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1.
一次地震的孕育过程由震源自身的演化过程和所受外界影响 2种因素决定。地震活动的复杂性主要由地震断层活动相互作用以及在这种作用下地震孕育过程发生复杂变化引起。本文在摩擦状态 -速率依从理论和断层相互作用理论的基础上 ,将地震看作是摩擦失稳现象 ,建立地震孕育及其活动特征的物理模型 ,研究地震触发现象和地震强度分布不均匀性的力学机制。1 大地震触发区域地震活动及其力学机制研究 美国兰德斯地震后诱发的距震中远达1 2 50 km的 1 4个区域出现的地震活动增强 ,被称为是大地震触发小地震的首次证据。本文对1 995年 1月 1 7日… 相似文献
2.
本文综述了近期基于应力变化的余震预测研究进展。从静态库仑应力触发角度对余震活动进行研究主要有两方面内容:一是集中于对主震触发余震机制的讨论;二是通过库仑应力变化分布区域与实际余震空间分布区域进行定性对比分析,并认为库仑应力变化为正的区域有利于余震的发生,而这正是余震活动与应力变化高度相关的重要证据。基于应力变化的余震预测研究的一项重要内容是建立在速率-状态依从摩擦定律基础之上的余震活动率研究,即将余震活动作为一系列独立的成核事件,从断层滑动触发地震的角度出发,结合静态库仑应力计算得到余震活动率,进而得到余震数量。余震活动是与断层面上的剪切应力变化相关联的,余震活动率受应力扰动幅度、应力加载速率、断层基本物理特性及背景地震活动率等的影响。考虑到“余震激发余震”的特点,ETAS 模型与静态库仑应力变化相结合的研究方法提供了一条统计学与物理学方法(应力变化)相结合、能更完整地刻画余震活动特征的可能途径。 相似文献
3.
余震触发机制的Dieterich解析模型被广泛应用于区域地震活动性的定量分析以及依赖时间的概率地震预测模型的建立等方面. 基于滑移速率和状态相依赖的摩擦定律和弹簧-滑块模型, 从Dieterich断层滑移速率方程出发, 给出了静态应力扰动下触发地震的时钟提前或推后的近似解, 从而明确地阐明了触发地震的产生机制与断层的演化过程密切相关, 并与传统位错模型下库仑应力扰动时间提前或推后量作了比较. 采用对数线性拟合方法求得了汶川MW7.9主震后余震序列持续时间, 符合Dieterich理论结果. 以汶川余震序列为例, 给出了两种不同的应力扰动模式在该余震序列中的应用. 结果表明, 经典Dieterich扰动解无法给出主震发生后即时余震数量的异常增加, 而考虑主震前后剪应力速率变化的Dieterich分段解则可反映出余震发生率及个数随时间的演化特征. 相似文献
4.
余震触发机制的Dieterich解析模型被广泛应用于区域地震活动性的定量分析以及依赖时间的概率地震预测模型的建立等方面.基于滑移速率和状态相依赖的摩擦定律和弹簧-滑块模型,从Dieterich断层滑移速率方程出发,给出了静态应力扰动下触发地震的时钟提前或推后的近似解,从而明确地阐明了触发地震的产生机制与断层的演化过程密切相关,并与传统位错模型下库仑应力扰动时间提前或推后量作了比较.采用对数线性拟合方法求得了汶川Mw7.9主震后余震序列持续时间,符合Dieterich理论结果.以汶川余震序列为例,给出了两种不同的应力扰动模式在该余震序列中的应用.结果表明,经典Dieterich扰动解无法给出主震发生后即时余震数量的异常增加,而考虑主震前后剪应力速率变化的Dieterich分段解则可反映出余震发生率及个数随时间的演化特征. 相似文献
5.
