中国三峡水库蓄水期间随时间变化的重力信号

从2003年开始，中国三峡水库将进入蓄水期。到2009年，从长江中段起大约600km长的广阔区域内注水，三峡水库将蓄水40km^3。蓄水过程代表着地球物理学的“控制实验”为详细研究经典的正向／反向模拟地表荷载问题提供了独一无二的机会。尽管Wang(2000)研究了局部尺度的大荷载效应，但我们的目标是从数百千米向上游更长的空间尺度，重点在通过新近发射的GRACE卫星可检测到的随时间变化的重力信号。该卫星寿命期为5年(至2007年)，将跨越主要蓄水期。我们采用PREM弹性地球模型用格林函数法所得结果表明，大地水准面高度的年增加值在直到20阶球谐函数的尺度上都高于GRACE卫星的观测灵敏度，而5年周期的累积增加值则在直到50阶球谐函数的尺度上(相当于波长800km)都高于观测灵敏度。     

白鹤滩水电站蓄水引起重力与库仑应力变化的模拟研究

白鹤滩水电站为中国第二大在建水电站,蓄水过程引起的重力和库仑应力变化对于该地区的水储量变化和触发地震研究具有重要参考价值.首先,本文给出了水电站库区临近区域均衡重力异常场,结果表明该地区基本处于均衡状态,较为稳定.其次,利用白鹤滩水电站库区地形数据,模拟计算了蓄水过程引起的地表和GRACE-FO (Gravity Recovery and Climate Experiment Follow-on)卫星观测的重力变化,并与GRACE-FO实际观测数据进行了对比分析.模拟计算的重力变化表明,蓄水引起的重力变化为毫伽量级,万有引力作用为库区重力变化的主因,该重力变化比弹性形变的结果大两个量级.模拟GRACE-FO重力变化表明,白鹤滩地区蓄水引起的卫星观测重力变化为微伽量级,GRACE-FO有可能观测到白鹤滩水电站蓄水的重力变化.最后,计算了蓄水引起的地壳内部应力变化,并给出了小江断裂带北段断层的库仑应力变化,该结果表明库仑应力变化在巧家以南和以北的两个区域大于0.01 MPa,该地区触发地震的可能性需密切关注.

     

河北省沧州地区重力变化的初步分析

重力复测资料表明,沧州地区出现趋势性变化,最大变幅达92×10~(-8)m/S~2。本文的分析结果认为,这种变化部分与沧州地区地面沉降有关,部分与地壳深部的变异因素有关,不排除该地区发生中强地震的可能性。     

北京白家疃台站重力非潮汐量变化及水储量影响的初步研究

The non-tidal variation gained from continuous gravity observations in stations usually reflects the regional continuous gravity changes. In this paper we focus on studying the non-tidal variation of Baijiatuan station, Beijing where there are two different gravimeters （namely, L＆R-804 and PET-031）. Based on the original raw tidal records of two gravimeters from 2008 to 2011, we first remove various interference from raw data by the standard procedure software-Tsoft; then we model the solid earth tides, ocean tidal loading and pole tide through related parameters; after that we adopt a new segmented polynomial fitting method based on Tsoft to fit the complex drift of spring gravimeter; and finally we calculate the atmospheric loading effects by a linear regression model. After a series of processing we gain the non-tidal variation of the two gravimeters at Baijiatuan site, Beijing. Furthermore, to analyze the non-tidal variation preliminarily, we study the main component of related tidal data by power spectral density. Comparing the non-tidal variation of two different gravimeters, we find seasonal fluctuations in non-tidal results, which are in accordance with the water storage change. Therefore, we take into account the relevance of gravity changes and water storage based on the gravity data of GRACE and water data of the CMAP model from 2003 to 2011 at different sites in the Chinese mainland （Beijing, Chengdu, Shenyang and Shiquanhe） , and make a preliminary analysis on the relationship between gravity changes and water storage.     

