Evolution of the deformation field and earthquake fracture precursors of strike-slip faults

Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquakes before their reoccurrence. In this research,we have performed a shear failure experiment on rock samples with prefabricated cracks to simulate the process of plate movement that forms strike-slip faults. We studied the evolution law of the deformation field to simulate the shear failure experiment, and these results gave us a comprehensive understanding of the elaborate strain distribution law and its formation process with which to identify actual fault zones. We performed uniaxial compression tests on marble slabs with prefabricated double shear cracks to study the distribution and evolution of the deformation field during shear failure. Analysis of the strain field at different loading stages showed that with an increase in the load, the shear strain field initially changed to a disordered-style distribution. Further, the strain field was partially concentrated and finally completely concentrated near the crack and then distributed in the shape of a strip along the crack. We also computed coefficients of variation(CVs) for the physical quantities u, v, and exy, which varied with the load. The CV curves were found to correspond to the different loading stages. We found that at the uniform deformation stage, the CV value was small and changed slowly,whereas at the later nonuniform deformation stage, the CV value increased sharply and changed abruptly. Therefore, the precursor to a rock sample breakdown can be predicted by observing the variation characteristics of CV statistics. The correlation we found between our experimental and theoretical results revealed that our crack evolution and sample deformation results showed good coupling with seismic distribution characteristics near the San Andreas Fault.

Vertical Differential Structural Deformation of the Main Strike-slip Fault Zones in the Shunbei Area,Central Tarim Basin:Structural Characteristics,Deformation Mechanisms,and Hydrocarbon Accumulation Significance

Vertical differential structural deformation(VDSD),one of the most significant structural characteristics of strike-slip fault zones(SSFZs)in the Shunbei area,is crucial for understanding deformation in the SSFZ and its hydrocarbon accumulation significance.Based on drilling data and high-precision 3-D seismic data,we analyzed the geometric and kinematic characteristics of the SSFZs in the Shunbei area.Coupled with the stratification of the rock mechanism,the structural deformations of these SSFZs in different formations were differentiated and divided into four deformation layers.According to comprehensive structural interpretations and comparisons,three integrated 3-D structural models could describe the VDSD of these SSFZs.The time-space coupling of the material basis(rock mechanism stratification),changing dynamic conditions(e.g.,changing stress-strain states),and special deformation mechanism of the en echelon normal fault array uniformly controlled the formation of the VDSD in the SSFZs of the Shunbei area.The VDSD of the SSFZs in this area controlled the entire hydrocarbon accumulation process.Multi-stage structural superimposing deformation influenced the hydrocarbon migration,accumulation,distribution,preservation,and secondary adjustments.

Deformation of a two-phase medium due to a long buried strike-slip fault

The aim of the present paper is to obtain the two-dimensional deformation of a two-phase elastic medium consisting of half-spaces of different ri- gidities in welded contact due to a buried long strike-slip fault. The solution is valid for arbitrary values of the fault-depth and the dip angle. The effect of fault-depth on the displacement and stress fields for different values of dip angle has been studied numerically. It is found that the displacement field varies significantly for a buried fault from the corresponding displacement field for an interface-breaking fault. The contour maps showing the stress field for various dip angles for buried and interface-breaking fault have been plotted. It has been observed that the stress field varies significantly for a buried fault from the corresponding stress field for an interface-breaking fault.

Tectonic deformation features and petroleum geological significance in Yinggehai large strike-slip basin, South China Sea

The subtle strike-slip tectonic deformation and its relationship to deposition, overpressure and hydrocarbon migration were studied on the basis of systematic sorting of tectonic data.(1) The local T(tension) fractures derived from sinistral strike-slip process were formed before 10.5 Ma, large in number in the nose structure of the eastern slope, and reactivated episodically under the effect of fluid overpressure in the late stage, they served as dominant vertical hydrocarbon migration paths in the slope area of basin.(2) The dextral strike-slip extension was conducive to the increase of depositional rate and formation of regional under-compacted seal, and induced generation of local T fractures which triggered the development of diapirs; in turn, the development of diapirs made T fractures grow in size further.(3) The sinistral strike-slip process weakened after 10.5 Ma, causing tectonic movement characterized by compression in the north and rotational extension in the south, and the uplift and erosion of strata in Hanoi sag and a surge in clastics supply for south Yinggehai sag. Finally, migrating slope channelized submarine fans and superimposed basin floor fans were developed respectively on the asymmetrical east and west slopes of the Yinggehai sag.

