首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Summary. In this paper computer modelling is used to test simple approximations for simulating strong ground motions for moderate and large earthquakes in the Mexicali–Imperial Valley region. Initially, we represent an earthquake rupture process as a series of many independent small earthquakes distributed in a somewhat random manner in both space and time along the rupture surface. By summing real seismograms for small earthquakes (used as empirical Green's functions), strong ground motions at specific sites near a fault are calculated. Alternatively, theoretical Green's functions that include frequencies up to 20 Hz are used in essentially similar simulations. The model uses random numbers to emulate some of the non-deterministic irregularities associated with real earthquakes, due either to complexities in the rupture process itself and/or strong variations in the material properties of the medium. Simulations of the 1980 June 9 Victoria, Baja California earthquake ( M L= 6.1) approximately agree with the duration of shaking, the maximum ground acceleration, and the frequency content of strong ground motion records obtained at distances of up to 35 km for this moderate earthquake. In the initial stages of modelling we do not introduce any scaling of spectral shape with magnitude, in order to see at what stage the data require it. Surprisingly, such scaling is not critical in going from M = 4–5 events to the M = 6.1 Victoria earthquake. However, it is clearly required by the El Centro accelerogram for the Imperial Valley 1940 earthquake, which had a much higher moment ( Ms ∼ 7). We derive the spectral modification function for this event. The resulting model for this magnitude ∼ 7 earthquake is then used to predict the ground motions at short distances from the fault. Predicted peak horizontal accelerations for the M ∼ 7 event are about 25–50 per cent higher than those observed for the M = 6.1 Victoria event.  相似文献   

2.
Most of the ancient town of Tindari (NE, Sicily) was settled on a plateau the most surficial layer of which was made of unconsolidated material. Ongoing excavations at the archaeological site at Tindari uncovered a large portion of the decumanus which suffered deformations preliminarily assigned to coseismic effects.
An analysis of the local dynamic response through the simulation of strong seismic shaking to the bedrock and modelling of spectral ratios of the bedrock-soft soil was carried out to verify the susceptibility of superficial terrains of the promontory to coseismic deformations. To perform this simulation the finite element method (FEM) was used. Four accelerometric recordings of three earthquakes of medium-high magnitude, recorded on rocky sites, were chosen to simulate the seismic shaking, using a constitutive law for the materials composing the promontory layers both of linear-elastic type and of elastoplastic type.
The analysis of the linear-elastic field allowed the definition of the frequencies for which the spectral ratios of the accelerations recorded the highest amplifications; in particular the frequency range 31.5–37.2 Hz can be combined with deformation of the paved floor of the decumanus. The analysis in the elastoplastic field highlighted the zones of promontory more susceptible to suffer plasticization process. The results show that the topmost layer of the decumanus is the most susceptible to suffer plasticization. Therefore, the performed analysis lends greater support to the hypothesis that the deformations were produced by seismic shaking.  相似文献   

3.
We systematically analysed shear wave splitting (SWS) for seismic data observed at a temporary array and two permanent networks around the San Andreas Fault (SAF) Observatory at Depth. The purpose was to investigate the spatial distribution of crustal shear wave anisotropy around the SAF in this segment and its temporal behaviour in relation to the occurrence of the 2004 Parkfield M 6.0 earthquake. The dense coverage of the networks, the accurate locations of earthquakes and the high-resolution velocity model provide a unique opportunity to investigate anisotropy in detail around the SAF zone. The results show that the primary fast polarization directions (PDs) in the region including the SAF zone and the northeast side of the fault are NW–SE, nearly parallel or subparallel to the SAF strike. Some measurements on the southwest side of the fault are oriented to the NNE–SSW direction, approximately parallel to the direction of local maximum horizontal compressive stress. There are also a few areas in which the observed fast PDs do not fit into this general pattern. The strong spatial variations in both the measured fast PDs and time delays reveal the extreme complexity of shear wave anisotropy in the area. The top 2–3 km of the crust appears to contribute the most to the observed time delays; however substantial anisotropy could extend to as deep as 7–8 km in the region. The average time delay in the region is about 0.06 s. We also analysed temporal patterns of SWS parameters in a nearly 4-yr period around the 2004 Parkfield main shock based on similar events. The results show that there are no appreciable precursory, coseismic, or post-seismic temporal changes of SWS in a region near the rupture of an M 6.0 earthquake, about 15 km away from its epicentre.  相似文献   

