基于GRACE的空间约束方法监测华北平原地下水储量变化

华北平原作为我国重要的工农业基地和政治经济中心,面临着严重的水资源危机.因此,开展对华北平原地下水储量变化的监测工作具有重要现实意义与科学价值.本文基于GRACE重力卫星的空间约束方法,研究了华北平原地下水储量变化的时空分布规律,并与地面水井实测与地下水模型结果进行了综合比较和分析.结果表明：2002—2014年,华北平原地下水存在明显的长期亏损,GRACE估计的亏损速率为-7.4±0.9 km³·a^-1,而地面水井资料估计的浅层地下水亏损速率为-1.2 km³·a^-1.对比两者之间的差异可以发现,华北平原的地下水亏损以深层地下水为主.2002—2008年,GRACE估计的华北平原地下水亏损速率为-5.3±2.2 km³·a^-1,这与华北平原两个地下水模型得到的平均亏损速率-5.4 km³·a^-1十分吻合.通过华北平原区域地下水模型的独立验证,说明GRACE可以有效评估华北平原的地下水储量变化趋势.除了长期亏损的趋势项之外,华北平原地下水还存在明显的年际变化特征,并与该地区年降雨量变化特征一致.在降雨偏少的2002年、2005—2009年和2014年,华北平原地下水储量显著减少.在空间分布上,GRACE结果表明,华北平原的地下水储量减少主要发生在山前平原和中部平原区,这也与水井实测资料和区域地下水模型结果较为吻合.与GRACE和区域地下水模型相比,目前的全球水文模型仍无法准确估计华北平原地下水变化的空间分布和亏损速率.上述研究表明,GRACE提供了评估华北平原地下水储量变化的重要监测手段.

     

The temporal-spatial evolutionary features of the seismic phases in the North China block and the greater North China

This paper has made a study of the relationship between the phases of seismic activities from 1966 to 1976 in the region of the North China Block and the temporal and spatial evolution of temperature anomalies from February 1960 to January 1979 of the greater North China. The main conclusions are: (1) The temperature variation from February 1960 (rise) to January 1977 (drop) and the temperature rises of September 1975 and February 1976 are connected with the beginning and conclusion of phases of seismic activity. (2) The relation between the time-duration and the extent of temperature anomaly and that between these two parameters and the energy released by an earthquake have high credibility. (3) If the time period of 16.5 years between February 1960 and July 28, 1976, the occurrence time of the the great Tangshan earthquake, is divided into 18 time intervals according to 0.618^N, the earthquakes in this phase of seismic activity and temperature rises fall just into the same intervals. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 76–82, 1993.     

南北地震带与华北地块强震间的相关迁移

地震震源机制解和地应力实测结果表明, 我国大陆地区存在近似于辐射状的区域应力场, 其辐射中心位于青藏地块东部. 本文首先定义我国大陆应力场近似辐射中心(35°N、 100°E)为动力源点, 在此基础上计算了1900年以来我国大陆东部地区(30°N—44°N、 104°E—125°E)所发生的34次M_S≥6.0地震震中到动力源点的距离与地震发生时间的关系. 结果表明, 20世纪南北地震带中北段发生M_S≥7.0地震后, 华北地块陆续发生了一系列M_S≥6.0地震, 且有随时间从南北地震带附近大体向东迁移的规律. 据此说明, 华北地块的地震主要受控于印度板块作用下青藏地块向我国大陆东部挤压的影响, 在其作用下产生了华北地块M_S≥6.0地震的系列东向迁移活动. 总体来看有4组明显的地震迁移活动, 每组地震“序列”的迁移视速度约为80 km/a. 华北地块首发M_S≥6.0地震距南北地震带中北段最近一次M_S≥7.0地震的时间间隔约为1个月至11.8年, 且60%的M_S≥6.0地震发震地点在(39°N±1.5°)区域内. 据此推测, 2008年汶川M_S8.0和2013年芦山M_S7.0地震后, 华北地块近年存在发生M_S≥6.0地震的可能, 晋冀蒙交界和环渤海及其附近地区值得重点关注.      