简单的启发式模型和数值计算表明，通常所用的地震失效模型不能解释地震活动性是由瞬态的或“动态”的应力变化(即，与地震波相联系的应力变化)所触发的。这类模型具有共同的特性：当断层以恒定速率加载(加应力)时，表征失效的物理量以加速速率增加。例如，经常采用的速率状态摩擦模型或亚临界失效生长模型，它们表征失效的特征量分别为滑动或失效长度。当生长速率加速到超过所谓临界阈值时，失效发生。这些加速的失效模型不能预测动态触发地震序列(如，余震或远距离地震)的有限持续时间。某些这类失效模型被用来解释余震的静态应力触发。这也许暗示动态触发的物理过程是不同的，或者说目前所用的静态触发模型需要修改。若前者是正确的，我们也许要求助于基于诸如饱和断层挤压导致孔隙压力增加或周期疲劳的振荡型变形的物理机制。然而，如果动态和静态触发机制不同，我们仍然要问：为什么忽略动态机制的静态触发模型似乎能解释许多观测现象。如果静态和动态触发机制相同，也许加速失效和(或)触发使一组要发生的地震提前发生的假设是不对的。 相似文献
6.
在地震滑动过程中,断层动态摩擦是地壳内控制地震破裂的决定性因素。天然地震的脆性裂纹理论[1-3]使得以下观点被普遍接受:在地震断层快速滑动的过程中,断层摩擦力减弱,即所谓的滑动弱化[1]。高速断层泥实验[4-5],以及最近关于热增压[6-7]和摩擦熔化[8]的试验都支持该理论。但是,这些研究均仅针对固定的断层滑动速率。在本文中,我们的实验展示了不同滑动速率下断层物质的摩擦行为——这一模型的设置更接近天然地震的特征。实验结果表明,在断层滑动加速和减速的过程中,断层摩擦经历了增长、弱化和再增长。这种摩擦变化可能可以由低滑动速率下和更现实的滑动速率之下的速率-状态摩擦行为[9-10]来解释,但包含了不同的物理机制和不同的规模。最初的摩擦增强可能会阻碍小破裂向大地震的发展。断层滑动减速过程中的摩擦增强可能导致地震破裂呈脉冲状[11-14],并使得静态应力下降到与动态应力变化相比较低的水平[15]。 相似文献
7.
基于单自由度弹簧-滑块模型,滑移速率和状态相依赖的摩擦关系可用于对断层内部地震成核和断层失稳过程的定量化描述.Dieterich(1994)余震触发理论模型首次给出中强震后区域应力场受到静态应力扰动后所导致的区域地震活动性的时空变化特征,近期研究也表明Dieterich理论模型可进一步推广至依赖时间的地震预测模型的建立.本文从简单直观的断层群体化概念模型出发,推导出了包括静态剪应力和正应力扰动作用下广义Dieterich解.同Dieterich经典解相比,广义Coulomb应力变化:ΔCFFG=Δτ－(μ0－α)Δσ取代了Dieterich方程中原有的剪切应力扰动Δτ.从而表明余震发生率R同作用于断层上的正应力的变化(扰动)有着密切的相关性.进一步,我们讨论了传统Coulomb应力变化(扰动)模型在地震预测过程中可能存在的局限性.以1976年MS7.8唐山大地震的主余震序列为例,采用本文中得到的结果,并结合视时窗分段方法,拟合了该地区地震活动性的时间演化过程.结果表明,除Coulomb应力变化(扰动)的影响外,主震前后加载于断层上的剪应力速率变化可对早期余震发生率产生很大影响. 相似文献
8.
汶川地震对芦山地震及周边 断层发震概率的影响 总被引：6，自引：0，他引：6
大震后区域静态库仑应力变化常常被用于解释区域地震活动性速率的变化、 主震断层外余震的发生以及即将失稳断层的地震发生概率的变化. 2013年4月20日芦山MS7.0地震的发生重新引起了对2008年5月12日汶川MS8.0大地震的热议. 利用含(滑移)速率和状态的摩擦定律, 结合汶川大地震前后的地震活动性水平, 定量化计算了汶川地震后雅安地区发震概率的变化, 并着重解释了芦山地震发震的可能根源. 此外, 还对库仑应力明显增加的鲜水河断层和熊坡断层进行了发震概率的定量化计算, 计算结果与中国地震台网中心的地震目录基本符合. 鲜水河断层从汶川地震后至今近5年来未发生M>6.0地震, 而M>6.0的发震概率已约为60%; 熊坡断层自汶川地震以来尚未发生M>4.0地震, 芦山地震后M>4.0的发震概率已接近90%. 所以, 我们认为鲜水河断层附近将成为M>6.0地震的重点防范地区, 熊坡地区将来仍旧存在发生中强地震的危险性. 相似文献
9.