4.
Dynamic stresses generated by earthquakes can trigger landslides. Current methods of landslide analysis such as pseudo-static analysis and Newmark's method focus on the effects of earthquake accelerations on the landslide mass to characterize dynamic landslide behaviour. One limitation of these methods is their use Mohr–Coulomb failure criteria, which only accounts for shear failure, but the role of tensile failure is not accounted for. We develop a limit-equilibrium model to investigate the dynamic stresses generated by a given ground motion due to a plane wave and use this model to assess the role of shear and tensile failure in the initiation of slope instability. We do so by incorporating a modified Griffith failure envelope, which combines shear and tensile failure into a single criterion. Tests of dynamic stresses in both homogeneous and layered slopes demonstrate that two modes of failure exist, tensile failure in the uppermost meters of a slope and shear failure at greater depth. Further, we derive equations that express the dynamic stress in the near-surface in the acceleration measured at the surface. These equations are used to approximately define the depth range for each mechanism of failure. The depths at which these failure mechanisms occur suggest that shear and tensile failure might collaborate in generating slope failure.  相似文献   

5.
Summary. The influence of a simple mountain range on seismic ground motion is studied. A two-dimensional model of the medium and vertically incident plane SH -waves are considered. Attention is devoted not only to the wavefield along the Earth's surface, but also within the medium. The wavefield is computed in two steps: (1) the computation of the impulse response by the finite-difference method, (2) the computation of the response to a time variation of the incident wave. approximately corresponding to a 'hundred-year' local earthquake at the site. Numerical results (the impulse response, the transfer function, the accelerograms, and their spectra) indicate strong spatial variability of the wavefield due to the topographical anomaly. The differences as large as 100 per cent in the peak amplitudes of the accelerograms, and of the order of 5 Hz in their predominant frequencies, at closely (∼ 200 m) spaced internal points of the medium have been found. Attention is focused also on the effect of causal absorption. Even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground motion, caused by the topography. A variability like this. implying the occurrence of underground differential strains, might be of engineering importance in the antiseismic design of underground structures (tunnels, for example) in mountainous seismic regions. The ground-motion variability along the surface of the mountain is considerably smaller than within the medium.  相似文献   

6.
Taiwan Chelungpu-fault Drilling Project (TCDP) was initiated to understand the physical mechanisms involved in the large displacements of the 1999 Taiwan Chi-Chi earthquake. Continuous measurements of cores (including laboratory work) and a suite of geophysical downhole logs, including P - and S -wave sonic velocity, gamma ray, electrical resistivity, density, temperature, electrical borehole images and dipole-shear sonic imager, were acquired in Hole-A over the depth of 500–2003 m. Integrated studies of cores and logs facilitate qualitative and quantitative comparison of subsurface structures and physical properties of rocks. A total of 10 subunits were divided on the basis of geophysical characteristics. Generally, formation velocity and temperature increase with depth as a result of the overburden and thermal gradient, respectively. Gamma ray, resistivity, formation density, shear velocity anisotropy and density-derived porosity are primarily dependent on the lithology. Zones with changes of percentage of shear wave anisotropy and the fast shear polarization azimuth deduced from Dipole Shear-Imager (DSI) are associated with the appearance of fractures, steep bedding and shear zones. The fast shear wave azimuth is in good agreement with overall dip of the bedding (approximately 30° towards SE) and maximum horizontal compressional direction, particularly in the Kueichulin Formation showing strong shear wave velocity anisotropy. Bedding-parallel fractures are prevalent within cores, whereas minor sets of high-angle, NNW–SSE trending with N- and S-dipping fractures are sporadically distributed. The fault zone at depth 1111 m (FZA1111) is the Chi-Chi earthquake slip zone and could be a fluid conduit after the earthquake. The drastic change in fast shear wave polarization direction across the underlying, non-active Sanyi thrust at depth 1710 m reflects changes in stratigraphy, physical properties and structural geometry.  相似文献   

