大震系的层次、频度及时间分布特征

根据地震构造类型、规模及大地震的强度和累积地震矩,将12个大震系划分为4个层次。在一个大震系中,累计的地震数为7—10次,最大地震的地震矩约为总地震矩的0.5左右。用分数维的概念对大震系中大震的频度和能量特征作了初步分析。对大震系内的地震的时间分布,可以用随机统计的方法给出其统计的规律。多数大震系的地震累计数N可近似地用时间t的指数函数表示:N=AeBt     

Probabilistic Assessment of Earthquake Hazard in Gujarat and Adjoining Region of India

The Gujarat and adjoining region falls under all four seismic zones V, IV, III and II of the seismic zoning map of India, and is one of the most seismically prone intracontinental regions of the world. It has experienced two large earthquakes of magnitude M _w 7.8 and 7.7 in 1819 and 2001, respectively and several moderate earthquakes during the past two centuries. In the present study, the probability of occurrence of earthquakes of M ≥ 5.0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely, Weibull, Gamma and Lognormal. A complete earthquake catalogue has been used covering the time interval of 1819 to 2006. The whole region has been divided into three major seismic regions (Saurashtra, Mainland Gujarat and Kachchh) on the basis of seismotectonics and geomorphology of the region. The earthquake hazard parameters have been estimated using the method of maximum likelihood. The logarithmic of likelihood function (ln L) is estimated and used to test the suitability of models in three different regions. It was found that the Weibull model fits well with the actual data in Saurashtra and Kachchh regions, whereas Lognormal model fits well in Mainland Gujarat. The mean intervals of occurrence of earthquakes are estimated as 40.455, 20.249 and 13.338 years in the Saurashtra, Mainland Gujarat and Kachchh region, respectively. The estimated cumulative probability (probability that the next earthquake will occur at a time later than some specific time from the last earthquake) for the earthquakes of M ≥ 5.0 reaches 0.9 after about 64 years from the last earthquake (1993) in Saurashtra, about 49 years from the last earthquake (1969) in Mainland Gujarat and about 29 years from the last earthquake (2006) in the Kachchh region. The conditional probability (probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake) is also estimated and it reaches about 0.8 to 0.9 during the time interval of about 57 to 66 years from the last earthquake (1993) in Saurashtra region, 31 to 51 years from the last earthquake (1969) in Mainland Gujarat and about 21 to 28 years from the last earthquake (2006) in Kachchh region.     

2008年汶川8.0级地震发生的历史与现今地震活动背景

为了了解2008年5月12日四川汶川M_S8.0地震发生的地震活动背景,本文综合历史与现代地震资料,从南北地震带中段及其邻区的视野研究了汶川地震前1~2千年的强震活动性,以及震前20年的地震活动性背景.结果主要表明：（1）至少在2008年之前的1100~1700年中,龙门山断裂带未发生M≥7的地震,相对其南、北两侧的其他活动断裂带（或段）形成一个地震空区,2008年汶川M_S8.0地震发生在该空区中;（2）17世纪以来,在由龙门山断裂带大部分地区、川北岷江-虎牙断裂带以及甘南文县-武都断裂带组成的巴颜喀拉块体东边界上共发生了12次M=6.5~8.0地震,显示出一个已持续了近400年、逐渐加速的应变能释放过程,2008年汶川M_S8.0地震属于该过程中两次巨大地震之一;（3）汶川地震前20年,龙门山断裂带中、南段不存在背景地震活动的平静,反而显示出比曾经发生过1879年M_S8地震的甘南文县-武都断裂带还略高的地震活动背景水平;（4）2008年汶川地震的强度远远超出龙门山断裂带的历史最大地震,说明仅基于数百年至一、两千年的历史地震记载,远不足以正确评估较低滑动速率的、大型活动断裂带的潜在地震危险性.     

北祁连山-河西走廊大震危险区预测

以青藏块体北部的北祁连山-河西走廊地震构造带为研究对象,在系统收集整理该区主干活动断裂新活动性特征、断裂滑动速率、历史地震及古地震资料的基础上,结合现今地震活动性,采用地震空区、空段识别方法和地震活动b值空间图像扫描方法,分析了研究区内历史地震及b值的分布特征.结果显示,该区的榆木山北缘断裂离逝时间较长,应力积累程度较...     