近年来,通过计算库仑破裂应力变化研究地震触发及断层的相互作用,进而估计地震灾害已经成为国际上研究的热点.研究中,为考察库仑模型触发地震的效果,计算时往往要改变模型参数进行检验,特别是让有效摩擦系数从0.0到0.8之间变化.许多研究人员的计算结果表明,库仑破裂应力随着摩擦系数的增加而增大,即断层上摩擦系数的增大可以导致触发地震能力的提高.这显然与我们的常识相违背:摩擦总是阻碍断层滑动、抑制地震发生的,即断层面上的摩擦越大,地震越是难以被触发.文中通过对库仑破裂应力的计算公式进行详细分析后发现,之所以出现摩擦越大,地震越容易被触发的现象,其原因是研究者在计算中没有考虑在构造应力作用的环境里,摩擦系数本身的变化所带来的附加库仑应力变化.若某个地震使一个位于地下15km的典型断层面上的正应力增加2 MPa,如果只考虑静岩压力,当摩擦系数从0.3增大到0.4后,传统库仑破裂应力变化为0.8 MPa;而综合库仑应力变化则大约为-39.2 MPa.所以,若从整体上来分析断层在地震位错及摩擦系数变化所造成的综合库仑应力改变,就不可能出现库仑应力随摩擦系数增加而增加的不正常现象.由此可见,今后在利用库仑模型研究地震触发问题时,应综合考虑构造应力场及摩擦系数本身变化所带来的库仑应力变化. 相似文献
10.
在过去几年里,许多研究者声称大地震产生的静态应力变化影响后续区域地震活动性的空间和对间分布,地震优先发生在应力增加区,而在应力降低区地震活动性降低。一些研究者提出了定量方法来检验静态应力触发的存在,但还未达成确定一致的认识。我们提出了一套检验静态应力触发的方法,它需要计算大地震发生期间的一组地震事件震源机制节面上的库仑应力变化。我们比较了计算得到的主震之前和之后这些地震事件应力变化的统计分布,目的是确定我们是否可以拒绝分布相同的假设,拒绝该假设将是应力能触发地震的证据。我们将这种检验用于1987年11月24日的埃尔莫尔牧场/苏必斯蒂森山地震序列,发现主震之后的地震事件应力至少增加0.01～0.03 MPa(0.1～0.3bar),在主震之后1.4～2.8年发生,这与主震产生的静态应力触发一致。 相似文献
11.
基于有限元方法,参照细胞自动机模型,建立了一个地震活动演化的动力学模型.在这个模型中,根据边界条件和单元介质参数的分布,利用有限元方法确定各单元的应力增长速率.每个单元设定初始应力和摩擦因数,利用破裂准则可得到单元破裂所需时间.当单元破裂后,将破裂单元作为内部边界,利用有限元方法计算由于这个单元破裂对系统其他单元造成的应力调整.根据上述规则,建立一个由30×40个节点组成,在定常位移速率边界条件作用下的地震活动模型,探讨了区域应力场的动态演化、地震活动图像和各种参数变化对地震活动的影响.结果表明该模型在研究地震活动方面有一定优势并具有实用价值. 相似文献
12.
GUI-PING LIU 《地震学报(英文版)》1999,12(3):277-284
The time and spatial feature of the regional seismicity triggered by the Hyogo-Ken Nanbu, Japan, M=7.2 earthquake on January 17,1995, was studied. The concerned region is about several hundred kilometers in length and breadth surrounding the epicenter (33°～37°N, 133°～138°E). It is divided into 16 subregions. The seismicity of these subregions from January of 1976 to June of 1996 has been analyzed. It is showed that,① there were significant seismicity changes in 10 subregions triggered by the Hyogo-Ken Nanbu, Japan, M=7.2 earthquake on January 17, 1995. These changes passed a Z statistic test exceeding 0.95 confidence level and the greatest epicenter distance of these subregions was 280 km;②seismicity changes were triggered within 1～5 days in three subregions near the main shock while in other subregions the seismicity changes were triggered within several ten days after the main shock;③ the greatest triggered event is 5.4, which is about the same size as the greatest aftershock;④the regional stress change resulted from the main shock may be the triggered mechanism of the regional seismicity. 相似文献
13.
