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1.
Himanshu Mittal Yih-Min Wu Ashok Kumar Arjun Kumar Babita Sharma 《Arabian Journal of Geosciences》2016,9(18):712
Uttarakhand, a state of India, is located in seismically active Himalayan region and in the proximity of plate boundaries. The effects of important ground motion parameters like magnitude, distance, and local geology and site conditions on acceleration response spectra are examined in Uttarakhand Himalayas in this work. A total of 447 strong ground motion histories (horizontal and vertical) from 42 earthquakes were selected. The results show that the shape of the acceleration response spectra is influenced by the local site conditions and regional geology. The studies are carried out for two categories of sites, i.e., rock sites and soft soil sites. The maximum average horizontal spectral amplification for rock sites is 2.7 at 0.1 s, while for soft soil sites, it is found to be 3.2 at 0.2 s. In the same way, the maximum average vertical spectral amplification for rock is found to be 2.7 at 0.1 s, while for soft soil, it is found to be 2.95 at 0.1 s. The average spectral amplification in vertical component also shifts from low period (rock) to high period (soft soil). The level of spectra increases with decrease in distance for rock sites as well as soft soil sites. When comparing different magnitude earthquakes in different geological conditions, the response spectra are found to follow each other up to 0.04 s, while for period greater than 0.04 s, the spectra of higher magnitude earthquake is observed on the higher side. For soft soil sites, spectra from different magnitude earthquakes are observed to follow each other up to 0.1 s, beyond which they get separated. 相似文献
2.
This article presents probabilistic seismic hazard analyses of northern Pakistan region carried out to produce macro-seismic hazard maps for the region that define new regional ground motion design parameters for 95-, 475-, 975- and 2475-year return period earthquakes as regional contour maps and horizontal uniform hazard at important cities. The Cornell–McGuire approach (Cornell in Bull Seismol Soc Am 58(05):1583–1606, 1968; McGuire in FORTRAN computer program for seismic risk analysis. US Geological Survey, Open file Report, 76-6768, 1976) is used to carry out the analyses at 0.1° rectangular grid. The seismotectonic model of the region used in analysis consists of shallow and deep area zones differentiated based on the focal depths of the earthquakes. Earthquake catalogue compiled and used in the analysis is a composite catalogue composed of 19,373 events. Ground motion prediction equations (GMPEs) used are calibrated using goodness-of-fitness measures and visual inspection with local strong motion data. Epistemic uncertainty in the GMPEs is taken into account through the logic tree approach. Comparison of ground motions due to deep earthquakes is made for the first time for the region. The comparison between ground motion due to shallow and deep earthquakes indicates that the seismic hazard would be underestimated if the deep earthquakes are excluded. Ground motion values obtained in this study considering all the earthquakes suggest ground motions are dominant towards the north east of the region. The proposed study indicates that the ground motion hazard values suggested by the current Building Code of Pakistan underestimate the seismic hazard. Final results of this study are in close agreement with the recent studies on the region. 相似文献
3.
The spectral characteristics of shallow water waves were studied at two locations along the eastern Arabian Sea during 2011. Wave spectra were single-peaked from June to October and predominantly double-peaked during the rest of the year. Even though both locations were subjected to open sea conditions, the percentage of single-peaked spectra was large (63 %) in the southern location compared to a location 350 km north (46 %), because of variation in local winds. Throughout the year, the double-peaked spectra were mostly swell dominated in the southern location. In the northern location, the double-peaked spectra during January to May and December were sea dominated due to the strong local winds blowing from north-west. For the double-peaked wave spectra, the average difference between the spectral peaks was 0.11 Hz, and the average ratio of the spectral energy density at the two peaks was 0.5. Significant wave heights up to 4.2 m and a maximum wave height of 7 m were observed during the south-west monsoon period. Fifty per cent of the waves recorded had spectral peak wave periods between 6 and 12 s. The narrowest directional spectra were found for waves with 10–12-s peak wave periods. Inverse wave age values were biased towards lower values with peaks in the range of 0.2–0.6, indicating a swell-driven wave regime along the eastern Arabian Sea. 相似文献
4.
5.
