东喜马拉雅构造结地区地震活动及其构造意义

东喜马拉雅构造结位于印度大陆与欧亚大陆碰撞前沿部位,其地下结构复杂,地震多发,是探索地震活动性与活动构造关系的理想场所。本研究首先对研究区构造背景、断层分布、历史大地震、近50年来的中小地震活动性及其震源机制解进行简单回顾。基于在研究区域布置的23个宽频带流动地震台的观测波形,对观测期间发生的9次较大地震进行精确定位,并对这些地震反映的构造意义进行了讨论。由于板块边界发生近90°突然偏转,导致现今的地下形变比较复杂,剪切作用伴随碰撞带挤压作用同时发生。     

燕山地区北西向和北西西向断裂构造基本特征初步探讨

本文根据近年来多次野外考察所积累的实际材料,总结了燕山地区北西向断裂构造基本特征。文章结合地质构造、地震和地球物理资料的分析,论证了基底北西西向断裂构造带的空间展布、形成发展、活动方式及其与地震活动的关系。提出北西西向断裂构造带属于地壳断裂范畴,既控制了断块构造的发育,又控制了现代地震活动。北西向断裂构造密集成带和雁列式展布是北西西向断裂构造带在沉积盖层的一种表现。同时认为,北西西向断裂构造带的活动方式是与断块构造相对运动密切关联。中、新生代以来,其活动方式除了表现差异运动外,还具有剪切活动的性质,并约在晚白垩世—早第三纪剪切活动方式有明显地转变     

内部张剪切断层与强震发生的构造部位

几个发生在较大规模拉分区附近的强震或特大地震震中区的构造分析表明:拉分区内部张剪切断层与新活动幅度大的次级走滑断层的交汇部位是强震或特大地震的发生场所。据库仑破裂准则及实验结果,对内部张剪切断层的力学成因机制进行了分析,认为内部张剪切断层是次级走滑断层所夹持的块体在简单剪切作用下,块体内部发育的里氏破裂。并从统计、地质方面的研究结果提出了内部张剪切断层的形成条件。     

唐山地震序列的构造过程

本文采用地质构造、地震活动图象、震源机制资料综合分析方法,对唐山地震序列主要的构造过程进行研究。其结果表明,唐山地震序列是一个由多条断裂参加并逐次活动的复杂构造过程。先后显示活动的断裂及其错动性质是:唐山断裂带右旋剪切、蓟运河断裂左旋剪切、滦县—乐亭断裂右旋剪切、卢龙断裂右旋剪切。北西向蓟运河断裂与唐山断裂带构成一对共轭剪切构造。沿唐山断裂带的主震破裂面由初始阶段的北北东向北东—北东东和南西方向扩展,形成不对称的“S”形曲面。与现代地壳应力场最大剪切应力方向不完全一致的先存断裂的活动和地震破裂面转向扩展,是序列震源机制解P、T轴取向离散的主要原因之一。     

北京及周围地区的垂直形变及其速度梯度与地震活动

分析了北京及周围地区１９６６～１９９１年的垂直形变速度和形变速度梯度特征。表明长趋势地形变与第四纪构造地貌形态基本相符，反映出现代趋势性构造活动与第四纪以来地壳的主导运动性质是一致的。指出该区的高梯度带是地块在引张作用下，沿活动断裂带发生剪切或剪切—正断而产生的，是强震活动的场所     

沂沭断裂带中段基底韧性剪切带

在沂沭断裂带中段的泰山群结晶基底中,存在着一系列北东、北北东走向的左行韧性剪切带。对其中发育糜棱岩的韧性剪切带的结构构造、应变测量、变形岩石的显微构造、显微组构以及长石粒度和含量的变化规律进行了观测分析。讨论了韧性剪切带的变形条件和机制。及其递进发展的趋势。指出基底韧性剪切带是沂沭断裂带元古宙时期断裂活动时在地壳较深层次上形成的构造表象。在此基础上,讨论了地壳不同层次上的断裂变形及断裂岩石的综合分类问题     