7.
Summary. As high-frequency elastic waves propagate through real media, it is common for caustics and focusing to occur. Typically, rays may envelop a caustic surface in space, or exceptionally they may all coalesce at a focal point. In strong motion seismology, the observed large fluctuations in peak acceleration and intensity of ground shaking may just be a consequence of focusing and caustics created by waves propagating through irregularly shaped sedimentary basins. These basins, acting as deformed optical lenses, are capable of producing a complex network of patches and seemingly isolated pockets of intensified damage or high intensity shaking where the caustic intersects the ground surface. We adapt methods from optics and catastrophe theory to study the properties of caustics induced by typical sedimentary basins. Several hypothetical examples are shown that reflect the fact that these properties are useful to assess quantitatively the degree of wavefield amplification to be expected. A good correlation is found between actual damage patterns and caustic locations computed for the Caracas, Venezuela earthquake of 1967.  相似文献   

8.
We model the ground motion from an aftershock of the 1995 January 17 Hyogo-ken Nanbu (Kobe) earthquake to investigate basin edge effects on wave propagation in Higashinada ward, downtown Kobe. Point-source finite-difference seismograms calculated using a double-couple solution and a 2-D basin structure are compared with the ground-motion velocity seismograms recorded in a small station array deployed at sites within and outside the heavily damage zone in Higashinada ward. The comparison suggests that in the frequency range 0.1-2 Hz that was analysed, the observed spatial amplitude variation of the aftershock ground motion is attributable mainly to the basin edge effects. We found that the basin edge effect, caused by the superposition of the direct S wave and the basin-edge-diffracted waves, amplified the ground motion in a narrow zone that is offset by about 0.7 km from the basin edge.  相似文献   

9.
Two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes: low-frequency and low-amplitude waves following the onset of a P wave ( P 1) are interrupted by the arrival of the second impulsive phase P2 enriched with high-frequency components. This observation suggests that a large shallow earthquake involves two qualitatively different stages of rupture at its nucleation.
We propose a theoretical model that can naturally explain the above nucleation behaviour. The model is 2-D and the deformation is assumed to be anti-plane. A key clement in our model is the assumption of a zone in which numbers of pre-existing cracks are densely distributed; this cracked zone is a model for the fault zone. Dynamic crack growth nucleated in such a zone is intensely affected by the crack interactions, which exert two conflicting effects: one tends to accelerate the crack growth, and the other tends to decelerate it. The accelerating and decelerating effects are generally ascribable to coplanar and non-coplanar crack interactions, respectively. We rigorously treat the multiple interactions among the cracks, using the boundary integral equation method (BIEM), and assume the critical stress fracture criterion for the analysis of spontaneous crack propagation.
Our analysis shows that a dynamic rupture nucleated in the cracked zone begins to grow slowly due to the relative predominance of non-coplanar interactions. This process radiates the P1 phase. If the crack continues to grow, coalescence with adjacent coplanar cracks occurs after a short time. Then, coplanar interactions suddenly begin to prevail and crack growth is accelerated; the P2 phase is emitted in this process. It is interpreted that the two distinct phases appear in the process of the transition from non-coplanar to coplanar interaction predominance.  相似文献   

