二维饱和地基中空沟主动隔振分析     

朱兵见  熊浩 《岩土力学》2013,34(2):462-467

根据饱和土Biot理论,在频域内提出了一种适用于弹性波波动问题的有限元-无限元解法,其中有限单元用于近场介质的模拟,而形函数基于一维解析解答的无限单元则被用于人工边界,它可反映波传递到无限远处的特性;应用该法计算算例,以证明其有效性与正确性。在此基础上,对饱和地基中空沟主动隔振效果进行了详细的数值分析,结果表明,空沟深度是影响隔振效果的主要因素,一般沟深越大,隔振效果越好;当沟深一定时,空沟到振源的距离不宜超过1.5倍饱和土剪切波长;空沟的宽度对隔振效果的影响相对较小。  相似文献   

Effects of open trench siding on vibration-screening effectiveness using the two-dimensional boundary element method     

P.H. Tsai  T.S. Chang 《Soil Dynamics and Earthquake Engineering》2009

The two-dimensional boundary element method in frequency domain is used to investigate the screening effectiveness of the open trench–wall barrier system on reducing vibration generated by a footing. Sheet piles or diaphragm walls are on both sides of the open trench as a vibration barrier in this study. The results showed that screening effectiveness of the open trench without siding is greater than that of the open trench–wall barrier system, which is essential for stabilizing the excavation surface in practice. The trench depth of the barrier system appears to govern the screening efficiency of the barrier, and increase in depth results in better vibration-screening effectiveness. The influence of the open trench width, the embedded length of the trench wall and the distance between the vibration source and the barrier are proven to be insignificant. The screening effectiveness of an open trench barrier with walls increases with the frequency of the vibration.  相似文献   

DISTRIBUTION OF YANGJIA VILLAGE-YAODIAN SECTION OF WEIHE FAULT AND THE CHARACTERISTICS OF ITS LATE QUATERNARY ACTIVITY          下载免费PDF全文

TIAN Qin-hu  ZHOU Ben-gang  LI Xiao-ni  SHI Jin-hu  WEI Qing-ke  BIAN Ju-mei 《地震地质》2016,38(1):141-151

The Yangjia Village-Yaodian segment of Weihe Fault, starting from Yangjia Village in the west, passing through Weijiaquan, Jinjiazhuang, Donger Village, Chenjiatai to Yaodian, occurs as a NE-striking fault dipping south with a total length of 33 kilometers. As a syn-depositional normal fault, it extends along the leading and trail edge of T₁, T₂ and T₃ terrace at the northern bank of Weihe River. Results of remote sensing interpretation, shallow seismic exploration, exploratory trench, and drilling show that the Yangjia Village-Yaodian section of Weihe Fault manifests as fault scarps, overlapping with the NE-extending terrace scarp at the northern bank of Weihe River. Weihe Fault broke the T₁ that can be distinguished on the shallow seismic profile and multiple profiles with broken signs from T₁ to the ground, which is the same with the cracks through the Han Tomb at the top of the exploratory trench in Yangjia Village. It shows that the fault may still be active from the late Pleistocene to Holocene. Through composite drilling section and the analysis of exploratory trench, there is no significant difference in activity between the Yangjia Village-Jinjiazhuang and Donger Village-Yaodian section. This segment has experienced a large displacement event since (46.0±3.3)ka BP, approximately 11.0~16.5m, with a vertical slip rate of 0.34~0.45mm/a. The most recent activity occurred approximately around 2.0ka BP. The left-step en echelon fracture zone at Jingjiazhuang separates this section into two minor ones, Yangjia Village-Jinjiazhuang section and Donger Villag-Yaodian section. Yangjia Village-Yaodian section in Weihe Fault and Yaodian-Zhangjiawan section which was found out in the Xi'an active fault detection and seismic risk assessment project can be combined into the Yangjia Village-Zhangjiawan section.  相似文献   

设定琉球海沟发生罕遇地震评估我国东南沿海地区的海啸风险          下载免费PDF全文

温燕林  于海英  朱艾斓  宋治平  李春峰 《地震工程学报》2016,38(2):285-291,317

根据构造相似条件分析,琉球海沟与日本海沟、智利海沟、印尼巽他海沟一样具备发生9级罕遇超巨大地震的可能。在对近几年来全球发生的超巨大地震参数及构造对比分析的基础上,设定琉球海沟9.0级地震参数,并将其引发的海啸进行数值模拟研究。结果表明,该地震可引发初始波高为8m的海啸,台湾东北部半小时后遭受10m以上海啸,3~4小时左右传至浙南、闽北沿岸,近岸各处波高在1~2m;5小时左右传至浙北、粤北沿岸,浙江近岸各处波高在2m左右,广东沿海、台湾海峡由于台湾岛的正面阻挡,海啸波高低于50cm;8小时后靠近上海海岸线,最大波高约1m。海啸的上岸高度与海岸附近的海深和海岸线的形态密切相关,我国东南海域地形变化复杂、海湾众多,对海啸波有放大作用,模拟结果可能比实际海啸偏小。我国沿海地区分布着不少已建和在建的核电厂,在核电设计时未考虑海啸,一旦发生这种罕遇地震海啸则影响不可忽视,尤其是若与风暴潮、天文大潮叠加则可能出现严重后果。由于核电安全要求万无一失,故须制订有效预警和应对措施。  相似文献   

