GPS观测得到的大地震前兆地壳形变震例

综合介绍2008年汶川大地震以来,GPS观测得到的国内外10多次6—9级,不同构造、不同类型的大地震前兆地壳形变震例:2008年汶川8级大地震、2011年东日本9级巨震、2013年芦山7级,直至2020年6月墨西哥7.4级地震和7月美国阿拉斯加州以南海域7.8级地震等。利用GPS连续观测站区域参考框架水平位移时间序列和水平位移场,特别是水平位移向量时间序列的研究证明,同震水平位移是研究地震前兆形变存在的关键;利用垂直位移和水平位移向量时间序列、同震垂直位移及同震水平位移向量的分解,揭示地震弹性回跳真实方式;提出了符合GPS观测和岩石破裂试验结果的地震压-剪弹性回跳模型;根据已有震例,提出预报不同震级地震的可能性和监测临震前兆形变的GNSS站布设设想。      

桩式地震表面波屏障减震试验与数值分析

在双层均质土地基条件下,以桩长和桩间距为参数,采用模型试验法和数值分析法研究屏障桩对地震表面波的减震效果。研究结果表明,设置屏障桩可有效减弱地震表面波在土体中的传播,使桩后方减震区域加速度响应明显减弱;屏障桩长度和间距均对地震表面波在土体中的传播影响显著;在桩长试验中,减震率变化同时受桩长和地基土层影响,实际工程中应根据地基中土层分布情况进行桩长设计;在桩间距试验中,减震区域减震率达46%～56%,桩间距宜取约1.5倍桩径。     

钢管混凝土框架-混凝土核心筒减震结构振动台试验研究

某超高层钢管混凝土框架-混凝土核心筒结构因指标超限在设计中采用了耗能减震技术,为了检验该减震结构的抗震性能,制作了1/35的缩尺模型,通过在钢管混凝土框架设置阻尼器或不设置阻尼器,进行模拟地震振动台对比试验,研究了模型结构的动力特性和不同烈度地震作用下的加速度、位移和应变响应。研究结果表明:地震作用下,该钢管混凝土框架-混凝土核心筒减震结构与钢管混凝土框架-混凝土核心筒结构相比,位移、加速度和应变响应均有一定程度的降低;罕遇地震作用下,通过设置耗能减震构件,层间位移角最大值从超过规范要求的1/84减低至满足规范要求的1/130,表明该减震结构具有更优良的抗震性能。     

中国西北地区强震前地磁短期异常特征分析

通过对祁连山中东段及共和盆地近几年来发生的５级以上地震前地磁异常特征及其时空分布特征分析,研究了中国西北地区强震的地磁短期异常特征和预报指标．结果表明,磁暴、低点位移和地磁垂直分量的相关性在强震前均出现了不同程度的异常．发震时间距低点位移异常开始的时间在１个月内,距磁暴出现的时间为倍九日期的±３天内．发震地点一般位于低点位移异常形成的分界线附近或低点位移异常所围绕的某个区域内．若相关系数异常持续５个月以上,在异常区内有发生中强地震的可能     

聚合阻尼耗能减震结构理论模型及振动台试验

提出一种高层减震结构体系,将核心筒与外框架采用柔性滑动连接,并集中设置聚合阻尼减震系统,充分利用内部核心筒和外框架的侧向变形差耗散地震能量;建立了聚合阻尼减震结构的简化质点系模型,并得到地震作用下的位移传递公式;完成了模型结构的振动台模型试验,验证了聚合阻尼耗能减震结构的减震效果;最后通过工程算例分析得到了聚合阻尼耗能减震结构内核心筒、外框架的地震响应和减震效果,进一步探讨了地震作用下不同结构体系的塑性损伤状态,理论和试验研究结果表明聚合阻尼耗能减震结构可有效控制结构构件的塑性损伤。     

千米级斜拉桥的纵向减震体系研究

针对漂浮型的千米级斜拉桥,研究地震作用下减小梁端纵向位移和主塔内力的方法。首先阐述了该类桥梁的纵向减震机理和方法;其次根据现有的理论和技术水平,在塔梁之间分别采用弹性连接装置、流体黏滞阻尼器、以及弹性连接装置与流体黏滞阻尼器组合的3种连接方式,设计了3种纵向减震体系;然后建立了千米级斜拉桥的有限元模型,分别采用上述3种纵向减震体系,进行了一系列动力分析,同时研究了纵向减震参数设置;最后,对模型计算结果进行了比较和讨论,并建议了千米级斜拉桥纵桥向的合理减震结构体系。     

