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1.
利用云南数字地震台网的区域地震波形资料，对川滇地区的地壳上地幔速度结构进行了初步研究. 结果表明，川滇地区上地幔顶部P波速度较小，约78 km/s，P波速度在上地幔表现为较小的正速度梯度，S波在100～160 km深度范围内表现为弱低速层. 对于较短的观测路径，不同路径的平均P波和S波速度存在明显的横向变化. 与川滇菱形块体内部的速度结构不同，在块体边界附近可以观测到比较明显的上地壳低速层，我们认为它可能与块体边界的断裂带有关；川滇菱形块体内部存在的下地壳低速层，有利于块体向南滑动，而中上地壳没有明显低速结构，可能表明川滇菱形块体向南滑动的解耦深度至少在下地壳. 根据不同路径的反演结果，给出了云南中部地区地壳内部的平均速度结构. 相似文献
2.
采用波形反演方法对青藏高原地区震中距8°-38°范围内的宽频带炸波波形进行拟合,研究该地区上地幔平均速度结构以及上地幔纵、横波速度的横向不均匀性结果表明青藏高原地区的平均地壳厚度约为68km,上地幔盖层平均厚度约为30－40km,速度约为8.10km／s雅鲁藏布江附近地壳厚度最大,约80km,相应的上地幔Pn速度为8．15km／s左右,青藏高原中部地区的地壳平均厚度约68-70km．位于拉萨地块北部的羌塘地块S波速度相对较低,其地壳和上地慢的平均S波速度分别比拉萨地块低1％和2％以上34°N以北,90°E附近的区域存在明显的上地幔P波低速异常区,P波的平均速度小于7．8km／s据此结果及前人工作,推断印度板块的俯冲可能以雅鲁藏布江缝合带附近为界,青藏高原巨大的地壳厚度是由于欧亚板块碰撞造成地壳缩短与增厚引起. 相似文献
3.
华北克拉通是世界上最古老的克拉通之一.我们利用布设于华北中部的ChinArray计划461个宽频带地震台阵的连续波形资料，基于背景噪声成像技术，获得了克拉通中西部5～45 s的Rayleigh波群速度频散曲线，并利用线性反演方法获得了研究区地壳上地幔顶部的S波速度结构.密集流动地震台阵使我们能够揭示研究区精细的地壳上地幔顶部速度变化，以深入探讨华北克拉通中西部深部结构及其对岩浆和地震的控制作用.8 km深度的S波速度切片显示低速与高速异常分别与地表的盆地和山脉对应良好.不同经度和纬度方向的S波速度剖面均表明，西部克拉通地壳大致可以分为上、中、下地壳三层.克拉通西部鄂尔多斯块体的下地壳S波速度介于3.7～3.8 km·s-1,暗示其下地壳以长英质岩石为主.大同火山区下方的S波低速异常从中地壳延伸至上地幔顶部，推测源自软流圈的地幔热流提供了近垂直的主干上涌通道，并控制了该区新生代岩浆活动.强震集中分布在上地壳高速体内部或高低速相间区，其下地壳乃至上地幔顶部都呈现明显的低速异常，推测源自上地幔/下地壳的深部热流沿地壳尺度的陡深断裂上侵，诱发上覆高应力刚性块体发生蠕动破裂... 相似文献
4.
2021年5月21日我国云南省大理州漾濞县发生了MS6.4级破坏性地震,该地震的深部孕震环境研究对理解其成因极为重要.本文利用滇西北地区 68个密集地震台站记录的远震波形数据,提取 P波接收函数,采用两步反演法和Bootstrap重采样统计技术,获取了滇西北地区精细的地壳上地幔 80 km深度范围内的 S波速度结构.结合前期所得地壳厚度与泊松比分布情况分析认为:滇西北地区地壳 S波速度结构在横向上和垂向上都具有强烈的非均匀性,浅表约有4 km厚的低速沉积层,中上地壳呈高低速相间分布特征;20～40 km深度范围内存在低速层,分布在维西—乔后—巍山断裂与红河断裂两侧.从横向上看,漾濞地震发生在维西—乔后—巍山断裂西侧的高低速过渡地区和泊松比高梯度带上.从垂直剖面上看,漾濞地震发生在中下地壳具有明显低速层、而上覆为相对高速的脆性地壳中,震源区地壳内存在的低速体为此次漾濞地震提供了可能的孕震环境.滇西北地区的中下地壳低速层被断层限制在特定的区域内,且该地区存在莫霍面隆起中心、非常高的泊松比值(＞0.3)以及上地幔低速异常,考虑到高热流、地幔高导层隆起、温泉幔源特征等综合分析推测低速体可能与地幔热物质上涌有关. 相似文献
5.