M. K. Rama Varma Raja G. C. Asnani P. S. Salvekar A. R. Jain D. Narayana Rao S. Venkoba Rao P. Kishore M. Hareesh 《Journal of Earth System Science》1999,108(4):287-295
Contrary to the prevalent belief that tropical region is characterized by convective clouds rather than by layer clouds, we
have suggested that deep convective clouds occur on meso-scale, but layer clouds occur on larger synoptic-scale with a relatively
small region of deep convective clouds. Sustenance of deep convective clouds is inhibited by the presence of inertio-gravity
waves, which have alternating layers of upward and downward motion in the vertical. We have also shown that inertio-gravity
waves generate regions of relatively strong horizontal velocity, vertically separated by layers of relatively weak horizontal
velocity. Layers of strong horizontal velocity are created by inertio-gravity wave system through convergence of vertical
flux of horizontal momentum. We have also suggested that horizontal convergence/divergence of moisture flux is generated by
inertio-gravity waves, giving rise to vertically alternating layers of high/low humidity, and visible or sub-visible clouds.
Layers of high humidity become layers of strong radar reflectivity at frequency of 53 MHz at which MST Radar at Gadanki, near
Tirupati, India, operates. These observations, more than 2,50,000 in number, for vertical grid points, spread over all the
months of the year, have helped us, among other observations, to arrive at these conclusions. Further, the analysis suggests
that the main source of strong MST radar reflectivity is not mechanical turbulence as is commonly believed. 相似文献
6.
A deterministic seismic hazard analysis was conducted to address the effect of local soil conditions on earthquake-induced strong ground motion in the Las Vegas Basin, Nevada (US). Using a large geological and geotechnical database, two response units were defined: a fine-grained unit, predominantly clay; and a coarse-grained unit, predominantly gravel. A moderate number of high-quality shallow shear wave velocity measurements were collected from which characteristic shear wave velocity profiles were developed for each response unit. An equivalent-linear one-dimensional site response model was used. The model was calibrated using a basin-wide, small-strain ground motion database. Calibration tests showed that ground motion projections become increasingly conservative with increasing ground-motion amplitude. Projections were overconservative for the coarse-grained response unit, likely due to the sparseness of the velocity database. For the earthquake response analyses, historical ground motions were used to model characteristic ‘bedrock’ motion for earthquakes on 10 faults judged to be critical. Response spectral envelopes were generated for each unit through Monte-Carlo simulations. For the fine-grained response unit, 95th percentile peak ground acceleration, peak spectral acceleration and predominant period were 310 cm/s2, 1100 cm/s2, and 0.29 s, respectively. With respect to codified design spectra, projections are lower at short periods and higher at long periods. Projections of peak spectral accelerations for the coarse-grained response unit, were more than double that of codified spectra; however, they are believed to be overconservative. Near-fault effects and basin-edge effects, though potentially important, were not considered in these analyses. 相似文献
7.
成都市多目标地球化学调查和双层采样的效果 总被引：2，自引：0，他引：2
成都平原多目标地球化学调查在元素基准值及分布特征，构造、农业、环境污染的研究，天然气的预测，pH值的计算等方面都取得了进展。调查中所采的深层样对于研究深部元素分布、构造、根深作物发育、天然气预测；浅层样对于浅层元素分布、农业地质、环境污染等方面有着特殊的作用。多目标地球化学调查及其双层采样方法可以推广。 相似文献
8.
区域农业生态地质调查内容与方法--以河北平原为例 总被引：7，自引：0，他引：7
区域农业生态地质调查，是我国建设可持续农业及农村经济、建设良好生态环境的重要保证。区域农业生态地质调查要以关键带的地质环境演化和对农业的影响来划分并确定调查的时段和重点，深部以编为主，浅部以验证调查为主；总体上为网膜控制，灰度界线，其工作精度由下部至上部逐步提高。以河北平原为例，划分了4个层段：地表层段，为调查重点，作为综合成果的主体；全新统上段和全新统层段，分别以洛阳铲和浅钻验证调查为主；第四系层段，开发已有资料，以编为主。综合性调查成果的主图及图例表反映调查区域的农业生态地质条件，镶图及辅表反映调查区域的农业生态地质工程区划等，剖面图辅助揭示区域农业生态地质背景条件。 相似文献
9.