大跨径钢管混凝土拱桥减震控制装置参数的研究

大跨度桥梁结构的减震控制研究对于桥梁结构的抗震安全具有重要意义。本文以主跨368m的茅草街大桥为研究对象,基于ANSYS建立了该桥的三维有限元模型,并采用子空间迭代法分析了该桥的动力特性。在此基础上进行了大跨度钢管混凝土拱桥的地震响应及减震控制研究,重点进行了弹性连接装置和粘滞阻尼器减震效果的参数敏感性分析,并对比分析了不同位置布设减震装置时的效果。结果表明,纵飘振型对该桥肋纵向相对位移的贡献最大;弹性连接装置和阻尼器均能有效减小地震作用下该桥的肋梁纵向相对位移;综合考虑各关键部位的地震响应时,同时采用两类减震装置并将其分散布置时的减震效果最佳。结论可供大跨度中承式钢管混凝土系杆拱桥的抗震设计参考。     

位移放大型油阻尼器减震结构减震效应分析

针对高层结构在地震作用下层间位移较小,阻尼器性能无法充分发挥的特点,提出一种用于油阻尼器的位移放大装置,可使油阻尼器两端的相对位移放大,提高其产生的阻尼力和耗能能力。以某实际工程结构为背景,基于SAP2000建立其多质点有限元模型,分析两种减震方案在3条地震波作用下的最大层间位移角、基底剪力、加速度放大系数、滞回曲线、能量耗散曲线,以检验位移放大型油阻尼器对结构地震响应的减震效应。结果表明,位移放大型油阻尼器能以更少的布置数量满足减震设计要求,同时获得较普通油阻尼器更为理想的减震效果。     

黏滞阻尼器减震框架结构保持正常使用功能的设计要求探讨

《建设工程抗震管理条例》要求两区八类建筑需采用减隔震技术,并保证设防地震时能够满足正常使用要求。目前针对减震结构满足正常使用功能的设计方法尚未达成共识。RISN-TG 046—2023《基于保持建筑正常使用功能的抗震技术导则》等新编标准针对减震结构提出了系统的基于性能的设计要求。基于一个8层RC框架采用黏滞阻尼器的减震结构案例,按照该标准及其他现行标准的不同要求进行了减震设计,对比了不同设计方案的土建成本及地震响应,并对减震结构的剪力、位移角和构件损伤进行了讨论,结果表明,在进行减震结构设计时,建议按照RISN-TG 046—2023《基于保持建筑正常使用功能的抗震技术导则》要求控制设防地震下的层间位移角,可按照DGJ 08-9—2013《建筑抗震设计规程》或JGJ 3—2010《高层建筑混凝土结构技术规程》或GB 50011—2010《建筑抗震设计规范》)控制承载力,为减震结构保持设防地震下正常使用功能的设计提供参考。     

大跨度斜拉桥横桥向减震研究

斜拉桥在横桥向采用塔-梁、墩-梁固结的约束体系,导致其整体刚度增加,地震惯性力增大,给边墩及其基础的抗震设计造成困难。分别采用位移相关型(方案1)和速度相关型(方案2)两类减震装置对一座斜拉桥的横桥向进行了减震研究。方案1在边墩-主梁间设置位移相关型减震装置,并对其屈服荷载进行了参数分析;方案2对速度相关型减震装置的安装位置和数量进行了优化分析,并对其参数取值进行了参数分析;对横桥向固结体系和减震体系的地震反应进行了对比。结果表明:地震作用下两类减震装置发生滞回变形,延长了结构在横桥向的周期,有效降低了边墩的地震剪力和弯矩反应;横桥向墩-梁间的相对位移会增大,可通过减震装置参数的选取将其控制在合理的范围内;塔底的地震剪力和弯矩反应变化不明显。2种方案均可用于斜拉桥横向减震。     

中国构造应力场与大震复发周期关系的数值模拟

由古地震资料推算得到的中国境内各活动断裂带上大震复发周期值存在很大差异,对于这种差异可从构造应力产生的弹性应变能分布去探讨其原因。经过对中国及邻区边界条件和受力方式进行较详细的分析后,先以最大主压应力方向为判据,用有限元数值模拟方法反演中国及邻区的板块边界力和区内的构造应力场,然后分析计算应变能随离板块边界的距离增大所呈现的衰减规律,由此换算出要达到相同应变能（一次地震）各地所需的积累时间,并将其与用古地震方法得到的一些已知断层带大震复发周期进行对比。结果表明用应力衰减图象能解释不同地区大震复发周期的显著差异     

Hastening of occurrences of earthquakes due to dynamic triggering: The observation at Matsushiro, central Japan

