共查询到20条相似文献，搜索用时 484 毫秒
1.
Tsuneji Rikitake 《Tectonophysics》1975,26(1-2)
Statistics of ultimate strain are improved by adding new data to the previous ones. The critical value for horizontal strain seems somewhat larger than that for vertical strain, although parameters of a Weibull distribution, which is customarily used for quality-control research and which fits in very well with the present statistics, are calculated for the whole set of data making no distinction between the two subsets because of their scantiness.On the basis of the parameters thus determined and strain rates obtained from geodetic data, probabilities of earthquake occurrence in a few regions in Japan and the U.S. are estimated. Probability of having an earthquake in an area southwest of Tokyo, where we had the 1923 earthquake (magnitude 7.9), at this time amounts to 20%, a value almost the same as that obtained in the previous papers. The probability will reach some 50 and 90% by 2000 and 2050, respectively. In the North Izu district, where an earthquake of magnitude 7.0 occurred in 1930, a shearing crustal motion is going on to an extent for which we have a probability for an earthquake recurring there in these 40 years amounting to 40%. By the end of this century, it will become as high as 85%.Similar estimates of such cumulative probabilities are made for the San Francisco and Fort Tejon regions, where great earthquakes occurred respectively in 1906 and 1857, yielding values of 30 and 80% at present. These probabilities are tentative because of possible errors in evaluating geodetic measurements and uncertainty of the ultimate crustal strain assigned to the San Andreas fault. 相似文献
2.
Yukio Hagiwara 《Tectonophysics》1975,26(1-2)
A large-scale earthquake is believed to be associated with a release of strain energy accumulated in the crust, probably by the motion of upper-mantle lithosphere. Such an earthquake mechanism is well simulated by a belt-conveyer model proposed by Utsu (1972). The probability of earthquake occurrence can be estimated on the assumption that the motion of a slider on the belt-conveyer is mathematically formulated as a Markov process.In the probabilistic expressions, the results of Mogi's (1962) rock-fracture experiments are applied to the hazard-rate function of earthquake occurrence. The hazard-rate function has two coefficients, A and B, to be determined by the experiments. It is concluded that, when B is small, a number of small-scale earthquakes occur in the early time after the accumulation of crustal strain energy starts, but that the accumulated strain energy changes catastrophically into a single large-scale earthquake, when B is large. 相似文献
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4.
In view of the growing importance of stochastic earthquake modeling in disaster preparation, the present study introduces a new family of exponentiated Weibull distribution and examines its performance in earthquake interevent time analysis in a stationary point process. This three-parameter (one scale and two shapes) distribution not only covers the Weibull distribution, exponentiated exponential distribution, Burr-type X distribution, Rayleigh distribution, and exponential distribution as special sub-families, but also offers monotone and non-monotone hazard shapes. Here we first describe some of the exponentiated Weibull distribution properties, such as the survival rate, mode, median, and hazard rate. We then provide statistical inference and goodness-of-fit measures to examine the suitability of exponentiated Weibull model in comparison with other popular models, like exponential, gamma, lognormal, Weibull, and exponentiated exponential. Finally, we conduct real data analysis to assess the usefulness and flexibility of exponentiated Weibull distribution in the context of seismic interevent time modeling and associated applications. Results suggest that the exponentiated Weibull distribution has a comparable performance with other popular distributions of its nature. However, further investigations are necessary to confirm the importance and flexibility of exponentiated Weibull distribution in statistical seismology. 相似文献
5.