优化减震距离

本文对中国大陆内部不同时段发生的七级地震和六级地震分别进行统计分析,求得不同震级的优势地震间距,减震距离以及地震间距随时间变化的关系式。提出地震间距的数值分布可用正态概率分布函数描述,并得到含有时间参量的地震间距概率密度函数。此外,根据弹性位错理论,求得一次地震后在减震距离处所产生的位移,进而求出平均位移速率。     

PRESTo,the earthquake early warning system for Southern Italy: Concepts,capabilities and future perspectives

PRESTo (PRobabilistic and Evolutionary early warning SysTem) is a software platform for regional earthquake early warning that integrates recently developed algorithms for real-time earthquake location and magnitude estimation into a highly configurable and easily portable package. The system is under active experimentation in Southern Italy on the Irpinia Seismic Network (ISNet), which is deployed in a seismogenic area that is expected to produce a large earthquake within the next 20 years. In this paper we describe the architecture of the system and test its performances using both small earthquakes (M<3.5) recorded at the ISNet and a large event recorded in Japan, through a simulation mode. The results show that, when a dense seismic network is deployed in the fault area, PRESTo can produce reliable estimates of earthquake location and size within 5–6 s from the event origin. Each estimate is provided as a probability density function, with an uncertainty that typically decreases with time: a stable solution is generally reached within 10 s from the origin.     

诱发前震图象与1995年1月17日日本阪神大地震

地震引起的应力场扰动随距离不断衰减，远程触发很难发生，只有极不稳定状态的断层才有这种可能。利用这一特点，可以预报下次地震的位置，为实施减灾措施和捕捉短临前兆提供机会。所以，紧随大地震之后发生的“诱发前震”就具有了特殊的前兆意义。统计表明，大地震（Ａ事件）可能触发远处临界失稳断层发生前兆地震（Ｆ事件），在Ｆ事件附近发生下次大震（Ｂ事件）的概率比自然概率高十几倍到几十倍。这一结论被从中国大陆、全球主要板块边界及日本列岛发现的众多ＡＦＢ图象所证实。对其发生的可能的物理机制在文末进行了讨论。     

准时间可预报复发行为与断裂带分段发震概率估计

反不确定性引入“时间可预报模式”，可将一次地震之后的平静时间表示成与这次地震位错量在小呈正相关的随机变量。称这种带有不确定性的地震原地复发行为为“准时间可预报行为”。对于历史地震资料，准时间可预报复发行为可由地震后平静时间的对数与地震烈度的回归方程。文中给出了估计一条枯断裂带不同段落以上一次地震烈度值为背景的平均复发时间间隔的方法，以及可用 于对未来地震潜势进行不确定评价的实时概率模型，并以鲜水河     

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.      

Paleoseismology of the Itoigawa-Shizuoka tectonic line in central Japan

The 150-km-long Itoigawa-Shizuoka tectonic line active fault system (ISTL)in central Japan is one of the most active Quaternary fault systems inJapan. Estimated slip-rates on the fault system are as large as 10 m/ka, butthe historic seismicity has been low since 841 A.D. with no largeearthquakes recorded. The high slip rates contrast with the long time sincethe last major earthquake on the ITSL and indicates the high potential of a largeearthquake from the ISTL. Based on slip-rate estimates, more than 10 mof potential slip may have accumulated on the fault system since the 841A.D. earthquake. Recent paleoseismolgical studies on the middle andnorthern parts of the ISTL have determined that the average recurrenceinterval of surface-faulting earthquakes on the middle ISTL is 680 to 825years (Gofukuji fault) and 1258 to 1510 years in the northern ISTL. These data suggest the most recent event on both northern and middleISTL occurred in 841 A.D. The results highlight the high seismic potentialof the ISTL. Additional studies of the entire ISTL are needed to define theextent of the next rupture.     

用累积地震矩法研究全球地震活动性

本文基于Lomnitz提出的MRI理论,用"累积地震矩(CSM)"算法对全球1900—1999年7级以上的地震进行了处理,试图通过分析大震前CSM图像的变化,来判断地震发生的可能性。对不同地区的6个地震震前CSM图像的分析表明:7级以上地震的CSM图像在震前5到10年内会改变,大部分地震发生在CSM的高值区或次高值区。通过实际运算发现:在不同的地区应使用不同的值可获得较好的结果,用于计算的地震数越多,获得的结果越好。有些大地震前CSM异常区域不是唯一的,往往会出现几个,这可能与研究区域的地震活动性有关。因此,笔者认为:若要获得可靠的CSM图像,除应当考虑不同地区的小震活动水平外,还应考虑地震断层对震后能量分布影响。统计结果表明:在目标地震发生后,下一次地震在空间上发生在原地及2度距离范围内的概率较大,在3度以外区域发生的概率相差不大;在时间上,发生在原地区震后1年内的概率最高,这可能与余震活动有关;在5年的时间里,下一次地震发生的次数占到全部地震的70%以上。因此,要注意大地震后,目标地震附近有地震能量进一步释放的危险性。     

Seismicity before and after the two great Sumatra earthquakes of 2004 and 2005

The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast. The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.     

