The Earth's natural pulse electromagnetic fields for earthquake time–frequency characteristics: Insights from the EEMD–WVD method          下载免费PDF全文

Guo‐Cheng Hao  Yu‐Xiao Bai  Hui Liu  Juan Zhao  Zuo‐Xun Zeng 《Island Arc》2018,27(4)

Monitoring the Earth's natural pulse electromagnetic field (ENPEMF) signal is a geomagnetic detection approach for the Earth internal and external studies, and it provides a reference for earthquake prediction. In this paper, the Ensemble Empirical Mode Decomposition–Wigner Ville Distribution (EEMD–WVD) method is used to process the time sequences of the ENPEMF signal detected by GR‐01 receiving devices during the Lushan M_S7.0 earthquake (April 20th, 2013). By obtaining the intrinsic mode function (IMF), the time–frequency–amplitude joint distribution and the energy spectrum of the ENPEMF signal, the suspected anomalies before the earthquake could be shown. The results illustrate the ENPEMF signal before an earthquake and its time–frequency characteristics based on an EEMD–WVD algorithm, proving useful information about the anomalies around the time of the earthquake.  相似文献   

Seismic response and energy dissipation of 3D complex steel buildings considering the influence of interior semi-rigid connections: low- medium- and high-rise     

Alfredo Reyes-Salazar  José M. Sauceda-Pimentel  Sonia E. Ruiz  Edén Bojórquez  Juan Bojorquez 《Bulletin of Earthquake Engineering》2018,16(11):5557-5590

A numerical investigation regarding the seismic behavior of complex-3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (GF) is conducted. The interior connections are assumed to be first perfectly pinned (PP) and then semi-rigid (SR); the two model responses are compared. Three steel building models representing low-, medium- and high-rise buildings, and several strong motions are used. The relative stiffness of SR connections is calculated according to the Richard Model and the Beam Line Theory. The Ruaumoko Computer Program is used to perform the required step-by-step nonlinear seismic analysis. Results indicate that interstory shears and interstory displacements at PMRF may be significantly reduced when interior connections are modeled as SR. Average reductions of up to 20, 46 and 11% are observed for interstory shears, for low-, medium-, and high-rise buildings, respectively. The corresponding reductions for interstory displacements are about 14, 44 and 15%. The contribution of GF to the lateral resistance is considerable, which significantly increases when the connections are modeled as SR; relative contributions larger than 80% are observed. The dissipated energy (DE) at PMRF is larger for the buildings with PP than for the buildings with SR connections indicating that damage at PMRF is reduced. Thus, the effect of the stiffness and the DE at interior connections should not be ignored. However, the design of some elements, particularly columns of the GF, has to be revised; these members may not be able to support the loads produced by the neglected lateral contribution if they are not properly designed.  相似文献   

The Tongliao MS5.3 Earthquake and Its Foreshock Determination     

Wang Shubo  Zhuoli Getu  Li Juan 《中国地震研究》2018,32(3):344-354

Taking the 2013 Tongliao MS5. 3 earthquake as a research subject, on the basis of statistical analysis of earthquake sequence using the HypoDD location method and focal mechanism solutions,the paper analyzes and discusses the relationship between the ML4. 4 and MS5. 3 earthquakes. The results show that the Tongliao MS5. 3 earthquake occurred under the background of medium-small earthquakes long-term quiescence and short-term enhancement in the epicentral area. The results of accurate seismic location shows that the Tongliao MS5. 3 earthquake sequence is distributed in the NW direction,extending 10 km,and the ML≥3. 0 aftershocks are concentrated south of the mainshock. The distance between the MS5. 3 mainshock and the ML4. 4 foreshock is about 1. 8 km,with a focal depth of 7. 208 km and 7. 089 km,respectively,their focal location is very close,and may have occurred on the same fault plane. The results of focal mechanism shows that the Tongliao MS5. 3 earthquake is of the strike-slip type,the focal mechanism of aftershocks are disordered,and with time lapse,the type is changed from strike-slip to thrust and normal faulting. The bigger foreshocks had similar focal mechanism and were all normal fault types,which exhibits to some extent,an obvious crustal medium anisotropy in the epicentral area before macroscopic rupturing,as represented by alignment fractures,with stress action enhanced,this"consistency"of seismic precursor regime would gestate the mainshock. According to the characteristics of temporal-spatial distribution of earthquake sequence and similarity of focal mechanism,we judge that the Tongliao MS5. 3 earthquake sequence is a foreshock-mainshock-aftershock type.  相似文献   