The purpose of this article is to study the three-parameter (scale, shape, and location) generalized exponential (GE) distribution and examine its suitability in probabilistic earthquake recurrence modeling. The GE distribution shares many physical properties of the gamma and Weibull distributions. This distribution, unlike the exponential distribution, overcomes the burden of memoryless property. For shape parameter β> 1, the GE distribution offers increasing hazard function, which is in accordance with the elastic rebound theory of earthquake generation. In the present study, we consider a real, complete, and homogeneous earthquake catalog of 20 events with magnitude above 7.0 (Yadav et al. in Pure Appl Geophys 167:1331–1342, 2010) from northeast India and its adjacent regions (20°–32°N and 87°–100°E) to analyze earthquake inter-occurrence time from the GE distribution. We apply the modified maximum likelihood estimation method to estimate model parameters. We then perform a number of goodness-of-fit tests to evaluate the suitability of the GE model to other competitive models, such as the gamma and Weibull models. It is observed that for the present data set, the GE distribution has a better and more economical representation than the gamma and Weibull distributions. Finally, a few conditional probability curves (hazard curves) are presented to demonstrate the significance of the GE distribution in probabilistic assessment of earthquake hazards. 相似文献
6.
Tsuneji Rikitake 《Tectonophysics》1974,23(3):299-312
Statistics of ultimate strain of the earth's crust are obtained on the basis of levelling and triangulation data over earthquake areas. The mean value of ultimate strain e0 is obtained as 5.3 · 10?5 with a standard deviation σ amounting to 3.3 · 10?5 on the assumption that the deviation from the mean value is described by a Gaussian distribution.Assuming that crustal strain increases linearly with time t from an approximately zero value immediately after a large earthquake, which occurred at t = 0, the probability of having a crustal rupture or an earthquake occurrence during a time-interval from 0 to t can be calculated from e0 and a along with the data for strain accumulation over the area concerned as brought out by repetitions of geodetic survey.Applying the above theory to an area southwest of Tokyo, where an earthquake of magnitude 7.9 took place in 1923, the probabilities for repetition of an earthquake there are estimated as 0.2, 0.5 and 0.8 respectively for periods 1925–1980, 1925–2030, and 1925–2080.Similar studies are made for the areas off eastern Hokkaido and the Tokai district in Central Japan. No geodetic data over focal regions are available in these cases because observations are made only on land more than 100 km distant from epicentral area off the coast. In the circumstances theoretical land deformations caused by a plate subduction, which is believed to be taking place at the trench axis, are compared to the deforma tions actually detected by repeated surveys. Although the reliability of probability calculated on the basis of such processes may be substantially lower than that based on data taken in an area immediately covering a focal region, it is striking that the probabilities of reoccurrence of a large earthquake for a time-interval from the last shock to the present are so high that they exceed 0.8 ~ 0.9 for reasonable values of parameters involved. 相似文献
7.
利用地震矩张量与GPS资料推算中国大陆现今地壳运动能量分布特征 总被引：3，自引：0，他引：3
在一次地震轮回时间段内,对于某个相对统一和完整的体系,应变能的积累与释放基本等量.地震资料得到的地壳变形场是现今地壳应变能已得到释放后的一种表现,而GPS资料得到的地壳变形场中则既包含地壳应变能量的释放量,也包含积累量.结合中同大陆及其邻区的地质构造与活动地块分布特点,将研究区划分为32个独立的分区.在此基础之上,利用地震和GPS资料分别计算得到了两组单位体积能量积累率,并对其进行了比较分析.研究表明,本次地震轮回中大多数区域的地壳应变能量已基本释放完毕,我国境内只有青藏北部、川滇、昆仑、阿尔金等儿个地区的地壳应变能量积累偏高,仍具有发生较强地震的可能性,是今后地震预测研究应该重点关注的地区. 相似文献
8.
原位地应力测量与实时监测在地震预报研究中的作用和意义 总被引：2，自引：2，他引：0
当2013年4月20日四川芦山Ms 7.0级大地震发生时,中国科学家已不再像2008年汶川Ms 8.0大地震发生时那样茫然和不知所措。其根本原因在于,2008年汶川大地震发生后,龙门山地区开展了大量的科学研究工作,已超前初步认知龙门山断裂带西南端具有潜在地震危险性,特别是原位地应力测量和实时监测已发现绝对地应力大小高值异常和相对地应力大小临震异常变化。论文简要介绍了地震预报国际主流观点与认识,梳理了地应力在地震预报研究中的作用和认识,探讨了2004 Parkfield earthquake钻孔应变监测结果给予的启示,详细介绍了原位地应力测量与实时监测在地震预报研究中应用的实践与探索。实践证明:地震预报是值得探索和研究的,原位地应力测量与实时监测是地震预报的有效方法之一。 相似文献
9.
