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1.
本文通过背斜褶皱变形与低温热年代学年龄(磷灰石和锆石(U-Th)/He、磷灰石裂变径迹)端元模型研究,约束低起伏度、低斜率地貌特征的四川盆地南部地区新生代隆升剥露过程.四川盆地南部沐川和桑木场背斜地区新生代渐新世-中新世发生了相似的快速隆升剥露过程(速率为~0.1 mm/a、现今地表剥蚀厚度1.0~2.0 km),反映出盆地克拉通基底对区域均一性快速抬升冷却过程的控制作用.川南沐川地区磷灰石(U-Th)/He年龄值为~10-28.6 Ma, 样品年龄与古深度具有明显的线性关系,揭示新生代~10-30 Ma以速率为0.12±0.02 mm/a的稳态隆升剥露过程.桑木场背斜地区磷灰石裂变径迹年龄为~36-52 Ma,古深度空间上样品AFT年龄变化不明显(~50 Ma)、且具有相似的径迹长度(~12.0 μm).磷灰石裂变径迹热演化史模拟表明桑木场地区经历三个阶段热演化过程:埋深增温阶段(~80 Ma以前)、缓慢抬升冷却阶段(80-20 Ma)和快速隆升剥露阶段(~20 Ma-现今),新生代隆升剥露速率大致分别为~0.025 mm/a和~0.1 mm/a.新生代青藏高原大规模地壳物质东向运动与四川盆地克拉通基底挤压,受板缘边界主断裂带差异性构造特征控制造就了青藏高原东缘不同的边界地貌特征. 相似文献
2.
Simon D. Carrière Thomas Health Pascale F. M. Rakotomandrindra Chloé Ollivier Riva E. Rajaomahefasoa Heritiana A. Rakoto Jean Lapègue Yves E. Rakotoarison Marie Mangin Jean Kempf Théodore Razakamanana Konstantinos Chalikakis 《水文研究》2021,35(3):e14108
Madagascar has one of the highest poverty rates in the world and consequently the long-term monitoring of groundwater resources is not a priority for the authorities. However, groundwater is often the only sustainable resource that has a satisfactory quality to supply the population. This is especially true in the south-west of the country, which is a semi-arid region and a global change hot spot (intense land use and climate changes). In response to the lack of data, the Groundwater Resource Observatory for Southwestern Madagascar (GROSoM) was established to monitor piezometry and meteorology over the longer term as part of a humanitarian response. The first site was setup in 2014 in a catchment located over a carbonate plateau; in 2018, a second site was installed in an alluvial setting within a crystalline basement catchment and a third site will be installed in 2020 to monitor groundwater dynamics in a coastal setting. The three sites, located between Toliara and Taolagnaro cities, are complementary and representative of various hydrogeological systems in Southwestern Madagascar. Each site includes a weather station and between 3 and 6 piezometric probes. The monitoring data indicate a strong inter-annual variability in precipitation, which induces a strong variability in aquifers recharge. One of the driest years in 2016 seems to be consistent with strong El Niño – Southern Oscillation (ENSO) effects observed at the global scale, while years with higher recharge appear to be related to cyclones such as Fundi in 2015 and Eketsang in 2019. Preliminary results of cross-disciplinary studies demonstrated a link between groundwater and health issues (i.e., admissions to basic health centres). This observatory aims to produce long-term data and has two objectives: (i) strengthening the early warning system for humanitarian crises in Madagascar; (ii) contributing to a better understanding of the effects of climate change on groundwater resources in this semi-arid region. 相似文献
3.
The recursive nature of rays in blocky models can be exploited to solve some difficult problems in seismic modelling. Each segment of a ray travels from an initial point up to a reflecting interface, where it is split into reflected and transmitted ray segments, which each continue in a similar way. The tree structure that thus emanates is conveniently handled by a recursive scheme. Recursion allows an automatic generation of all phases on a seismogram, together with all information necessary to analyse or select them. By operating recursively with a ray cell, bounded by a pair of vicinal rays in 2D, or a triplet of vicinal rays in 3D, and two successive isochrons, the two-point ray-tracing problem is reduced to a simple interpolation. Also, the cellular approach allows for a stable and robust evaluation of dynamic ray quantities without any paraxial tracing, which is cumbersome in blocky models of realistic complexity. Geometric shadows are filled by recursively generated diffractions. The recursive ray tracer has found applications in the fast computation of Green's functions in target-oriented inversion and in phase identification in VSP. 相似文献
4.