合理描述土体动力本构关系对场地设计地震动参数取值的准确性有显著影响。以苏州城区200 m深的钻孔剖面为研究对象,对比分析了一维等效线性波传分析法（ELA法）和基于修正Matasovic本构模型的多自由度集中质量非线性分析法（NLA法）给出的深厚场地地震反应,研究了基岩输入地震动特性和地震基岩面的选取对深厚场地地震反应的影响。结果表明：（1）随基岩地震动强度（PGA）的增大,ELA法给出的地表PGA呈单调递增的特征,而NLA法给出的地表PGA呈先快速增大后缓慢减小或几乎不变的趋势;（2）ELA法和NLA法给出的地表加速度反应谱（Sa谱）在短周期范围内存在明显差异,ELA法对基岩高频地震动具有显著的滤波效应,而NLA法对基岩高频地震动的影响表现为随基岩PGA的增大先放大后减小的特征;（3）随地震基岩面深度的增大,地表Sa谱的谱值呈现出稍许增大的趋势,但对周期T<0.1 s部分,NLA法给出的地表Sa谱的谱值则呈现出稍许减小的现象;（4）中、大震作用下,地表地震动持时不仅与基岩地震动特性有关,还与地震反应分析方法和地震基岩面的选取密切相关,NLA法能更合理地反映基岩地震动强度和上覆土层厚度对地表地震动持时的影响。 相似文献
10.
近年来地幔地球物理三维成像为地下深部构造和物质运动提供了大量数据和信息,促进了人们对浅地幔系统物质运动的特征和动力学作用的认知。按照运动的方向不同,浅地幔系统的物质运动可分为三种主要形式:水平运动、向上涌动和向下沉动。浅地幔系统物质向下运动由地球引力势能引起,其他方向的运动主要由热能和动能引起。除了动力来源之外,浅地幔系统物质运动的方向还取决于岩石圈和软流圈的物质属性,因为高黏度介质阻挡物质运动,而低黏度介质加速物质运动。软流圈物质的水平蠕动差异,产生了岩石圈的伸展、拆离和推覆等复杂构造,速度和动能较大软流圈物质的蠕动,一定会带动岩石圈板块物质的运动和变形。软流圈物质的向上涌动又可以进一步细分为上涌运动、上拱运动和穿刺运动三种方式,它们对上方岩石圈的作用效果是不同的。浅地幔系统的物质下沉运动有多种形式,包括俯冲、拆沉和交代作用,也经常伴随有软流圈物质上涌,在微观上是一种对偶运动。这种对偶运动造成了克拉通地壳的底垫和岩石圈的陆根。软流圈大规模的物质运动,包括大洋中脊物质上涌、大陆碰撞造山和大洋俯冲的前陆拉张,在全球地震层析成像图上都有清晰的反映。中国东南沿海一带是浅地幔系统物质运动的一个特殊地区,可能是由于白垩纪伊佐奈崎板块俯冲,激发东亚大陆边缘软流圈上涌,然后又造成大陆边缘岩石圈局部拆沉等一连串动力学作用叠加形成的。 相似文献
11.
远场大地震作用下大尺度深软场地的非线性地震效应分析 总被引：1，自引：0，他引：1
基于ABAQUS软件自行研制的并行计算显式算法集群平台,针对苏州城区典型地层剖面,建立了大尺度深软场地的二维精细化非线性有限元分析模型,对人工地震波和大地震远场地震动作用下深软场地的非线性地震效应进行了比较研究。研究结果表明：（1）与人工地震波作用时深软场地的地表峰值加速度放大效应相比,大地震远场地震波作用时的放大效应尤为显著,由于土介质的横向不均匀性及其非线性,使不同地表的峰值加速度放大效应存在明显的变异性。（2）深软场地对周期小于0.3 s的高频地震波均具有显著的滤波效应;大地震远场地震波作用时,深软场地对周期0.85～1.65 s的长周期地震波的放大效应非常显著,但对2.5～7.0 s的长周期地震波呈现出明显的滤波效应。（3）地震动峰值加速度PGA值沿土层深度和横向的分布形态呈现出明显的高低起伏现象,在不同成因的土层更迭面附近及土介质横向不均匀性显著的区域,地震波的局部聚焦放大和过滤减小现象尤为明显,且大地震远场地震动作用时,20 m以浅土层的PGA值呈现出非常显著的放大效应。（4）地震波的频谱特性、土层的横向不均匀性对深软场地地表加速度反应谱? 谱的谱形有显著影响;给出了描述加速度反应谱沿土层深度变化特征的三维谱形曲线,可以直观地展示出深软场地中细长地下结构地震反应可能存在类共振现象的土层深度。 相似文献
12.
