction of the harmonic function on the Earth’s topography, which is generated from the EGM2008 or EIGEN-6C4 global geopotential model, is presented. The obtained FVM solutions show that refining of the computational grid leads to more precise results. The last experiment deals with local gravity field modelling in Slovakia using terrestrial gravity data. The GNSS-levelling test shows accuracy of the obtained local quasigeoid model. 相似文献
3.
Gregor Muri Branko Čermelj Radojko Jaćimović Tina Ravnikar Andrej Šmuc Janja Turšič Polona Vreča 《Journal of Paleolimnology》2018,59(4):411-426
Increased eutrophication was recently observed in the 5th (5J) and 6th (6J) Triglav Lakes, two remote Slovenian mountain lakes. Sediment phosphorus (P) pools were analysed and potential external P sources affecting the lakes (atmospheric deposition, terrestrial export and nearby hut) evaluated, to assess the effects of internal and external changes on the lakes. A sequential extraction procedure was used to quantify five P fractions from the sediments: adsorbed (NH4Cl–P), redox-sensitive (BD–P), aluminium- (NaOH–P) and calcium- (HCl–P) bound, and refractory organic (Res–P) P. Total phosphorus (TP) contents in surface sediment of 5J and 6J were 1430 and 641 µg P g?1 dry weight sediment (dw), respectively. TP varied with depth in 5J sediments, but displayed no discernible pattern, whereas it decreased steadily downcore in 6J. Contents of all P forms were distinctly higher in 5J than 6J, but their rank order and relative abundances were similar in the two lakes. Res–P was the most abundant P fraction, followed by HCl–P. Together, the two P forms accounted for nearly 80 and 90% of TP in 5J and 6J sediments, respectively. BD–P and NaOH–P were less abundant, with each fraction accounting for 3 to 9% of TP, whereas NH4Cl–P was least abundant. Atmospheric deposition and terrestrial export were substantial sources of P for the lakes. Delivery of the former was estimated to be at least 7.5 mg P m?2 yr?1 and the latter around 20 mg P m?2 yr?1. We concluded that P was not retained in the catchment effectively, likely because of only slightly acidic soil pH (5.9), relatively low aluminium content and high organic matter content (53%) in soils, resulting in higher vulnerability of the studied lakes to eutrophication. The mountain hut could also be a significant source of P for the lakes. Each year, it could potentially contribute ~12 kg of soluble P to the environment, but the true impact of the hut on lake trophic status remains unclear. 相似文献
4.
Bojan Vršnak Mateja Dumbović Jaša Čalogović Giuliana Verbanac Ivana Poljanǐć–Beljan 《Solar physics》2017,292(9):140
We present an analysis of the geoeffectiveness of corotating interaction regions (CIRs), employing the data recorded from 25 January to 5 May 2005 and throughout 2008. These two intervals in the declining phase of Solar Cycle 23 are characterised by a particularly low number of interplanetary coronal mass ejections (ICMEs). We study in detail how four geomagnetic-activity parameters (the Dst, Ap, and AE indices, as well as the Dst time derivative, \(\mathrm{dDst}/\mathrm{d}t\)) are related to three CIR-related solar wind parameters (flow speed, \(V\), magnetic field, \(B\), and the convective electric field based on the southward Geocentric solar magnetospheric (GSM) magnetic field component, \(\mathit{VB}_{s}\)) on a three-hour time resolution. In addition, we quantify statistical relationships between the mentioned geomagnetic indices. It is found that Dst is correlated best to \(V\), with a correlation coefficient of \(\mathrm{cc}\approx0.6\), whereas there is no correlation between \(\mathrm{dDst}/\mathrm{d}t\) and \(V\). The Ap and AE indices attain peaks about half a day before the maximum of \(V\), with correlation coefficients ranging from \(\mathrm{cc}\approx0.6\) to \(\mathrm{cc}\approx0.7\), depending on the sample used. The best correlations of Ap and AE are found with \(\mathit{VB}_{s}\) with a delay of 3 h, being characterised by \(\mathrm{cc}\gtrsim 0.6\). The Dst derivative \(\mathrm{dDst}/\mathrm{d}t\) is also correlated with \(\mathit{VB}_{s}\), but the correlation is significantly weaker \(\mathrm{cc}\approx 0.4\)?–?0.5, with a delay of 0?–?3 h, depending on the employed sample. Such low values of correlation coefficients indicate that there are other significant effects that influence the relationship between the considered parameters. The correlation of all studied geomagnetic parameters with \(B\) are characterised by considerably lower correlation coefficients, ranging from \(\mathrm{cc}=0.3\) in the case of \(\mathrm{dDst}/\mathrm{d}t\) up to \(\mathrm{cc}=0.56\) in the case of Ap. It is also shown that peak values of geomagnetic indices depend on the duration of the CIR-related structures. The Dst is closely correlated with Ap and AE (\(\mathrm{cc}=0.7\)), Dst being delayed for about 3 h. On the other hand, \(\mathrm{dDst}/\mathrm{d}t\) peaks simultaneously with Ap and AE, with correlation coefficients of 0.48 and 0.56, respectively. The highest correlation (\(\mathrm{cc}=0.81\)) is found for the relationship between Ap and AE. 相似文献
5.
