雅鲁藏布江下游沿岸更新世末—全新世软沉积物变形构造特征、成因及其地质意义

林芝地区雅鲁藏布江下游位于喜马拉雅东构造结附近,这里一直是青藏高原构造演化的重要地区,许多断裂活动和重要构造事件都发生在该地区。通过对雅鲁藏布江沿岸大量软沉积物沉积类型、特征和成因等观察分析,发现了大量与地震活动有关的震积岩,形成了与地震活动有关的多种类型的软沉积物变形构造。主要包括液化卷曲变形、层内错断、负载构造和火焰构造等,表明了该区曾遭受过大范围的地震活动和构造运动。通过对该区软沉积物变形构造的研究,有助于补充该区古地震记录,这对于研究该区的构造活动性具有重要的地质意义。     

华北中元古界雾迷山组中地震驱动的软沉积物变形构造及其地质意义

软沉积物变形构造是确定古地震存在的关键证据之一。拒马河流域野三坡地区雾迷山组中识别出2个软沉积物变形事件层，分别位于雾迷山组的底部、岩性段I的顶部。典型的变形构造有丘槽构造、水压破碎构造和液化脉构造。丘槽构造可进一步分成2类     

晚寒武世早期河北北部柳江盆地发生的强地震

在河北省北部柳江盆地发现了距今5亿年前的地震记录。 震积岩发育在上寒武统崮山组中部。 沉积物变形构造主要有地裂缝、 地震楔、 砂脉、 砂层液化、 包卷层理等。 这些特征沉积构造是地震波作用于潮上—潮间带沉积环境中软沉积物而形成的。 在古沙垄顶部的内碎屑微晶灰岩中有沉积物液化产生扰动层理和流体逃逸形成的砂脉。 显微镜下可见沉积物液化流动显微构造和结构, 如微褶皱、 纹层断错、 液化颗粒等。 水面下在生物礁或沙垄斜坡局部可见重力流形成的包卷层理。 包卷层理核部为浅黄色和紫红色竹叶状灰岩, 中部为浅灰色破碎流化微晶灰岩碎屑, 外部为浅色和紫色内碎屑微晶灰岩。 崮山组的岩性组合和这些软沉积物变形构造表明, 崮山期柳江盆地构造活动剧烈, 沉积环境水深反复变化、 逐步变浅, 伴有地震发生, 估计产生震积岩的古地震的强度为7级左右。 该古地震事件的确定有益于研究地震活动和构造活动规律。     

岷江断裂羌阳桥一带古堰塞湖沉积及构造变形与古地震

在支援茂县汶川地震灾后恢复重建期间,发现在现今叠溪堰塞湖(小海子)上游30km的岷江沿岸及其支流断续有第四纪湖相层出露。通过对羌阳村一带古堰塞湖沉积层的研究,获得了岷江断裂全新世活动的证据。分析认为:岷江断裂沿线古堰塞湖相沉积及其构造变形反映了岷江断裂的多次活动。羌阳桥古堰塞湖沉积及其构造变形可能反映岷江断裂的多次古地震活动。较肯定的是:第1次地震活动导致羌阳桥堰塞湖的形成,堆积第1套湖相沉积;第2次地震活动使湖相层变形;第3次地震活动使第1,2套湖相地层变形;第4次地震活动错断了湖相层之上最新的堆积物。全站仪实测结果表明最后一次古地震活动的垂直位移约为2.6～3.6m     

地震振动液化形变的研究

多种地质作用可造成年青的松散沉积物发生变形。为了判别沉积形变中的地震振动液化形变形迹,着重讨论了振动液化形成机制、形变几何形态特征以及它们与融冻变形和准同生变形构造的区别。认为振动液化形变形迹可以作为鉴别古地震标志之一。     