腾冲火山地热区地壳结构的地震学研究 总被引：23，自引：7，他引：23
根据腾冲火山地热区实施的人工地震测深剖面资料 ,用有限差分反演和正向走时拟合方法确定了地壳二维 P波速度结构 .地壳模型显示 ,在腾冲的热海热田附近上地壳存在低速异常体 ,它与火山地热活动可能有关 .测线的二维地壳结构上显示出两条地壳断裂 :龙陵—瑞丽断裂和腾冲断裂 ,其中腾冲断裂可能切穿莫霍界面 .同时 ,根据远震波形资料反演腾冲热海热田地区的 S波速度结构 ,也显示出该地区上地壳存在 S波的低速异常 .本文从深部结构方面探讨腾冲火山的成因 .腾冲火山地热区地壳具有低 P波和 S波速度、低电阻率、高热流值和低 Q值 ,以及上地幔也具有低 P波速度的特点 .由此推测地壳内岩浆来源于上地幔 ,腾冲附近地区存在的上地壳低速度异常可与岩浆的分异作用相联系 .与地球上大多数的活动火山一样 ,腾冲火山位于移动板块之间的边界附近 ,属于“板块边界”火山 相似文献
6.
利用接收函数研究哀牢山-红河断裂带地壳上地幔特征 总被引：9，自引：1，他引：9
对哀牢山-红河断裂带附近宽频带数字地震台阵的远震体波记录, 采用接收函数方法研究台站下方地壳上地幔S波速度结构, 并估算了平均地壳厚度、波速比(Vp/Vs)和泊松比. 研究结果显示, 哀牢山-红河断裂带的壳幔边界不具有简单的速度间断面特征, 表现为速度递增的梯度带, 在Moho深度处速度增大较快, 而上地幔顶部速度偏低, 并呈缓慢递增趋势, 速度结构具有壳幔过渡带特征; 地壳泊松比值偏高(0.26~0.28), 可能与下地壳中镁铁质含量增加有关; 断裂带两侧地壳平均厚度突变, 在断裂带的西南侧约36~37 km, 而东北侧约为40~42 km, 表明红河断裂是陡立的超壳断裂; 下地壳表现为S波低速, 是地壳与壳下岩石圈解耦的有利部位. 相似文献
7.
利用北京——丰镇及其邻区三分向宽角反射/折射DSS剖面(总长340.0 km)所获信息和利用数字处理技术,充分识别、提取了地壳和上地幔顶部的多种S波折射、反射震相(波组)．结合P波解释结果,计算了包括S波速度vS和泊松比在内的二维物性结构,并综合近垂直反射、地质及其它地球物理等资料,给出了该区内深部构造轮廊和相应的解释推断:该剖面的地壳厚度由东边顺义的35.0 km左右向西呈增加之势,至丰镇以东为42.0 km左右,壳内于延庆以东的下地壳和延庆至涿鹿间的中地壳以及天镇以西的上地壳内各存在一低速体;地壳中由东向西有一厚约5.0～9.0 km的壳幔过渡带;大部分地区上、中地壳的值为0.25,下地壳的值一般为0.27,上地幔顶部的值为0.28．表明了该区上、中地壳整体呈脆性,下地壳和上地幔顶部整体呈塑性的特征;延庆至涿鹿间,上地壳的低值,可能反映该处岩体裂隙(孔隙)发育且呈干燥充气状态,而中地壳的高值,则可能反映该处岩体充液(或呈部分熔融状);根据震相特点、值的横向变化特征,确定了该区数条深部断裂．地震大多发生在断裂附近,即值显著变化处,并集中于值较低一侧的脆性岩体中． 相似文献
8.