模板匹配滤波技术在地震数据处理中的应用 总被引：1，自引：0，他引：1
模板匹配滤波技术(Matched Filter Technique,MFT)是一种近几年发展迅速的可用于检测遗漏信号的算法,在图像识别、行星探测等众多领域均有广泛应用。在地震学中,该技术通过扫描连续波形找出模板事件附近发生的、与模板事件相关性较好的遗漏地震事件,可用于完善地震目录,实现对地震活动性以及区域应力状态的更好刻画。本文综述了模板匹配滤波技术在地震数据处理中的应用,首先概述基本原理,其次介绍该方法用于探测各类地震事件的实例,包括前震和余震、远程动态触发地震、诱发地震和非火山震颤等,最后展望了用于提高算法效率及探测精度的一些改进方法。 相似文献
14.
Triggered earthquakes and deep well activities 总被引：1，自引：0，他引：1
Earthquakes can be triggered by any significant perturbation of the hydrologic regime. In areas where potentially active faults are already close to failure, the increased pore pressure resulting from fluid injection, or, alternatively, the massive extraction of fluid or gas, can induce sufficient stress and/or strain changes that, with time, can lead to sudden catastrophic failure in a major earthquake. Injection-induced earthquakes typically result from the reduction in frictional strength along preexisting, nearby faults caused by the increased formation fluid pressure. Earthquakes associated with production appear to respond to more complex mechanisms of subsidence, crustal unloading, and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material. As each of these different types of triggered events can occur up to several years after well activities have begun (or even several years after all well activities have stopped), this suggests that the actual triggering process may be a very complex combination of effects, particularly if both fluid extraction and injection have taken place locally. To date, more than thirty cases of earthquakes triggered by well activities can be documented throughout the United States and Canada. Based on these case histories, it is evident that, owing to preexisting stress conditions in the upper crust, certain areas tend to have higher probabilities of exhibiting such induced seismicity. 相似文献
15.
More than 1000 aftershocks were recorded within a month after the occurrence of the ML 5.5, 5 August 2014 Orkney earthquake. The events were relocated using the double difference method as part of an effort to identify the fault which might be the source of the events. A north–south trend of seismicity was revealed by the relocated events, with a diffuse cluster to the north of the main event. A depth profile shows these two clusters: one at a depth of about 2 km to the north of the main event and the other at depth between 3 and 6 km south of the main event. Focal mechanism solutions of 18 aftershocks were determined using first motion polarities from seismic stations of the Council for Geoscience cluster networks. Stress inversion analysis results from the focal mechanism solutions show a dominant extensional stress field in the region; the main event had a strike-slip fault plane solution. This is consistent with the regional stress field which is predominantly related to the East African rift system. It is possible that the occurrence of the main event triggered seismicity on shallower faults within the mining horizons oriented in a different direction to the fault on which the main event occurred. The area has a complex heterogeneous faulting structure as indicated by the observed low p values and complex focal mechanism solutions. 相似文献
16.
Ralf Fritschen 《Pure and Applied Geophysics》2010,167(1-2):77-89
Coal mining in the Saar mine, Germany, is accompanied by mining-induced seismic events. Strong events occur only in certain areas of the mine, other areas exhibit almost no seismicity. Shear events occur simultaneously to non-shear events. The shear events occur in different depths but their epicenters do concentrate in bands. The strike of the bands coincides with the strike of larger regional faults in the area. The seismic events of the Saar mine show some characteristics which distinguish them from seismic events observed in other German coalfields. The Gutenberg–Richter relation, for example, does not hold for these events. Furthermore, radiated seismic energy and extracted coal volume are not correlated. In the Primsmulde field a strong seismic event was observed even before mining in that region started. The event was triggered just by driving roadways into the field. The shear events cannot be explained by the mining process alone. They are presumably induced in certain regions (bands) under tectonic load by an interaction of mining-induced and tectonic stresses. In February 2008, extraction in the Primsmulde field induced a seismic event of magnitude 4, which led to surface vibrations reaching 93 mm/s. After this event, the Primsmulde field had to be abandoned. Future extraction of the Saar mine will be restricted to some small areas not intersected by the event bands found in the Dilsburg Ost and Primsmulde fields. The Saar mine will close in 2011. 相似文献
17.