黄河上游积石峡史前滑坡堰塞湖形成年代与发展演变研究

黄河上游史前大洪水与积石峡史前巨型滑坡堰塞湖、及其与中原地区"大禹治水"和夏王朝的关系问题,受到中外学术界和媒体的广泛关注.其中,关于黄河积石峡古堰塞湖的形成、发展演变和消亡形式问题,成为地学家必须准确回答的前沿性的科学问题.最近七年来,我们在黄河上游循化盆地、积石峡和官亭盆地进行了深入细致的调查研究,通过对古滑坡堆积体和堰塞湖厚达37m沉积物的野外宏观特征观测,沉积物磁化率、粒度、地球化学元素的测定,沉积物成因综合分析论证,以及光释光(OSL)技术断代,结果表明积石峡中段狐跳峡巨型滑坡堰塞事件发生在全新世中期(8.25±0.39)ka.巨大的滑坡堆积体堵塞黄河形成了堰塞湖,它并没有发生突然地垮坝溃决形成异常大洪水,而是持续存在了2600多年.滑坡堰塞坝体受到溢流缓慢的切割,堰塞湖逐渐变浅消亡,期间有反复地收缩和扩张变化,最终在全新世中期(5.65±0.21)ka消失,黄河逐渐贯通.也就是说,积石峡古堰塞湖消亡的年代要早于官亭盆地喇家遗址毁灭废弃的年代约1800年.在积石峡堰塞坝体下游的调查,没有发现所谓"堰塞湖溃决大洪水"的沉积物.这说明积石峡古堰塞湖的形成演变及其消亡过程与官亭盆地喇家遗址的毁灭废弃没有关系.这些研究结果,对于揭示青藏高原东北缘黄河上游史前时期自然灾害发生的规律,正确认识史前时期的人地关系发展演变,准确回答国际学术界和媒体对于黄河上游"堰塞湖溃决大洪水与大禹治水和夏王朝"关系问题的疑问,具有重要的科学意义.     

雅鲁藏布江大峡谷入口河段最近两期古堰塞湖事件的年龄

在雅鲁藏布江大峡谷入口河段,分布着多级含湖相沉积的阶地,在河床下还埋藏有巨厚的河湖相覆盖层。通过对阶地沉积和河床覆盖层浅部沉积物的光释光和14C测年,初步建立了河谷上部沉积的地层年代学框架,揭示出雅鲁藏布江大峡谷入口河段在末次盛冰期以来至少发育2期古堰塞湖(古堰塞湖Ⅰ,古堰塞湖Ⅱ),其沉积年龄分别为7~9ka、20~30ka,并形成2级连续的海拔高度分别为2906~2 956m、3100~3 060m的堆积阶地(T1,T2)。古堰塞湖的沉积时间与青藏高原地区末次冰期冰盛期和全新世早期低温事件相对应,推测是南迦巴瓦峰西坡的则隆弄冰川活动形成冰川堰塞坝堵塞河道的结果。古堰塞湖Ⅰ分布范围较小,在大渡卡—米瑞发育湖相沉积,湖尾大致在米林县城附近,沉积厚度5~8m。古堰塞湖Ⅱ发育范围较广,湖相沉积在大渡卡—卧龙均有出露,湖尾大致在朗县附近,最大沉积厚度超过100m。古堰塞湖Ⅱ被后期河流冲刷,可形成1~3级次级阶地。     

胶州上白垩统史家屯段中地震产生的震火山岩及软沉积物触变变形

首次从胶州市上白垩统红土崖组史家屯段中识别出了一些震火山岩和强地震引起的软泥砂质沉积物的触变变形构造(震积岩)。震火山岩是强地震破坏火山喷出物形成的具同震变形构造的火山岩。震积岩是强地震触动饱和-半固结的软沉积物发生液化、触变、断裂、裂开、充填等形成的具软沉积物变形构造的沉积岩层。红土崖组史家屯段主要由玄武质火山岩夹河湖相泥砂质(砂质泥和泥质砂)沉积层组成。史家屯段中,震火山岩的主要类型为具同震裂隙的震裂玄武岩和震碎玄武岩(震碎玄武质角砾岩)等;软泥砂质沉积物的触变变形主要包括触变泥砂质脉和具曲折边界的触变泥砂质层。受强地震作用,饱和泥砂质沉积物不会发生液化,但会发生触变,即其结构会被破坏而具较强的流动性。由于玄武质火山岩层被地震破坏(震裂、震碎),强地震致使触变泥砂质沉积物沿玄武岩中的震裂隙而流动,结果形成了触变脉变形构造,也使火山岩层与泥砂质层的边界变得十分曲折。在重力和震动力的联合作用下,被震碎的玄武质岩块沉入触变泥砂质中,形成了触变泥砂质沉积物的包体。这些晚白垩世末期的强地震事件记录,所反映的地震烈度约Ⅶ至Ⅹ度以上。史家屯段主要分布在诸城凹陷北部的百尺河断裂以南地带,晚白垩世末该断裂发生强构造与地震活动,也为当时的玄武岩浆上侵和喷发提供了通道。晚白垩世末,玄武岩浆多次沿百尺河断裂间歇式地上侵和喷发,同时产生的火山地震或由百尺河断裂的活动产生的构造地震,致使火山熔岩和下伏的红色饱和泥砂层发生了上述变形,结果形成了地震成因的火山岩与泥砂质沉积层的变形构造。因此,它们所记录的地震事件,应是晚白垩世诸城凹陷发生强构造裂陷和百尺河断裂发生激烈断裂活动的响应。文中具地震成因的岩土层变形构造,也为分析类似岩土地基的地震力破坏效应提供了新资料。     

