龙门山山前疑似汶川M_S 8.0地震地表破裂的浅层地震反射调查

2008年5月12日发生在龙门山构造带的汶川MS8.0大地震是映秀-北川断裂突发错动的结果。此次地震不但使NE向的映秀-北川断裂和灌县-江油断裂发生了地表破裂,而且,在成都平原区的什邡、绵竹等地也出现了不同程度的地表裂缝、公路拱曲以及带状的喷砂冒水现象。此项探测研究以出现在什邡市师古镇附近的疑似地震地表破裂带为切入点,通过采用可控震源以及高精度的浅层地震反射勘探方法,获得了深度15～800m范围内高分辨率的地下结构和构造图像。结果表明,在地表破裂之下存在向平原区逆冲的隐伏断层和反向的逆冲断层,地震过程中隐伏逆断层的活动可能是近地表地层出现褶皱变形和地表破裂的主要原因     

芦山县龙门乡芦山“4·20”7.0级强烈地震地表破裂迹象与讨论

在芦山县龙门乡发现芦山“4·20”7.0级强烈地震地表破裂的迹象,这些迹象点呈NE-SW向线状分布,总体走向N40°～50°E,长2～ 3km.根据水泥路面变形推断水平缩短量为8cm,垂直抬升量1 ～ 2em.地表未见走滑分量,运动学特征表现为由NW向SE的推挤作用.在地震地表破裂的力学性质方面,有斜向剪切裂缝,也有挤压对冲逆断层性质,但更多地表现为张性裂缝,这与拱曲顶部的局部张性应力场有关.虽然这些地表破裂组合特征不同,性质也有差异,但均反映了龙门乡一带受到NW-SE向挤压作用以及逆断层发震构造沿线近地表常见的拱曲作用.与大川-双石断裂(前山断裂)、大邑-名山断裂(山前断裂)相比,芦山-龙门隐伏推测断裂更有可能是此次地震的发震断裂,这一推论也与此次地震序列的精定位结果以及地震烈度分布特征相符.有关芦山“4·20”7.0级强烈地震发震断裂的认识,对研究此次地震的发震构造特征以及评价未来山前地带地震危险性具有重要意义.     

断层活动方式与地震地表变形分布特征研究

基于断层弹性位错理论及断层滑动非均匀模型,用三维有限元方法计算了发震断层逆断、正断和水平走滑三种不同活动方式下的地表变形,探讨了断层不同活动方式下的地震应变与位移的分布规律及震级、断层倾角对地震地表变形分布的影响。研究结果表明,地震地表变形影响因素很多,如地质构造条件、岩性介质特征、断层活动强度、断层产状和区域构造应力场等,但分布形态最终决定于断层活动方式,变形大小则决定于断层活动强度,其它均为局地因素,只影响分布形态的局部扭曲。断层不同活动方式下的地震地表变形分布各有其自身的规律和特点,这些分布特征可作为地震研究及近活动断层建筑工程抗震设计或加固防护参考。     

汶川地震震中映秀地区地表破裂特征

汶川8级大震的震中位于映秀镇,地震在映秀地区造成了多处地表破裂,如公路拱曲、地震陡坎,坡中槽新变形等,长度达300余米.经实地全站仪和GPS测量,定量分析了地表破裂的垂直分量与水平分量以及两者之间的比值,以此揭示了映秀-北川断裂的运动性质为逆冲兼右行走滑,在映秀地区逆冲分量大于走滑分量.将本次地震造成的位错数据与震前资料对比,发现汶川地震产生的地表破裂位置与地质历史上映秀-北川断裂造成的断层位错位置是相当吻合的,说明映秀地区Ⅳ级阶地上40余米的的断层陡坎可能是地质历史时期若干次大地震的结果.     

隐伏和出露地表断层近断层地表运动特征的研究进展

本文介绍了在强震地震学研究方面国内外目前所关注的重要问题：隐伏断层和出露地表断层在地震发生时近断层地表运动特征存在着明显的差异。根据近几十年全球发生的中强地震的地表运动参数的统计分析所得的结果表明,由隐伏断层所造成的近断层地表运动强度（速度、加速度）大于出露地表断层所产生的地表运动强度,虽然发生在出露地表断层的地震往往可造成较大的近断层地表位移,但是当地震矩震级（MW）达到 7.5 级以上的时候,近断层地表加速度和速度在近源区却出现了饱和现象。对该问题的深入研究有着十分重要的科学意义和工程应用价值。本文着重介绍了当前国际上对该问题的研究现状,并且建议在此基础上利用三维有限差分断层动力学模型,模拟断层的动态破裂过程以及近断层地表运动的特征。     