首次观测到的由地震引起的绝对重力变化

首次用绝对重力测量观测到明确的同震重力变化。恰好在1次M6．1地震的前1天和震后7天进行了绝对重力测量。观测到的绝对重力变化为－6μGal,显著地大于约1μGal的观测误差。特别有意义的是，所观测到的空间重力变化与仅用位移数据建立起来的弹性位错模型预测的结果非常一致。该结果强烈地激励我们对重力和位移同时进行反演，以更好地了解地震。     

孕震过程中重力位、重力、重力梯度变化的数值模拟研究

简要介绍了为探索和解释地震前后重力变化的各种孕震模式,推导了由孕震引起的密度变化和位移与地面重力位、重力、重力梯度之间的变化关系。摸拟计算了孕震位移和密度变化引起的重力位、重力、重力梯度变化的空间分布并分析了重力位、重力、重力梯度变化的空间分布特征。与此同时,采用广义司托克斯云积分和有限差分方法对云南丽江7. 0级地震前重力位、重力、重力水平梯度进行了计算。结果表明,强震前重力位、重力、重力梯度有其自身的变化特征,这对预测强震有实际意义。     

首都圈地区重力变化及其映震能力

对首都圈流动重力观测成果进行非潮汐信息的提取，得到了首都圈地区１９８４—１９９３年期间的重力动态变化图像，认为重力变化与区域构造活动有一定的相关性。以大于２倍均方差作为异常判断标准，统计了北京小网的段差重力异常与地震的对应关系。结果表明：对于测网内发生的４级左右的地震，有异常出现的段差数占总数的１６．９％，对于距测网１００ｋｍ以内发生的５级以上的地震有异常出现的段差数占总数的３７．５％。西北部测环的段差异常出现率比南部和东北部高。     

京都大学重力基准点(京都C)的绝对重力变化

京都大学大学院理学研究科地球物理学教室重力基准点 (京都C)自被确认为国际重力基准网 1 971 (简称IGSN 71 )的重力基准点以来 ,已进行过许多次重力测量 ,尤其是作为相对重力测量的基准点而发挥了巨大的作用。不仅如此 ,京都C还被列为国际绝对重力基准网的B重力点而成为监测地形变地区重力变化的重要基准点。近年 ,由于简便的移动式绝对重力仪的普及 ,日本国内的一些单位可以到各地开展重力测量。例如 ,国土地理院和国立天文台水泽站就到京都C进行过绝对重力测量。京都大学大学院理学研究科 1 999年 3月购入了高分辨率绝对重力仪FG 5,…     

三峡工程蓄水对洞庭湖水情的影响格局及其作用机制

三峡工程建成投入运行后,汛末蓄水将使坝下河湖水情发生变化,长江中下游秋季来水减少成为常态.为客观分析三峡蓄水对洞庭湖水情的影响分量、空间格局及其作用机制,选取三峡工程典型的蓄水过程,运用长江中游江湖耦合水动力学模型计算了因上游来水变化引起的洞庭湖水情时空变化.结果表明:1)三峡汛末蓄水对洞庭湖水位影响具有明显的"北高南低,东强西弱"的格局,即东洞庭湖最为显著、南洞庭湖东部和西洞庭湖北部次之,南洞庭湖西部和西洞庭湖南部最小.2)洲滩湿地受蓄水影响最明显的主要为东洞庭湖、南洞庭湖和湖泊洪道两侧的条带状洲滩.3)三峡蓄水对洞庭湖水位的影响机制有二:长江干流水位快速消落加速湖泊水体下泄以及削减长江三口分流补给湖泊的水量.     

长江三峡地区三维重力反演研究

本文根据最新获得的长江三峡工程坝区及外围1/50万完全布格重力异常图和人工地震测深结果,利用Parker-Oldenburg快速位场反演方法研究了该区地壳深部结构.在计算过程中,通过采用模型分解、正则化及自下而上逐层反演等方法,首次获得了该区上、中、下地壳分界面的展布图象,并围绕着该区地壳深部构造的几个共同关心的问题讨论了它们的地质构造意义.     