岷江上游晚更新世湖相沉积的古地震及物源分析

青藏高原东缘是中国大陆内部最显著的地貌梯度带,也是青藏高原周缘新构造与活动构造最为复杂、活动断裂发育密度最高的区域。岷江上游地处"南北向地震构造带"中段,受岷江断裂、虎牙断裂及龙门山逆冲推覆构造带的影响,不仅强震及大震活动非常频繁,而且崩滑流等外动力地质灾害也极为显著,是内外动力作用耦合最为显著的地区。自2008年汶川MS8.0强震以来,随后又发生了2010年玉树MS7.1、2013年芦山MS7.0、2017年九寨沟MS7.0等4次7级以上地震,使得了解青藏高原东缘在地质和历史时期的地震活动成为迫切的科学需求。然而,岷江上游地区多为高山峡谷地貌,侵蚀作用强烈,滑坡、泥石流等地质灾害频繁,人为破坏严重,使得探槽开挖困难,古地震研究程度偏低。已有的少数古地震研究多数集中在全新世,揭露的古地震事件次数也相对较少。区域广泛分布的古堰塞湖湖相沉积连续性好、分辨率高,可能记录更多的地震事件,使得湖相沉积古地震研究受到越来越多的关注。本论文在整理前人资料的基础上,对岷江上游晚更新世湖相沉积出露点展开了详细的野外地质调查、剖面测量和系统采样等工作。首先,通过沉积学手段进行岩性描述、地层划分、层理识别,分析和划分沉积环境与沉积相。其次,对湖相沉积记录的宏观软沉积物变形和层理构造(丘状交错层理)进行研究,重点对软沉积物变形的类型划分、形态描述、成因厘定、变形过程和演化模型进行分析;然后对软沉积物变形的类型、形态和强弱变化与地震震级和震中位置关系进行讨论。再次,利用地球物理(粒度、磁化率)、地球化学等微观指标,并结合端元模型,对湖相沉积记录的事件层和非事件层进行分析和解释,以期获得湖相沉积中连续的构造和气候信息。采用OSL和14C相结合的方法,建立湖相沉积年代,获得古地震活动历史、大致震级等参数。最后采用主微量元素和碎屑锆石U-Pb定年,探讨青藏高原东缘到四川盆地碎屑物质的释放、搬运过程和路线等,以及青藏高原东缘构造活动造山带是如何影响四川盆地的?通过上述研究,得到如下认识:(1)通过OSL和14C测年,初步获得了岷江上游新磨村Ⅰ(XMCⅠ)、新磨村Ⅱ(XMCⅡ)和太平(TP)3个湖相沉积剖面的年代,沉积年龄属于末次冰盛期向全新世过渡时期;沙湾(SW)湖相沉积剖面的时代应属末次冰消期到全新世时期。(2)XMCⅠ、XMCⅡ、SW和TP 4个湖相沉积剖面中,共发现17个变形层,7种类型的软沉积物变形,分为韧性变形(负载构造、火焰构造、假结核构造、球枕构造和液化卷曲)和脆性变形(微断层和液化角砾)两种。软沉积物变形最可能的触发机制为地震作用,代表强液化或(和)流化作用。另外,4个湖相剖面中有12个中厚层向上变细的粉砂层,其成因与地震引起的滑坡、碎屑物质及细颗粒粉尘等被风力或流水搬运到湖泊中并快速沉积有关。(3)当沉积物中记录的软沉积物变形(负载、球枕构造)为地震成因时,其代表的震级可能为6.0～7.0级,震中距约为20～70 km。同等变形强度的负载、球枕构造,地震震级最强的为湖相沉积,其次是河湖相沉积和海相沉积。负载、球枕构造变形的宽度和厚度与地震震级具有正相关关系:即变形层宽度越大、厚度越厚,其记录的震级就越大。球状体变形尺度及球状半径大小,也与震级大小有一定的正相关关系,即球状半径越大,其震级越大。而岩性与地震震级大小没有直接的对应关系。利用软沉积物变形所对应的地震震级估算距震中距离,或者采用软沉积物变形距断层距离估算地震震级的方法都是可行的。(4)根据软沉积物变形类型、变形强弱、扰动厚度、累积厚度、最大液化距离等方法进行古地震震级估算。SW剖面可能记录了6次6.0～7.0级和1次7.0级以上地震;XMCⅠ剖面可能记录了3次5.0～6.0级和2次6.0～7.0级地震;XMCⅡ剖面可能记录了2次5.0～6.0级和3次6.0～7.0级地震;TP剖面可能记录了1次6.0～7.0级地震。(5)基于粒度的粒径分布、频率及累积曲线、岩性三角图、C-M图、粒度象限及萨胡判别公式对XMCⅠ、XMCⅡ和TP 3个湖相沉积剖面进行成因厘定,沉积物多为粘土、粉砂和极细砂沉积,均显示风成成因特点,多为近距离风力搬运并迅速堆积到湖泊中;而SW湖相沉积剖面则为风成和水成两种成因特点。