The Seismic Induced Soft Sediment Deformation Structures in the Middle Jurassic of Western Qaidamu Basin

Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types： seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.

When will it end? Long-lived intracontinental reactivation in central Australia

The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580 -520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results,from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by40 Ar/39 Ar muscovite and U e Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by Ue Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust,from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende40 Ar/39 Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect,40 Ar/39 Ar muscovite and zircon(Ue Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600-660℃. Subsequent cooling to 150 -220℃ of the core of the orogen occurred between ca. 480 Ma and 400 Ma(zircon [Ue Th]/He data)during reactivation of the Woodroffe Thrust, coincident with the 450 -300 Ma Alice Springs Orogeny.Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016(Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9 -7.0℃/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.

Characteristics of tectonic deformation field about strike－slip earthquake－generating structure in the Chinese mainland

This paper is the second one of the serial papers about the study on strike slip earthquake-generating structure in the interior of the Chinese mainland. In the first part of the paper,the deformation field model of strike slip earthquake-generating structure is elucidated.It puts forward that a strike slip fault is not dominated by horizontal displacement everywhere along the whole belt,its deformation characteristics is different from section to section, only the central main body shows strike slip feature,the two ends take vertical deformation as the major feature.In the second part,through the discussion of deformation field characteristics about strike slip earthquake-generating fault for several clearly investigated large earthquakes with M≥7.0 that occurred recently in the Chinese mainland, it is further confirmed that although each of these earthquakes possesses its own complicated features,they also share the common feature that the earthquake-generating faults have the deformation field characteristics similar to those of the above-mentioned strike slip earthquake-generating structure.

LARGE-SCALE STRIKE SLIP FAULT: THE MAJOR STRUCTURE OF INTRACONTINENTAL DEFORMATION AFTER COLLISION

Intracontinental deformation is one of the most interesting problems in tectonics. But so far little attention has been paid to rock deformation, metamorphism and magmatism related with large-scale displacement and rotation of these blocks. In this note, we take the Ailaoshan-Red River fault (ARF)zone in western Yunnan as an example and discuss the kinematics and dynamics of the fault With its neighbouring blocks in the Tertiary.

Late Jurassic Intracontinental Extension and Related Mineralisation in Southwestern Fujian Province of SE China:Insights from Deformation and Syn-Tectonic Granites

Late Mesozoic igneous intrusions and extensional structures in Carboniferous to Permian sequences in the SW Fujian region acted as important controls on the localisation of Fe-polymetallic de-posits.Here we document the identification of extensional deformation at shallow crustal levels and syn-tectonic granites related to normal faults.Based on spatial distribution and structural features,the extensional deformation can be divided into cover-only and basement-intersecting styles.A series of syn-tectonic plutons were emplaced into the footwall of normal faults.Representative samples of the Tangquan Granite have high SiO2(66.4 wt.%-73.9 wt.%)assays and Mg#values(37-59).The samples also have relatively homogenous initial 87Sr/86Sr(0.7083-0.7089)andεNd(-9.2--10.2)values.Geochemical and isotopic evidences indicate that the Tangquan granite originates from a hybrid source including lower crustal-derived felsic and lithospheric mantle-derived mafic magmas.Zircon U-Pb dating indicates that the granodiorite phase from the pluton crystallised at 161±4 Ma and the monzogranite phase crystallised at 159±1 Ma.Combined with the granitic rocks in a wider region of SE China,the widespread granitic magmatism and polymetallic mineralisation have been synchronous during the Late Mesozoic,probably resulting from extensional tectonics related to the lithospheric thinning.

