尔多斯盆地盐池地区延安组孢粉组合的发现及其古气候意义

为恢复鄂尔多斯盆地盐池地区早—中侏罗世古气候,重建古环境,对宁东2井进行孢粉分析和黏土矿物测试,建立孢粉组合、孢粉谱。延安组下部为Inaperturopollenites- Psophosphaera- Protopinus组合,地质年代为早侏罗世托阿尔期晚期;延安组上部为Cyathidites- Deltoidospora- Cycadopites组合,地质年代为中侏罗世早期,下/中侏罗统界线位于钻孔2144. 5~2153. 0 m之间。据孢粉谱建立的古气候和古植被得出,早侏罗世托阿尔期晚期为暖温带半湿润型气候,植被类型为针叶林,中侏罗世早期总体为亚热带湿润型,植被面貌有早期的针阔叶混交林- 草丛型向晚期的针叶林- 稀草型转变。两组合总体上反映的早侏罗世托阿尔期晚期至中侏罗世早期湿度由半湿润向湿润转变,温度由低向高转变,孢粉谱所指示的气候变化趋势与黏土矿物指标所反映的气候变化趋势一致。气候的转变对该地区聚煤作用有着明显的促进作用。     

三角洲沉积模式存在的问题与讨论

三角洲是一类非常重要的沉积相,是油气聚集的有利场所。准确可靠的三角洲沉积模式,对指导油气的勘探和开发有重要意义。关于教科书中经典的三角洲沉积模式和一些相关概念,很少有人质疑过。但研究发现,该模式及一些相关概念存在许多问题,诸如对于三角洲平原、三角洲前缘和前三角洲等亚相的定义含糊不清,各亚相之间缺乏明确的、具可操作性的界限。由于海(湖)平面是波动的,模式中未明确三角洲平原与三角洲前缘究竟以哪种海(湖)平面为界。三角洲平原与正常河流冲积平原的边界、三角洲前缘与前三角洲的边界、前三角洲与正常海(湖)的边界均未明确,也没有系统总结它们各自的识别、区分标志,致使不同的研究者根据自己的理解对古代同一地层可能得出不同的结论。三角洲有多种类型,且不同类型的三角洲沉积特征不同,应有各自的沉积模式,但许多研究者将曲流河三角洲沉积模式用于所有三角洲亚相、微相划分。经典沉积模式中,三角洲前缘发育水下分支河道和水下天然堤,但笔者等研究表明这2个微相不存在。而三角洲平原上普遍发育的砂体——汊口滩与并口滩,在经典三角洲沉积模式中未提及。作者针对三角洲沉积模式存在的各种问题,进行了深入讨论,并结合现代沉积,系统总结了能用于古代沉积不同亚相和微相的识别、区分标志。     

Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°, the slip angle is -156.08°, the fault length is about 80 km, the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault, southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result.     

黄骅坳陷歧北斜坡区薄层湖相碳酸盐岩沉积相模式及演化特征

歧北斜坡区沙一下亚段湖相碳酸盐岩储层较薄（多数集中在0.5~8 m）,地震资料难以指导内部小层及滩体划分,沉积相模式、演化规律及主控因素认识不清,采用标志层控制、静-动态资料相互拟合的方法,利用岩心、测井、地球化学、古生物等资料,结合示踪剂、吸水剖面等动态资料对薄层湖相碳酸盐岩储层进行综合研究。研究结果表明：超覆地层对比模式符合研究区薄层湖相碳酸盐岩地层真实发育情况,并识别出5期明显的湖岸线;湖水首先沿着港西断层形成的断槽及中部的斜坡低洼区由东向西主发生湖侵;研究区主要发育滨浅湖亚相,包括生屑滩、混积滩等6种沉积微相,生屑滩面积占60%以上;沉积模式显示出沉积早期,地形坡度大、湖侵范围小、滨浅湖面积也最小,主要沉积沿岸碎屑岩砂坝;沉积中后期,水体越过坡折带,滨浅湖面积不断扩大,并迅速超覆至全区,生屑滩沉积面积达到最大的演化规律。歧北斜坡区湖水咸化、湖相碳酸盐岩广泛沉积的主要原因,是海侵作用致使湖水初步咸化和浅水缓坡台地环境导致混合水蒸发浓缩二次咸化双重作用的结果。强烈的剥蚀和填平补齐导致的近似平台型古地貌特征和古生物的大量繁殖,也是控制北斜坡区沉积相类型及演化的主要因素之一。     

缅甸弧地区地震的空间分布和震源机制特征

缅甸弧作为印度板块的东边界,印度板块在此俯冲到缅甸板块之下.缅甸弧代表了主喜马拉雅碰撞带与安达曼弧的转换地带,是特提斯构造体系正向碰撞和侧向走滑的转换部位.同时缅甸弧地震带是喜马拉雅地震带上地震最活跃的地区之一,也是中源地震集巾的地区之一.中国川滇及西藏东部的地震活动可能与缅甸北部的地震带有密切的联系,这里显然受到了印度板块和欧亚板块相互作用的影响.     

