GPS measurements of postseismic deformation due to October 8, 2005 Kashmir earthquake

Relaxation of the coseismic stresses following an earthquake causes postseismic crustal deformation, which can last for days to years. Continuous monitoring of postseismic deformation facilitates the understanding of the mechanism of deformation and postseismic relaxation and viscous rheology. After the October 8, 2005 Kashmir earthquake, global positioning system data for 8 months, starting from October, 2005 have been analyzed from three continuous sites located at Gulmarg, Amritsar, and Jaipur. The average velocity during the observation period at Gulmarg (8.6 cm/year) is significantly higher than the Indian plate velocity exhibiting postseismic crustal deformation. The velocity at Amritsar (5.9 cm/year) and Jaipur (5.1 cm/year) is comparable to the Indian plate velocity. At Gulmarg, the logarithmic function fits well to the north–south component of postseismic transients (~in the coseismic slip direction). The nature of decay in these transients suggests that the deformation is mainly due to an afterslip, and the second possible contribution may be from the viscous relaxation process. This paper presents the characteristics of postseismic transients and possible contributions from various postseismic mechanisms subsequent to the Kashmir earthquake.     

基于地壳分层的唐山地震断层震后变形分析

本文利用球体粘弹性地球模型研究唐山地震断层基于地壳分层的震后变形影响，计算四种不同类型的地球分层模型（均匀模型和三种地壳分层模型）产生的震后变形场，分析不同模型对地表变形的影响异同，定量研究了实际地壳分层模型与均匀地壳模型计算的地表变形差异.计算结果显示，相对均匀粘弹性地球模型，利用分层的地壳结构模型，计算的唐山地震断层附近区域震后28年积累的变形，两者最大差值水平方向可达20mm，垂直变形相差10mm左右.计算的结果显示地壳结构的差异对震后地表变形的影响很大，超过现有高精度测量技术的精度.如果利用该区的实测资料进行反演研究，必须根据实际地壳构造情况考虑地壳分层的影响.     

Longitudinal integral response deformation method for the seismic analysis of a tunnel structure

For the longitudinal seismic response analysis of a tunnel structure under asynchronous earthquake excitations, a longitudinal integral response deformation method classified as a practical approach is proposed in this paper. The determinations of the structural critical moments when maximal deformations and internal forces in the longitudinal direction occur are deduced as well. When applying the proposed method, the static analysis of the free-field computation model subjected to the least favorable free-field deformation at the tunnel buried depth is performed first to calculate the equivalent input seismic loads. Then, the equivalent input seismic loads are imposed on the integral tunnel-foundation computation model to conduct the static calculation. Afterwards, the critical longitudinal seismic responses of the tunnel are obtained. The applicability of the new method is verified by comparing the seismic responses of a shield tunnel structure in Beijing, determined by the proposed procedure and by a dynamic time-history analysis under a series of obliquely incident out-ofplane and in-plane waves. The results show that the proposed method has a clear concept with high accuracy and simple progress. Meanwhile, this method provides a feasible way to determine the critical moments of the longitudinal seismic responses of a tunnel structure. Therefore, the proposed method can be effectively applied to analyze the seismic response of a long-line underground structure subjected to non-uniform excitations.     

The Santa Barbara earthquake of 13 august, 1978

Although the Santa Barbara earthquake was only a moderate seismic event, it was the most destructive earthquake in the United States in 1978 causing more than $7 million damage and at least 65 injuries. Reported Richter magnitudes ranged from 5–1 to 5–7, but estimates based on strong motion records yielded about 5–8. Due to the geologic features of the earthquake, the intensity of strong shaking was geographically asymmetrical, being much larger in the Goleta area north and west of the epicentre. Peak ground accelerations of 0–40 g were recorded near Goleta, while 0–23 g was recorded closer to the epicentre in Santa Barbara. The duration of strongest shaking was only about 2–3 s. The earthquake caused light cracking of shear walls in multi-storey reinforced concrete structures, as well as damage to highway overcrossings, many mobile homes and to rooftop mechanical equipment. Presented in this paper are the results of preliminary investigations of the engineering features of this earthquake.     