一种确定断层运动方式和主应力方向的方法

断层的运动方式和主应力方向的判断是构造分析的一个重要方面。本文提出一种判断断层运动和主应力方向的新的简单方法。 断层呈雁列式是剪切带的构造组合特点。在这些雁列断层的连接区发育了各种次级构造。因此可以通过这些次级构造和雁列类型的关系,来判断断层的运动和主应力方向。     

渤海海域主要新构造活动断裂带

渤海位于渤海湾盆地的东部,是我国华北地区新构造活动最强烈的地区之一,盆地内的沉积盖层(N-Q)中断裂极为发育。许多研究者从不同角度对渤海新构造进行过研究,但认识不一。笔者基于以往的工作,对该区新构造作了较深入的分析,确定渤海新构造运动起始于中新世晚期(12~10Ma BP)。从三维空间分析盖层断裂,并按其与盆地基底断裂的成因关系,将新构造活动的断裂分为继续活动断裂和新生断裂,并划分出3条主要的新构造活动断裂带:北东(偏北)向营口-潍坊断裂带北段是继续活动构造带,右旋逆平移活动,活动性弱;北西西向北京-蓬莱断裂带亦为继续活动构造带,左旋正平移活动,活动性较强;北东向庙西北-黄河口断裂带为新生构造带,右旋平移活动,活动性强。后两者组成一对以庙西北-黄河口断裂带为主的偏共轭活动构造带,该区域地震活动与之关系密切。最后探讨了渤海地区新构造期北东东-南西西至近东西向水平挤压的构造应力场及其与新构造活动断裂带发育的关系。提出新构造应力场与古近纪盆地裂陷阶段的应力场截然不同,新构造为地壳共轭剪切破裂系统,古近纪盆地构造是发育于地壳上部的伸展构造系统,这是两期不同体制的构造系统。     

中国松辽盆地构造环境及东北地区地震活动特征分析

对中国松辽盆地的构造环境、演化历史和成因机制进行了分析,认为松辽盆地主要是在中国东北前中生代这一特殊的大地构造背景下由简单剪切作用形成的,根据中浅层构造和地层特点,可将松辽盆地划分为6个一级构造单元和31个二级构造单元.     

1．由振幅反演小震机制

本文提出一种用地震波振幅反演矿震机制的方法和一个简单的剪切内向压爆机制模型。用最小二乘方法对理论的和观测的辐射图像进行比较，并且对描述剪切－滑动的参数以及内向压爆和剪切位错比作了最优化处理。即使在台站数量少的情况下，把这个方法应用于捷克斯洛伐克的两个矿区的微弱矿震。也证明是有效的。结果发现微弱矿震的机制以剪切为主，并且其节面与局部构造有明显的相关性。     

Influence of shear angle on hangingwall deformation during tectonic inversion

Tectonic inversion is a common phenomenon in island arc settings, especially in back‐arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault‐related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep‐sided half‐graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn‐extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5° during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.     

震源应力场与构造应力场

每个地震按照双力偶模型所得到的震源应力场,有的反映构造应力场,有的反映转换应力场。凡是在已存在的活动断裂上由粘滑发震的震源机制解而得出的P、B和T轴与构造应力场的最大、中等、最小的压力主轴是对应的,只是略有偏离。分析了岩块相对滑动产生的转换应力场,证明由转换应力场所产生的脆性剪切破裂而发震的震源机制解得出的P、B、T轴则与构造应力场三个主轴方向可以完全不符。通过对具体震例分析表明,当考虑了转换应力场之后可对几个地震区的应力场得到统一的解释。因此,在一个地区根据震源机制解来恢复构造应力场时必须先判明:是构造应力的直接作用下的粘滑或剪切破裂,还是转换应力场所形成的、共轭剪切破裂,前者可直接恢复构造应力场,后者则应经过转换寸能恢复构造应力场。     

