Tectonic analysis of an oceanic transform fault zone based on fault-slip data and earthquake focal mechanisms: the Húsavík–Flatey Fault zone, Iceland

The Húsavík–Flatey Fault (HFF) is an oblique dextral transform fault, part of the Tjörnes Fracture Zone (TFZ), that connects the North Volcanic Zone of Iceland and the Kolbeinsey Ridge. We carry out stress inversion to reconstruct the paleostress fields and present-day stress fields along the Húsavík–Flatey Fault, analysing 2700 brittle tectonic data measured on the field and about 700 earthquake focal mechanisms calculated by the Icelandic Meteorological Office. This allows us to discuss the Latest Cenozoic finite deformations (from the tectonic data) as well as the present-day deformations (from the earthquake mechanisms). In both these cases, different tectonic groups are reconstructed and each of them includes several distinct stress states characterised by normal or strike-slip faulting. The stress states of a same tectonic group are related through stress permutations (σ₁−σ₂ and σ₂−σ₃ permutations as well as σ₁−σ₃ reversals). They do not reflect separate tectonic episodes. The tectonic groups derived from the geological data and the earthquake data have striking similarity and are considered to be related. The obliquity of the Húsavík–Flatey Fault implies geometric accommodation in the transform zone, resulting mainly from a dextral transtension along an ENE–WSW trend. This overall mechanism is subject to slip partitioning into two stress states: a Húsavík–Flatey Fault-perpendicular, NE–SW trending extension and a Húsavík–Flatey Fault-parallel, NW–SE trending extension. These three regimes occur in various local tectonic successions and not as a regional definite succession of tectonic events. The largest magnitude earthquakes reveal a regional stress field tightly related to the transform motion, whereas the lowest magnitude earthquakes depend on the local stress fields. The field data also reveal an early extension trending similar to the spreading vector. The focal mechanism data do not reflect this extension, which occurred earlier in the evolution of the HFF and is interpreted as a stage of structural development dominated by the rifting process.     

藏西北黑石北湖一带新近纪火山岩的特征及构造意义

青藏高原西北部黑石北湖一带发育的橄榄安粗岩系列火山岩具有由早到晚从基性到中性连续演化的特征，3期火山活动期次分明，以中心式喷发为主，K-Ar年龄分别为9．23Ma、3．19Ma和3Ma。该火山岩的稀土元素、微量元素、同位素组成特征与藏北其他地区的新生代火山岩基本相近。火山活动为新构造活动的响应，受控于青藏高原隆升过程中产生的走滑断裂。     

试论吐鲁番—哈密盆地为剪切—背驮型盆地

本文从大地构造背景，构造地貌，现今应力场，运动学特征，构造模型等５个方面论证了吐鲁番－哈密盆地的性质，认为吐－哈盆地是背驮于博格达推覆席体上的盆地，侏罗纪以来盆内的许多构造与沉积特征都取决博格达推覆构造与反冲推覆构造活动的强度。     

辽河油田东部凹陷中段走滑断层与油气的关系

走滑构造不仅加速含油气盆地油气的运移和富集,而且在促使油气圈闭的形成过程中也促使形成圈闭中的优良储集层。在具备生、储、盖地质条件时,花状构造样式的含油气性优于其他构造样式,不仅控制着油气藏的分布,而且走滑断层的应力释放区往往是油气富集区。扭应力作用使生油层中的分散油气被“强拧”驱赶、运移至花状构造背斜核部,在负花状构造的上升盘中形成高产油气流。辽河坳陷内的黄沙坨和欧利坨子地区便是郯庐断裂在辽河坳陷东部凹陷中段的应力释放区,对该区走滑断层的识别和解释,不仅对东部凹陷中段油气藏的形成、分布及富集有了新的认识,而且可为寻找同类油气藏提供依据。     

地震地质综合解释在辽河油田东部凹陷中段构造解释的应用

地震资料解释一个地区时综合使用地震和地质资料非常重要。作者在辽河油田东部凹陷的构造解释中,首先,利用野外观察到的地质构造现象, 建立地质露头模型;然后根据典型露头照片所示的构造特征对断层进行组合和构造解释;进而结合地震剖面特征分析油气的运移、聚集和成藏特征。通过地震地质综合解释的研究,推断出研究区内的走滑断层为油气的主控因素,走滑断层发育地区为油气富集的有利地带,同时对黄沙坨和欧利坨子油田的构造样式以及和油气之间关系进行了分析和研究。     

The application of seismic-geological integrated interpretation in the eastern depression of the Liaohe oil field

It is very important to comprehensively interpret areal seismic data with geological data in a research area. For the structural interpretations in the middle depression of the eastern basin of Liaohe oilfield, we first analyze and study geological phenomena on outcrop pictures collected in the field and establish geological outcrop models. Second, we make fault and structural interpretations based on the structural characteristics of the outcrop pictures. Third, we analyze the migration, accumulation, and formation of oil and gas using characteristics of seismic profiles. By geologic and geophysical comprehensive interpretation, it is inferred that, in the research area, the dominant factor controlling oil and gas accumulation is strike-slip faults. Structural modes and the relationship of the oil and gas in the Huangshatuo and Oulituozi oil fields are also analyzed and investigated.     