华北克拉通东部地壳与地幔盖层结构——长观测距深地震测深剖面结果

利用文登—阿拉善左旗长观测距地震宽角反射/折射剖面东段资料,辩识出4组地壳震相和3组地幔盖层震相.采用二维射线追踪走时反演和正演拟合交替计算方法,得到了包括鲁东隆起和华北裂陷盆地在内的地壳和地幔盖层二维速度结构.研究结果表明:华北裂陷盆地基底深达6km以上,研究区壳内界面C1埋深约15km,C2界面深约25km,Moho面平均埋深约35km.上地壳速度6.0~6.1km·s-1,且横向变化较大;中地壳速度相对均匀约为6.2~6.4km·s-1;下地壳速度为6.5~7.0km·s-1,速度梯度较大.地壳平均速度与隆起和坳陷构造相关.研究区岩石圈底界面一般为75~80km,西端接近太行隆起构造时深至90km左右,向西呈明显加深趋势,地壳厚度呈现相同的增厚特征.地幔盖层上部速度8.0~8.2km·s-1,具明显正梯度特征.岩石圈平均速度在郯庐断裂带附近显著偏低.PmP和PLP震相存在不同程度的复杂性,意味着在本地区Moho界面和岩石圈界面有较为复杂的结构,可能具有一定厚度或过渡带性质.结合其他研究结果认为,地幔盖层和下地壳速度梯度、界面性质差异与华北克拉通破坏相关,意味着破坏是一个渐变、缓慢和不均匀的过程.郯庐断裂带附近的低速应是其为软弱带的证据.     

华南块体中部上地壳剪切波分裂特征

本文采用剪切波分裂分析方法,使用华南流动地震台阵（HN Array）和国家地震台网记录的近场波形资料,分析华南块体上地壳介质的地震各向异性特征.结果显示,华南块体快剪切波优势偏振方向整体表现为近东西向,与区域最大主压应力方向基本一致.结合华北块体地震各向异性特征,推测太平洋板块西向俯冲和菲律宾板块北西向俯冲作用,是中国大陆东部中上地壳各向异性的重要构造背景,导致中国大陆东部表现出近东西向的构造应力特征.苏鲁—大别造山和江南造山带的快剪切波偏振方向发生明显区域性变化,揭示了块体之间相互作用产生局部复杂构造特征和应力分布特点.研究显示,各向异性观测结果会因地壳结构的多样性变得复杂,通过江汉盆地的地震各向异性特征揭示出盆地内存在不同尺度的应力场.研究认为,岩石组分对中上地壳地震各向异性有重要贡献,华夏块体东部广泛存在的变质岩导致东西华夏块体各向异性偏振方向存在明显差异.

     

Active blocks and strong seismic activity in North China region

The active North China block consists of three second-order blocks: Ordos, North China Plain, and East Shandong-Huanghai Sea blocks. Two active tectonic zones, the Anyang-Heze- Linyi and Tangshan-Cixian zones, exist in the active North China Plain block and have separated the active block into 3 third-order active blocks, Taihangshan, Hebei-Shandong, and Henan-Huai blocks. The 3 third-order active blocks are characterized by their entire motion and are clearly different in their Cenozoic structures and deep structures. The active boundary tectonic zones between the third-order active blocks are less than those between the first- and second-order active blocks in their movement strength, extent, and seismic activity. The density of M ≥ 6 earthquakes in the boundary zones between active blocks is higher than that within the blocks by 9-22 times in the North China region, up to one order of magnitude on average. M ≥ 7 earthquakes occurred basically in the boundary zones between active blocks. The difference is not occasional, but reflects the nature of intraplate movement and the characteristics of strong seismic activity and is the powerful evidence for hypothesis of active blocks.     

Aseismio fault slip and block deformation in North China

In North China, the tectonic fault-block system enables us to use the Discontinuous Deformation Analysis (DDA) method to simulate the long-term cross-fault survey and other geodetic data related to aseismic tectonic deformation. By the simulation we have found that: (1) Slips on faults with different orientation are generally in agreement with the ENE-WSW tectonic stress field, but the slip pattern of faulting can vary from nearly orthogonal, to pure shear along the strike of the faults, this pattern cannot be explained by simple geometric relation between the strike of the fault and the direction of the tectonic shortening. This phenomenon has been observed at many sites of cross-fault geodetic surveys, and might be caused by the interactions between different blocks and faults. (2) According to the DDA model, if the average aseismic slip rate along major active faults is at the order of several tenths of millimeter per year as observed by the cross-fault geodetic surveys, the typical strain rate inside a block is at the order of 10^–8 year^–1 or less, so that the rate of 10^–6 year^–1, as reported by observations in smaller areas, cannot be the representative deformation rate in this region. (3) Between the slips caused by regional compression and block rotation, there is a possibility that the sense of slip caused by rigid body rotation in two adjacent blocks is opposite to the slip caused by the tectonic compression. But the magnitude of slip resulting from the tectonic compression is much larger than that due to the block rotation. Thus, in general, the slip pattern on faults as a whole agrees with the sense of tectonic compression in this region. That is to say, the slip caused by regional compression dominates the entire slip budget. (4) Based on (3), some observed slips in contradiction to ENE tectonic stress field may be caused by more localized sources, and have no tectonic significance.     