通过对XMCⅠ、XMCⅡ、XMCⅢ和TP 4个剖面粒度数据的端元模拟显示,均可以分离出2个粒径端元,其中EM1为非地震期间的湖泊沉积;EM2为极端灾变(地震、滑坡等)期间的湖泊沉积。SW剖面可以分离出3个粒径端元,EM1代表非地震期间的湖泊沉积,EM2和EM3代表极端灾变(地震、滑坡等)期间的湖泊沉积。结合粒度、磁化率、地球化学及端元模型,XMCⅠ、XMCⅡ、XMCⅢ、TP和SW 5个湖相沉积剖面分别识别出22次,18次,26次,23次和12次可能的地震事件层。地震事件层与非地震事件层区别明显,虽然各个事件层所处的演化阶段(AB、BC和CD段)不太一样,但事件层都具有相同或类似的演化模式,即粒度突然变粗,向上缓慢变细,进而逐渐变细到以粉砂质粘土为主的正常沉积。基本对应于地震发生时粗颗粒碎屑物质的突然释放;地震短时间尺度内粗碎屑颗粒与细颗粒物质充分混合阶段;震后长时间尺度,以分选好的细颗沉积阶段。(6)根据宏观软沉积物变形层、微观粒度和磁化率识别的地震事件层,并对这两种方法识别的地震频次、震级大小进行对比分析和相互校正,初步获得了古地震发生的频次和震级大小。其中,XMCⅠ剖面初步识别了15次5.0～6.0级,5次6.0～7.0级,2次7.0～8.0级,共22次地震事件。XMCⅡ剖面初步识别了11次5.0～6.0级,5次6.0～7.0级,2次7.0～8.0级,共18次地震事件。XMCⅢ剖面初步识别了4次5.0～6.0级,18次6.0～7.0级,4次7.0～8.0级,共26次地震事件。SW剖面初步识别了4次5.0～6.0级,5次6.0～7.0级,3次7.0～8.0级,共12次地震事件。TP剖面初步识别了6次5.0～6.0级,15次6.0～7.0级,2次7.0～8.0级,共23次地震事件。(7)新磨村剖面(XMC)共发现227层丘状交错层理,其中XMCⅠ剖面为135层,XMCⅡ剖面为76层,XMCⅢ剖面为16层。二维形态测量显示:长度为1.7～24 cm,平均8.40 cm;厚度仅0.1～2.7 cm,平均0.56 cm,长度与厚度比为10～20;三维形态为波浪的薄板状,波长2.6～10 cm,平均5.9 cm;波高0.4～6 cm,平均2.3 cm;波长与波高比在2～5之间,并有明显的铁锈氧化圈。丘状交错层理的粒度测量显示,沉积物颗粒较细,多为粉砂和极细砂,显示风成成因特点。进一步的地球化学数据表明,沉积物多为近距离风力搬运并迅速堆积到湖泊中。丘状交错层理明显受水流作用影响,作为一种非常重要的沉积构造,常出现在正常的浪基面与风暴浪基面之间,可能为极端气候条件下的风暴波浪成因。类似的变形构造在堰塞湖中也可以保存。(8)从青藏高原东缘的岷江上游到四川盆地,采集8个样品(基岩、湖相沉积物、现代河砂、风成沉积物)进行碎屑锆石U-Pb定年及粒度测量,结果显示,岷江上游的基岩(XMC15-08、DL15-03和LX15-01),现代河砂(WC15-01)和风成沉积物(DY15-01)的锆石颗粒较粗;而湖相沉积(XMC15-01、DL15-02和LX-14)锆石颗粒较细。有趣的是,河砂样品与风成沉积碎屑锆石颗粒度参数很相似。碎屑锆石主要有5个年龄组分,分别是180～350 Ma(早侏罗纪—石炭纪);350～550 Ma(泥盆纪—寒武纪);700～1 000 Ma(新元古代);1 600～2 200 Ma(中元古代—古元古代);2 200～2 600 Ma(古元古代—新太古代),大致对应于长江流域5次花岗岩岩浆事件的年龄(印支—震旦系/燕山期、海西、加里东期、晋宁期、吕梁期)。基于碎屑锆石年龄分布和非计量多元尺度模拟(MDS)显示:岷江连接着理县的湖相沉积;汶川、乐山、宜宾和大渡河的现代河砂及大邑砾岩,暗示着大邑砾岩是由河流搬运堆积,而非冰川侵蚀搬运。伴随着青藏高原东缘频繁的地震活动,诱发了大量的滑坡等碎屑物质,随后经过河流搬运到四川盆地西部,堆积形成厚的沉积物,并有2个巨厚的沉积中心,而相对较细的沉积物又被地形风或者阵风搬运至四川盆地北部,例如德阳地区。因此,岷江搬运的碎屑物质是四川盆地西部主要的物质来源,同时也为四川盆地北部提供大量的粉尘物质。而嘉陵江和大渡河对四川盆地西部的物质贡献较小。     