中亚造山带中部大型韧性走滑双重构造的形成、机制与涵义

大型走滑双重构造是造山带中重要构造,它可以发育于造山带演化的不同阶段,同时也是陆内变形的重要方式。大型走滑双重构造的形成具有特殊的边界条件,在不同类型造山带演化过程中起到的作用也不一样,然而目前还缺少足够的认识。中亚造山带是全球显生宙规模最大的增生型造山带,大规模的走滑作用在该造山带的演化中起到了关键作用。目前在该造山带中段的阿拉善地区识别出了一个大型的近东西向的走滑双重构造,该双重构造由7~8条不同方向的次级韧性剪切带组成,东西长约500 km,南北宽约350 km,面积约200000 km^(2)。形成一个巨大的S-C like构造,发育时间为古生代末期—早中生代,区域运动学性质为韧性右行走滑,单条剪切带的走滑位移10~60 km,累积走滑距离250~500 km。它是中亚造山带南缘晚古生代末期—早中生代巨型韧性剪切系统的一部分,也是古亚洲洋关闭后中亚造山带整体变形的一部分。该走滑双重构造分别连接了西侧天山以及东侧兴蒙造山带不同类型的走滑变形,它的形成与较热的岩石圈以及不均一的造山带组成有关,而走滑双重构造的作用也是造成造山带内部结构均一化的过程。结合造山带的类型,一般走滑双重构造多发生在增生型造山带,而碰撞型造山带一般由于较冷的岩石圈而相对缺乏此类构造。阿拉善大型走滑双重构造是中亚造山带中少有报道的大型构造,它是造山带不均一的物质组成、强烈的岩浆作用以及华北克拉通的阻挡而造成的应变集中所导致,它不仅是连接中亚造山带东西的枢纽,而且也是构建中亚造山带结构的重要约束。

北山-阿拉善晚新生代变形的特征与机制

北山-阿拉善地区位于中亚造山带中部,新生代晚期受控于印度-欧亚板块的碰撞,发生了不同程度的陆内变形,是青藏高原与蒙古高原应力传递区,是研究印度-欧亚碰撞远程效应的关键地区。北山-阿拉善地区晚新生代变形区别于中亚造山带西段的天山以及阿尔泰地区,表现为发育一系列近东西向的左行走滑断层及其间一系列北东向的正断层及其控制的断陷(拉分)盆地。近东西向的左行走滑断层规模较大,走向延伸很长,成为北山-阿拉善新生代晚期变形的骨干构造。整体上北山-阿拉善地区之间的晚新生代变形是在北侧北东东向南蒙古—天山左行走滑断层和南侧北东东向阿尔金断层之间阶区内的变形,在这个左行-左阶的区域内,变形表现为边界走滑断层派生出的近东西向次级走滑断层(P剪切)和北东向伸展盆地(如额济纳盆地和旧井盆地)。该区域是一个左行张剪区域,使得该区成为区别于蒙古戈壁阿尔泰的右行压剪构造,而阶区内区域性的伸展导致了本区平坦的地势并成为主要的汇水盆地区。GPS速度场以及上地幔-下地壳各向异性资料表明,塔里木克拉通在青藏高原向北的扩展过程中起重要作用,青藏高原北缘上地幔-下地壳在遇到塔里木克拉通后沿着该克拉通东南边缘转向,向北东流动,而塔里木本身则继续向北北东传递应力,导致天山的崛起并挤压准噶尔盆地,进而形成了阿尔泰山北北西走向的右行剪切变形;向北东方向流动的上地幔—下地壳则导致北山-阿拉善地区以及南蒙古地区的晚新生代左行剪切变形,该地区的变形宏观上呈现弥散性特点,区别于塔里木-天山-准噶尔地区新生代变形集中天山和阿尔泰山一带的现象。

陆内走滑断裂构造特征及活动性分析

为探求鄂尔多斯盆地大牛地区块走滑断裂构造特征及其对碳酸盐岩储层油气储集和运移的控制作用,本研究基于大牛地区块约2000 m^(2)高精度三维地震资料,提取多种地震属性,择取断裂表征效果较好的相干和倾角属性指导断层解译。本研究首次识别和判定大牛地区块北侧发育的条大型走滑断裂,并将其命名为台格庙断裂,主要发育层位为奥陶系碳酸盐岩.