Dynamic stress/strain changes associated with the passage of seismic waves perturb the state of stress of a fault.We hypothesize that this perturbation increases the instability of the fault and that it hastens the occurrence of an earthquake that would otherwise occur somewhat later.To test this hypothesis, we investigate a time interval defined as a time difference between the occurrence of a dynamic strain change and the origin time of the first subsequent earthquake.If the occurrence of an earthquake is hastened by the strain change, the time interval would be shortened, compared with a case of a random occurrence.Here we used two datasets: 1) origin times of earthquakes at Matsushiro, Nagano Prefecture, central Japan, with magnitudes of 1.6 or greater, between November 1984 and December 1994; and 2) strainmeter records of remote earthquakes at the Matsushiro Seismological Observatory over the same period.We applied a statistical test to the distribution of the observed time intervals between dynamic strain changes due to remote earthquakes and the first earthquakes at Matsushiro subsequent to the strain changes, in order to compare it to the distribution of expected time intervals generated by a random (Monte Carlo) simulation.Because of limitations of the statistical test, we could not establish the quantitative relationship between the degree of hastening and the amplitude of the strain changes, but we found a statistically significant decrease of the observed time intervals.We also investigated the number of the earthquakes before and after the strain changes, and found that dynamic triggering has little significant impact on the occurrences of earthquakes at Matsushiro.Therefore, we conclude that dynamic triggering at Matsushiro is weaker than those reported in previous studies and that the time interval might be an important parameter for a statistical study of weak dynamic triggering.     

前震序列与一般小震群活动规律的探讨

研究前震序列的活动规律及其与一般小震群的区别,对于研究地震孕育过程及地震预报都是有益的。为此,我们处理了我国近十几年来资料较详细的17个地震,发现其前震活动是在主震前较早时间就开始的,它与波速变化似有某种对应关系。选择主震前适当的时间间隔,其中的前震频数一般随时间接近主震而按指数增长。并且,大地震的一个4级以上前震与一般小震群中的同量级地震发生前的应变释放速率是不同的。     

Seismic Empirical Relations for the Tellian Atlas, North Africa, and their Usefulness for Seismic Risk Assessment

Seismic events that occurred during the past half century in the Tellian Atlas, North Africa, are used to establish fundamental seismic empirical relations, tying earthquake magnitude to source parameters (seismic moment, fault plane area, maximal displacement along the fault, and fault plane length). Those empirical relations applied to the overall seismicity from 1716 to present are used to transform the magnitude (or intensity) versus time distribution into (1) cumulative seismic moment versus time, and (2) cumulative displacements versus time. Both of those parameters as well as the computed seismic moment rate, the strain rate along the Tellian Atlas strike, and various other geological observations are consistent with the existence, in the Tellian Atlas, of three distinct active tectonic blocks. These blocks are seismically decoupled from each other, thus allowing consideration of the seismicity as occurring in three different distinct seismotectonic blocks. The cumulative displacement versus time from 1900 to present for each of these tectonic blocks presents a remarkable pattern of recurrence time intervals and precursors associated with major earthquakes. Indeed, most major earthquakes that occurred in these three blocks might have been predicted in time. The Tellian Atlas historical seismicity from the year 881 to the present more substantially confirms these observations, in particular for the western block of the Tellian Atlas. Theoretical determination of recurrence time intervals for the Tellian Atlas large earthquakes using Molnar and Kostrov formalisms is also consistent with these observations. Substantial observations support the fact that the western and central Tellian Atlas are currently at very high seismic risk, in particular the central part. Indeed, most of the accumulated seismic energy in the central Tellian Atlas crust has yet to be released, despite the occurrence of the recent destructive May 2003 Boumerdes earthquake (M _w = 6.8). The accumulated seismic energy is equivalent to a magnitude 7.6 earthquake. In situ stress and geodetic measurements, as well as other geophysical field data measurements, are now required to practically check the validity of those observations.     

Assessment of earthquake hazard by simultaneous use of the statistical method and the method of fuzzy mathematics

A probabilistic method and a retrieval method of fuzzy information are simultaneously studied for assessment of earthquake hazard, or earthquake prediction. Statistical indices of regional seismicity in three adjacent time intervals are used to predict an earthquake in the next interval. The indices are earthquake frequency, the maximum magnitude, and a parameter related to the average magnitude (orb-value) and their time derivatives. Applying the probabilistic method, we can estimate a probability for a large earthquake with magnitude larger than a certain threshold occurring in the next time interval in a given region. By using the retrieval method of fuzzy information we can classify time intervals into several classes according to the regional seismic activity in each time interval and then evaluate whether or not the next time interval belongs to seismically hazardous time interval with a large earthquake. Some examples of applying both methods to the North section of the North-South Seismic Zone in China are shown. The results obtained are in good agreement with actual earthquake history. A comparison of the probabilistic method with the method of fuzzy mathematics is made, and it is recommended that earthquake hazard be assessed by simultaneous use of both methods.     