本研究使用中国数字地震台网（CDSN）（2009—2016）走时数据开展青藏高原地壳地震波速度三维层析成像研究,获得分辨率达到1°×1°×20 km的青藏高原地壳S波三维速度结构和泊松比分布.结果表明,分布在可可西里和羌塘北部的高钾质和钾质火山岩带,其上地壳到下地壳都存在S波波速扰动负异常和高泊松比.说明第三纪青藏高原隆升过程中,由于大陆碰撞使三叠纪的东昆仑缝合带重新破裂,造成大量壳幔混合熔融物质上涌和火山喷发,进而揭示了青藏高原北部新生代火山岩的存在与青藏高原的形成和隆升密切相关;青藏高原新生代裂谷位于中下地壳S波速度扰动负异常带的两侧,裂谷带之下的中下地壳泊松比减小到0.22以下.裂谷带之下中下地壳的S波速异常分布和泊松比值可以推断青藏高原新生代裂谷深达中地壳底部,这个推论与密度扰动三维成像的相关结论一致.青藏高原S波速度和泊松比在下地壳至壳幔边界随深度产生急剧变化,说明地壳内部发生了大规模的层间拆离和水平剪切;青藏高原东构造结之下泊松比高达0.29~0.33,S波速度扰动为负异常,推断东构造结下方地壳主要由坚硬的蛇纹石化橄榄岩组成;青藏高原中下地壳S波速负异常区范围大面积扩大,地壳底部几乎被S波速低值区全部覆盖.下地壳S波异常分布特点可能反映下地壳管道流的影响. 相似文献
9.
本文利用瑞利波群速度频散资料和层析成像方法,研究了中国西部及邻近区域(20°N—55°N,65°E—110°E)的岩石圈S波速度结构.结果表明这一地区存在三个以低速地壳/上地幔为特征的构造活动区域:西蒙古高原—贝加尔地区,青藏高原,印支地区.西蒙古高原岩石圈厚度约为80 km,上地幔低速层向下延伸至300 km深度,说明存在源自地幔深部的热流活动.缅甸弧后的上地幔低速层下至200 km深度,显然与印度板块向东俯冲引起俯冲板片上方的热/化学活动有关.青藏高原地壳厚达70 km,边缘地区厚度也在50 km以上并且具有很大的水平变化梯度,与高原平顶陡边的地形特征一致.中下地壳的平均S波速度明显低于正常大陆地壳,在中地壳20~40 km深度范围广泛存在速度逆转的低速层,这一低速层的展布范围与高原的范围相符.这些特征说明青藏高原中下地壳的变形是在印度板块的北向挤压下发生塑性增厚和侧向流动.地幔的速度结构呈现与地壳显著不同的特点.在高原主体和川滇西部地区上地幔顶部存在较大范围的低速,低速区范围随深度迅速减小;100 km以下滇西低速消失,150 km以下基本完全消失.青藏高原上地幔速度结构沿东西方向表现出显著的分段变化.在大约84°E以西的喀喇昆仑—帕米尔—兴都库什地区,印度板块的北向和亚洲板块的南向俯冲造成上地幔显著高速;84°E—94°E之间上地幔顶部速度较低,在大约150~220 km深度范围存在高速板片,有可能是俯冲的印度岩石圈,其前缘到达昆仑—巴颜喀拉之下;在喜马拉雅东构造结以北区域,存在显著的上地幔高速区,可能阻碍上地幔物质的东向运动.川滇西部岩石圈底界深度与扬子克拉通相似,约为180 km,但上地幔顶部速度较低.这些现象表明青藏高原岩石圈地幔的变形/运动方式可能与地壳有本质的区别. 相似文献
10.
云南的地壳S波速度与泊松比结构及其意义 总被引：11，自引：0，他引：11
利用远震三分量宽频数字记录获取了云南地区23个台站下方的体波接收函数, 以此反演得到云南地区的地壳S波速度结构与地壳泊松比的分布特征. 结果表明, 云南地区地壳厚度从北到南逐渐减小, 西北端的中甸地壳厚度可达62.0 km, 而最南端的景洪仅为30.2 km. 特别值得注意的是在楚雄地区存在一个近乎南北向走势的Moho面隆起区域, 在东川地区存在一个大概与之平行的Moho面凹陷. 另外, 云南地区地壳上地幔S波速度结构存在明显的横向不均匀性, 有的地区不但在上地壳10.0 ～ 15.0 km范围内存在低速层, 而且在下地壳30.0 ～ 40.0 km之间还存在低速层. 地壳泊松比整体偏高, 但与地壳的速度结构有较好的对应关系, 在这样一个高泊松比的背景上仍呈现出了明显的块体分布特征. 综合分析速度结构和泊松比分布, 发现在以小江断裂为东边界, 玉龙雪山断裂为西边界的"川滇菱形块体"上, 除了地震活动十分频繁外, 还具有高泊松比和复杂的壳幔速度结构特征. 这一特征与周边地区存在明显的差别, 这将为深入研究青藏高原岩石圈物质东向流动提供了地球物理学证据. 相似文献
11.
