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991.
Prosanta Kumar Khan 《International Journal of Earth Sciences》2011,100(7):1749-1758
Present study addresses the role of major plate-driving forces, particularly the slab pull and slab resistive forces, for
the generation of 26 December 2004 M
w > 9.0 off Sumatra megathrust earthquake. Major controls on the plate-driving forces are normally visualized through age,
speed, and average dip of the slab during subduction. Wide variation in age, plate obliquity, stress obliquity, subduction
rate, dip angle, and flexing depth of the subducting oceanic lithosphere between Andaman and Sumatra thus allowed us for quantitative
evaluation of the slab pull (F
SP) and slab resistive (F
SR) forces in three well-defined sectors (I, II and III). Computed values of these forces in the three sectors: (1) F
SP = 1.29 × 1013 N/m, F
SR = 1.41 × 1013 N/m; sector I, (2) F
SP = 2.10 × 1013 N/m, F
SR = 1.13 × 1013 N/m; sector II, and (3) F
SP = 2.08 × 1013 N/m, F
SR = 2.72 × 1013 N/m; sector III clearly suggest a spatial variation of stress regime in the subducting oceanic lithosphere. Excess F
SR in sectors I and III are interpreted as the causative forces behind the triggering of major seismic energy bursts near Sumatra
and Andaman on 26 December 2004. A gap of minimum seismic energy burst near Great Nicobar possibly was controlled by the excess
of F
SP in sector II. This study further advocates that the cyclic stress, resulted from unbalanced component of slab resistive force,
had a definite control on the occurrence of 2004 off Sumatra megathrust earthquake around the flexing zone of the subducting
lithosphere. 相似文献
992.
Nataša Ravbar Juan Antonio Barberá Metka Petrič Janja Kogovšek Bartolomé Andreo 《Environmental Earth Sciences》2012,65(8):2259-2272
In this study a multi-tracer test with fluorescent tracers was combined with time series analyses of natural tracers to characterize
the dynamics of the solute transport through different recharge pathways and to study hydraulic behaviour of a binary karst
system under low-flow conditions. Fluorescent tracer testing included the introduction of uranine, amidorhodamine G, or naphthionate
at three injection points. Sampling and monitoring took place at two karst springs (Malenščica, Unica) and at two underground
rivers (Pivka, Rak) recharging the Unica River at the Polje of Planina, SW Slovenia. Other monitored parameters included precipitation,
spring or underground river discharge, water temperature, and electrical conductivity. Water samples were collected and analyzed
for total organic carbon, Mg2+, SO4
2−, and NO3
− in the laboratory. In the study area, results of the tracer test suggest that contaminant transport in karst may be retarded
for several weeks during low-flow conditions followed by increases in contaminant concentrations after subsequent rainfall
events. Based on interpretation of tracer concentration breakthrough curves, low apparent dominant flow velocities (i.e.,
between 5.8 and 22.8 m/h through the well developed karst conduits, and 3.6 m/h through the prevailing vadose zone with a
dominant influence of a diffuse recharge) were obtained. Together with analyses of hydro-chemographs the artificial tracing
identified different origins of water recharging the studied aquifer. During prolonged low-water conditions the Malenščica
spring is mainly recharged from the karst aquifer and the Unica spring by the sinking Pivka River. After more intensive rainfall
events allogenic recharge from Cerknica prevails in the Malenščica spring, while the Unica spring drains mainly the allogenic
water from the Pivka Valley. These findings of alternating hydraulic connections and drainage areas due to respective hydrological
conditions are important and should be considered when monitoring water quality, implementing groundwater protection measures,
and optimizing future water exploitation. 相似文献
993.
Samples from diamondiferous pipes in the Mengyin and Fuxian regions were investigated. The chemical compositions of Cr spinels
in kimberlites of China were found to be similar to those in kimberlites of the Arkhangelsk province in Russia. A long and
complex evolution that was individual for each pipe was demonstrated. The kimberlites of the Shandong Province proved to be
rich in high-Cr chromites. This means that the kimberlites formed at large depths in the field of diamond thermodynamic stability.
Variations in the redox conditions were noted. They manifested themselves as a wide range of fluctuations of the chemical
composition of microcrystalline spinels, up to formation to Ti-magnetite and magnetite. 相似文献
994.