据断层附近布格重力异常分布反推地质时期断层运动的探讨

本文应用变形介质位移场产生的附加重力场的积分表达式,对麦克斯威尔介质半空间中断层长期活动引起的永久变形与现今布格重力异常分布的关系作了定量分析,并提出了由断层附近布格异常分布特征反推地质时期断层运动趋势的一般方法。其主要应用于平原地区断层运动(特别是扭动方式)的判别。文中以滦南断裂为实例,通过数值积分,计算了几种断层运动可能产生的地表重力异常。经理论计算与实测重力资料相对比,该断层曾发生过下盘上升的正倾滑运动,并具有顺扭走滑运动分量     

正倾滑活动断裂垂直位移定量研究中相关问题的讨论

当探槽开挖长度未跨过断层变形带时，得到的断层垂直位移将偏离断层活动的真实情况，在缺少依据帮助确定断层陡坎原始下坡角的具体位置时，通过断层陡坎高度获得的断层垂直位移也将与实际情况有较大的偏离，文中对此进行了讨论。并讨论了应用断层两侧近水平地层累积变位量的分解确定古地震事件期次的方法，以及探槽剖面中断层两侧同层地层厚度差异是断层活动事件的反映等问题。引用了内蒙古大青山山前断裂和狼山山前断裂、北京平原夏垫断裂和南口－孙河断裂及日本丹那断层探槽开挖的实例。     

近断层地震动的基本特征

本文对近断层地震动的基本特征作了详细分析,这些基本特征主要包括近断层强地震动的集中性、地表破裂、地面永久变形、破裂的方向性效应、近断层速度大脉冲和上盘效应。这些特征虽然在一次地震中不一定同时出现,但它们是已经被强震观测资料和数值模拟证实了的,在模拟和预测近断层地震动时,必须充分考虑这些特点,合理的近断层地震动模拟或预测模型和方法应当在结果中再现这些特点。     

库车坳陷东部秋里塔格背斜带的活动断层及其形成机制

在详细调查盐水沟以东秋里塔格背斜带地质、地貌特征的基础上,结合地震反射剖面揭示的深部构造形态,讨论了背斜区地表断层的分布特征、活动性及形成机制。盐水沟以东的秋里塔格背斜带包括库车塔吾背斜和东秋里塔格背斜。库车塔吾背斜核部断层是发育于古近系盐膏层中的滑脱断层向地表的延伸,在晚更新世仍持续活动。库车塔吾背斜北翼断层为受局部挤压应力控制而产生的褶皱调节断层,发育于北翼山前活动枢纽内,成组近平行出现,走向上展布不连续;探槽开挖结果表明,该断层全新世有过断错地表的古地震事件。发育于东秋里塔格背斜南翼靠近核部的博斯坦断层为较大规模的低倾角逆冲断层,向下可能与控制表层背斜生长的断坡相连。东秋里塔格背斜南翼断层是发育于断展褶皱陡倾前翼的剪切逆冲断层,亦平行成组出现,断续分布,在哥库洛克一带断层错断了全新世洪积扇。活动褶皱及其褶皱相关断层均为深部断层滑动经过复杂的褶皱变形传播到近地表的表现,是深部断层活动的指示构造。褶皱调节断层仅是褶皱过程中产生的局部变形,与控制褶皱生长的深部断层仅存在间接的关系。此类断层的滑动位移、速率等不代表深部控制背斜生长断层的运动学参数,但这些次级断层部分记录了活动褶皱区的古地震事件。     

渭河盆地东南缘铲形正断层上盘活动特征

本文根据野外和力学分析，认为渭河盆地东南缘铲形正断层上盘块体沿凹曲的断层面向下滑动和旋转作用，在山前冲洪积平原区产生了同向断层、反向断层和上盘横断层。这些构造的差异活动及其在地表的表现特征，可作为铲形正断层分段的重要标志。     