10.
The magnitude m bLg 5.0 Mont-Laurier earthquake of 1990 October 19, in Quebec, Canada, was one of the largest to have occurred in eastern North America during the past decade. High-frequency ground motions recorded on regional network instruments exceeded values anticipated for an event of its size by a factor of 3. A commonly favoured explanation for the discrepancy is that the source was a rare 'high-stress' event. In this paper, detailed fault-slip models are derived to fit waveform and spectral characteristics of the regional data. The results establish that the effective rupture stress was normal (about 100 bars), that the fault rupture developed asymmetrically, and that the average slip time for points inside the rupture area (approx. 0.1 s) was significantly less than that associated with the standard Brune (1970) source spectral model. The rupture area developed in at least four distinct episodes, each extending the previously ruptured area. Taken together with similar results for the m bLg 6.5 Saguenay earthquake of 1988 November, the results indicate that a widely used assumption in hazard analyses, that earthquake spectra are adequately represented by the standard Brune spectral model, is unreliable for the interpretation and prediction of strong ground motion.  相似文献   

11.
Shear-wave splitting is analysed on data recorded by the High Resolution Seismic Network (HRSN) at Parkfield on the San Andreas fault, Central California, during the three-year period 1988-1990. Shear-wave polarizations either side of the fault are generally aligned in directions consistent with the regional horizontal maximum compressive stress, at some 70° to the fault strike, whereas at station MM in the immediate fault zone, shear-wave polarizations are aligned approximately parallel to the fault. Normalized time delays at this station are found to be about twice as large as those in the rock mass either side. This suggests that fluid-filled cracks and fractures within the fault zone are elastically or seismically different from those in the surrounding rocks, and that the alignment of fault-parallel shear-wave polarizations are associated with some fault-specific phenomenon.
Temporal variations in time delays between the two split shear-waves before and after a ML = 4 earthquake can be identified at two stations with sufficient data: MM within the fault zone and VC outside the immediate fault zone. Time delays between faster and slower split shear waves increase before the ML = 4 earthquake and decrease near the time of the event. The temporal variations are statistically significant at 68 per cent confidence levels. Earthquake doublets and multiplets also show similar temporal variations, consistent with those predicted by anisotropic poroelasticity theory for stress modifications to the microcrack geometry pervading the rock mass. This study is broadly consistent with the behaviour observed before three other earthquakes, suggesting that the build-up of stress before earthquakes may be monitored and interpreted by the analysis of shear-wave splitting.  相似文献   

12.
Seismic hazard maps of central-southern Africa where hazard has been expressed in terms of peak ground acceleration for an annual probability in excess of 10-1 show relatively high values that distinguish the seismic hazard potential of the Deka fault zone, the mid-Zambezi basin-Luangwa rift and western central Mozambique. In areas such as central-southern Africa where little is known about the geology of the region and the fault systems have not been fully mapped, seismic hazard potential may be estimated from seismicity and broad-scale fault features. For this region, such potential is based on earthquake magnitude Ms ≥ 6. Events of such magnitude have recently occurred in the mid-Zambezi basin, southern Zimbabwe and western-central Mozambique. This paper follows the conventional probabilistic hazard analysis procedure, defining seismic source zones from seismicity based on instrumental records from a cataloque that spans a period of 83 years. Geological and geomorphological features in the region are described on the mesoscale and are correlated with the seismicity as broad fault zones. The scarcity of strong-motion accelerogram data necessitated the formulation of attenuation values based on random vibration theory (RVT).  相似文献   