STABILITY ANALYSIS OF COFFERDAM SLUMP AND ITS APPLICATION IN THE CLOSURE OPERATION OF THREE GORGES PROJECT

I.INTRODUCTIONTheclosureoperationofThreeGorgesprojectisfamousintheworldforitslargedischarge,deepwater,lowvelocityinclosuregaps,largequantitiesandhighintensityforfillingmaterials.Thus,thedikeconstT'Uctionintheclosureoperationprocessisverydifficult.Sothedesign,researchandconstrUctiongroupshavepaidmuchenergyinthedesignprinciplesandoptimalitymeasuresofthegrandriverclosureoperation.FromtheexperimentsofhydraulicsanddikeslumpinthesecondperiodofclosureoperationattheResearchinstitUteofYangtZeR…     

长江三峡地区三维重力反演研究

本文根据最新获得的长江三峡工程坝区及外围1/50万完全布格重力异常图和人工地震测深结果,利用Parker-Oldenburg快速位场反演方法研究了该区地壳深部结构.在计算过程中,通过采用模型分解、正则化及自下而上逐层反演等方法,首次获得了该区上、中、下地壳分界面的展布图象,并围绕着该区地壳深部构造的几个共同关心的问题讨论了它们的地质构造意义.     

SEDIMENT RESEARCH FOR THE THREE GORGES PROJECT ON THE YANGTZE RIVER SINCE 1993

This article addresses sediment research carried out for the Three Gorges Project since 1993, when the construction of the project was formally started. Emphasis of the research has been placed on the solution of relevant problems arising from design and construction of various structures, including sedimentation problems in the Chongqing reach; layout of the upper lock approach channel and ways and means to mitigate its deposition; increasing reservoir capacity by optimizing reservoir operation; compensating depth of flow required by navigation below the Gezhouba Project caused by scouring; mitigation of adverse effects of erosion on the reach from Zhicheng to Jiangkou; and evaluating scour of the Jinjiang reach caused by releasing flows of low concentrations from the TGP. In addition, reduction of the sediment load entering into the reservoir area of the TGP in the recent years as well as that expected of the projected construction of large hydropower stations on the Jinsha River upstream of the TGP reservoir is also noted and discussed.     

PREDICTION OF IMPACT OF THE THREE GORGES PROJECT ON ESTUARY BEACH OF THE YANGTZE RIVER

ＰＲＥＤＩＣＴＩＯＮＯＦＩＭＰＡＣＴＯＦＴＨＥＴＨＲＥＥＧＯＲＧＥＳＰＲＯＪＥＣＴＯＮＥＳＴＵＡＲＹＢＥＡＣＨＯＦＴＨＥＹＡＮＧＴＺＥＲＩＶＥＲＷｅｉｂｉｎｇＦＥＮＧ１ＹｉｇａｎｇＷＡＮＧ２ａｎｄＸｉｕｃｈｅｎｇＺＨＯＮＧ３ＡＢＳＴＲＡＣＴＡｌｔｈｏ...     

MODELING OF THE DIVERSION CHANNEL CLOSURE FOR THE THIRD STAGE OF THE THREE GORGES PROJECT

The closure of third stage diversion channel for the Three Gorges Dam is characterized by large closure discharge, large drop in water surface, and high gap velocity. 1D and 2D flow mathematical models were used in this paper to simulate the hydraulic conditions during the closure. The variation of discharge in the diversion channel and the drops in water surface shared by the upstream and downstream cofferdams were computed using the ID model, and the detailed hydraulic patterns in the diversion channel were simulated using the 2D model. The computed results indicate that the designed closure scheme for discharge of 9,010 m^3/s was feasible for construction, while the designed closure scheme for discharge of 12,200 m^3/s was inapplicable.     