LATE QUATERNARY SINISTRAL STRIKE-SLIP ACTIVITIES OF SANWEI SHAN FAULT IN THE NORTH OF TIBETAN PLATEAU

Sanwei Shan Fault is located in the north of Tibet, which is a branch of eastern segment of Altyn Tagn fault zone. This fault is distributed along the boundary of fault facet and the Quaternary, with the total length of almost 150km. The fault is a straight-line structure read from the satellite image. Based on the spatial distribution of the fault, three segments are divided, namely, Xishuigou-Dongshuigou segment, Dongshuigou-West Shigongkouzi segment and West Shigongkouzi-Suangta segment, these three segments are distributed by left or right step.Though field microgeomorphology investigation along Sanwei Shan Fault, it has been found that two periods of alluvial-pluvial fans are distributed in front of Sanwei Shan Mountain, most of which are overstepped. Comparing the distribution of alluvial-pluvial fans with their formation age in the surrounding regions, and meanwhile, taking the results of optical stimulated luminescence(OSL) dating, it's considered that the formation age of the older alluvial-pluvial fans, which are distributed in northern Qilian Shan, inside of Hexi Corridor and western Hexi Corridor(including the Sanwei Shan piedmont fans), is between later period of late Quaternary and earlier period of Holocene. The gullies on the older fan and ridges have been cut synchronously. The maximum and minimum sinistral displacement is 5.5m and 1.7m, but majority of the values is between 3.0~4.5m. Taking the results from the OSL dating, we conclude that the minimum sinistral strike-slip rate is(0.33±0.04) mm/a since 14 ka BP and(0.28±0.03) mm/a since 20 ka BP.     

FIRST REPORT OF BERO ZECO ACTIVE FAULT IN GÊRZÊ, NORTHERN TIBET

In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ₁)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ₁, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms.     

龙陵-瑞丽断裂(南支)北段晚第四纪活动性特征

遥感影像解译和野外地质地貌调查表明,龙陵-瑞丽断裂(南支)北段是以左旋走滑为主兼张性正断的区域性活动断裂。根据一些断错地貌点的大比例尺填图、实地测量及其年代学分析,确定了该断裂为全新世活动断裂,断裂晚更新世以来的平均水平滑动速率为2.2mm/a,平均垂直滑动速率为0.6mm/a;全新世以来的平均水平滑动速率为1.8～3.0mm/a,平均垂直滑动速率为0.5mm/a。断裂晚更新世以来的滑动速率在不同的时间尺度上变化不大,反映了该断裂晚更新世以来的活动强度比较平稳     

THE SLIP RATE AND PALEOEARTHQUAKES OF THE YUMEN FAULT IN THE NORTHERN QILIAN MOUNTAINS SINCE THE LATE PLEISTOCENE

The Yumen Fault lies on the west segment of the north Qilian Fault belt and adjacent to the Altyn-Tagh Fault,in the north margin of the Tibet Plateau.The tectonic location of the Yumen fault is special,and the fault is the evidence of recent activity of the northward growth of Tibetan plateau.In recent twenty years,many researches show the activity of the Yumen Fault became stronger from the early Pleistocene to the Holocene.Because the Yumen Fault is a new active fault and fold belt in the Qilian orogenic belt in the north margin of the Tibet Plateau,it is important to ascertain its slip rate and the recurrence interval of paleoearthquakes since the Late Pleistocene.Using the satellite image interpretation of the Beida river terrace,the GPS measurement of alluvial fans in front of the Yumen Fault and the trench excavation on the fault scarps,two conclusions are obtained in this paper.(1) The vertical slip rate of the Yumen Fault is about 0.41~0.48mm/a in the Holocene and about 0.24~0.30mm/a in the last stage of the late Pleistocene.(2) Since the Holocene epoch,four paleoearthquakes,which happened respectively in 6.12~10.53ka,3.6~5.38ka,1.64~1.93ka and 0.63~1.64ka,ruptured the surface scarps of the Yumen Fault.Overall,the recurrence interval of the paleoseismic events shortens gradually and the activity of the Yumen Fault becomes stronger since the Holocene.Anther characteristic is that every paleoearthquake probably ruptured multiple fault scarps at the same time.     

华山山前断裂中段晚第四纪活动的地貌表现及响应

调查了华山山前断裂中段（石堤峪-杜峪）晚更新世以来,尤其是全新世以来的断层构造地貌,讨论了它们的成因、特点及对断裂活动的响应关系。断层构造地貌主要包括：断层三角面、断层陡坎、洪积阶地、埋藏型洪积扇以及冲沟裂点。对各大沟峪峪口的洪积阶地进行了大比例尺微地貌测量,并在部分沟峪两侧沿断层崖陡坎及冲沟沟床布置了测线。结合T1、T2级洪积阶地位错测量结果及其14C年龄计算得到,华山山前断裂中段6000a-2000aB.P.的垂直滑动速率为1.485mm/a;2000aB.P.以来的垂直滑动速率为3.73mm/a。最后结合野外调查与理论认识,建立了正断层作用下洪积阶地与埋藏型洪积扇的演化模式。本研究结果支持华山山前断裂是1556年华县814级地震发震构造的观点。     