内置空心钢球的圆截面钢管混凝土柱抗震性能试验          下载免费PDF全文

程晨  李鲲  范霏然  陈娟  杜国锋 《世界地震工程》2020,(4):042-52

为研究带空心钢球的钢管混凝土柱的抗震性能,以空心率和含钢率为参数,设计制作9个内置空心钢球的圆截面钢管混凝土柱和3个薄壁圆截面钢管混凝土柱,并进行拟静力试验,结合破坏形态通过延性系数和累积耗能等参数探讨了试件的抗震性能。研究结果表明:含钢率对内置空心钢球的薄壁圆形钢管混凝土柱极限荷载,峰前耗能的影响较大,空心率对试件延性系数,峰后耗能的影响显著;内置空心钢球的薄壁圆形钢管混凝土柱较实心薄壁圆形钢管混凝土柱极限荷载有所降低;试件水平荷载时程曲线的"V"字形波动的折线可以较直观的反映出结构损伤破坏过程,并在曲线数形与试验现象关联上和滞回曲线形成较好的一致性;可以通过优化内置空心钢球的大小和壁厚设计钢管混凝土柱,并取得与实心钢管混凝土柱同样的抗震性能,为同类钢管混凝土组合结构的设计提供了依据。  相似文献   

Two types of hyperthermal events in the Mesozoic-Cenozoic: Environmental impacts,biotic effects,and driving mechanisms     

Hu  Xiumian  Li  Juan  Han  Zhong  Li  Yongxiang 《中国科学:地球科学(英文版)》2020,63(8):1041-1058

A deeper understanding of hyperthermal events in the Earth's history can provide an important scientific basis for understanding and coping with global warming in the Anthropocene. Two types of hyperthermal events are classified based on the characteristics of the carbon isotope excursion(CIE) of the five representative hyperthermal events in the Mesozoic and Cenozoic. The first type is overall characterized by negative CIEs(NCHE) and represented by the Permian-Triassic boundary event(PTB, ～252 Ma), the early Toarcian oceanic anoxic event(TOAE, ～183 Ma), and the Paleocene-Eocene Thermal Maximum event(PETM, ～56 Ma). The second type is overall characterized by positive CIEs(PCHE) and represented by the early Aptian oceanic anoxic event(OAE1 a, ～120 Ma) and the latest Cenomanian oceanic anoxic event(OAE2, ～94 Ma).Hyperthermal events of negative CIEs(NCHE), lead to dramatic changes in temperature, sedimentation, and biodiversity. These events caused frequent occurrence of terrestrial wildfires, extreme droughts, acid rain, destruction of ozone layer, metal poisoning(such as mercury), changes in terrestrial water system, and carbonate platform demise, ocean acidification, ocean anoxia in marine settings, and various degree extinction of terrestrial and marine life, especially in shallow marine. In contrast,hyperthermal events of positive CIEs(PCHE), result in rapid warming of seawater and widespread oceanic anoxia, large-scale burial of organic matter and associated black shale deposition, which exerted more significant impacts on deep-water marine life,but little impacts on shallow sea and terrestrial life. While PCHEs were triggered by volcanism associated with LIPs in deep-sea environment, the released heat and nutrient were buffered by seawater due to their eruption in the deep sea, thus exerted more significant impacts on deep-marine biota than on shallow marine and terrestrial biota. This work enriches the study of hyperthermal events in geological history, not only for the understanding of hyperthermal events themselves, large igneous provinces, marine and terrestrial environment changes, mass extinctions, but also for providing a new method to identify the types of hyperthermal events and the inference of their driving mechanism based on the characteristics of carbon isotopic excursions and geological records.  相似文献   

人工湿地研究现状与展望   总被引：7，自引：0，他引：7  

成水平  王月圆  吴娟 《湖泊科学》2019,31(6):1489-1498

自1950s开始系统性研究以来,人工湿地研究日趋深入,也得到了广泛的应用.本文基于文献报道,对人工湿地研究的历程特别是我国的研究进行了分析,分为起步探索、迅猛发展和规范应用三个阶段.梳理了人工湿地的研究现状,主要集中在如何提高脱氮除磷效率、对新兴污染物的去除、人工湿地根区微生物结构与功能以及人工湿地模型四个方面.核心还是提高人工湿地对污染物的去除效率并解释其机理.未来需要长期监测数据支撑的理论实践结合的设计规程;进一步揭示人工湿地的生物过程;建立合理简化的模型,对系统进行准确预测.  相似文献   