In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January. 相似文献
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13.
3He/4He ratios up to 3.5 times the ratio of atmospheric He were found in groundwater samples. The3He enrichment can be attributed to radiogenic3He produced by in-situ beta-decay of3H. This shows that tritiogenic3He is accumulating in confined waters. From tritiogenic3He and3H concentrations, ages of groundwaters can be calculated. Detection of tritiogenic3He gives a tool to trace a tritium contamination which occurred in the past and cannot be assessed only by the3H counting method. 相似文献
14.
Observations of trace gases (SO2, NH3, NO2 and O3) were made during the period 1981 to 1984 at 6 different locations representative of urban industrial, urban, nonurban, thermal power plant and marine environment. Diurnal variations of the trace gases were studied in an urban environment. Except in the urban industrial environment, the concentration of NH3 was found in the range of background values. Also, the average concentrations of NO2 and O3 at the different environments were in the order of background values. However, the concentrations of SO2 were substantially higher by about 7 times, in urban industrial and thermal power plant environments. The diurnal variations of SO2, NH3 and NO2 showed anitphase relationship with surface temperature at the urban environment station which is relatively free of industrial pollution. Discussion is centred on trace gas variations in different environments in India together with the values reported for various countries in the world. 相似文献
15.
The aim of this study is to estimate likely changes in flood indices under a future climate and to assess the uncertainty in these estimates for selected catchments in Poland. Precipitation and temperature time series from climate simulations from the EURO-CORDEX initiative for the periods 1971–2000, 2021–2050 and 2071–2100 following the RCP4.5 and RCP8.5 emission scenarios have been used to produce hydrological simulations based on the HBV hydrological model. As the climate model outputs for Poland are highly biased, post processing in the form of bias correction was first performed so that the climate time series could be applied in hydrological simulations at a catchment-scale. The results indicate that bias correction significantly improves flow simulations and estimated flood indices based on comparisons with simulations from observed climate data for the control period. The estimated changes in the mean annual flood and in flood quantiles under a future climate indicate a large spread in the estimates both within and between the catchments. An ANOVA analysis was used to assess the relative contributions of the 2 emission scenarios, the 7 climate models and the 4 bias correction methods to the total spread in the projected changes in extreme river flow indices for each catchment. The analysis indicates that the differences between climate models generally make the largest contribution to the spread in the ensemble of the three factors considered. The results for bias corrected data show small differences between the four bias correction methods considered, and, in contrast with the results for uncorrected simulations, project increases in flood indices for most catchments under a future climate. 相似文献
16.
Changes in thermal extremes of the climate of Poland in 1951–2010 are examined. Warm extremes have become more frequent, while cold extremes have become less frequent. In the warming climate of Poland, the increase in the number of extremely warm days in a year and the decrease in the number of extremely cold days in a year have been observed. Also the increase of the maximum number of consecutive hot days in a year and the decrease of the maximum number of consecutive very cold and extremely cold days in a year have been observed. However, the trends are not of ubiquitous statistic significance, as the natural variability is strong. 相似文献
17.
Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values. 相似文献
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19.
M. MONIRUL QADER MIRZA 《水文科学杂志》2013,58(5):613-631
Abstract The basin area of the Ganges River in Bangladesh is extremely dependent on a regular water supply from upstream to meet requirements for agriculture, fisheries, navigation, salinity control, and domestic and industrial sectors. In 1975, India commissioned a barrage on the Ganges River at Farakka to divert a significant portion of the dry season flow in order to make the Calcutta Port navigable. Statistical analyses of discharge and water level data have been carried out to determine if significant changes have occurred in the hydrology of the Ganges system in Bangladesh in the post-Farakka period. Siltation of the Gorai River (an offtake of the Ganges River) has also been examined using the stage-discharge relationship and regression analysis. The analyses show that the diversion has caused considerable hydrological changes in the Ganges system in Bangladesh. The water supply in the dry season has been reduced substantially, while siltation of the Gorai River has increased significantly. 相似文献
20.
Ermakova G. S. Gorelits O. V. Zhbakov K. K. Zemlyanov I. V. Milyutina I. Yu. 《Water Resources》2022,49(4):616-629
Water Resources - The results of studies of extreme floods in Crimean rivers in the summer of 2021 are presented. Analytical and historical generalization is made for the problem of the adverse... 相似文献