Karla Salvagni Heineck Rosemar Gomes Lemos Juan Antônio Altamirano Flores Nilo Cesar Consoli 《Geotechnical and Geological Engineering》2010,28(4):325-335
Flexible-wall hydraulic conductivity tests were carried out on bottom ash, fly ash and compacted specimens of sand with additions
of 0, 3, 6, 9 and 18% of bentonite. In order to study the effect of bentonite inclusion and particle morphology on the hydraulic
conductivity of the admixtures, an investigation was undertaken based on thin section micrographs. It was found that, for
both bottom and fly ash admixtures, bentonite addition reduced only one order of magnitude the hydraulic conductivity, from
1.78 × 10−6 m/s to 1.39 × 10−7 m/s. On the other hand, the sand hydraulic conductivity was reduced five orders of magnitude, from 3.17 × 10−5 m/s to 5.15 × 10−10 m/s. Among several factors that can be responsible for the difficulty in reducing hydraulic conductivity, such as ash grain
size distribution and elevated cation concentration (leached from the ash) in pore water, it can also be recalled the high
particle voids observed in the ash by means of microscopic analysis. The same is not true with the sand, which has solid particles,
without inner voids. 相似文献
995.
Bernard Pelletier Pierre Dutilleul Guillaume Larocque James W. Fyles 《Mathematical Geology》2004,36(3):323-343
In geostatistical studies, the fitting of the linear model of coregionalization (LMC) to direct and cross experimental semivariograms is usually performed with a weighted least-squares (WLS) procedure based on the number of pairs of observations at each lag. So far, no study has investigated the efficiency of other least-squares procedures, such as ordinary least squares (OLS), generalized least squares (GLS), and WLS with other weighing functions, in the context of the LMC. In this article, we compare the statistical properties of the sill estimators obtained with eight least-squares procedures for fitting the LMC: OLS, four WLS, and three GLS. The WLS procedures are based on approximations of the variance of semivariogram estimates at each distance lag. The GLS procedures use a variance–covariance matrix of semivariogram estimates that is (i) estimated using the fourth-order moments with sill estimates (GLS1), (ii) calculated using the fourth-order moments with the theoretical sills (GLS2), and (iii) based on an approximation using the correlation between semivariogram estimates in the case of spatial independence of the observations (GLS3). The current algorithm for fitting the LMC by WLS while ensuring the positive semidefiniteness of sill matrix estimates is modified to include any least-squares procedure. A Monte Carlo study is performed for 16 scenarios corresponding to different combinations of the number of variables, number of spatial structures, values of ranges, and scale dependence of the correlations among variables. Simulation results show that the mean square error is accounted for mostly by the variance of the sill estimators instead of their squared bias. Overall, the estimated GLS1 and theoretical GLS2 are the most efficient, followed by the WLS procedure that is based on the number of pairs of observations and the average distance at each lag. On that basis, GLS1 can be recommended for future studies using the LMC. 相似文献
996.
997.
O. Bourgeois M. Ford M. Diraison C. Le Carlier de Veslud M. Gerbault R. Pik N. Ruby S. Bonnet 《International Journal of Earth Sciences》2007,96(6):1003-1031
The development of the Alpine mountain belt has been governed by the convergence of the African and European plates since
the Late Cretaceous. During the Cenozoic, this orogeny was accompanied with two major kinds of intraplate deformation in the
NW-European foreland: (1) the European Cenozoic Rift System (ECRIS), a left-lateral transtensional wrench zone striking NNE-SSW
between the western Mediterranean Sea and the Bohemian Massif; (2) long-wavelength lithospheric folds striking NE and located
between the Alpine front and the North Sea. The present-day geometry of the European crust comprises the signatures of these
two events superimposed on all preceding ones. In order to better define the processes and causes of each event, we identify
and separate their respective geometrical signatures on depth maps of the pre-Mesozoic basement and of the Moho. We derive
the respective timing of rifting and folding from sedimentary accumulation curves computed for selected locations of the Upper
Rhine Graben. From this geometrical and chronological separation, we infer that the ECRIS developed mostly from 37 to 17 Ma,
in response to north-directed impingement of Adria into the European plate. Lithospheric folds developed between 17 and 0 Ma,
after the azimuth of relative displacement between Adria and Europe turned counter-clockwise to NW–SE. The geometry of these
folds (wavelength = 270 km; amplitude = 1,500 m) is consistent with the geometry, as predicted by analogue and numerical models,
of buckle folds produced by horizontal shortening of the whole lithosphere. The development of the folds resulted in ca. 1,000 m of rock uplift along the hinge lines of the anticlines (Burgundy–Swabian Jura and Normandy–Vogelsberg) and ca. 500 m of rock subsidence along the hinge line of the intervening syncline (Sologne–Franconian Basin). The grabens of the
ECRIS were tilted by the development of the folds, and their rift-related sedimentary infill was reduced on anticlines, while
sedimentary accumulation was enhanced in synclines. We interpret the occurrence of Miocene volcanic activity and of topographic
highs, and the basement and Moho configurations in the Vosges–Black Forest area and in the Rhenish Massif as interference
patterns between linear lithospheric anticlines and linear grabens, rather than as signatures of asthenospheric plumes.