Temporal and spatial variation characteristics of present stress field in the northern area of North China

From focal mechanism solutions of the earthquakes in the northern part of North China during the period of 2002～2006,the directions of principal stress axes in 4 stress sub-districts are analyzed using a grid test method.The characteristic of present crustal stress directions is discussed.Based on this result and on the focal mechanism solutions calculated for some events in the period of 1977～1998,in combination with some other study results,the temporal variation of present crustal stress directions in the northern part of North China is investigated.The re-sults confirm that the direction of crustal principal stress in some regions had somewhat rotated after the 1976 Tangshan M7.8 earthquake.The mean P axes of the focal mechanism solutions rotated clockwise not only in Tangshan sub-district,but also in Beijing and Xingtai sub-districts after the Tangshan earthquake.In Beijing and Xingtai sub-districts the orientations of principal stress axes in the period of 2002～2006 are consistent with that before the Tangshan earthquake,implying that the stress orientations has rotated back to the state before the Tang-shan earthquake in these two sub-districts.The directions of the mean P axes are nearly E-W in Tangshan sub-dis-trict since the M7.8 earthquake.The present stress field in the sub-district northwest to Beijing,or in the western part of the Zhangjiakou-Bohai fault zone,is relatively stable during the time period concerned in this study.Because of the limitation of data,this paper only states a possible variation of stress field in the northern part of North China in the recent decades.     

Discussion on the Relationship between Different Earthquake Magnitude Scales and the Effect of Seismic Station Sites on Magnitude Estimation

Based on the earthquake catalog reported by the Chinese digital seismic network in recent years, we select the earthquakes with both surface wave magnitude and local magnitude and fit them into a relationship between the two magnitudes. The systematic difference is found from the formula which has been used for 30 years. Because of a large dynamic range and wide frequency range of the current digital observation system, in addition to a larger number of stations and earthquakes being used compared to before, the relation obtained in this paper seems more reliable. Our calculation shows that there is no significant difference before and after magnitude conversion so we suggest the abandonment of magnitude conversion. The site response of a station consists of amplification at different frequencies. The amplification is equal to about 1 and changes little with frequency at stations located on basement rock, and it is greater than 1 at low frequency ranges and less than 1 at high frequency ranges at stations located on sediment layers. The difference between magnitudes from single station located on sediment layer and the average magnitude from the whole network increases from negative to positive with period. It seems that there is no fixed station correction factor and the station correction method does not work to improve the accuracy and magnitude estimates.     

张北强余震前震源机制解的一致性特征

取层状介质中一点源位错模型,由计算综合地震图得到-↑P、-↑S各自最大振幅,通过其最大振幅比值与观测资料拟合的方式来确定震源机制。我们系统地查阅了北京台网、河北台网的数字化记录并补充内蒙古的兴和临时台、集宁台和宝昌台1998年～1999年3月的记录,读取垂直向的-↑P、-↑S最大振幅数据,经反演计算得到145个小地震的震源机制解。这些解的优势取向和华北构造应力场的方向相同。定义各个震源机制解的P、N、T轴和构造应力场的3个应力主轴在三维空间的夹角之和为一致性参数,发现在1999年发生的强余震前一致性参数出现异常变化,我们认为这是具有预测意义的现象。     

水下惯性导航系统姿态算法的适用性分析

针对水下潜器搭载的惯性导航系统圆锥运动这一复杂特性,研究经典多子样算法、优化多子样算法、扩展圆锥误差补偿算法和基于四元数微分方程迭代算法的姿态求解精度与适用性情况,并以圆锥运动作为测试输入进行仿真实验.结果表明,采用子样数大于3的迭代算法进行水下重力辅助惯性导航姿态解算,能够满足角度漂移小于1″/h的精度要求.     

基于局部重力场建模的Tikhonov正则化点质量核径向基函数方法

针对点质量核径向基函数应用于局部重力场建模中的设计矩阵严重病态问题,本文引入Tikhonov正则化方法对传统点质量核径向基函数方程进行改造,建立了相应的正则化模型。通过模拟数据进行仿真实验,以传统格网化方法作为对比试验,利用"标靶法"确定两种模型的最优结构。实验结果表明:正则化点质量核径向基函数可以直接利用离散数据进行局部重力场建模。在两种模型的最优结构下,当实测数据无污染时,正则化方法达到与传统格网化方法相当的精度;当实测值中加入3 mGal的高斯白噪声时,正则化方法的精度获得了27.9%的提升。这说明本文方法可以应用于局部重力场建模中,且模型结构更优,抗干扰能力更强。