K. K. ABDUL AZEEZ 《《地质学报》英文版》2016,90(3):884-899
Lower crustal earthquake occurrence in the Central Indian Tectonic Zone(CITZ) of the Indian sub-continent was investigated using magnetotelluric(MT) data. MT models across the CITZ, including the new resistivity model across the 1938 Satpura lower crustal earthquake epicenter, show low resistive(80 ?m) mid-lower crust and infer small volume(1 vol%) of aqueous fluids existing in most part of lower crust. This in conjunction with xenoliths and other geophysical data supports a predominant brittle/semi-brittle lower crustal rheology. However, the local deep crustal zones with higher fluid content of 2.2%–6.5% which have been mapped imply high pore pressure conditions. The observation above and the significant strain rate in the region provide favorable conditions(strong/moderate rock strength, moderate temperature, high pore pressure and high strain rate) for brittle failure in the lower crust. It can be inferred that the fluid-rich pockets in the mid-lower crust might have catalyzed earthquake generation by acting as the source of local stress(fluid pressure), which together with the regional stress produced critical seismogenic stress conditions. Alternatively, fluids reduce the shear strength of the rocks to favor tectonic stress concentration that can be transferred to seismogenic faults to trigger earthquakes. 相似文献
10.
基于1999～2018年GPS水平运动速度场数据,解算并分析了四川“Y”形构造区各周期网格速度场、地壳应变率场,并讨论了近20年尺度的地壳应变场演化过程。研究表明：1）2008年汶川地震前1999～2007期GPS速度场相对稳定,整体“Y”型构造区地壳运动变化不大,但汶川地震后龙门山断裂带发生较大变化,由4.0 mm/a增至10.0 mm/a。2）1999～2007年,整个四川“Y”型构造区应变场演化特征微弱,而汶川地震之后的两个周期,最大剪应变自龙门山山前断裂向西到汶川一带,形成了由高到低、平行于龙门山断裂带走向的高密度梯度带。龙门山断裂带以ES或EES向的主压应变为主,其量值变化范围为 5.0×10-8 /a～12.0×10-8 /a;鲜水河断裂由震前主拉应变,改为震后近EW向的主压应变特征。面膨胀结果则显示龙门山断裂带由震前低密度梯度带瞬间变为平行于龙门山断裂带走向的高密度变化区。3）2008年汶川地震和2013年芦山地震是最为重要的时刻分割点。近20年的应变率场变化,更似一个“时间—地壳构造运动”的大轮回,目前四川“Y”型构造区整体处于2008年汶川地震前较为稳定的活动周期。龙门山断裂带仍值得我们做出更为深入的研究。 相似文献
11.
壳内低速层与地震活动关系 总被引：11，自引：0，他引：11
本文根据华北、扬子地台、青藏高原等地区的速度结构、介质特征、地震活动分布等特征,认为地壳中的低速层是在地壳中的弱化层,它与壳内低阻或高导层相对应,在地质构造上反映中地壳大型层间韧性剪切带,与地震活动的层状分布深度范围相对应,粘滑机制是壳内地震活动非常重要的机制,反映了岩石变形呈脆韧性过渡状态。 相似文献
12.
龙门山多层分层拆离地壳结构:新构造变形与深部构造证据 总被引：5，自引：0，他引：5
2008年5.12汶川地震发生后,对于龙门山地壳结构及其与汶川地震的成生联系成为构造地质学研究极为关注的科学问题。然而,现有的多种龙门山地壳结构模式在综合解释表层构造变形及深部构造时与调查和探测资料均有不符。利用前人地球物理探测成果,结合穿过龙门山主要发震构造单元彭灌杂岩及雪隆包岩体的综合构造剖面,将地表构造与深部地壳探测资料结合进行了综合解释,认为龙门山逆冲构造带中的多重冲断推覆构造由约10 km深处的拆离断层分隔,因而应该只是浅层次构造变形的组合样式;在中、下地壳韧性流壳层的主导下,扬子地块基底被动?入并形成多层拆离的韧性流变构造组合。5.12汶川地震及余震是由于以彭灌杂岩和雪隆包岩体为代表的刚性体,在上部韧性流壳层前端的持续推挤作用下,发生破裂而形成的。 相似文献
13.