1986-2017年太湖出、入湖水量变化分析     

季海萍  吴浩云  吴娟 《湖泊科学》2019,31(6):1525-1533

作为流域内水资源调蓄和调度的中枢,太湖的出、入湖水量格局随着一系列工程、非工程措施的实施已然改变.基于1986-2017年近30年的环湖出、入湖水量资料,采用Mann-Kendall趋势检验法、突变检验法和滑动t检验法,对环湖及地区出、入湖水量变化进行了定性、定量研究,并讨论了产生变化的可能原因.结果表明:1986-2017年,环湖年入湖水量增加趋势显著,在20世纪90年代后期突变增加,年出湖水量增加趋势显著,在21世纪初后期突变增加;多年平均年入湖总量突变后较突变前增加了29.66亿m3,多年平均年出湖总量增加了18.63亿m3;江苏入湖水量增长率、增长贡献率分别为53%和84%,出湖水量增长率、增长贡献率分别为31%和48%;浙江入湖水量增长率、增长贡献率无明显改变,出湖水量增长率、增长贡献率分别为26%和31%;望虞河出入湖增长率最大,但增长贡献率不大;太浦河出湖增长率、增长贡献率无明显变化;出、入湖水量的变化抬升了太湖年平均水位和年最低水位,对年最高水位影响较小;水利工程调度对出、入湖水量的影响逐渐占据主导作用.  相似文献   

A method for classifying pre‐stack seismic data based on amplitude–frequency attributes and self‐organizing maps          下载免费PDF全文

Erik Molino‐Minero‐Re  Ernesto Rubio‐Acosta  Héctor Benítez‐Pérez  Juan Marcos Brandi‐Purata  Nora Isabel Pérez‐Quezadas  Demetrio Fabián García‐Nocetti 《Geophysical Prospecting》2018,66(4):673-687

  相似文献   

RC structures cyclic behavior simulation with a model integrating plasticity,damage, and bond‐slip          下载免费PDF全文

Bashar Alfarah  Juan Murcia‐Delso  Francisco López‐Almansa  Sergio Oller 《地震工程与结构动力学》2018,47(2):460-478

The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics‐based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond‐slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond‐slip of 2 or more crossing reinforcing bars in beam‐column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond‐slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation.  相似文献   

1960年以来太湖水生植被演变   总被引：9，自引：5，他引：4  

赵凯  周彦锋  蒋兆林  胡娟  张秀山  周洁  王国祥 《湖泊科学》2017,29(2):351-362

太湖的富营养化污染日益严重,针对太湖水生植被的研究工作非常重要,然而全面的太湖水生植被调查已经有将近二十年未见报道.基于2014年夏季全湖水生植被调查结果,结合历史资料,比较分析1960年以来太湖水生植被演变情况.结果表明,1960年以来,共有23种水生植物从太湖消失,其中1981、1997和2014年分别消失7、4和12种.从分布区面积来看,1960年以来太湖水生植被总体呈北部湖区水生植被消失,东北部、东部及南部湖区水生植被分布区面积持续扩张的态势,1981年全湖水生植被分布区面积占8%,到2014年已经有33.82%的水面有水生植被分布.从生物量组成来看,太湖水生植被先升后降,从1960年的10×10⁴ t,持续上升到1988年的44.72×10⁴ t,1997年下降到36×10⁴ t,2014年进一步下降到29.09×10⁴ t.但挺水植被以外的水生植被,尤其是浮叶植被的生物量一直保持上升态势.总生物量的下降与东太湖挺水植被大面积消失有关,到2014年全湖挺水植被生物量比重仅占5.15%,东太湖沼泽化问题已不复存在.从群落组成变化情况来看,苦草（Vallisneria natans）群落分布区面积锐减,马来眼子菜（Potamogeton malaianus）和荇菜（Nymphoides peltatum）分布区持续扩张.目前太湖水生植被管理面临的主要问题是北部湖区水生植被恢复和东部湖区水生植被过量生长.  相似文献