W. E. Bardsley 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(3):1059-1061
One mechanism giving rise to the hypergeometric distribution is the number of matches in a random reordering of a sequence of forecasts of binary events. This provides a simple means of invalidating a time series of binary forecasts if in fact the forecasting method has no skill. The hypergeometric distribution has a long history of application in this context but appears not to have a high profile in the environmental sciences. Attention is drawn to the utility of the distribution as a simple nonparametric test of the null hypothesis of no skill when forecasting binary environmental outcomes. 相似文献
5.
M. V. Mikhailova 《Water Resources》2006,33(5):523-534
Sediment balance at river mouths—a physical basis of delta dynamics—is considered. The specific features of relationships between sediment balance components at a mouth of a river are established for a stable, rising, or dropping sea level. The development of the delta of the Chilia branch at the Danube mouth is considered as an example of delta dynamics under the conditions of a relatively stable sea level. The evolution of the Sulak delta in the Caspian Sea with a highly variable level is considered as an example of delta dynamics in the case of a considerable rise and drop of water level in the water body. The anthropogenic reduction of sediment runoff of the rivers (by a factor of two in the Danube, and by a factor of nine in the Sulak) is taken into account. The relationship between the sediment runoff of a river and the volume of the “backwater prism” that formed due to sea level rise is shown to be the key factor in the development of delta in the case of sea level rise. In the case of a drop in the sea level, the relationship between the “active” and “passive” progradation of the delta into the sea is determined by the sediment runoff of the river, the rate of sea level drop, and the bed slope in the coastal area of the nearshore zone. 相似文献
6.
7.
The sessile and mobile macrobenthos on artificial hard bottoms was studied in 12 stations of the Sacca di Goro lagoon, a brackish, highly stressed water basin in the delta of the river Po, open to the Northwestern Adriatic Sea. Three sampling surveys were carried out in June and September 2000 and June 2001 in order to make three types of temporal comparisons: (i) on a seasonal scale, before and after a summer dystrophic event; (ii) on an annual basis, before and after the works of excavation of a canal through the outer sand bank; (iii) on a multiannual scale, comparing the data with those of a survey carried out in 1988. The biocoenoses did not show large fluctuations after a moderately severe summer dystrophic crisis, while the digging of the canal caused clear changes in the macrobenthos community structure after one year. The long-term comparison showed a shift in the community patterns after a decade. 相似文献
8.
Zhang Guomin Geng Lumin and Shi YaolinCenter for Analysis Prediction Beijing China 'Graduate School Academia Sinica Beijing China 《中国地震研究》1995,(1)
Based on the study of activity of earthquakes with M**********>7.0 in mainland China,we have found a dynamic pattern,i.e.,the cyclic characteristics in time and migration from one seismic zone to another in space.In order to understand the physical mechanism of this pattern,we use a nonlinear dynamic model to simulate the seismic activity in fault zones under a unified tectonic stress field.The basic elements in our model consist of a Maxwell body and a rigid sliding block.Basic elements in a column represent a fault,and coupling elements connecting different columns simulate the interaction among faults and fault segments.The results provide insights to the cyclic activity of strong earthquakes and to the feature of mutual influence between strong earthquakes in groups in the climax of seismic activity. 相似文献
9.
Active lava tubes have much higher temperatures than the surrounding rocks. Any change in the tube temperature produces a
change in the temperature distribution in the rocks and induces a thermoelastic deformation in them. We calculate such a deformation
by solving the equilibrium equation of linear thermoelasticity. We assume that the initial temperature distribution in the
medium is the steady-state solution of the heat equation for a very long cylindrical tube at constant temperature, embedded
in a medium with uniform thermal conductivity. We calculate the displacement and stress fields in the medium following to
a temperature change of the tube. A temperature increase produces a dilatation of the medium and a contraction of the tube,
while a temperature decrease produces the opposite effect. For a temperature change equal to 100 K, thermal stresses in the
order of 10 MPa are produced, which are large enough to fracture the rocks surrounding the tube. 相似文献
10.
R. SCHULZ 《Geophysical Prospecting》1985,33(8):1240-1253
Gradient measurements in a homogeneous electrical primary field can easily be interpreted for simple models. The simplified solution (conducting or resistant body in a homogeneous space in a homogeneous electrical field) is often sufficiently accurate, as comparisons with the exact solution (body of finite resistivity in a homogeneous half-space in a quasihomogeneous electrical field) show. The exact geometry of the body cannot be determined by gradient measurements; the same anomaly of apparent resistivity can be caused by different bodies. In particular, the similarity between a sphere and a cube of the same volume is very high. There is a distinct influence of the resistivity of the overburden: the higher this resistivity is, the stronger is the effect caused by a buried body. If a deviation of 10% of the apparent resistivity is assumed as the lower boundary at which a buried body can be detected by gradient measurements, the depth of investigation for a three-dimensional body is approximately equal to its width; in the two-dimensional case the thickness of the overburden can be twice the width. If the overburden has a resistivity which is higher than the resistivity of the substratum, these depths are greater. The greatest possible depth is approximately three times the width of the body. 相似文献
11.