Cambrian-Ordovician sequence stratigraphy on the northern Tarim Platform and its correlation with Yangtze Platform and North China Platform

The Cambrian and Ordovician on the northern Tarim Platform are mainly composed of carbonates. On the basis of detailed outcrop analysis, the sequence stratigraphic system of the Cambrian-Ordovician in the northern Tarim Platform is outlined in this paper. Altogether 35 third-order sequences, 12 supersequences, 4 supersequence sets and 2 megasequences are recognized. The characteristics of the major sequence boundaries have been documented with an integrated examination of outcrop, seismic and borehole data, and the ages of these sequence boundaries have been calibrated through the combination of sequence stratigraphy with biostratigraphy. It is discovered that there is good correlation of the sequence stratigraphy of the Cambrian-Ordovician among Tarim, Yangtze and North China platforms. This may illustrate that the development of the Cambrian-Ordovician carbonate sequences in these three platforms is mainly controlled by regional or global sea level changes. This forms the theoretical basis for the construction of high-resolution chronostratigraphic system of the Cambrian-Ordovician in the three platforms in China.     

东北地区至华北北缘地壳结构的区域差异: 地壳厚度与波速比的联合约束

本文通过对分布相对均匀的127个固定台站下方接收函数的H-κ叠加分析,并结合前人对97个线性密集流动台站的研究结果,获得了东北地区和华北克拉通北缘地壳厚度(H)与平均波速比(κ).结果表明研究区域地壳总体较薄,波速比变化复杂,地壳密度横向变化大,暗示着地壳在中—新生代经历了显著的不均匀破坏与改造.东北和华北北缘都存在明显的东西向差异.东北地区西侧兴蒙造山带地壳大致随着海拔增高逐渐增厚,H和κ分别主要在31~39 km和1.71~1.83之间变化,平均值分别为~35 km和~1.77;东侧吉黑褶皱带地壳厚度与海拔不成镜像关系,H和κ集中在28~37 km和1.72~1.89范围, 平均值分别为~33 km和~1.79.华北北缘西侧燕山带地壳由东往西逐渐增厚,H和κ主要在28~40 km和1.70~1.91范围内变化, 平均值分别为~34 km和~1.79.东侧辽东台隆地壳表现为中间厚四周薄,H和κ集中在29~35 km和1.71~1.83范围, 平均值分别为~32 km和~1.77.东北地区吉黑褶皱带相对薄的H和变化范围大的κ表明,该区域可能由于其自身的地壳结构复杂性和紧邻太平洋板块前缘从而在中新生代遭受到了与太平洋板块俯冲相关的更为强烈的地壳减薄与改造.华北北缘燕山带H和κ复杂的变化特征表明,该地区可能受到中亚造山带增生和太平洋板块俯冲的共同影响,从而发生了更为复杂的地壳改造变形.     

华北地区中强以上地震与前兆震群的相关分析

应用“八五”攻关推广的有关震群参数计算的软件 ,对华北地区 (33°～ 43°N,1 1 4°～ 1 2 4°E)自 1 970年以来所发生的 40次震群事件的各项参数 (b,U,H,K,F,ρ等值 )进行了计算 ,旨在依据前兆震群的判定指标 ,寻找前兆震群与中强以上地震 (MS≥ 434)的对应关系。结果表明 ,无论是单项指标或综合指标的报准率均在 65%左右 ,仅有个别达到 75%以上 ,并且有约30 %具有前兆意义的震群属于漏报和虚报。所以 ,如何判定前兆震群和充分利用前兆震群预报地震和监视未来地震活动有待更深入的研究和探讨。