吕梁隆起中段冲断构造解析

吕梁隆起是认识华北克拉通的重要窗口,对于克拉通的形成、保存与演化具有重要参考意义。目前对于吕梁隆起的构造样式及其演化特征的研究仍然偏弱。本文对吕梁隆起中段核部吴城镇白马仙洞一带的构造进行解析,通过野外地质调查,建立了东西向构造地质剖面,应用2D-Move、FaultFold软件对剖面进行反演与正演模拟,分析其构造样式与构造演化特点。研究认为:吕梁隆起核部在燕山期受到强烈的东西向挤压作用而发生隆升,早期在基底发育区域性滑脱面,滑脱面之上发育了两条逆断层(F1、F2),上覆地层形成断层传播褶皱,基底发生滑脱卷入,此时处于快速隆升阶段;燕山期中期F1、F2逆断层持续活动,断层端点向上破裂至石炭系,此时处于慢速隆升阶段;燕山期晚期断层F1、F2持续向上突破所有地层,倾角达70°,东侧新产生一新的断层F3,上覆地层以及基底太古界花岗岩形成断层转折褶皱,进入快速隆升阶段;其后风化剥蚀最终形成现今构造格局。该区地层总缩短量为3.17 km,总缩短率为13.4%。本文为之后研究吕梁隆起的陆内构造变形及其矿产资源提供了参考依据。

大陆地质与大陆构造和大陆动力学

当代地球科学发展的新需求与板块构造对大陆地质的深化研究,使大陆问题成为21世纪地学发展的前沿研究领域、热点和关键。文中在提出"大陆动力学"研究20多年后的今天,进行关于大陆研究的新思考,从讨论厘定大陆研究的有关争议概念、大陆的基本问题、中国大陆构造的典型实例以及与世界同类范例的简要对比出发,综合概括了大陆地质与大陆构造和大陆动力学研究的关键科学问题与进一步探索研究的思考课题。提出了在大陆研究中,在进一步精确深化板块构造对大陆的研究的同时,应突出加强大陆构造中有无非板块构造动力及其远程效应的大陆内的、在深部动力学与陆块间差异非均衡背景下由陆内陆块间相互作用导致的真正陆内构造及其动力学问题的研究,以便为深化发展板块构造、认知大陆、探索大陆动力学、构建包括板块构造在内新的行星地球构造观作出努力与探索。

中国大陆现今构造变形GPS观测数据与速度场

利用 1991— 1999年间 36 2个全球定位系统 (GPS)测站的观测资料 ,初步获得了中国大陆及周边地区现今地壳水平运动的统一速度场。该速度场主要涵盖青藏高原 ,天山 ,塔里木、川滇 ,河西走廊 ,福建东南沿海等重要构造活动区 ,测定精度总体优于 2～ 3mm/a ,速度场站点的分布和测定精度基本上满足中国大陆现今构造变形和动力学研究的需求。现代大地测量第一次比较全面、定量地展示出中国大陆在周边板块作用下大幅度构造变形的图像 ,为模拟大陆岩石圈动力过程提供了基础性的运动学约束条件。

雪峰山陆内复合构造系统印支—燕山期构造穿时递进特征

通过分析雪峰山陆内变形构造区内三叠系—白垩系中不整合面的分布以及不整合面上下地层的夹角情况,明确了早-中三叠世构造运动波及范围以及高角度不整合和低角度不整合分布的分界线,且变形具有由东向西的逐渐减弱的规律;自晚三叠世以来,构造运动仍体现出由东向西的穿时递进扩展变形,继而得出各时期变形时间的分界线。另外,通过计算各时期穿时变形的传递速率,并且通过传递速率作为联系纽带,得出燕山期向西递进变形的直接原因为湘赣及华夏陆块等地岩石圈减薄软流圈上涌,而间接原因是古太平洋板块对欧亚板块的俯冲方式,而滑脱层在燕山期构造传递过程中也扮演了重要角色。

中国侏罗纪构造变革与燕山运动新诠释

随着一系列新构造观察资料和高精度同位素测年数据的累积,加深了对发生在中国东部晚侏罗世—早白垩世时期构造变革事件的认识,对燕山运动的性质、时限和动力学内涵有了新的诠释。中—晚侏罗世初期(165±5Ma)东亚多板块拼贴运动学发生重大调整,构造体制发生重大转换,启动了以中朝地块为中心、来自北、东、南西不同板块向东亚大陆"多向汇聚"的构造新体制,形成以陆内俯冲和陆内造山为特征的东亚汇聚构造体系。同时大陆地壳岩石圈发生显著增厚,并紧随早白垩世以剧烈的大陆岩石圈伸展和火山—岩浆活动为特征的岩石圈巨量减薄和克拉通破坏,导致燕辽生物群灭绝和热河生物群兴盛的重大生物群更替,成为中国大陆和东亚重大构造变革事件,这是燕山运动的基本内涵。本文依据燕山运动构造变形型式、动力学背景以及产生的深部过程,将"燕山运动"定义为起始于165±5Ma的"东亚多向汇聚"构造体制及其形成的广泛陆内造山和构造变革,并将中国东部岩石圈巨量减薄视作燕山期陆内造山和陆内变形的后效。

