Evidence of multistage late Quaternary strong earthquakes on typical segments of Longmenshan Active Fault Zone in Sichuan,China

Investigation of offset landforms and trench excavation are important means to acquire the evidence of multistage activities of active faults. Here we present the result of fault trough investigation in Beichuan County and the Pingtong Town of Pingwu County along the Longmenshan Central Fault Belt, as well as the result from trench excavation at the platform foreslope in Hanwang Town of Mianzhu County on the Longmenshan Front Range Fault Belt. These results show that at least three fault activity events, in...     

昆仑8.1级地震同震形变特征及其对响应地震活动的制约机制

本文定义”响应地震”的概念统一表述昆仑山口西8.1级地震所引发的主破裂两侧临近构造及部分块体边界上的显著地震活动.其主体活动区域集中在昆仑地震主破裂的西南侧和东北侧及祁连山断裂.同时,地壳运动在主破裂北侧的甘青块体中西部出现与背景运动场反向的特征性变化,祁连山断裂出现应变弱化.弹性位移-应力阶跃模型模拟结果显示,昆仑地震造成其东北侧甘青块体中西部地壳运动的反向运动(相对背景场).并形成东北部和西南部两个体应变张性区域,绝大部分响应地震都发生在应变张性区中和块体张性边界上.这种强烈挤压剪切背景中出现的相对松弛状态与昆仑地震后青藏块体地震弱活动背景中出现的显著活跃的响应地震活动的正相关性可能反映了断层约束状态的相对减弱对滑动的触发作用.说明在考虑地震发生条件时,不能只着眼于应力场是否增强,断层摩擦强度,或更广义地说,构造约束条件的变化也是一个不容忽视的重要因素.     

Role of southeastern Sanandaj–Sirjan Zone in the tectonic evolution of Zagros Orogenic Belt,Iran

Geological studies indicate that the southeastern Sanandaj–Sirjan Zone, located in the southeastern Zagros Orogenic Belt, is subdivided transversally into the Esfahan–Sirjan Block with typical Central Iranian stratigraphic features and the Shahrekord–Dehsard Terrane consisting of Paleozoic and Lower Mesozoic metamorphic rocks. The Main Deep Fault (Abadeh Fault) is a major lithospheric fault separating the two parts. The purpose of this paper is to clarify the role of the southeastern Sanandaj–Sirjan Zone in the tectonic evolution of the southeastern Zagros Orogenic Belt on the basis of geological evidence. The new model implies that Neo‐Tethys 1 came into being when the Central Iran Microcontinent split from the northeastern margin of Gondwana during the Late Carboniferous to Early Permian. During the Late Triassic a new spreading ridge, Neo‐Tethys 2, was created to separate the Shahrekord–Dehsard Terrane from Afro–Arabian Plate. The Zagros sedimentary basin was formed on a continental passive margin, southwest of Neo‐Tethys 2. The two ophiolitic belts of Naien–Shahrebabak–Baft and Neyriz were developed to the northeast of Neo‐Tethys 1 and southwest of Neo‐Tethys 2 respectively, related to the sinking of the lithosphere of the Neo‐Tethys 1 in the Late Cretaceous. It can be concluded that deposition of the Paleocene conglomerate on the Central Iran Microcontinent and Pliocene conglomerate in the Zagros Sedimentary Basin is directly linked to the uplift generated by collision.     

Dynamic link between the level of ductile crustal flow and style of normal faulting of brittle crust

In a rheologically layered crust, compositional layers have an upper, elasto-plastic part and a lower, viscous one. When broken, the upper elastic part undergoes flexure, which is upward for the foot-wall and downward for the hanging wall. As a consequence of bending, stresses will develop locally that can overcome the strength of the plate and, therefore, impose the migration of active fault. In the lower, viscous part of each compositional layer, rocks can potentially flow. Numerical modelling of the behaviour of a crust made up of two compositional layers, during and following extension, shows that flow can take place not only in the lower crust but also, and more importantly, in the lower part of the upper crust. The ability of crustal rocks to flow influences the style and kinematics of rifted regions. When no flow occurs, subsidence will affect the extending areas, both hanging wall and foot-wall will subside with respect to an absolute reference frame such as sea level, and there will be a strict proportionality between extension and thinning. In addition, the downward movement of the fault blocks will decrease the local stresses created in the foot-wall and increase those of the hanging wall, thereby imposing a migration of fault towards the hanging wall. This is the behaviour of extensional settings developed on stabilised crust and which evolved in a passive margin. When flow does take place, middle crustal rocks will move towards the rifting zone causing isostatically driven upward movements that will be superimposed on movements associated with crustal and lithospheric thinning. Consequently, fault blocks will move upwards and the crust will show more extension than thinning. The upward movements will decrease the stresses developed in the hanging walls and increase those of the foot-wall. Faults will then migrate towards the foot-wall. Such a mode of deformation is expected in regions with thickened crust and has its most apparent expression in core complexes.     