A Bayesian Approach to Seismic Hazard Estmation: Maximum Values of Magnitudes and Peak Ground Accelerations

Earthquake Researeh in Ch一na461 .METHODLet R be some value measured or estimated as a sequenee ina’‘Past”time interval(一丁,O)(I)万‘月,=(RI,…,R。),R,之R。,R=nlaX l二f匕11(RI,…,R,,) Values(l)eould have an arbitrary Physieal nature.BelowweshalleonsiderEq.(l)asearthquakemagnitudes in a given seismic aetive region or logarithms of seismie Peak ground aeeelerations at习given site.Ro isa而nimum eutoff value;it 15 defined by Possibilities of registration systems or wasehosen as the …     

中国大陆6级以上强震前的地震应变场研究

以地震应变场作为地震活动的变量,通过自然正交函数展开方法,计算了中国大陆6级以上强震前的地震应变场,提取出震前时间因子的异常变化.计算结果分析发现大地震前时间因子在平稳背景上会出现突跳上升或突跳下降变化,且震前地震应变场前4个典型场中至少有3个典型场会出现异常变化,具有多分量显示异常的特点,而异常出现的最早时间大约在震前3年,并且一些地震前出现短临的时间因子异常变化特征.通过震例研究表明用地震应变场分析地震活动异常,提取的时间因子异常结果比应用地震能量场更具有独特的优越性,并讨论了应变场与能量场的差异.     

Identification of High Frequency Pulses from Earthquake Asperities Along Chilean Subduction Zone Using Strong Motion

The Chilean subduction zone is one of the most active of the world with M?=?8 or larger interplate thrust earthquakes occurring every 10?years or so on the average. The identification and characterization of pulses propagated from dominant asperities that control the rupture of these earthquakes is an important problem for seismology and especially for seismic hazard assessment since it can reduce the earthquake destructiveness potential. A number of studies of large Chilean earthquakes have revealed that the source time functions of these events are composed of a number of distinct energy arrivals. In this paper, we identify and characterize the high frequency pulses of dominant asperities using near source strong motion records. Two very well recorded interplate earthquakes, the 1985 Central Chile (Ms?=?7.8) and the 2007 Tocopilla (Mw?=?7.7), are considered. In particular, the 2007 Tocopilla earthquake was recorded by a network with absolute time and continuos recording. From the study of these strong motion data it is possible to identify the arrival of large pulses coming from different dominant asperities. The recognition of the key role of dominant asperities in seismic hazard assessment can reduce overestimations due to scattering of attenuation formulas that consider epicentral distance or shortest distance to the fault rather than the asperity distance. The location and number of dominant asperities, their shape, the amplitude and arrival time of pulses can be one of the principal factors influencing Chilean seismic hazard assessment and seismic design. The high frequency pulses identified in this paper have permitted us to extend the range of frequency in which the 1985 Central Chile and 2007 Tocopilla earthquakes were studied. This should allow in the future the introduction of this seismological result in the seismic design of earthquake engineering.     

由地震活动参数分析安宁河-则木河断裂带的现今活动习性及地震危险性

利用区域台网地震资料, 分析了川西安宁河-则木河断裂带不同段落的现今活动习性，进而鉴别潜在大地震危险的断裂段. 文中由异常低b值的分布圈绘出凹凸体，发展和应用了由多个地震活动参数值的组合判定断裂分段活动习性的方法，尝试了利用凹凸体段的震级频度关系参数估计特征地震的平均复发间隔. 结果表明，该研究断裂带存在5个不同现今活动习性的段落. 其中，安宁河断裂的冕宁-西昌段属于高应力下的闭锁段，其核心部分为一较大尺度的凹凸体；则木河断裂的西昌-普格段则表现为低应力下的微弱活动状态. 重新定位的震源深度分布，显示出上述闭锁段和微弱活动段的断层面轮廓. 冕宁-西昌段是未来大地震的潜在危险段. 该段从最晚的1952年6.7级地震起算，至未来特征地震的平均复发间隔估值为55～67年, 未来地震的震级估值为7.0～7.5. 本研究也初步表明，同-断裂段的活动习性可随时间动态演变.      

华北地区地震迁移规律的数学模拟

本文描述了一个解时空反演问题的方法.通过把华北地区看成是由24条主要断裂带组成的地质构造骨架,在15公里深处按照平面应变的理想塑性体处理,用有限单元方法计算了本地区在均匀边界外力作用下发生地震危险的地带.然后用逐次降低断层内摩擦系数的办法,模拟近十二年来历次大地震,计算释放应力后应力场的变化、断层的错动.将计算结果和实测资料进行对比,对各个力学参数和构造骨架进行了多次修改,使它们尽量接近.结果说明本方法能够基本上重复近十二年来的地震迁移规律,并可望对未来的地震危险区提出参考意见.结果还说明地震以后在沿断层错动方向的左前方有一狭窄扇形地带安全度增加,而其余较大地区由于断层处的应力释放使剪破裂的危险度有些增加.