东昆仑、玉树、汶川地震的发生规律和形成机理:兼论大陆地震成因与预测 总被引：6，自引：3，他引：3
青藏高原东北部东昆仑、汶川、玉树等强震的同震地表破裂不对称发育,伴随余震有规律地分别向东、南东和北北东方向迁移,很可能是源于恒河盆地流经亚东、当雄、安多、库赛湖、治多、玉树、甘孜、汶川的弧形下地壳“热河”的流速和流向变化形成的,下地壳热流物质正在向云南及邻区汇聚形成下地壳“热海”,导致长时间跨季度构造热干旱,其影响超过大气环流的作用。地表破裂不一定受断层控制,震源也不在断层面上,下地壳流动导致中地壳发震并进一步影响上地壳形成同震脆性破裂系统。大陆板内盆山过渡带地震密集,大陆板内地震是在下地壳层流的热动力作用下导致活动地壳分层变形的产物。在大陆盆山耦合、圈层耦合的非线性开放系统中,从大洋底部的软流圈层流进入大陆底部使得地幔软流圈加厚,底辟上升为大陆下地壳流动,为地震活动提供了巨量热能;热软化的下地壳缓慢的韧性流动孕育了大陆板内地震;中地壳韧 脆性剪切带易于积累能量,发生热能与应变能的转化,产生地震,形成震源层;上地壳脆性断层活动和地表破裂是地震释放深部能量的载体和方式之一。地壳稳定性评价的依据应当是地壳的活动性而不是断层的活动性。大陆活动构造区地震活跃期与平静期交替实际上是下地壳地震能量的聚散过程,体现在下地壳热主导的韧性流动构造与上地壳应力主导的脆性破裂构造之间的相互作用。下地壳热软化物质流动过程中流速、流向等突然改变触发地震,并产生共振波。大陆下地壳流层在厚度、温度、粘度、流速、流向上的变化产生一定程度的温度异常、流体异常及与其相关的大气层、电场、磁场、重力场、地球化学场、应力场、应变场、生物场等异常。合理布置天空网、地面网、地下网,综合立体监测有效的地震前兆,系统地开展长期、中期和短临地震预测,能够不断地提高地震预测水平。 相似文献
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15.
Yukio Hagiwara 《Tectonophysics》1974,23(1-2)
The hazard rate, the number of fracture occurrences per unit time, which has been obtained from laboratory experiments of rock fracture, is obtained for the earth's crust by analysing the statistical distribution of geodetically-observed ultimate strain. The associated hazard function has two coefficients, A and B, to be determined. Comparison of the coefficients obtained by the results of rock-fracture experiments with the geodetically determined ones discloses that B is independent of the size-effect. It is therefore concluded that, if A is estimated from the statistics of the geodetically observed ultimate strain and B is obtained from fracture experiments of rock forming a local part of the crust, the probability of a local large-scale earthquake occurrence can be estimated. 相似文献
16.