印支地块思茅地区早白垩世古地磁结果及其构造意义

对印支地块思茅地区的早白垩世红层开展详细的岩石磁学和古地磁学研究,获得镇沅剖面特征剩磁方向Ds=52.4°,Is=45.5°,κ=77.9,α95=6.3°;普洱剖面特征剩磁方向Ds=46.2°,Is=46.6°,κ=50.9,α95=5.6°;江城剖面特征剩磁方向Ds=8.6°,Is=42.2°,κ=117.1,α95=4.0°。对普洱和江城剖面进行E-I磁倾角偏低检验,结果显示江城剖面不存在磁倾角偏低,普洱剖面由于偏角较分散,导致其伸展方向出现假象,推测的磁倾角偏大,出现实测磁倾角偏低的假象。思茅地区各采样剖面之间的磁偏角差异表明,块体内部发生过差异性旋转变形,其变形的过程不仅受控于边界深大断裂,也与内部小断裂的活动有密切关系。若进一步考虑华南地块白垩纪可能存在的磁倾角偏低现象,则该结果说明印度支那地块思茅地区白垩纪以来相对于华南地块向南滑移量为570±310km,接近构造地质研究推测的红河大断裂左行滑移量。

对中国大陆构造格架的讨论

大陆动力学的理论与研究开启了人们一个新的思路:在确认中国大陆构造格架、划分构造单元时,除了前寒武纪基底、南华—印支期生物地层格架以外,不能不考虑中-新生代以来重大的陆内变形事件所产生的陆内变形(大型走滑断裂、推覆构造、挤出构造)对印支与前印支期所形成大陆构造格架大幅度的改造,因此对前印支期构造单元的性质需要通过构造复位来重新认识。通过构造复位认为:阿拉善、中祁连—柴达木、北羌塘等微陆块和塔里木板块是一个整体的克拉通——西域板块,不存在整体的昆(仑)—祁(连)—秦(岭)海洋板块,早古生代满加尔—北祁连坳拉槽-小洋盆和晚古生代东昆仑—阿尼玛卿—金沙江裂陷洋盆可能是由古特提斯洋脊楔入所引起的,类似于现今的红海—亚丁湾。本文拟从阿拉善、北羌塘地块的构造归属、西域板块的确认;中国境内北亚构造域的构造划分和晚侏罗—早白垩世陆内变形、中亚挤出构造;中朝与扬子—华南板块划分和南北黄海、朝鲜半岛的构造归属等方面,来讨论有关中国及邻区大陆构造格架的一些争议问题。

川东—武陵地区构造格局及其演化

陆内变形是现今大陆动力学研究的重要内容之一。川东—武陵地区位于扬子地块的内部,远离板块边界,是研究陆内变形的绝佳场所。通过野外断裂构造详细的解析、褶皱构造的形态分析以及沉积地层接触关系的研究,建立了川东—武陵地区显生宙构造格局,探讨了多期构造演化过程。晚中生代以来的两次构造作用奠定了研究区的构造格架,认为滑脱层的深度及数量从根本上控制了川东—武陵地区侏罗山式褶皱变形的差异,褶皱与断裂构造几乎同时形成,川东地区的隔挡式褶皱为单层滑脱变形的结果,而武陵地区的褶皱构造是由于多层次滑脱背景下、差异隆升剥蚀造成的不同构造层次褶皱出露的结果。结合区域地质演化,提出川东—武陵地区显生宙时期主要经历了五期构造演化。晚志留—中泥盆世、石炭纪末和中、晚三叠世之交,研究区均以整体的抬升作用为主,不发育任何褶皱构造;晚侏罗—早白垩世发生大规模褶皱-逆冲作用;新生代晚期,受印度与欧亚大陆汇聚作用的影响,区内断裂带走滑方向发生反转,早期构造被强烈改造。