汶川地震同震模型新解及震后InSAR观测和初步分析

汶川地震的形变观测在一定程度上来说,取得了前所未有的成功,特别是在龙门山这样一个特殊的地质构造单元上。通过干涉雷达(InSAR)手段获得断层上盘的形变观测,用C波段雷达观测几乎是不可能的,因为剧烈的地面起伏和致密的植被覆盖会使得雷达后向散射信号在观测期间变得完全不相干。同时超厚的水汽分布,使得大气对雷达波的延迟作用变强,造成显著的观测误差。然而,利用L波段雷达观测,前面一个问题得到部分解决;同时,日本宇航机构JAXA在震后紧急调整卫星轨道,获得了相当一部分覆盖汶川地震的小基线干涉像对,进一步降低了干涉去相干作用,最终使得我们得到了比较全面的InSAR形变观测结果。     

形变多手段监测与地震预报

1 研究背景我国将大地测量用于地震监测预报始于1966年邢台地震,现已逐步发展成为具有多手段、多队伍的地形变监测学科,积累现象了大量监测资料.在地震的中长期预测、中短期预报中有较为成功的实例,但错报、漏报现象也不少.地震预报水平与防震减灾的实际需求仍有较大差距,实事求是地总结成功经验与失败教训,有利于清醒认识地震监测...     

Crustal deformation due to Alaska–Yakutat collision

The region of Alaska and adjacent northwest Canada is tectonically active and is subjected to multiple tectonic processes including plate subduction and terrane accretion. These tectonic processes and the forces originating thereof are responsible for high seismicity in the region and deformation of the crust. In the present-day tectonic setting, the Yakutat terrane is obliquely colliding with Alaska along the Aleutian Trench. Also, flat subduction due to under thrusting of a thickened crust, probably of oceanic affinity, is contributing to the tectonic evolution of this region in a basal traction collision style. This study uses the 2D, planform, thin-viscous-sheet model to investigate the effect of the Yakutat terrane colliding with Alaska and adjacent northwest Canada. Along with the obliquity and velocity of convergence, the lateral strength heterogeneities in the crust are considered in this investigation. The results of the numerical model are constrained with the observed topography and stress orientation in Alaska. It is shown that the Alaska–Yakutat collision is producing asymmetric deformation of the crust with respect to the normal to the collision boundary and that lateral strength heterogeneities contribute significantly to the deformation of the crust. Also, the influence of this collision can be observed up to a distance of 700 km inland from the collision boundary.     

不同底面积与埋深的结构-土体系地震反应分析

对结构-土相互作用体系中结构基础底面积和结构基础埋深对体系地震反应的影响进行了研究.基于有限元分析方法建立了结构-土相互作用三维计算模型,通过改变结构底面积及基础埋深在不同地震动下进行了地震反应分析.结果表明,考虑相互作用时,在同一种地震动作用下,结构顶层总位移及基础转动随着结构底面积的增大而明显减小,上部结构本身位移在总位移中所占比例随着底面积的增加而增大;底面积相同,结构顶层总位移及基础转动均随着埋置深度的增大而减小,上部结构本身位移在总位移中所占比例随着埋置深度的增加而增大.比较不同特性的地震动,不同底面积及埋深结构顶层总位移、基础转动、基础平动和结构自身位移的变化规律趋势相同.     

Damage to coastal villages due to the 1992 Flores Island earthquake tsunami

A field survey of the 1992 Flores Island earthquake tsunami was conducted during December 29, 1992 to January 5, 1993 along the north coast of the eastern part of Flores Island. We visited over 40 villages, measured tsunami heights, and interviewed the inhabitants. It was clarified that the first wave attacked the coast within five minutes at most of the surveyed villages. The crust was uplifted west of the Cape of Batumanuk, and subsided east of it. In the residential area of Wuring, which is located on a sand spit with ground height of 2 meters, most wooden houses built on stilts collapsed and 87 people were killed even though the tsunami height reached only 3.2 meters. In the two villages on Babi Island, the tsunami swept away all wooden houses and killed 263 of 1,093 inhabitants. Tsunami height at Riang-Kroko village on the northeastern end of Flores Island reached 26.2 meters and 137 of the 406 inhabitants were killed by the tsumani. Evidence of landslides was detected at a few points on the coast of Hading Bay, and the huge tsunami was probably formed by earthquake-induced landslides. The relationship between tsunami height and mortality was checked for seven villages. The efficiencies of trees arranged in front of coastal villages, and coral reefs in dissipating the tsunami energy are discussed.     

On the interpretation of slow ground deformation precursory to the 1976 Friuli earthquake

During three years preceding the 1976 Friuli earthquake, a continuous southward ground tilt was recorded by a tiltmeter placed near Tolmezzo, 15 km north-west of the epicentre of the impending earthquake. The cumulative ground tilt amounted to as much as 3 minutes of arc. Since the tiltmeter was placed in the proximity of an active fault, such a tilt can be explained if the fault slipped aseismically on its shallower section during the same three year period. Aseismic slip on the fault might have been caused by the same mechanism which concentrated stress in the region and eventually produced the 1976 earthquake.     