13.
We analyze geomorphic properties extracted from LiDAR and SRTM (Shuttle Radar Topography Mission) data to test whether the damage zone along the central San Jacinto Fault (SJF) zone can be resolved with remotely-sensed data in a quantitative fashion. The SJF is one of the most active faults in southern California, with well expressed geomorphology and a fast slip rate, as seen in the geology and by GPS. We use ArcMap and the TauDEM toolbox to compare several morphometric parameters, including drainage density (Dd), on both sides of the fault, using a 1 km and a 5 km buffer for the LiDAR and SRTM data, respectively. We also analyze the spatial patterns of Dd near the fault, using two different definitions of spatial Dd. The high resolution of the LiDAR data allows us to focus on a single fault, eliminating the effects of parallel nearby faults. From the LiDAR data we find that the highest Dd values occur in areas between two fault strands, followed generally by rocks on the northeast side of the fault, with the lowest Dd values occurring on the southwest side of the fault. The SRTM data shows a band of high Dd values centered on the main fault trace with ~ 1 km width. Our results indicate that there is a strong correlation between drainage density and proximity to the fault, with zones of structural complexity along the fault displaying the highest Dd. We interpret this to largely be an effect of degree of rock damage, as these are areas that are expected to be more damaged, and field observations support this contention. If we are correct, then it appears that the northeast side of the SJF is generally more damaged. South of the trifurcation area there is evidence that the signal is reversed on the larger scale, with more damage on the southwest side of the fault inferred from the SRTM data, possibly caused by extension between the Coyote Creek and Clark faults. The implications of the observed asymmetry could be geological evidence for rupture propagation direction, because a preferred propagation direction is predicted to produce asymmetric damage structure that would be recorded in the volume of rock surrounding a fault.  相似文献   

14.
Summary. Most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the Earth's surface to a depth of a few tens of kilometres at most. A model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth-dependent power-law rheology. A frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone. Such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth. Assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates, it is found that there exists a maximum depth H below which tectonic stress can never reach the frictional threshold: this may be identified as the maximum depth of earthquake nucleation. The value of H is consistent with observations for plausible values of the model parameters. The stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation. A change in rigidity with depth, which is also introduced in the model, may reproduce the high vertical gradient of shear stress, which has been measured across the San Andreas fault, and the fact that most earthquakes are nucleated at some depth in the seismogenic layer. A crack which drops the ambient stress to the dynamic frictional level is then introduced in the model. To this aim, a crack solution is employed without a stress singularity at its edges, which is compatible with a frictional stress threshold criterion for fracture. A constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer.  相似文献   

15.
 利用DMT公司生产的连续流单过饱和度云凝结核计数器2007年8月在内蒙古自治区阿拉善左旗、宁夏回族自治区石嘴山市惠农区进行观测,并利用机载PMS观测资料,探讨贺兰山两侧云凝结核(CCN)在近地面和高空的垂直变化。分析表明,CCN主要来源于下垫面,污染地区的浓度明显高于沙漠地区,城市污染对CCN浓度的影响很大。CCN浓度的日变化非常明显。不同过饱和度下粒子谱谱型不同,主要表现为单峰型。过饱和度越大,活化的CCN数目越多,产生的粒子半径越大。高空观测表明,CCN、气溶胶数浓度在近地面较高,随高度的上升逐渐降低,遇到逆温层会出现浓度的跃升,其活化液滴谱型表现为双峰型,与地面相比,粒子谱向大粒子端移动,峰值半径在4 μm和6 μm左右。气溶胶粒子浓度主要集中在粒径0.3 μm以下;根据公式N＝CSK对地面的CCN活化谱进行拟合,接近大陆型核谱。不同地区及同一地区不同时间范围,CCN浓度、活化谱及活化后的液滴谱存在差异,需要在不同地区、不同季节对CCN谱型演变特征进行长期连续观测,从而认识CCN浓度及谱型的变化对云雾降水过程及气候变化的作用。不同地区可充当CCN气溶胶的谱分布及表面化学成分不同,其对CCN数浓度及谱分布的影响也不同,在观测中需要增加化学成分的观测,深入了解CCN浓度的时空分布特征。  相似文献   