Relation between electrical resistivity and earthquake generation in the crust of West Anatolia, Turkey 总被引：1，自引：0，他引：1
In this paper, we present a relation between the earthquake occurrence and electric resistivity structures in the crust, in West Anatolia and the Thrace region of Turkey. The relationship between magnetotelluric georesistivity models and crustal earthquakes in West Anatolia, during a period from 1900 to 2000, is investigated. It is found that most of the large crustal earthquakes occurred in and around the areas of the highest electrical resistivity in the upper crust, although rare small magnitude earthquakes are observed in some parts of the conductive lower crust in West Anatolian extensional terrain. The high-resistivity zones may represent rocks that are probably mechanically strong enough to permit sufficient stress to accumulate for earthquakes to occur in western Anatolia and the Thrace region. However, some recent studies state that the generation of a large earthquake is not only a pure mechanical process, but is closely related to fluid existence. We also reviewed recent world-wide researches including results from the Anatolian data for the first time and discussed all general findings in combination. Our findings show that the boundary between the resistive upper crust and the conductive lower crust correlates well with the cutout depth of the seismicity in West Anatolia and Thrace. This boundary is also attributed to the fluid bearing brittle–ductile transition zone in world literature. Fluid migration from the conductive lower crust to the resistive upper crust may contribute the seismicity in resistive zones. Alternatively, the upper–lower crust boundary may act as a stress concentrator and fluids may help to release strain energy in brittle parts of lower crust, by small magnitude earthquakes, whereas they may help in focusing strain in mechanically strong and electrically resistive zones for large earthquakes to occur. 相似文献
17.
北京城市未来发展中地壳环境的潜在危机 总被引：2，自引：0，他引：2
通过研究北京地区不同时期和不同时间尺度内地壳运动的规律性和特殊性，认为地震是北京城市未来发展中较为重要的潜在危机之一：（１）北京地区ＮＥ和ＮＷ向两组主控断层目前仍在活动，大多属继承性活断层；（２）４５ａ来北京地区地形变具有北升南降和西升东降特点。地形变等值线的区域分布具有突出的上升区、下降区及高梯度区；（３）３０ａ来断层活动具有明显的周期性，今后应进一步加强超短周期断层活动规律性的监测，以利于地震预报的研究；（４）目前北京地区仍处在本世纪６０年代以来华北地壳强活动期内，推论今后发生较强烈地震的长趋势将依然存在。 相似文献
18.
A. Manglik S. Thiagarajan A. V. Mikhailova Yu. Rebetsky 《Journal of Earth System Science》2008,117(2):103-111
Deep lower crustal intraplate earthquakes are infrequent and the mechanism of their occurrence is not well understood. The
Narmada-Son-lineament region in central India has experienced two such events, the 1938 Satpura earthquake and the 1997 Jabalpur
earthquake, having a focal depth of more than 35 km. We have estimated elastic stresses due to the crustal density and mechanical
properties heterogeneities along the Hirapur-Mandla profile passing through the Jabalpur earthquake region to analyse conditions
suitable for the concentration of shear stresses in the hypocentral region of this earthquake. Elastic stresses have been
computed by a finite element method for a range of material parameters. The results indicate that the shear stresses generated
by the density heterogeneities alone are not able to locally enhance the stress concentration in the hypocentral region. The
role of mechanical properties of various crustal layers is important in achieving this localization of stresses. Among a range
of material parameters analysed, the model with a mechanically strong lower crust overlying a relatively weak sub-Moho layer
is able to enhance the stress concentration in the hypocentral region, implying a weaker mantle in comparison to the lower
crust for this region of central India. 相似文献
19.
本文利用现有各种地球物理资料、地震地质资料,探讨了重磁场特征、地壳结构、活动断裂与地震的关系,进而总结出地震震中在地壳介质中的空间分布规律。在此基础上建立了地壳稳定性评价分级指标,并对本区的地壳稳定性进行了评价。 相似文献
20.
Luminiţa Ardeleanu 《Natural Hazards》1999,19(2-3):151-164
A parameterization derived from the Weibull distribution is used to model the seismic activity of the Vrancea region.The analysis of 498 crustal earthquakes with local magnitudes greater than 2.0, and 1377 subcrustal events with local magnitudes greater than 2.5 emphasizes that the shallow sequences show a strong clustering tendency, while the intermediate depth mainshock sequences are modeled by a completely random pattern in space and time. These results are not influenced by the magnitude threshold and the width of the time window.The difference between the seismicity patterns in the crust and in the subcrustal zone correlates with the difference between the stress field within these two regions. 相似文献