Vulnerability of floating tunnel shafts for increasing earthquake loading

Fragility curves constitute the cornerstone in seismic risk evaluations and performance-based earthquake engineering. They describe the probability of a structure to experience a certain damage level for a given earthquake intensity measure, providing a relationship between seismic hazard and vulnerability. In this paper a numerical approach is applied to derive fragility curves for tunnel shafts built in clays, a component that is found in several critical infrastructure such as urban metro networks, airport facilities or water and waste water projects. The seismic response of a representative tunnel shaft is assessed using tridimensional finite difference non-linear analyses carried out with the program FLAC^3D, under increasing levels of seismic intensity. A hysteretic model is used to simulate the soil non-linear behavior during the seismic event. The effect of soil conditions and ground motion characteristics on the soil-structure system response is accounted for in the analyses. The damage is defined based on the exceedance of the concrete wall shaft capacity due to the developed seismic forces. The fragility curves are estimated in terms of peak ground acceleration at a rock or stiff soil outcrop, based on the evolution of damage with increasing earthquake intensity. The proposed fragility models allows the characterization of the seismic risk of a representative tunnel shaft typology and soil conditions considering the associated uncertainties, and partially fill the gap of data required in performing a risk analysis assessment of tunnels shafts.     

Description and analysis of building damage due to Pyrgos, Greece earthquake

On March 1993 an earthquake of magnitude M_s = 5·5 shook Pyrgos, a town in Western Peloponnissos, one of the most seismic prone areas in Greece. The damage induced to modern reinforced concrete buildings was rather light in contrast to the damage induced to historic and traditional buildings of adobe, stone or brick masonry which was severe. In order to study the causes of structural damage, detailed data are collected from a rather large statistical sample of 1023 masonry buildings and 22 reinforced concrete framed buildings with visible damage. For each building the number of storeys, the material of construction, as well as the type and the degree of damage are recorded. In addition, consideration is given to the site of the building within the town and the corresponding soil conditions. For reinforced concrete buildings, damage occured mostly in areas with relatively high estimated spectral accelerations and fundamental soil periods of vibration close to those of the buildings. Nevertheless, further analysis is required to explain the selective damage of a very small number of buildings. For masonry houses, the effect of soil conditions is more systematic. Moreover, the effects of the number of storeys as well as the age and material of construction appear to be dominant.     

计及城市房屋建筑装修破坏的地震经济损失评估方法研究

本文通过对比、分析我国目前地震经济损失评估中存在的一些问题,提出了城市房屋计及装修费用的地震损失评估方法.通过汶川地震现场调查、收集造价资料和问卷调查的形式给出了几个关键参数的合理取值,如:装修破坏损失比、中高档装修重置单价、中高档装修房屋在不同发达水平城市中所占比例及修正系数等.利用本文方法对内蒙古包头西6.4级地震、汶川8.0级地震及深圳经济特区的房屋建筑地震损失进行了评估和预测,并与实际统计结果进行了对比分析,结果表明考虑装修费用损失后的损失评估结果增加了10%～30%.     

张北地震在北京市激发的二维强地面运动的模拟

张北县距离北京市约200多km,1998年1月的张北地震是近期北京周边地区发生的一次较强规模的地震,研究它在北京地区引起的强地面运动,有助于分析首都圈内的地震危害性,为地震减灾提供理论帮助.本文利用新的计算工具-局域离散波数法,模拟了张北地震激发的包括来自上地壳、moho面反射波、首播等在内的全波场在北京西部引起的2D强地面运动,分析了该区内第三纪、第四纪沉积地层对于地震的放大效应,得出的主要结论有,薄的第四纪沉积盖层的地点放大效应比厚的第三纪盖层的大很多,说明介质物性是决定地点放大效应的根本原因;不同物性的沉积盖层,在R、Z分量上的放大作用不一样,体现了地点放大效应的复杂性,值得在今后的研究中继续探讨.     

Earth''''s deformation due to the dynamical perturbations of the fluid outer core

Introduction The fluid outer core separates the solid inner core from the solid elastic mantle, and as a result, makes the free and forced movement of this mechanical system more complicated and profuse. As the elastic mantle, the free oscillations may occur within the Earths fluid outer core (FOC) due to excitation of a strong and deep earthquake (Crossley, 1975b; Friedlander, Siegmann, 1982; Shen, 1983; Friedlander, 1985). However, compared with the oscillations of the elastic mantle, i…