南海东部现时地壳运动、震源机制及晚中新世以来的板块相互作用          下载免费PDF全文

孙金龙  曹敬贺  徐辉龙 《地球物理学报》2014,57(12):4074-4084

南海东部的板块汇聚带是了解南海和菲律宾海晚中新世以来构造演化的一个重要窗口.针对这一区域地壳运动的研究,获得了该区内微块体的现时地壳运动特征及其动力机制,在此基础上结合俯冲板片形态和震源机制资料提出了该区晚中新世以来的板块汇聚作用特征.研究发现:晚中新世晚期,菲律宾海板块西缘在南、北部的西向运动均受到限制的情况下,位于中间区域的吕宋岛北部则由于其西侧相对自由而继续往NW方向运动.该过程中,菲律宾大断裂等汇聚带内部的走滑断裂对于协调不同块体之间的地壳运动速度差异有着重要作用.受南、北阻挡的影响,中间部分的西向运动速率呈现出中间大(吕宋岛北部)两端小的特征.因而北吕宋西侧的马尼拉海沟也以相对于南部更快的速率不断向NW迁移.然而俯冲的南海岩石圈受其下方SE向地幔流的影响,未能发生相应的俯冲板片后撤,而是在两板块之间的直接接触面形成强烈推挤并发生反向弯曲.结合这一板块作用特征认为,马尼拉海沟现今的构造形迹是在上述背景下北段多次向NW方向变迁形成的,而双火山弧的形成则主要是由菲律宾海板块在吕宋岛弧南、北部的西向运动速率差异引起的.  相似文献   

茅口晚期黔中台沟相锰矿地质特征及控矿条件   总被引：9，自引：3，他引：6  

刘平  廖友常  韩忠华  杨光龙  樊正烈 《贵州地质》2005,22(1):31-38

依据地层学的对比研究,云南格学、贵州水城——纳雍和遵义的锰矿均产于中二叠统茅口晚期黔中台沟相带的茅口组第二段,它们在同一成矿地质背景下,其矿床地质特征相似,物质来源相同,具有一定亲缘关系的可比性。该区(带)的锰矿,主要受被动大陆边缘强烈拉张及同生沉积断裂作用,茅口晚期黔中台沟相带和基性火山喷发活动,以及硅灰泥锰矿组合等条件的严格控制。  相似文献   

Two contrasting magmatic types coexist after the cessation of back-arc spreading   总被引：7，自引：0，他引：7  

Osamu Ishizuka  Makoto Yuasa  Rex N. Taylor  Izumi Sakamoto 《Chemical Geology》2009,266(3-4):283-305

Amongst island arcs, Izu–Bonin is remarkable as it has widespread, voluminous and long-lived volcanism behind the volcanic front. In the central part of the arc this volcanism is represented by a series of seamount chains which extend nearly 300 km into the back-arc from the volcanic front. These back-arc seamount chains were active between 17 and 3 Ma, which is the period between the cessation of spreading in the Shikoku Basin and the initiation of currently active rifting just behind the Quaternary volcanic front. In this paper we present new age, chemical and isotopic data from the hitherto unexplored seamounts which formed furthest from the active volcanic front. Some of the samples come from volcanoes at the western limit of the back-arc seamount chains. Others are collected from seamounts of various sizes which lie on the Shikoku Basin crust (East Shikoku Basin seamounts). The westernmost magmatism we have sampled is manifested as a series of volcanic edifices that trace the extinct spreading centre of the Shikoku Basin known as the Kinan Seamount Chain (KSC).Chemically, enrichment in fluid-mobile elements and depletion in HFSE relative to MORB indicates that the back-arc seamount chains and the East Shikoku Basin seamounts have a significant contribution of slab-derived material. In this context these volcanoes can be regarded as a manifestation of arc magmatism and distinct from the MORB-like lavas of the Shikoku back-arc basin. ⁴⁰Ar/³⁹Ar ages range from 15.7 to 9.6 Ma for the East Shikoku Basin seamounts, indicating this arc magmatism started immediately after the Shikoku Basin stopped spreading.Although the KSC volcanoes are found to be contemporaneous with the seamount chains and East Shikoku Basin seamounts, their chemical characteristics are very different. Unlike the calc-alkaline seamount chains, the KSC lavas range from medium-K to shoshonitic alkaline basalt. Their trace element characteristics indicate the absence of a subduction influence and their radiogenic isotope systematics reflect a mantle source combining a Philippine Sea MORB composition and an enriched mantle component (EM-1). One of the most remarkable features of the KSC is that their geochemistry has a distinct temporal variation. Element ratios such as Nb/Zr and concentrations of incompatible elements such as K₂O increase with decreasing age and reach a maximum at ca. 7 Ma when the KSC ceased activity.Based on the chemical and temporal information from all the data across the back-arc region, we have identified two contrasting yet contemporaneous magmatic provinces. These share a tectonic platform, but have separate magmatic roots; one stemming from subduction flux and the other from post-spreading asthenospheric melting.  相似文献   