This study addresses the impact of nonlinear wave evolution on the resulting wave force values on a vertical wall. To this end, the problem of interaction between non-breaking water waves and a vertical wall over constant depth is investigated. The investigation is performed using a two-dimensional wave flume model which is based on the high-order spectral method. Wave generation is simulated at the flume entrance by means of the additional potential concept. This model enables to preserve full dispersivity. Therefore, the model enables to examine the role of nonlinear evolution in the formation of extreme wave force values on a vertical wall for a wide range of water depths. The results for the force exerted on a vertical wall are presented for shallow and deep water conditions. In shallow water, extreme wave force values occur due to the formation of an undular bore. In deep water, extreme wave forces have been obtained as a result of disintegration process of incident wave groups into envelope solitons. Multiple maximum force values have been detected for each of the highest run-up peaks. This phenomenon has been introduced in shallow water conditions and is extended here for deep water conditions. 相似文献
13.
浅层地温场中热对流数值模拟 总被引：1，自引：0，他引：1
温度示踪的研究区域大多在地表浅层,浅层地温场主要受气象和水文影响。气温波动可用傅立叶级数精确表示,由此建立了在表层气温和垂向水流共同影响下的浅层地温场瞬态分析模型,用Laplace变换的方法得到其解析解,并用有限元模拟了垂向水流对浅层地温的影响。模拟结果表明：浅层地温有季节波动,在地下水补给区,气温波动振幅衰减速率明显减缓,表现为表层气温波动可以影响到更深的深度;在排泄区,温度波振幅衰减很快。另外,还模拟了水平集中渗漏带附近的瞬态温度场,发现由于热对流的传热能力远大于热传导,强渗漏带温度迅速与补给源温度相一致,温深剖面出现异常,温度异常带形成后,继而通过热传导改变较大范围内地质体热量分布。离低温补给源越近,地质体降温越快,温度改变越多;反之则越慢,温度改变越少。因此,由温深剖面的温度异常,可精确探查渗漏带位置。 相似文献
14.
This paper presents an investigation into various factors that may affect the ground response to multi-directional earthquake loading, focusing mainly on the behavior of vertical ground motion and its relation with the horizontal counterpart. The factors investigated herein include the intensity of input motion and the associated soil nonlinearity, the location of input motion (rock outcrop versus bedrock), the variation of water table, and the damping property of soil. Influence of these factors is studied on the characteristics of site amplification in both vertical and horizontal directions, the response spectra of vertical and horizontal ground surface motions, the spectral ratio between the two components (V/H) at the ground surface, and the distributions of stresses and strains in the ground. One of the main results is that varying water table can bring about a significant impact on vertical motion and the relationship between vertical and horizontal motions. The surface response spectral ratio (V/H) can largely exceed the rule-of-thumb value of 2/3 at low periods with lowering the water table, but does not appear to be substantially affected at long periods. 相似文献
15.
Eva Pacioni Marco Petitta Ezio Burri Maria Fanelli Piero Mazzeo Fabrizio Ruggieri 《Environmental Earth Sciences》2010,61(1):201-216
This paper analyses flow and transport of pesticides from the unsaturated zone to groundwater so as to predict concentration
of those contaminants in the Fucino Plain’s groundwater, by site investigations and numerical simulations. Pesticides were
detected in surface water (peaks of 13 μg L−1) and groundwater (peaks of 0.37 μg L−1). Modelling tools made it possible to identify that pattern of precipitation, organic matter content, and root thickness
are the key factors involved in vertical seepage of pesticides. Numerical simulations indicated that a significant fraction
of contaminants is leached from the most surficial soil layers through runoff, while only a secondary fraction is mobilised
towards groundwater. Likelihood of contaminating deep groundwater is fairly low, whereas surface waters show higher susceptibility.
Results of the proposed conceptual hydrogeological model show that pesticides are more likely to be entrained by mixing of
stream water with shallow groundwater in periods of high water exploitation from shallow wells. 相似文献
16.