中甸-大具断裂南东段晚第四纪活动的地质地貌证据

中甸-大具断裂南东段位于哈巴和玉龙雪山北麓,属于川西北次级块体西南边界,断裂总体走向310°~320°,是一条重要的边界断裂。了解该断裂的活动性质、活动时代和滑动速率等对分析川西北次级块体运动,研究该断裂与玉龙雪山东麓断裂的交切关系等问题具有重要意义。文中基于1︰5万活动断层地质填图,对断裂沿线地层地貌、陡坎地貌、地表破裂、典型断层剖面以及河流阶地等进行了详细的研究。研究表明:1)中甸-大具断裂南东段按几何结构、断错地貌表现、断裂活动性可分为马家村—大具次级段和大具—大东次级段。2)通过野外地质调查发现,马家村—大具次级段断错了全新世冲洪积扇,形成了地表破裂,为全新世活动段;而大具—大东次级段虽然也断错了晚更新—全新世地层,但其断错规模及滑动速率均较小,由此认为其全新世以来活动较弱。3)通过分析断裂沿线断层陡坎、水平位错及地表破裂等地质地貌问题,认为马家村—大具次级段的活动性质为右旋走滑兼正断,其晚更新世以来的垂直滑动速率为0.4~0.8mm/a,水平滑动速率为1.5~2.4mm/a;大具—大东次级段以右旋走滑为主、正断为辅,其晚更新世晚期以来的垂直滑动速率为0.1mm/a。4)在大具盆地内发现的NW向地表破裂带的形成时代很年轻,不排除是1966年中甸6.4级地震或1996年丽江7.0级地震造成的地表破裂。     

青藏高原中部五道梁-曲麻莱断裂系西段晚第四纪滑动速率厘定

五道梁-曲麻莱断裂系位于青藏高原中部,关于其晚第四纪活动性迄今鲜有介绍.由高分辨率卫星影像解译和野外地质考察可知,断裂系西段由五道梁南山北缘断裂和五道梁南山南缘断裂组成,二者分别断错了五道梁南山两侧的各级洪积扇.通过洪积扇上的断错地貌分析和光释光测年方法得到南缘断裂缩短速率为(0.25±0.11)mm/a,北缘断裂缩短...     

Holocene activities of the Taigu fault zone, Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

Introduction The Taigu fault is located on the eastern boundary of the Jinzhong basin in the Shanxi fault depression system, which is one of the 12 major active basin boundary faults, and is also less studied among them. The reason for this is, firstly, the Jinzhong basin has no historical earth-quakes with M 7, while the two basins linked together in the northern and southern sides, the Linfen and Xinding basins all have had historical earthquakes with M 7; secondly, because the Jiaochen…     

ACTIVE FAULTS AND THEIR FORMATION MECHANISM IN THE EAST SEGMENT OF QIULITAGE ANTICLINE BELT,KUQA DEPRESSION

Based on geological and geomorphologic characteristics of the surface faults acquired by field investigations and subsurface structure from petroleum seismic profiles, this paper analyzes the distribution, activity and formation mechanism of the surface faults in the east segment of Qiulitage anticline belt which lies east of the Yanshuigou River and consists of two sub-anticlines:Kuchetawu anticline and east Qiulitage anticline. The fault lying in the core of Kuchetawu anticline is an extension branch of the detachment fault developed in Paleogene salt layer, and evidence shows it is a late Pleistocene fault. The faults developed in the fold hinge in front of the Kuchetawu anticline in a parallel group and having a discontinuous distribution are fold-accommodation faults controlled by local compressive stress. However, trenching confirms that these fold-accommodation faults have been active since the late Holocene and have recorded part of paleoearthquakes in the active folding zone. The fault developed in the south limb near the core of eastern Qiulitage anticline is a low-angle thrust fault, likely a branch of the upper ramp which controls the development of the eastern Qiulitage anticline. The faults lying in the south limb of eastern Qiulitage anticline are shear-thrust faults, which are developed in the steeply dipping frontal limb of the fault-propagation folds, and also characterized by group occurrence and discontinuous distribution. Several fault outcrops are discovered near Gekuluke, in which the Holocene diluvial fans are dislocated by these faults, and trench shows they have recorded several paleoearthquakes. The surface anticlines of rapid growth and associated accommodation faults are the manifestations of the deep faults that experienced complex folding deformation and propagated upward to the near surface, serving as an indicator of faulting at depth. The fold-accommodation faults are merely local deformation during the folding process, which are indirectly related with the deep faults that control the growth of folds. The displacement and slip rate of these surface faults cannot match the kinematics parameters of the deeper fault, which controls the development of the active folding. However, these active fold-accommodation faults can partly record paleoearthquakes taking place in the active folding zone.     

毛毛山断裂带断层岩的特征及其意义

对毛毛山断裂带断层岩进行了宏观及微观的观察和分析，特别是对断层岩中石英颗粒的形貌特征、溶蚀类型及断层岩的组分进行了研究。结果表明该断裂是一条具有多期活动的全新世活动断裂．滑动性质以粘滑为主，断裂的东段较西段更为明显。