阿尔金断裂带最大累积走滑位移量——900km？

通过变形构造几何学、岩石学和区域构造对比研究,认为阿尔金断裂西北侧的阿尔金山北缘、南缘近EW走向的蓝片岩-榴辉岩高压变质带、榴辉岩超高压变质带分别与阿尔金断裂东南侧的北祁连山、柴北缘NW—SE/NWW—SEE走向的蓝片岩-榴辉岩高压变质带、榴辉岩超高压变质带相对应,并且,高压变质带与超高压变质带的宽度和走向在断裂两侧存在较大的变化。这种在断裂带中宽度变窄、角度趋于与断裂带走向一致的变化是韧性或韧脆性走滑过程中产生的拖曳构造。因此,阿尔金断裂带走滑过程中存在较大的韧性变形,它的最大累积走滑位移量应由韧性和脆性走滑位移量组成,至少大于500km,小于1000km。另外,拖曳构造的几何特征,以及西昆仑库地北蛇绿岩、阿尔金南缘蛇绿岩和柴北缘蛇绿岩在年龄、岩石组合及地球化学特征方面均具有相似之处,暗示在早古生代时期西昆仑和阿尔金南缘、柴北缘很可能处于相同的构造背景之中,后被阿尔金断裂所切割。因此,综合得出了阿尔金断裂带最大累积左旋走滑位移量为900～1000km。     

2022年1月8日青海门源MS 6.9地震地表破裂考察的初步结果及对冷龙岭断裂活动行为和区域强震危险性的启示

2022年1月8日青海门源M_S 6.9地震发生在青藏高原东北缘的祁连山断块内部,仪器震中位于海原活动断裂系西段的冷龙岭断裂带上,是该断裂系自1920年海原8.5级大地震后再次发生M>6.5的强震。考察结果的初步总结表明,此次门源地震产生了呈左阶斜列分布、总长度近23 km的南北两条破裂,在两者之间存在长约3.2 km、宽近2 km的地表破裂空区。南支破裂(F₁)出现在托来山断裂的东段,走向91°,长约2.4 km,以兼具向南逆冲的左旋走滑变形为主,最大走滑位移近0.4 m。北支主破裂(F₂)出现在冷龙岭断裂的西段,总长度近20 km,以左旋走滑变形为主,呈整体微凸向北东的弧形展布,包含了走向分别为102°、109°和118°的西、中、东三段,最大走滑位移出现在中段,为3.0±0.2 m。此外,在北支主破裂中—东段的北侧新发现一条累计长度约7.6 km、以右旋正断为主的北支次级破裂(F₃),累计最大走滑量约0.8 m,最大正断位移约1.5 m。综合分析认为,整个同震破裂以左旋走滑变形为主,具有双侧破裂特点,宏观震中位于北支主破裂的中段,其地表走滑位移很大可能与震源破裂深度浅有关,其中的右旋正断次级破裂可能是南侧主动盘向东运移过程中拖曳北侧块体发生差异运动所引起的特殊变形现象。印度与欧亚板块近南北向强烈碰撞挤压导致南祁连断块沿海原左旋走滑断裂系向东挤出,从而引发该断裂系中的托来山断裂与冷龙岭断裂同时发生破裂,成为导致此次强震的主要动力机制。在此大陆动力学背景下,以海原左旋走滑断裂系为主边界的祁连山断块及其周边的未来强震危险性需得到进一步重视。      

走滑断层和逆断层位错作用下地铁隧道损伤特征对比分析

隧道作为重要的轨道交通工程,近年来在地震中受到了不同程度的破坏,特别是跨断层的隧道,其抗震性能越来越受到人们的关注。为了能够更好地评价隧道的整体损伤情况及把握其损伤特征,以北京地铁7号线为研究对象,利用有限元软件ABAQUS建立模型,采用拟静力法,以隧道直径变化率作为损伤指标分析了隧道在走滑断层以及逆断层位错作用下的损伤特征,对比了两种断层位错作用下损伤状态与地震强度之间的关系、损伤范围和位置以及损伤程度。结果表明:跨断层隧道在断层错动作用下损伤只发生在断层带附近;当震级处于6.0～8.0级时,隧道衬砌损伤程度随震级的增大而增大;在覆土厚度相同的条件下,同震级时逆断层位错作用下隧道损伤程度要比走滑断层作用下大得多;走滑断层位错作用下隧道结构损伤主要发生在拱腰处,逆断层位错作用下主要发生在拱肩－拱脚以及拱顶－拱底处。