Exploration and Study of Major Faults in Anshan City,Liaoning Province

In order to provide a basis for the earthquake resistance protection zoning of Anshan City, westudied the activity of faults. In the study, the synthetic geophysical prospecting techniqueswere used. These techniques include the shallow artificial earthquake method, electric method,geologic radar method, etc., with shallow artificial earthquake sounding as the main means.In the meantime, the data of geophysical prospecting and borehole record of this city werecollected and the methods of field investigation and sample age dating were also used incombination. The results show that there are 5 hidden or semi-hidden faults in Anshon City.Among these faults, Dashitou-Songsantai fault, Ningyuantun fault and Dayangqi fault trendNW, the middle Pleistotene Tanggangzi fault trends NE, while the early Pleistocene or Pre-Quaternary Ertaizi fault trend NW. According to the definition of active faults, none of thesefaults is active. This paper also discussed the cause for the formation of seriously damagedareas in Ans     

Geomorphic Evidence for and Rate of Sinistral Strike-slip Movement Along Northwest-trending Faults in Chaoshan Plain

Two sets of active faults,northwest-and northeast-trending faults,are developed in the Chao-shan Plain of East Guangdong.After detailed interpretation of aerophotos,we have found outthat there is the clear phenomenon of sinistral dislocation of drainage system on the Huang-gang-shui fault and part of Fengshun-Shantou fault.Field investigation confirmed that the geo-morphic bodies along the two faults have undergone displacement.Large-scale topographicmapping was made at three displaced sites and samples for age dating were collected from thegeomorphic booies.Calculation indicates that the average rate of sinistral strike-slip movementin the Holocene time amounts to 1.11±0.09～2.69±0.24mm/a along the Huanggangshuifault and 3.26±0.26mm/a along the Fengshun-Shantou fault.These two more active NW-trending faults extend into sea area,where they intersect the NE-trending strongly active Nius-han Island-Xiongdi Isle-Nanpeng Isles fault at a depth of 40～50m in water.The intersection isa location favorable fo     

对青海锡铁山矿区几个关键地质问题的认识

锡铁山矿区晚奥陶世滩间山群与早元古代达肯大坂群间的接角关系为隐蔽不整合,其间发育基底剥离断层（Ｆ１）,基底剥离断层之下的“过渡带”实际上是一条退条质的下滑型韧性剪切带。而滩间山群则被构造肢解为Ｏ３ｔｍ＾ａ－ｂ褶叠层与Ｏ３ｔｎ＾ｃ－ｄ褶皱冲断岩片,其间发育上剥离断层（Ｆ２）,两条剥离断层面上、下因构造剥蚀充失了大厌地层。并认为和里东晚期的伸展构造体制形成锡铁山变质核杂岩,海西期的抗日压构造体制形成褶     

Shear partitioning in the Philippines: Constraints from Philippine Fault and global positioning system data

Abstract The Philippine Fault is a major left-lateral structure formed in an island arc setting. It accommodates a component of the oblique convergence between the Philippine Sea Plate and the Philippine archipelago. This observation is quantified through a series of global positioning satellite experiments between 1991 and 1996. The formation of the Fault marks the onset of a new geodynamic regime in the Philippine region. In the central Philippines, this event corresponds to the creation of a new tectonic boundary separating the Philippine Mobile Belt and the Philippine Sea Plate, following the latter's kinematic reorganization that occurred around 4 Ma ago. During this event, the Philippine Sea Plate changed its relative movement with respect to Eurasia from a northward to a north-westward motion, favoring the formation of a Philippine Fault–Philippine Trench system under a shear partitioning mechanism.     

辽宁鞍山市主要断裂的探测与研究

为了给鞍山市抗震设防区划提供依据,我们采用了以浅层人工地震为主的综合地球物理探测技术,包括浅层人工地震、电法和地质雷达等方法,同时收集了城市已有的物探和钻井资料,并结合野外调查及样品年龄测试对断裂的活动性进行了研究。结果表明,鞍山市存在５条隐伏或半隐伏的断裂,北西向的大石头－宋三台断裂、宁远屯断裂、大阳气断裂和北东向的汤岗子断裂为中更新世断裂,北西向的二台子断裂为早更新世或前第四纪断裂,按活断层义     

视密度反演在东海及邻区重力异常解释中的应用

简要介绍了基于位场分离的视密度反演法的原理,并利用该技术对东海的重力异常进行处理并进行了区域地质解释应用.视密度反演的方法在对研究区内的区域性大断裂如郯庐断裂、江绍断裂以及东引—海礁隐伏断裂有很好的分辨能力.不同深度的视密度切片信息能够帮助我们了解这些大断裂的发育深度和规模.在沟弧盆等地形以及构造复杂地区利用视密度反演法研究深部地质构造,可以揭示不同深度上补偿质量分布情况,从而推测莫霍面的起伏情况.