远古时代京津唐地区一次大震的研究

本文介绍了京津唐地区内埋藏在全新世地层中的一次古地震遗迹和构造变形。通过对本区全新世地层、古环境的研究确定这次地震事件为距今4000年、本区海侵结束时发生的,恰恰与史料纪载的“地震传说”一致。文章最后对发震背景,砂基液化以及震中、震级等问题进行了一些讨论     

新丰江水库区地震构造及其活动特征的初步研究

本文介绍了库区的地震构造,并依据重、磁及地壳垂直形变与震源机制资料,论述了它的活动特征;进而讨论了共轭发震构造,它的成因类型以及在地震预报中的作用     

Tectonic styles of the Archaean rock groups in the North-Central Liaoning province, China

Two major Archaean rock groups, the Tiejiashan Group and the overlying Anshan Group, have been divided and described in the area under consideration. From the techniques of tectonic analysis, including detailed observation and data collection in the field, together with necessary projection methods, structural succession and style variations of both groups were established in order to clarify the intricate deformation and evolutionary histories of these two major units. We have first discerned two episodes of deformation in the Tiejiashan Group during tectonic cycle I and four in the Anshan Group during cycle II, and thus reconstructed the full sequence of deformations for these rocks.The Tiejiashan Group is mainly composed of migmatized tonalitic-granodioritic gneiss. It contains a pervasive gneisses foliation which dnotes the early episode of tectonic cycle I, and it describes oval-shaped folds or domes that are considered to be results of flexural-flow mechanism with accompanying flow component under extensive vertical movement (perhaps diapiric) during a slightly later episode. This style characterizes the tectonic state of deep levels of the Archaean crust.Rock types of which the overlying Anshan Group are made up include plagioclase-amphibolite, biotite-plagioclase-gneiss and leucocratic gneiss—the metamorphosed equivalents of a succession typical of Archaean greenstone belts. Tectonic elements formed during four episodes of deformation show systematic style variation which can easily be distinguished from that of the Tiejiashan Group. Tectonic anisotropy is evident and shown by the development of pronounced linear structures such as folds, as well as planar structures and other related elements of contrasting ages and scales—diagnostic for the importance of horizontal displacement in the formation of structures in a greenstone belt. Patterns of fold interference are ubiquitous at all scales, and they are described in terms of Ramsay's classification. Factors controlling the interference patterns are many; in addition to those which have been pointed out by Ramsay and others, size contrast between interfering folds is another important one to be considered.Style variations between the Archaean rock groups suggest a tendency of tectonic development from planar to linear types. This reflects a transition from a tectonic regime controlled by the earlier widespread vertical movements to a largely horizontal compressional regime. This may also be an indication of the major change during the tectonic evolution of the basement of the North China platform.     