The December 5th, 1456 Central Italy Earthquake: A Discussion of a Possible Reshaping of Intensity Distribution by Vectorial Modelling

--A study of the intensity distribution of the earthquake of December 5th 1456, which affected a large area of central and southern Italy was carried out, verifying, through a recently proposed methodology, the two hypotheses assumed by different authors for one single seismic event and three distinct and close ones. This methodology is based on a vectorial modelling of the macroseismic intensity distribution which aims at determining the epicentre and the principal (minimum and maximum) attenuation directions.¶The study was structured, considering each of the two assumed hypotheses, in a set of tests obtained for the macroseismic field and the intensity map, by analysing different configurations of the observed intensity distribution.¶The results obtained are in agreement with the hypothesis of the time coexistence of three distinct seismic events, for which the calculated epicentres and the principal attenuation directions are compatible with the observed intensity distribution and with the tectonic trend of the Apennine region, respectively.     

青藏高原东北缘地震时空迁移的有限元数值模拟

地震在大陆内部断层系统中的时空迁移和丛集的基本力学机制一直是地球科学家关注的重要问题.青藏高原东北缘地震活动频繁,其地震时空迁移和地震丛集现象显著,是研究这个问题的重要区域.我们建立了一个三维黏弹塑性有限元模型,模拟了青藏高原东北缘主要活动断层系统的地震循环和地震时空迁移;计算了断层系统的应力演化;并探讨了断层之间的相互作用及地震时空迁移和地震丛集的原因.模拟结果显示断层之间的相互作用通过增加或降低断层上的库仑应力,加速或延缓了地震发生,使得区域地震可以在短时间内集中发生,从而形成地震丛集;另外,区域经过多个地震循环的长期演化,一些孕震断层上的应力状态恰好都达到屈服的临界状态附近,从而也可以导致这些断层上的地震在短期内集中发生,因此产生地震丛集和地震迁移.我们发现当区域经历地震丛集之后,该区域的应力大大释放,区域进入地震平静期;随着构造加载的持续,区域应力逐渐恢复,为下一次地震丛集或地震序列累积应力和能量;上述过程可以重复发生.因此地震丛集期与平静期交替出现.我们还统计了各个断层的大地震相互迁移的模拟结果,结果显示青藏高原东北缘下一次大地震有很大的概率会发生在海原断层上.     

Seismic gaps and plate tectonics: Seismic potential for major boundaries

The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by aftershocks, tend to abut rather than overlap, and large events occur in regions with histories of both long- and short-term seismic quiescence are used in this paper to delineate major seismic gaps.In detail, however, the distribution of large shallow earthquakes along convergent plate margins is not always consistent with a simple model derived from plate tectonics. Certain plate boundaries, for example, appear in the long term to be nearly aseismic with respect to large earthquakes. The identification of specific tectonic regimes, as defined by dip of the inclined seismic zone, the presence or absence of aseismic ridges and seamounts on the downgoing lithospheric plate, the age contrast between the overthrust and underthrust plates, and the presence or absence of back-arc spreading, have led to a refinement in the application of plate tectonic theory to the evaluation of seismic potential.The term seismic gap is taken to refer to any region along an active plate boundary that has not experienced a large thrust or strike-slip earthquake for more than 30 years. A region of high seismic potential is a seismic gap that, for historic or tectonic reasons, is considered likely to produce a large shock during the next few decades. The seismic gap technique provides estimates of the location, size of future events and origin time to within a few tens of years at best.The accompanying map summarizes six categories of seismic potential for major plate boundaries in and around the margins of the Pacific Ocean and the Caribbean, South Sandwich and Sunda (Indonesia) regions for the next few decades. These categories range from what we consider high to low potential for being the site of large earthquakes during that period of time. Categories 1, 2 and 6 define a time-dependent potential based on the amount of time elapsed since the last large earthquake. The remaining categories, 3, 4, and 5, are used for areas that have ambiguous histories for large earthquakes; their seismic potential is inferred from various tectonic criteria. These six categories are meant to be interpreted as forecasts of the location and size of future large shocks and should not be considered to be predictions in which a precise estimate of the time of occurrence is specified.Several of the segments of major plate boundaries that are assigned the highest potential, i.e., category 1, are located along continental margins, adjacent to centers of population. Some of them are hundreds of kilometers long. High priority should be given to instrumenting and studying several of these major seismic gaps since many are now poorly instrumented. The categories of potential assigned here provide a rationale for assigning prorities for instrumentation, for future studies aimed at predicting large earthquakes and for making estimates of tsunami potential.Lamont-Doherty Geological Observatory Contribution No. 2906.     