Akiho Miyashiro 《Earth and Planetary Science Letters》1973,19(2):218-224
The Troodos ophiolitic complex in Cyprus has been widely regarded as a fragment of oceanic crust that was created in a mid-oceanic ridge. However, about one-third of the analyzed rocks of the lower pillow lavas and sheeted complex in it follows a calc-alkalic trend. This strongly suggests that the massif was created as a basaltic volcano in an island arc with a relatively thin oceanic-type crust rather than in a mid-oceanic ridge. Other chemical features and the structure of the massif are also consistent with an island arc origin. Some other ophiolitic complexes also appear to have been formed in island arcs. 相似文献
12.
Stuart G Wakeham 《Marine pollution bulletin》1976,7(11):206-211
Hydrocarbon distribution in sediments from three lakes are related to the level of human activity in the respective drainage basins. Petroleum hydrocarbon contamination is found in surface sediments of a lake surrounded by a major city, compared to no detectable contamination in a lake located in a National Park. 相似文献
13.
Time delays associated with processes leading to a failure or stress relaxation in materials and earthquakes are studied in
terms of continuum damage mechanics. Damage mechanics is a quasi-empirical approach that describes inelastic irreversible
phenomena in the deformation of solids. When a rock sample is loaded, there is generally a time delay before the rock fails.
This period is characterized by the occurrence and coalescence of microcracks which radiate acoustic signals of broad amplitudes.
These acoustic emission events have been shown to exhibit power-law scaling as they increase in intensity prior to a rupture.
In case of seismogenic processes in the Earth's brittle crust, all earthquakes are followed by an aftershock sequence. A universal
feature of aftershocks is that their rate decays in time according to the modified Omori's law, a power-law decay. In this
paper a model of continuum damage mechanics in which damage (microcracking) starts to develop when the applied stress exceeds
a prescribed yield stress (a material parameter) is introduced to explain both laboratory experiments and systematic temporal
variations in seismicity. 相似文献
14.
Upscaling is a major issue regarding mechanical and transport properties of rocks. This paper examines three issues relative
to upscaling. The first one is a brief overview of Effective Medium Theory (EMT), which is a key tool to predict average rock
properties at a macroscopic scale in the case of a statistically homogeneous medium. EMT is of particular interest in the
calculation of elastic properties. As discussed in this paper, EMT can thus provide a possible way to perform upscaling, although
it is by no means the only one, and in particular it is irrelevant if the medium does not adhere to statistical homogeneity.
This last circumstance is examined in part two of the paper. We focus on the example of constructing a hydrocarbon reservoir
model. Such a construction is a required step in the process of making reasonable predictions for oil production. Taking into
account rock permeability, lithological units and various structural discontinuities at different scales is part of this construction.
The result is that stochastic reservoir models are built that rely on various numerical upscaling methods. These methods are
reviewed. They provide techniques which make it possible to deal with upscaling on a general basis. Finally, a last case in
which upscaling is trivial is considered in the third part of the paper. This is the fractal case. Fractal models have become
popular precisely because they are free of the assumption of statistical homogeneity and yet do not involve numerical methods.
It is suggested that using a physical criterion as a means to discriminate whether fractality is a dream or reality would
be more satisfactory than relying on a limited data set alone. 相似文献
15.
Rossby wave patterns in zonal and meridional winds 总被引：1，自引：0，他引：1
The propagation properties of Rossby waves in zonal and meridional winds are analyzed using the local dispersion relation in its wave number form, the geometry of which plays a crucial role in illuminating radiation patterns and ray trajectories. In the presence of a wind/current, the classical Rossby wave number curve, an offset circle, is distorted by the Doppler shift in frequency and a new branch, consisting of a blocking line with an eastward facing indentation, arises from waves convected with or against the flow. The radiation patterns generated by a time harmonic compact source in the laboratory frame are calculated using the method of stationary phase and are illustrated through a series of figures given by the reciprocal polars to the various types of wave number curves. We believe these results are new. Some of these wave patterns are reminiscent of a “reversed” ship wave pattern in which cusps (caustics) arise from the points of inflection of the wave number curves; whilst others bear a resemblance to the parabolic like curves characteristic of the capillary wave pattern formed around an obstacle in a stream. The Rossby stationary wave in a westerly is similar to the gravity wave pattern in a wind, whereas its counterpart in a meridional wind exhibits caustics, again arising from points of inflection in the wavenumber curve. 相似文献
16.