地震基岩深度和土体动力本构模型的选取对核岛场地地震效应评价结果的合理性具有重要影响。以拟建某沿海核电厂深度470 m沉积土夹火山岩层场地的3个钻孔剖面为研究对象,采用一维等效线性波传分析（ELA）法、基于Matasovic本构模型和Davidenkov-Chen-Zhao（DCZ）本构模型的一维非线性分析（NLA）法,选取不同剪切波速的5个岩土层作为地震基岩,研究了输入地震动特性、地震基岩深度和土体动力本构模型的选取对巨厚沉积土夹火山岩层场地非线性地震反应特性的影响。结果表明：（1）以浅层硬岩夹层或深部土层作为地震基岩,NLA法计算的5%阻尼比的地表谱加速度SA的短周期部分较之ELA法的计算值大,但两者计算的地表SA谱的长周期部分几乎一致;（2）基于Matasovic模型和DCZ模型的NLA法计算的地表SA谱谱形和峰值加速度随深度的变化趋势基本一致;（3）从NLA法计算的地表峰值加速度和累积绝对速度而言,以剪切波速约2 500 m/s的浅层硬岩夹层作为地震基岩是适宜的。 相似文献
17.
Coseismic changes in groundwater levels have been investigated throughout the world, but most studies have focused on the effects of one large earthquake. The aim of this study was to elucidate the spatial patterns of level changes in response to several earthquakes, and the relationship of the patterns to shallow and deep groundwater in the same area. We selected the Kumamoto City area in southwest Japan, a region with one of the richest groundwater resources in Japan, as our study site. Data from hourly measurements of groundwater levels in 54 wells were used to characterize the coseismic responses to four earthquakes that occurred in 2000, 2001, 2005, and 2008. Although the distance to the hypocenter (12–2573 km), and seismic energy (Mw = 5.0–8.0) of these earthquakes varied, systematic groundwater level changes were observed in the range of 0.01–0.67 m. Spatial patters of the level changes were clarified by interpolating the point data by a spline method. The zones where coseismic rises were observed were generally wider for deep groundwater than for shallow groundwater, probably as a result of an increase in compressive stress. General trends in the changes in groundwater levels, and calculated pressure changes, were clarified to be consistent in the deep groundwater, but the coseismic increases or decreases in compressive stress in the shallow groundwater were variable, depending on the distance to the earthquake epicenter. We developed a conceptual model of the mechanism underlying this phenomenon by assuming permeability enhancement induced by elastic strain and pore-pressure change over the depth range. In addition, the importance of local geology was identified, because levels in the area of Togawa lava (a porous andesite) tended to change more in magnitude, and more quickly, with a shorter recovery time, than levels measured in the area outside the lava. 相似文献
18.
航磁异常深部弱信号提取技术研究 总被引：1，自引：0，他引：1
磁异常通常是地下不同深度磁性地质体产生磁场的叠加,在规范高度的航磁测量结果中,深部磁性体所产生的异常通常表现为弱而平缓,其水平与垂向分辨率均较低,在航磁资料处理解释中难以有效捕获。因此,应用适当方法提取由深部地质体引起的弱磁信息是十分必要的。本文采用精度高且稳定的位场延拓技术将航磁异常向下延拓,可以稳定增强磁异常幅度,随着延拓面与场源之间距离的减小,浅成磁信号与深成磁信号的视深度差异将增大,在对数功率谱上可以将其区分,而后可利用匹配滤波方法将浅部信号剥离,从而得到深部弱信号,同时可计算深部弱信号的视深度。 相似文献
19.
南堡凹陷中浅层火成岩类型多、非均质性强,利用单一技术方法难以有效刻画火成岩和砂岩储层的空间分布,制约了中浅层砂岩油气藏的勘探开发。在岩石物理交会分析基础上,利用对岩性响应敏感的纵波阻抗、伽马、泊松比和甜点4类地震属性和PCA主组分降维技术,对玄武岩、蚀变火成岩、砂岩、泥岩四类岩性进行了有效的区分,利用创新的井控综合解释技术获得了最终岩性体数据,达到在复杂岩性背景下准确识别砂岩储层的目的。结果表明,地震预测与实钻情况吻合程度较高,达到87.1%,预测的火成岩与砂岩分布特征与区域地质认识相匹配,为研究区滚动开发和开发调整提供了有力技术支撑。 相似文献