FLUVIAL PROCESSES IN THE LOWER JINGJIANG RIVER：IMPACT OF THE THREE GORGES RESERVOIR IMPOUNDMENT

Sediment supply to the lower Jingjiang River will be subject to substantial reduction after the impoundment of the Three Gorges Reservoir, which could result in an excess of carrying capacity and serious bank erosions in the downstream alluvial channel, threatening the bank protection works and the safety of the Jingjiang Dyke. This paper presents a summary of research works concerning the fluvial processes in the lower Jingjiang River and the possible impact of the Three Gorges Reservoir impoundment on the variation of its channel pattern. Three different predictions have been put forward by researchers: 1) the Jingjiang River will evolve towards a more sinuous, meandering channel pattern, with extensive bank erosion taking place along the river; 2) the river channel will be straightened and broadened because no point bar can be formed due to reduced sediment supply while bank erosion develops in the concave bank, and 3) this river reach will maintain its present channel pattern without significant change, although the sinuosity may be slightly reduced, since: a) the Three Gorges Reservoir mainly intercept sediment particles with sizes larger than 0.025mm, and b) the complex interaction between the Yangtze River and the Dongting Lake helps to reduce the negative effect of channel erosion through certain self-adjusting mechanism in fluvial processes. Discrepancy between these predictions shows that further research efforts are needed to understand the impact of Three Gorges Reservoir operation on the downstream fluvial processes. Meanwhile, there is an urgent need to closely monitor future development in the fluvial processes of the Jingjiang River and its influence on the safety of the Jingjiang Dykes.     

三峡水库首区重力固体潮观测资料分析

介绍了中国科学院测量与地球物理研究所的LCR-ET20重力仪和中国地震局地震研究所的DZW-9重力仪在三峡水库首区的重力固体潮比对观测.获得了该地区高精度的重力固体潮潮汐参数,估算了DZW-9重力仪的格值,其值为（-756.06plusmn;0.05）times;10-8（mbull;s-2）/v. 分析了相应仪器的重力观测残差, 数值结果表明DZW-9重力仪的长期漂移具有线性特征, 观测精度与LCR-ET20重力仪在同一量级. 本文提供的相关结果可为该地区地表和空间大地测量观测提供有效的重力潮汐改正模型.      

APPARENT STRESS VARIATION CHARACTERISTICS BEFORE AND AFTER BADONG EARTHQUAKE IN THE THREE GORGES RESERVOIR AREA

The causes of earthquakes in the Three Gorges reservoir area are complex. In order to study the cause of earthquakes happening in the region, we calculated the source parameters of 394 M_L ≥ 2.0 earthquakes occurring in Three Gorges reservoir area based on waveform data observed by the regional seismic network of Hubei Province and Three Gorges, obtained the apparent stress spatial-temporal variation map of Three Gorges reservoir area, and analyzed apparent stress spatial-temporal variation characteristics before and after the main earthquakes in the Three Gorges reservoir area. The results show that:1)Before the Badong M_L5.5, Zigui M_L4.7 and Zigui M_L5.1 earthquake, high apparent stress of earthquakes with different magnitudes is concentrated in Xinhua-Shuitianba Fault and Gaoqiao Fault. The distribution of high value area shows the high degree of synergism before the earthquake and the scattering after the earthquake, which indicates that the area accumulated a high stress before the earthquake, and the fault was in a locked state; 2)In the study area, the apparent stress before and after the earthquake showed significant rise in the first and then decline, the earthquake occurred in the process of rising; 3)Apparent stress depth profiles show that apparent stress at different depths has a positive correlation with the size of magnitude of earthquake, and the phenomenon of "small magnitude and strong apparent stress" did not appear. The small earthquakes occurring after the major earthquakes in the study area belong to low strain release under the background of low stress release, and there are no new apparent stress anomaly concentration areas appearing, this indicates that the Badong-Gaoqiao Fault, Zhoujiashan-Niukou Fault and Zigui Xiannushan Fault have been effective in releasing after the Badong earthquake and Zigui earthquakes and the probability of destructive earthquake is small on these faults.     

Gravity change and its mechanism after the first water impoundment in Three Gorges Project

Introduction During and before the construction of the Three Gorges Project, the annual observation was continuously undertaken by the Three Gorges gravity observation network established around the head area of the reservoir (the section between Sandouping and Badong). This network has pro-vided substantial high precise data related to seismic activity. However, the annual gravity survey together monitoring of the existed observation stations can hardly effective monitor some potential sei…