甘孜-玉树断裂带的近代地震与未来地震趋势估计

通过对甘孜－玉树断裂带上近代地震的震级、震中位置和地震地表破裂的空间展布特征的研究，采用Ｎｉｓｈｅｎｋｏ和Ｂｕｌａｎｄ（１９８７）发展的“特征地震复发时间通用分布”概率模型，即“ＮＢ”模型，对甘孜－玉树断裂带各段落未来５０ａ内强震趋势进行了估计。根据研究结果识别出，未来５０ａ内本断裂带内马尼干戈断裂段具有强震复发的高危险性，当江断裂段强震复发的可能性也不能排除，这为地震中长期预报提供了重要依据     

Damage‐based design with no repairs for multiple events and its sensitivity to seismicity model

Conventional design methodology for the earthquake‐resistant structures is based on the concept of ensuring ‘no collapse’ during the most severe earthquake event. This methodology does not envisage the possibility of continuous damage accumulation during several not‐so‐severe earthquake events, as may be the case in the areas of moderate to high seismicity, particularly when it is economically infeasible to carry out repairs after damaging events. As a result, the structure may collapse or may necessitate large scale repairs much before the design life of the structure is over. This study considers the use of design force ratio (DFR) spectrum for taking an informed decision on the extent to which yield strength levels should be raised to avoid such a scenario. DFR spectrum gives the ratios by which the yield strength levels of single‐degree‐of‐freedom oscillators of different initial periods should be increased in order to limit the total damage caused by all earthquake events during the lifetime to a specified level. The DFR spectra are compared for three different seismicity models in case of elasto‐plastic oscillators: one corresponding to the exponential distribution for return periods of large events and the other two corresponding to the lognormal and Weibull distributions. It is shown through numerical study for a hypothetical seismic region that the use of simple exponential model may be acceptable only for small values of the seismic gap length. For moderately large to large seismic gap lengths, it may be conservative to use the lognormal model, while the Weibull model may be assumed for very large seismic gap lengths. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessing current faulting behaviors and seismic risk of the Anninghe-Zemuhe fault zone from seismicity parameters

Introduction Strong and large earthquakes are prepared and generated on specific segments of active fault zones, especially on the asperity parts of the zones (Aki, 1984; Wiemer, Wyss, 1997; Wyss, et al, 2000). Therefore, both the faulting-behavior identification and the rupture segmentation mainly based on the method of active tectonics are always important aspects in active fault research (DING, et al, 1993). The purposes of the two aspects of research focus on determining fault units tha…     

Ground motion characteristics of the Chi‐Chi earthquake of 21 September 1999

The purpose of this paper is to investigate the ground motion characteristics of the Chi‐Chi earthquake (21 September 1999) as well as the interpretation of structural damage due to this earthquake. Over 300 strong motion records were collected from the strong motion network of Taiwan for this earthquake. A lot of near‐field ground motion data were collected. They provide valuable information on the study of ground motion characteristics of pulse‐like near‐field ground motions as well as fault displacement. This study includes: attenuation of ground motion both in PGA and spectral amplitude, principal direction, elastic and inelastic response analysis of a SDOF system subjected to near‐field ground motion collected from this event. The distribution of spectral acceleration and spectral velocity along the Chelungpu fault is discussed. Based on the mode decomposition method the intrinsic mode function of ground acceleration of this earthquake is examined. A long‐period wave with large amplitude was observed in most of the near‐source ground acceleration. The seismic demand from the recorded near‐field ground motion is also investigated with an evaluation of seismic design criteria of Taiwan Building Code. Copyright © 2000 John Wiley & Sons, Ltd.