本文以1996年丽江MS7.0地震为例,以地震目录和强震震源模型为输入参数,将力学计算与统计分析相结合,反演计算了1986～1996年间丽江震区2.5°×3.0°空间范围内的地壳应力状态.结果表明,丽江地区应力场最大主应力为近南北向,方位角为355°,最小主应力方位角为241°,二者倾角为近水平,应力形因子为0.398,最大主应力大小约为53 MPa,远小于完整岩石的强度.该方法可获得地壳深部绝对应力大小、有效摩擦系数,反演获得的震区地壳深部应力状态的方向性特征与震源机制解结果基本一致;该研究表明地震活动的空间分布可以为我们提供有关强震孕震的地壳深部应力状态信息.这些结果对了解震区应力场具有理论上和实践上的意义. 相似文献
18.
大震后区域静态库仑应力变化直接影响地震活动性速率的变化、主震断层外余震和即将失稳断层的发震概率的变化.利用滑移速率和状态相依赖的摩擦定律,结合2008年3月21日于田地震前后的地震活动性水平,定量计算了2008年于田地震后该地区周边断层发震概率的变化,着重解释了2014年于田地震发震的可能根源.此外,本文还对库仑应力明显变化的周边三条断层进行了发震概率的定量计算.贡嘎错断裂中段、贡嘎错断裂西南段和康西瓦断裂中段分别经历了发震概率先降后升、先升后升和先降后降两个阶段,充分显示了库仑应力的细微变化造成的周边断层的危险性的变化.这三条断裂发生7.0级以上地震的发震概率超越95%均需要500年左右;贡嘎错断裂西南段发生中强地震的可能性较大,而康西瓦断裂中段活跃度较低. 相似文献
19.
The rapid release of strain energy is an important phenomenon leading to seismic events or rock failures during the excavation of deep rock.Through theoretical analysis of strain energy adjustment during blasting and mechanical excavation,and the interpretation of measured seismicity in the Jin-Ping Ⅱ Hydropower Station in China,this paper describes the characteristics of energy partition and induced seismicity corresponding to different energy release rates.The theoretical analysis indicates that part of the strain energy will be drastically released accompanied by violent crushing and fragmentation of rock under blast load,and this process will result in seismic events in addition to blasting vibration.The intensity of the seismicity induced by transient strain energy release highly depends on the unloading rate of in-situ stress.For mechanical excavation,the strain energy,which is mainly dissipated in the deformation of surrounding rock,releases smoothly,and almost no seismic events are produced in this gradual process.Field test reveals that the seismic energy transformed from the rock strain energy under high stress condition is roughly equal to that coming from explosive energy,and the two kinds of vibrations superimpose together to form the total blasting excavation-induced seismicity.In addition,the most intense seismicity is induced by the cut blasting delay; this delay contributes 50% of the total seismic energy released in a blast event.For mechanical excavation,the seismic energy of induced vibration(mainly the low intensity acoustic emission events or mechanical loading impacts),which accounts only for 1.5‰ of that caused by in-situ stress transient releasing,can be ignored in assessing the dynamic response of surrounding rock. 相似文献
20.
Regional seismicity triggered by the Ms=7.8 Tangshan event on July 28, 1976 and the static stress field change 总被引：2，自引：0，他引：2
GUI-PING LIU 《地震学报(英文版)》2000,13(1):19-28
We studied the seismicity before and after the MS=7.8 Tangshan event on July 28, 1976 (39(28(N, 118(11(E) and the results show that in 3 regions outside of the source zone, seismicity rate increasing were observed, which was significant in 0.99 significance level using Z-statistic test and was proposed to be triggered by the MS=7.8 Tangshan earthquake. The magnitude of the greatest triggered event was 5.5. The epicenter distances of these earthquakes were several ten kilometers to 300 km. The static stress change (CFS of Coulomb failure was calculated using an elastic dislocation model in half space and the (CFS on the major rupture directions in these three regions were positive. 相似文献