利用重力异常反演马里亚纳海沟海底地形     

范雕  李姗姗  孟书宇  邢志斌  冯进凯 《吉林大学学报(地球科学版)》2018,48(5):1483-1492

针对利用船舶测量海底地形效率低和成本高的缺点,选取西太平洋板块俯冲菲律宾板块而形成的马里亚纳海沟所在海域作为实验区域,依据重力地质方法（GGM）,利用重力异常数据反演海底地形。采用移去恢复技术确定了重力地质法模型的密度差异常数为2.32 g/cm³。分析比较了GGM海深模型、ETOPO1模型和直接将船测点海深数据格网化（模型1）3种海深模型之间的差异,并依据反演结果对"挑战者深渊"两侧地貌进行了研究。结果表明：GGM模型反演海底地形的结果优于ETOPO1模型,更优于将船测点海深数据直接格网化的结果;模型相对误差与海深的关系不大,受海底地形变化影响明显;在船测数据匮乏或者过于稀疏的海域,模型间海深差值结果较大;"挑战者深渊"海沟两侧的地貌有明显差异,在海沟南侧水深小于5 000 m的浅海部分,坡度平缓（2°~5°）,而在水深大于5 000 m的部分,坡度明显增大（10°~15°）;海沟北侧在整个下降阶段坡度很大（10°~15°）,11°45'N附近出现一个缓冲地带。  相似文献   

公元512年山西省北部7.5级地震发震断层初探   总被引：2，自引：0，他引：2  

丁学文  程新源 《地震研究》1999,22(4):390-396

根据野外断层露头,探槽及热释光年龄样数据,揭示了大同盆地内黄花梁－山自皂断层为公元５１２年强震的发震断层,这对确定该次地震宏观震中及研究大同盆地地震活动性具有重要意义。  相似文献   

From incipient island arc to doubly‐vergent orogen: A review of geodynamic models and sedimentary basin‐fills of southern Central America          下载免费PDF全文

Christian Brandes  Jutta Winsemann 《Island Arc》2018,27(5)

Southern Central America is a Late Mesozoic/Cenozoic island arc that evolved in response to the subduction of the Farallón Plate beneath the Caribbean Plate in the Late Cretaceous and, from the Oligocene, the Cocos and Nazca Plates. Southern Central America is one of the best studied convergent margins in the world. The aim of this paper is to review the sedimentary and structural evolution of arc‐related sedimentary basins in southern Central America, and to show how the arc developed from a pre‐extensional intra‐oceanic island arc into a doubly‐vergent, subduction orogen. The Cenozoic sedimentary history of southern Central America is placed into the plate tectonic context of existing Caribbean Plate models. From regional basin analysis, the evolution of the southern Central American island arc is subdivided into three phases: (i) non‐extensional stage during the Campanian; (ii) extensional phase during the Maastrichtian‐Oligocene with rapid basin subsidence and deposition of arc‐related, clastic sediments; and (iii) doubly‐vergent, compressional arc phase along the 280 km long southern Costa Rican arc segment related to either oblique subduction of the Nazca plate, west‐to‐east passage of the Nazca–Cocos–Caribbean triple junction, or the subduction of rough oceanic crust of the Cocos Plate. The Pleistocene subduction of the Cocos Ridge contributed to the contraction but was not the primary driver. The architecture of the arc‐related sedimentary basin‐fills has been controlled by four factors: (i) subsidence caused by tectonic mechanisms, linked to the angle and morphology of the incoming plate, as shown by the fact that subduction of aseismic ridges and slab segments with rough crust were important drivers for subduction erosion, controlling the shape of forearc and trench‐slope basins, the lifespan of sedimentary basins, and the subsidence and uplift patterns; (ii) subsidence caused by slab rollback and resulting trench retreat; (iii) eustatic sea‐level changes; and (iv) sediment dispersal systems.  相似文献