1990年青海共和7.0级地震的地震构造和构造力学

本文根据地球物理，地震学资料及区域构造应力场的分布，研究了１９９０年４月２６日发生了７．０级地震的共和盆地邻近地区的隐伏构造，本文提出，在微观上该地震由沿震源区存在的东西向断裂的左旋剪切运动所引起；在宏观上则由区域性东西几构造的端部破裂所产生，同时，研究结果也表明深部发震构造并不与地表构造特征一致。     

强震孕育与发生的实验研究

应用激光全息光弹性实验研究将我国７个强震的孕育构造划分为枢纽型、交汇型和阶区型３类，并定量分析了它们在现代构造应力场作用下的形变场及主应力、剪应力的分布特征。研究结果提出了这３种孕震构造的动力学过程、地震重复发生的力学机制以及影响地震震级的构造因素     

The structural characteristics,age of origin,and tectonic attribute of the Erguna Fault,NE China

The Erguna Fault runs along the east bank of the Erguna River in NE China and is a large-scale ductile shear zone comprising granitic mylonites. This paper reports on the geometry, kinematic indicators, and 40Ar/39 Ar biotite ages of the granitic mylonites, to constrain the structural characteristics, forming age, and tectonic attribute of the Erguna ductile shear zone. The zone strikes NE and records a top-to-the-NW sense of shear. A mylonitic foliation and stretching lineation are well developed in the mylonites, which are classified as S-L tectonites. Logarithmic flinn parameters(1.18–2.35) indicate elongate strain which approximates to plane strain. Kinematic vorticity numbers are 0.42–0.92 and 0.48–0.94, based on the polar Mohr diagram and the oblique foliation in quartz ribbons, respectively, suggesting that the ductile shear zone formed under general shear, or a combination of simple and pure shear. According to finite strain and kinematic vorticity analyses, the Erguna Fault is a lengthening-thinning ductile shear zone that formed by extension. The deformation behavior of minerals in the mylonites indicates that the fault was the site of three stages of deformation: an initial stage of middle- to deep-level, high-temperature shear, a post-stress recovery phase of high-temperature static recrystallization, and a final phase of low-temperature uplift and cooling. The 40Ar/39 Ar plateau ages of biotite from the granitic mylonites are 106.16 ± 0.79 and 111.55 ± 0.67 Ma, which constrain the timing of low-temperature uplift and cooling but are younger than the ages of metamorphic core complexes(MCCs) in the Transbaikalia-northeast Mongolia region. Using measured geological sections, microtectonics, estimates of finite strain and kinematic vorticity, and regional correlations and geochronology, we conclude that the Erguna Fault is an Early Cretaceous, NNE-trending, large-scale, sub-horizontal, and extensional ductile shear zone. It shares a similar tectonic background with the MCCs, volcanic fault basins, and large and super-large volcanic-hydrothermal deposits in Transbaikalia-northeast Mongolia and the western Great Khingan Mountains, all of which are the result of overthickened crust that gravitationally collapsed and extended in the Early Cretaceous after plate collision along the present-day Sino-Russia-Mongolia border tract.     

龙门山构造带壳幔电性结构特征及其与汶川、芦山强震关系

青藏高原东缘龙门山构造带是研究青藏高原地壳物质向东侧向挤出的焦点地区.为探索龙门山构造带活动构造特征及其与发震构造的关系,本文通过布置垂直龙门山构造带南段芦山地震震源区的大地电磁测深剖面,运用多种数据处理手段,得到研究区可靠的电性结构,并通过与已有龙门山中段和北段剖面进行对比分析.研究表明：（1）青藏高原东缘岩石圈存在明显的低阻异常带--松潘岩石圈低阻带,该低阻异常带沿龙日坝断裂-岷山断裂-龙门山后山断裂分布,形成松潘-甘孜地块向扬子地块俯冲的深部动力学模式,通过统计研究区的历史强震,发现震源主要沿低阻异常带东侧分布,同时,低阻异常带也是低速度、低密度异常带,松潘岩石圈低阻带可能是扬子地块的西缘边界;（2）青藏高原物质东移过程中,受到克拉通型四川盆地的强烈阻挡,龙门山构造带表层岩块和物质发生仰冲推覆,表现为逆冲推覆特征的薄皮构造,中下地壳和上地幔顶部物质向龙门山构造带岩石圈深部俯冲,印支运动晚期,扬子古板块持续向华北板块俯冲,在上述构造运动作用下,呈现出刚性的上扬子地块西缘高阻楔形体向西插入柔性青藏块体的楔状构造;（3）根据电性结构推断,芦山地震受到深部上里隐伏壳幔韧性剪切带向上扩展的影响,构成芦山地震的深部主要动力来源;汶川地震的发生,在龙门山南段形成应力加载区,是触发或加快芦山地震孕育发生的另一个动力来源.     