Earthquake-controlled event deposits and its tectonic significance from the Middle Permian Wandrawandian Siltstone in the Sydney Basin,Australia

Earthquake is a disaster event resulting from rapid and intensive crustal vibration caused by fault activity, volcanic eruption, or block dilapidation. Heezen and Ewing[1] and Heezen and Dyke[2] were the first to note earthquake-related mass movement and associated deposits in connection to the turbidity currents and submarine slumps triggered by the Grand Bank Earthquake in 1929. Seilacher[3] defined redeposited sedimentary beds, disturbed and modified by earth- quakes, as seismite. Since t…     

Ancient Constructions as Markers of Tectonic Deformation and Strong Seismic Motions

Many ancient structures such as temples were constructed on the basis of a very strict plan and excellent workmanship. For this reason, even their slight deformation due to various effects (ground instability, earthquake oscillations, etc.) can be identified, and it is possible to discriminate between different types of deformation due to earthquakes and those due to other natural causes or to anthropogenic effects. Two study cases are presented here: the Propylaia on the Acropolis and the temple of Hephaistos (Hephaisteion) in the Agora at Athens. In both buildings deformation was produced by earthquakes.     

基于自由场局部变形的地下结构抗震Pushover分析方法

对地下结构抗震Pushover分析方法进行了改进,采用自由场局部变形峰值作为目标位移,局部变形峰值时刻对应的土层水平加速度作为等效惯性加速度输入。给出了局部变形峰值和等效惯性加速度确定方式,详细介绍了基于自由场局部变形的地下结构抗震Pushover分析方法实施步骤、使用方法和功能特点。该方法更有针对性地考虑了强地震作用下不同埋深地下结构与土体的非线性特征以及两者之间的相互作用,通过分析变形和受力情况可以得到完整的能力曲线,更好地评估地下结构抗震性能。使用本文方法对3种埋深的地下结构进行计算,并与动力非线性分析结果进行对比研究。结果表明:本方法在计算稳定性和模拟精度方面优于基于自由场整体变形的Pushover方法;对于不同的输入地震波,能力曲线的吻合程度更高;在强震和罕遇地震情况下,对于深埋地下结构,计算结果略大于动力非线性结果,对实际工程而言更加安全。     

青藏高原东北缘深地震测深震相研究与地壳细结构

通过对青藏高原东北缘不同构造单元深地震测深资料震相的综合分析,利用反射率理论地震图方法对实际记录模拟计算,进一步研究东北缘区域内部不同构造单元地壳细结构.结果显示：西秦岭褶皱造山带分隔了南北不同性质的地壳结构,北侧为相对稳定的临夏—兰州新生代盆地、南侧为强烈改造的松潘—甘孜地块;松潘—甘孜地块在青藏高原东北缘的构造演化过程中改造为萎缩的若尔盖高原盆地和盆地边缘褶皱造山两类不同的地壳结构;青藏高原东北缘中下地壳普遍存在以多层高低速相间、低速度结构为主的破碎松弛结构,这种特征在缝合带和造山带尤为明显,显示为地壳形变增厚、流变滑动的重要场所;结合二维速度结构及GPS研究结果,对青藏高原东北缘地壳形变及动力学过程进行了讨论.     