Diffusion of a magnetic field through a plasma is discussed in one-, two- and three-dimensional configurations, together with the possibility of describing such diffusion in terms of a magnetic flux velocity, which, when it exists, is in general non-unique. Physically useful definitions of such a velocity include doing so in terms of the energy flow or in such a way that it vanishes in a steady state. Straight field lines (or plane flux surfaces) diffuse as if flux is disappearing at a neutral sheet, whereas circular field lines (or cylindrical flux surfaces) do so as if flux is disappearing at an 0-type neutral line. In three dimensions it is not always possible to define a flux velocity, for example when the magnetic flux through a closed field line is changing in time. However, in at least some such cases it is possible to describe the behaviour of the magnetic field in terms of a pair of quasi-flux-velocities. 相似文献
17.
Tae-Woong Kim Hosung Ahn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(3):367-376
Missing data in daily rainfall records are very common in water engineering practice. However, they must be replaced by proper
estimates to be reliably used in hydrologic models. Presented herein is an effort to develop a new spatial daily rainfall
model that is specifically intended to fill in gaps in a daily rainfall dataset. The proposed model is different from a convectional
daily rainfall generation scheme in that it takes advantage of concurrent measurements at the nearby sites to increase the
accuracy of estimation. The model is based on a two-step approach to handle the occurrence and the amount of daily rainfalls
separately. This study tested four neural network classifiers for a rainfall occurrence processor, and two regression techniques
for a rainfall amount processor. The test results revealed that a probabilistic neural network approach is preferred for determining
the occurrence of daily rainfalls, and a stepwise regression with a log-transformation is recommended for estimating daily
rainfall amounts. 相似文献
18.
This paper gives a synthesis on a series of studies demonstrating the possibility to have a direct access to in situ soil damping, exploiting the thermal dissipation due to irreversible mechanical phenomena under severe seismic conditions. The introduction provides a background to the three steps of such a study: instrumentation, modelling and inverse identification problem. Section 2 recalls the principle of the Seismic Harmonic System, equipment able to generate powerful in situ soil accelerations in the vicinity of a well. Evidence of a significant in situ soil temperature elevation is given under such seismic conditions. Section 3 reviews the mechanical and related thermal simulations for the prediction by a direct problem procedure of the mean temperature elevation in the vicinity of the borehole, using a two- or three-parameter behaviour model depending on the intensity of the actions. Section 4 is a synthesis of the possibilities offered by thermal in situ measurements to contribute, in parallel with mechanical measurements, to the identification and/or the validation of the damping characteristics of an in situ soil. 相似文献
19.
The various boundary-element methods, well established in the frequency domain, are developed in the time domain for a foundation embedded in a layered halfspace. They are the weighted-residual technique and the indirect boundary-element method, based on a weighted-residual equation, and the direct boundary-element method based on a reciprocity equation, both equations involving time and space. In the indirect approach, formulating the weighted-residual equation over the last time step only results in the truncated indirect boundary-element formulation which requires a reduced computational effort. In all cases, convolution integrals occur. The truncated indirect boundary-element method leads to a highly reliable algorithm, as is verified when a linear analysis in the time domain is compared to the corresponding one in the frequency domain. This boundary-element formulation, which is non-local in space and time, represents a rigorous generally applicable method taking into account a layered halfspace in a non-linear soil-structure interaction analysis. As an example, the non-linear soil-structure interaction analysis of a structure embedded in a halfspace with partial uplift of the basemat and separation of the side wall is investigated. 相似文献
20.
We report on a field test of a transportable version of a superconducting gravimeter (SG) intended for groundwater storage monitoring. The test was conducted over a 6-month period at a site adjacent to a well in the recharge zone of the karstic Edwards Aquifer, a major groundwater resource in central Texas. The purpose of the study was to assess requirements for unattended operation of the SG in a field setting and to obtain a gravimetric estimate of aquifer specific yield. The experiment confirmed successful operation of the SG, but water level changes were small (<0.3 m) leading to uncertainty in the estimate of specific yield. Barometric pressure changes were the dominant cause of both water level variations and non-tidal gravity changes. The specific yield estimate (0.26) is larger than most published values and dependent mainly on low frequency variations in residual gravity and water level time series. 相似文献