双向剪切—晋北张性构造区形成演化的一种模式

晋北张性区的形成，是山西构造带与燕山构造带共同作用的结果，山西断陷带的右旋剪切与弱山构造带的左旋剪切即双向剪切作用，在其交汇处即晋北构造区造成了局部的引张应力场，并最终控制了晋北区的形成和发展。     

鄂尔多斯地块西缘定边-景泰地壳和上地幔电性结构分析

给出了定边－景泰大地电磁剖面探测结果并对其进行了分析．鄂尔多斯块体内部电性结构简单,电性界面成层性好,而在其西缘弧形断裂带,电性结构复杂,电导率横向变化较大．在弧形断裂带上地幔低阻层埋藏深度加大,这与北面的银川断陷盆地上地幔结构上隆形成反照,经分析认为银川断陷盆地属于拉张性质,而弧形断裂带属于挤压性质,由于均衡调整作用,造成了两者上地幔结构的反差．深部电性结构在大罗山－惠安堡之间有一局部上隆,经分析认为此处可能为深大断裂,南北构造带仅在此通过．     

The mechanism of small mining tremors from amplitude inversion

A method of inverting seismic wave amplitudes from mining tremors is proposed to reveal their mechanism. A simple shear-implosive model of a mechanism is proposed. The shapes of theoretical and observed radiation patterns are compared in the least squares norm and the parameters describing the shear-slip together with the ratio of implosive and shear dislocations are optimized. The efficiency of the method, even in the case of a small number of stations, is demonstrated by applying it to weak mining tremors from two mine regions in Czechoslovakia.The weak mining tremors are found to be of a predominantly shear mechanism with a clear coincidence of nodal planes to local tectonics, which could imply their tectonic nature.     

INTERPRETATION OF BOREHOLE STRAIN ANNUAL CHANGE AT GUZAN STATION BY NUMERICAL SIMULATION

China is one of the earliest countries to start borehole strain observation aiming to predicting earthquake.YRY-4 and other borehole strain instruments developed by China have reached the world advanced level,with a resolution of 10^-10 and can work stably.In order to capture the tectonic stress signals and analyze the relationship with seismicity,it is firstly necessary to identify and exclude the non-structure stress signals (caused e.g.by rainfall,pressure change,groundwater level fluctuation,river fluctuation etc).Annual strain change signals have been observed by YRY-4 borehole strain instrument at some stations (e.g.Guzan station in Dadu River valley).The signal is on the wave crest in spring and trough in autumn.Up to now,no relative papers have interpreted the physical mechanism causing such strain signals.In this paper,we manage to explain the physical mechanism by using numerical simulation.Considering the terrain factor of Dadu River valley,we set up a 3D finite-lement thermoelastic coupling model to compute the heat stress caused by annual change of surface temperature.The computing results are in good accordance with observation values,which illustrates that the annual change of strain signals is caused by annual change of surface temperature.We suggest that high-resolution borehole strain instrument (e.g.YRY-4 strain instrument) should avoid installing in a terribly undulate area,but choose a flat one.Although the strain signal with an annual change is a noise signal,to a certain extent,the signal illustrates that the current borehole strain instrument has a high resolution.This gives us more confidence to use this instrument to measure the structural strain.