Magnetic fabric study of the SE Rhenohercynian Zone (Bohemian Massif): Implications for dynamics of the Paleozoic accretionary wedge 总被引：2，自引：0，他引：2
The progressive deformation recorded in the magnetic fabric of sedimentary rocks was studied in the SE Rhenohercynian Zone (RHZ), eastern margin of the Bohemian Massif, Czech Republic. Almost 800 oriented samples of the Lower Carboniferous mudstones and graywackes were collected from the SSE part of the Czech RHZ, so-called the Drahany Upland. The anisotropy of magnetic susceptibility (AMS) is predominantly controlled by the preferred orientation of paramagnetic phyllosilicates, mainly iron-bearing chlorites. A regional distribution of the magnetic fabric within the Drahany Upland revealed an increasing deformation from the SSE to the NNW. In the SE, the magnetic fabric is bedding-parallel with magnetic lineation scattered in the bedding plane or trending N–S to NNE–SSW. Further to the NW, the magnetic foliation rotates from the bedding-parallel orientation to the orientation parallel to the evolving cleavage. This rotation is accompanied by a decrease of the anisotropy degree and the prolate nature of the anisotropy ellipsoids. The magnetic lineation is parallel to the strike of the bedding, bedding/cleavage intersection, pencil structure or the fold axes on a regional scale. In the NW part of the Drahany Upland, the magnetic foliation becomes parallel to the cleavage accompanied by an increase of the anisotropy degree and the oblate nature of the anisotropy ellipsoids. The increasing trend of deformation corresponds to the SSE–NNW increase in the degree of anchimetamorphism; both trends being oblique to the main lithostratigraphic formations as typically observed in the sedimentary rocks of the accretionary wedges. The SSE–NNW increase in deformation and anchimetamorphism continues to the Nízký Jeseník Mts., representing the northern part of the same accretionary wedge. The kinematics of deformation could not be unambiguously assessed. The observed magnetic fabric may reflect either lateral shortening or horizontal simple shear or a combination of both mechanisms. Regarding the subduction process, it seems that the sedimentary sequences of the Drahany Upland were subducted, partly offscraped and accreted frontally or partly underplated as opposed to the Nízký Jeseník Mts. where some return flow must have occurred. 相似文献
6.
Anisotropy of magnetic susceptibility and structural geology of the ca. 1.45 Ga Karlshamn pluton (southern Sweden) are used
to study its emplacement and structural evolution. The Karlshamn pluton is one of the largest metaluminous A-type granitoid
intrusions in southern Sweden. It is a multiphase body made up of two suites that differ in composition but which have similar
crystallization ages. The magmatic foliation, ductile shear zones and granite–pegmatite filled fractures were mapped as well
as the metamorphic foliation and extension lineation in the metamorphic host rocks. The anisotropy of magnetic susceptibility
was used to map the magnetite petrofabric of the pluton, providing a larger data set for both the magmatic foliations and
lineations, which could not be mapped in the field. The fabrics within the pluton are continuous with the metamorphic fabrics
in the country rocks. Both the pluton and the country rock fabrics were folded during ENE–WSW compression, while the pluton
was still a magma mush. The stress field orientation during cooling of the pluton is determined on the basis of magmatic,
ductile and brittle structures in the Karlshamn pluton that formed successively as the pluton cooled. The compressional event
is referred to as the Danopolonian orogeny and therefore the Karlshamn granitoids, and other plutons of similar composition
and age in central and southern Sweden, on the Danish Island of Bornholm, and in Lithuania, may be considered as syntectonic
intrusions and not as anorogenic, as was previously thought. 相似文献
7.