相似文献
O. BourgeoisEmail: |
998.
Pengfei Si Jordan Aaron Scott McDougall Ji Lu Xiping Yu Nicholas J. Roberts John J. Clague 《Landslides》2018,15(4):711-726
This paper proposes and demonstrates a two-layer depth-averaged model with non-hydrostatic pressure correction to simulate landslide-generated waves. Landslide (lower layer) and water (upper layer) motions are governed by the general shallow water equations derived from mass and momentum conservation laws. The landslide motion and wave generation/propagation are separately formulated, but they form a coupled system. Our model combines some features of the landslide analysis model DAN3D and the tsunami analysis model COMCOT and adds a non-hydrostatic pressure correction. We use the new model to simulate a 2007 rock avalanche-generated wave event at Chehalis Lake, British Columbia, Canada. The model results match both the observed distribution of the rock avalanche deposit in the lake and the wave run-up trimline along the shoreline. Sensitivity analyses demonstrate the importance of accounting for the non-hydrostatic dynamic pressure at the landslide-water interface, as well as the influence of the internal strength of the landslide on the size of the generated waves. Finally, we compare the numerical results of landslide-generated waves simulated with frictional and Voellmy rheologies. Similar maximum wave run-ups can be obtained using the two different rheologies, but the frictional model better reproduces the known limit of the rock avalanche deposit and is thus considered to yield the best overall results in this particular case. 相似文献
999.
The prediction and prevention of floor water inrush is directly related to the safety of the coal mine production. The previous evaluation method of floor water inrush was more one-sided and lacked main control factors related to mining conditions. In order to evaluate the floor water inrush more accurately, under the project background of geological data of Wanglou coal mine, stope width, mining depth, fault scale index, water pressure, water abundance and thickness of aquifer were selected as main controlling factors of floor water inrush. Combined with the subjective weight analytical hierarchy process and the objective weight variation coefficient method, the weight coefficients corresponding to the main controlling factors were obtained respectively. The thematic map of the risk assessment of coal seam floor water inrush was drawn by combining the constructed comprehensive weight vulnerability index model and geographic information system. The results show that: ① according to the actual geological data of mine, two fault related factors were removed. And stope width and mining depth were increased as the main controlling factors to evaluate floor water inrush. It is easier to compare and calculate the weight of evaluation factors. ② The constructed comprehensive weight vulnerability index model can comprehensively evaluate the risk of floor water inrush. And the results of the evaluation are more accurate. ③ The related thematic maps can directly reflect the risk of floor water inrush, which is of guiding significance for the prediction and prevention of coal seam floor water inrush. 相似文献
1000.
Measuring and analyzing internal dam temperature may provide insight into evaluating the integrity of earthen dams. Temperature in a dam, with the advent of modern distributed temperature sensing (DTS) technique, is conveniently measured. The analysis of the temperature is conducted based on a hydro-thermal coupled analysis technique. In this study, DTS-based temperature data and VS2DHI (a finite difference code for analyzing two-dimensional heat transport in porous media) were used to analyze the hydro-thermal coupled behavior in a dam. The results of this analysis show that the temperature variation in an earthen dam is closely related to seepage conditions. Additionally, a localized high-temperature (26 °C) zone found in the measured data of the dam, which raised concern to engineers on site, is explained through either hot water infiltration into the foundation layer or lower permeability of the foundation layer than the magnitude that appeared in the design document. These findings demonstrate that hydro-thermal coupled analysis has the potential for evaluating the integrity of earthen dams. 相似文献