16.
南迦巴瓦峰与托木尔峰山地垂直自然带的比较   总被引：2，自引：0，他引：2  
徐慧  彭补拙 《山地学报》2002,20(4):432-437
南迦巴瓦峰地处喜马拉雅山脉东端雅鲁藏布江大拐弯的内侧，托木尔峰地处天山山脉的西端，二者独特的自然地理特征及其高大的山体为山地垂直自然带谱的形成和发展提从了十分有利的自然环境，发育了相当完整的山地垂直系列。比较二者的垂直带谱，可以发现无论在垂直带谱的形成条件，基带，性质和结构类型，还是景观特征，垂直分异影响因素及南北坡差异程度等方面，都存在着较大的差异。南峰垂直带谱为以森林－草原－荒漠土壤系列为特征的季风性湿润，法湿润带谱系统，垂直分异的主导因素为温度；托峰垂直带谱为以荒漠－－草原－荒漠土壤系列为特征的大陆性干旱带谱系统，垂直分异的主导因素为湿度。不同的垂直自然带特征决定了不同的资源开发利用和保护措施。  相似文献   

17.
We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter  τ c   and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from  τ c   and the peak ground-motion velocity ( PGV ) from Pd . The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P -wave trigger is constantly monitored. When a trigger occurs,  τ c   and Pd are computed. We found the relationship between  τ c   and magnitude ( M ) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds.  相似文献   

18.
The mechanisms which control the formation and maintenance of pool–riffles are fundamental aspects of channel form and process. Most of the previous investigations on pool–riffle sequences have focused on alluvial rivers, and relatively few exist on the maintenance of these bedforms in boulder-bed channels. Here, we use a high-resolution two-dimensional flow model to investigate the interactions among large roughness elements, channel hydraulics, and the maintenance of a forced pool–riffle sequence in a boulder-bed stream. Model output indicates that at low discharge, a peak zone of shear stress and velocity occurs over the riffle. At or near bankfull discharge, the peak in velocity and shear stress is found at the pool head because of strong flow convergence created by large roughness elements. The strength of flow convergence is enhanced during model simulations of bankfull flow, resulting in a narrow, high velocity core that is translated through the pool head and pool center. The jet is strengthened by a backwater effect upstream of the constriction and the development of an eddy zone on the lee side of the boulder. The extent of flow convergence and divergence is quantified by identifying the effective width, defined here as the width which conveys 90% of the highest modeled velocities. At low flow, the ratio of effective width between the pool and riffle is roughly 1:1, indicating little flow convergence or divergence. At bankfull discharge, the ratio of effective width is approximately 1:3 between the pool and downstream riffle, illustrating the strong flow convergence at the pool head. The effective width tends to equalize again with a ratio of 1:1 between the pool and riffle during a modeled discharge of a five-year flood, as the large roughness elements above the pool become drowned out. Results suggest that forced pool–riffle sequences in boulder-bed streams are maintained by flows at or near bankfull discharge because of stage-dependent variability in depth-averaged velocity and tractive force.  相似文献   

19.
Quaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 103 to 105 year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year?1 during the late Holocene, ca. 0.03 mm year?1 during the last glacial and at least 0.07 mm year?1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.  相似文献   

20.
基于策勒绿洲78个取样点的地下水的观测资料,结合地理信息系统,运用地统计学方法和Sigmaplot10.0中的Piper模块,研究塔里木盆地南缘策勒绿洲区地下水TDS（Total Dissolved Solids）的时空变异,揭示地下水水化学特征及其演变的主要水化学过程。结果表明:①地下水TDS存在强烈的空间相关性,其空间相关距离为4.4 km,在步长为6 km范围之内,地下水TDS的空间变异是各向同性的,当步长大于6 km时,4个方向上的半变异函数发生了不同的变化;②绿洲南部区域为地下水TDS的低值区,最小值为551 mg·L-1,由南向北地下水TDS呈增加的趋势,在北部地下水埋深低值区的TDS最大值为7 192 mg·L-1;从地下水水流方向上看,即从绿洲西南的低值区向北,再转向东北区方向,地下水TDS逐渐增加,最大值为3 677 mg·L-1;③浅层地下水化学类型变化复杂,主要从Na-Ca—SO4-Cl-HCO3、Na-Ca—SO4-Cl型向Na—SO4-Cl-HCO3和Na—SO4-Cl型演化。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号