Here, we address the sediment dynamics in the Black Sea based on analysis of remote sensing data from the Medium Resolution
Imaging Spectrometer and numerical simulations with Nucleus for European Modelling of the Ocean model. Boundary conditions
consist of realistic meteorological forcing, including significant wave height generated by wave prediction model. A number
of sensitivity runs was analysed with the aim to find the most suitable parameters governing sediment fluxes. The comparison
between numerical simulations and remote sensing data gives credibility to the quality of simulations. The combined effect
of wind waves and currents in the bed layer controls the sediment resuspension that appears to be the major basin-wide source
of sediment. Sensitivity experiments included or excluded different forcing terms, e.g. sediment flux from rivers enable to
determine the spatial extensions of different point sources. It is concluded that wind-wave forcing is manifested in the sediment
dynamics through episodic high energy events contributing to the increase of horizontal sediment fluxes over the northwestern
shelf. Both satellite images and numerical model simulations demonstrated that the penetration of suspended sediment into
the basin interior was governed by the dynamics of coastal and open-ocean eddies. While fine sediment at sea surface could
cross the continental slope propagating into the open ocean, coarser fractions follow the bottom and their penetration into
the open ocean is limited. The conclusion is thus that the deposition patterns correlate with the specific shape of Black
Sea topography, and the largest depositions are observed in the area of continental slope. 相似文献
8.
In the computation of paraxial travel times and Gaussian beams, the basic role is played by the second-order derivatives of
the travel-time field at the reference ray. These derivatives can be determined by dynamic ray tracing (DRT) along the ray.
Two basic DRT systems have been broadly used in applications: the DRT system in Cartesian coordinates and the DRT system in
ray-centred coordinates. In this paper, the transformation relations between the second-order derivatives of the travel-time
field in Cartesian and ray-centred coordinates are derived. These transformation relations can be used both in isotropic and
anisotropic media, including computations of complex-valued travel times necessary for the evaluation of Gaussian beams. 相似文献
9.
Pavel Koten Pavel Spurný Ji&#x;í Borovi
ka Stephen Evans Andrew Elliott Hans Betlem Rostislav &#x;tork Klaas Jobse 《Meteoritics & planetary science》2006,41(9):1305-1320
Abstract— In this paper, we provide an overview of meteors with high beginning height. During the recent Leonid meteor storms, as well as within the regular double station video observations of other meteor showers, we recorded 164 meteors with a beginning height above 130 km. We found that beginning heights between 130 and 150 km are quite usual, especially for the Leonid meteor shower. Conversely, meteors with beginning heights above 160 km are very rare even among Leonids. From the meteor light curves, we are able to distinguish two different processes that govern radiation of the meteors at different altitudes. Light curves vary greatly above 130 km and exhibit sudden changes in meteor brightness. Sputtering from the meteoroid surface is the dominating process during this phase of the meteor luminous trajectory. Around 130 km, the process switches to ablation and the light curves become similar to the light curves of standard meteors. The sputtering model was successfully applied to explain the difference in the beginning heights of high‐altitude Leonid and Perseid meteors. We show also that this process in connection with high altitude fragmentation could explain the anomalously high beginning heights of several relatively faint meteors. 相似文献
10.
Jiří Borovička Pavel Koten Pavel Spurný Rostislav Štork 《Earth, Moon, and Planets》2008,102(1-4):485-493
We present an analysis of sporadic meteor number 07406018, observed by image intensified video cameras at two stations, which
showed a pronounced deceleration along its trajectory. We have applied the erosion model to analyze simultaneously the deceleration
and light curve. We have found that the meteoroid had a low density of about 500 kg m−3, consistent with its cometary orbit. The meteoroid structure was, nevertheless, markedly different from the Draconid meteoroids,
studied recently with the same model. The size of the constituent grains was larger and the erosion energy was higher than
in Draconids. The meteor spectrum was also different from Draconid spectra and showed very bright Na lines. The meteoroid
composition was probably different from normal cometary composition. 相似文献