Quantifying the seismic response of structures with flexible diaphragms

Floor diaphragm in-plane stiffness affects building response to horizontal ground accelerations. This paper describes a series of elastic and inelastic time history analyses of symmetric structures with different deformation types, configurations and heights to quantify these effects. It is shown that displacements of single storey elastically responding structures tend to be most significantly affected by diaphragm flexibility. Analyses of these structures were cross-verified by a closed-form mechanics-based formulation developed to describe the response. Simple relationships were proposed to allow designers to conservatively estimate the increase in peak in-plane displacement resulting from diaphragm flexibility. Copyright © 2012 John Wiley & Sons, Ltd.     

Earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation,North China,and their geologic implications

Soft-sediment structures are key to defining seismites. Two soft-sediment deformation horizons, bounded by undeformed carbonate strata, have been found in the Wumishan Formation in the Jumahe region, 175 km southwest of Beijing. One is in the lowest part of Wumishan Formation; and the other is in the uppermost part of Litho-member I. The soft-sediment structures in these two horizons fall into three categories: mould-and-sag structures, hydraulic shatterings and liquefaction dikes. The mould-and-sag structures are divided into two types: one developed in tidal-flat sediments, accompa-nied by many liquefaction-related structures and characterized by autochthonous post-earthquake sediments in sags, and the other type developed in deep-water environments, is not associated with liquefaction structures, and is overlain immediately by seismogenic tsunamites. The hydraulic shat-terings are composed of pockets of fluidization conglomerate, sand intrusions, and syndepositional faults. The liquefaction dikes fall into two categories: hydraulic-fracturing dikes and lateral-spreading dikes. The former are steep, planar, and pinch out upwards. The latter are snake-like and characterized by no diapir-related drag structures in surrounding rocks. Examination of the attitudes and strati-graphic positions of these structures suggests that these soft-sediment structures are seismogenic, and consequently, are seismites. Most seismites in the Wumishan Formation are developed near the former western, margin fault of Yanliao rift. This occurrence suggests that they could be related to movements on this fault. Other geological implications are discussed.     

Soft‐sediment deformation structures in Cretaceous non‐marine deposits of southeastern Gyeongsang Basin,Korea: Occurrences and origin

A variety of soft‐sediment deformation structures formed during or shortly after deposition occurs in the Cretaceous Seongpori and Dadaepo Formations of the southeastern Gyeongsang Basin exposed along coastal areas of southeastern Korean Peninsula for 0.5–2 km. These are mostly present in a fluvial plain facies, with interbedded lacustrine deposits. In this study, the features of different kinds of soft‐sediment deformation structures have been interpreted on the basis of sedimentology of structure‐bearing deposits, comparison with normal sedimentary structures, timing and mechanism of deformation, and triggering mechanisms. The soft‐sediment deformation structures can be classified into four morphological groups: (i) load structures (load casts, ball‐and‐pillow structures); (ii) soft‐sediment intrusive structures (dish‐and‐pillars, clastic dykes, sills); (iii) ductile disturbed structures (convolute folds, slump structures); and (iv) brittle deformation structures (syndepositional faulting, dislocated breccia). The most probable triggering mechanisms resulting in these structures were seismic shocks. These interpretations are based on the following field observations: (i) location of the study area within tectonically active fault zone reactivated several times during the Cretaceous; (ii) deformation structures confined to single stratigraphic levels; (iii) lateral continuity and occurrences of various soft‐sediment deformation structures in the deformed level over large areas; (iv) absence of depositional slope to indicate gravity sliding or slumping; and (v) similarity to the structures produced experimentally. The soft‐sediment deformation structures in the study areas are thus interpreted to have been generated by seismic shocks with an estimated magnitude of M > 5, representing an intermittent record of the active tectonic and sedimentary processes during the development and evolution of two formations from the late Early Cretaceous to the Late Cretaceous.     

地震力作用下单排与双排桩支挡结构性状试验对比分析

桩板式挡土结构由抗滑桩发展而来,可用于一般地区、浸水地区和地震区的边坡工程支挡;对于地震区边坡,采用单排或双排支挡结构的形式及其支挡效果尚缺少深入研究.本文基于地震力作用下单排、双排桩板结构在不同加载等级时的桩身土压力、土体加速度、桩身位移等变化的振动台模型试验结果,对比采用单排、双排桩板结构边坡的支挡效果,得出静力状...