The probability of occurrence of largest earthquqkes in the European area — Part II

Summary The previous investigation of the probability of occurrence of largest earthquakes in the European area continued by applying the Gumbel theory of largest values to three periods 1901–1930, 1901–1955 and 1901–1967, respectively. The values of magnitudes which will be exceeded with the probabilityP=1%, 2% and 10% were determined from the lines fitting the distributions of magnitudes and corresponding probabilities for all three periods. It was assumed that the relationship between the differences M _P% ^[k](67)=M _k,P%–M ₆₇,P% (k=30, 55, 67) and the observation period follow the hyperbolic law. This tendency was used for the estimation of the probability line corresponding to an infinite observation period.Presented at The Sixth UMC Symposium on Geophysical Theory and Computers in Copenhagen in 1969.     

Error propagation in time-dependent probability of occurrence for characteristic earthquakes in Italy

Time-dependent models for seismic hazard and earthquake probabilities are at the leading edge of research nowadays. In the framework of a 2-year national Italian project (2005–2007), we have applied the Brownian passage time (BPT) renewal model to the recently released Database of Individual Seismogenic Sources (DISS) to compute earthquake probability in the period 2007–2036. Observed interevent times on faults in Italy are absolutely insufficient to characterize the recurrence time. We, therefore, derived mean recurrence intervals indirectly. To estimate the uncertainty of the results, we resorted to the theory of error propagation with respect to the main parameters: magnitude and slip rate. The main issue concerned the high variability of slip rate, which could hardly be reduced by exploiting geodetic constraints. We did some validation tests, and interesting considerations were derived from seismic moment budgeting on the historical earthquake catalog. In a time-dependent perspective, i.e., when the date of the last event is known, only 10–15% of the 115 sources exhibit a probability of a characteristic earthquake in the next 30 years higher than the equivalent Poissonian probabilities. If we accept the Japanese conventional choice of probability threshold greater than 3% in 30 years to define “highly probable sources,” mainly intermediate earthquake faults with characteristic M < 6, having an elapsed time of 0.7–1.2 times the recurrence interval are the most “prone” sources. The number of highly probable sources rises by increasing the aperiodicity coefficient (from 14 sources in the case of variable α ranging between 0.22 and 0.36 to 31 sources out of 115 in the case of an α value fixed at 0.7). On the other hand, in stationary time-independent approaches, more than two thirds of all sources are considered probabilistically prone to an impending earthquake. The performed tests show the influence of the variability of the aperiodicity factor in the BPT renewal model on the absolute probability values. However, the influence on the relative ranking of sources is small. Future developments should give priority to a more accurate determination of the date of the last seismic event for a few seismogenic sources of the DISS catalog and to a careful check on the applicability of a purely characteristic model.     

Model of earthquake occurrence in the European area

Summary The time distribution of earthquake occurrence in the European area is investigated by statistical laws. The original data of shallow-focus earthquakes are taken from the European catalogue 1901–1967. Evidence is given that the process with the negative binomial entries as a model describing the occurrence of shallow-focus earthquakes is better than the Poisson process. Further, the influence of magnitude classes and magnitude threshold value on the time distribution of earthquake occurrence is examined.Communication presented at the XIII General Assembly of the European Seismological Commission in Brasov in 1972.     

Uncertainties in probability of occurrence of strong earthquakes for fault sources in the Central Apennines,Italy

Using the characteristic earthquake model, we calculate the probability of occurrence of earthquakes M _w > 5.5 for individual fault sources in the Central Apennines for the 30-year period (2007–2037). We show the effect of time-dependent and time-independent occurrence (Brownian passage time (BPT) and Poisson) models together with uncertain slip rates and uncertain maximum magnitudes and, hence, uncertain recurrence times. In order to reduce the large prior geological slip rate uncertainty distribution for most faults, we obtain a posterior slip rate uncertainty distribution using a likelihood function obtained from regional historical seismicity. We assess the uncertainty of maximum magnitude by assuming that the uncertainty in fault width and length are described by a normal distribution with standard deviation equal to ±20% of the mean values. We then estimate the uncertainties of the 30-year probability of occurrence of a characteristic event using a Monte Carlo procedure. Uncertainty on each parameter is represented by the 16th and the 84th percentiles of simulated values. These percentiles bound the range that has a 68% probability of including the real value of the parameter. We do these both for the Poisson case and for the BPT case by varying the aperiodicity parameter (α value) using the values 0.3, 0.5, and 0.7. The Bayesian posterior slip rate uncertainties typically differ by a factor of about 2 from the 16th to the 84th percentile. Occurrence probabilities for the next 30 years at the 84th percentile typically range from 1% to 2% for faults where the Poisson model dominates and from 2% to 21% where one of the BPT models dominates. The uncertainty in occurrence probability under the time-dependent hypothesis is very large, when measured by the ratio of the 84th to the 16th percentile, frequently being as much as two orders of magnitude. On the other hand, when measured by standard deviation, these standard deviations range from 2% to 6% for those faults whose elapsed time since previous event is large, but always 2% or less for faults with relatively recent previous occurrence, because the probability of occurrence is always small.     

更新模型在缺少大震离逝时间的活动断裂强震发生概率计算中的应用研究

利用更新模型计算未来几十年内发生强震的条件概率需要给出上一次大震的离逝时间T,而很多活动断裂上缺少历史大震的记载,若采用泊松模型则可能会低估强震发生的概率.针对这种缺少大震离逝时间的活动断裂,本文提出一种以记载完整的强震平静期长度Ts为参数的条件概率计算方法.以东昆仑断裂带塔藏段为实例,利用本文给出的条件概率计算方法得到该段未来50年发生强震的可能性为0.064 9.     

一种基于蒙特卡罗模拟的发震概率计算方法

针对大震发生概率计算过程中的不确定性, 本文分别对不确定性及其处理方法进行了探讨． 考虑到不确定构成的复杂性, 提出了一种基于蒙特卡罗模拟的大震发生概率计算方法, 并以东昆仑断裂带塔藏段为计算实例, 利用蒙特卡罗法处理发震概率计算过程中的各种不确定性. 结果表明, 古地震数据的不完整性对计算结果的影响很大. 本文采用逻辑树法考虑古地震数据的不完整性, 得到塔藏段未来100年的大震发生概率为0.12．      

地震前兆异常的综合概率与中强震发生的关系

通过河北省各前兆学科对1970年－2000年6月观测资料的系统清理，应用综合概率方法提取出了多学科多个前铛因子判断中强地震的综合概率指标（P≥5.55), 其结果对河北省及其邻区Ms5.0级以上地震对应效果较好，R值评分为0.467,表明该方法具有一定程度的预测能力。     

Probabilities of occurrence of large earthquakes in the Aegean and surrounding area during the period 1986–2006

Repeat times of large shocks are obtained for 17 seismic fracture zones of the Aegean and surrounding area, from times of historic and present century earthquakes. The mean standard deviation of the repeat times is approximately 50% of any one observation.A probabilistic approach is then used to forecast the likelihood of large future earthquakes in each fracture zone, using as input the time of the last large shock, the average repeat time and its standard deviation. Shallow and intermediate depth earthquakes are examined separately. The calculated probabilities are high for the entire Hellenic arc, both for shallow and intermediate depth seismicity, for the area of Leucas island (Ionian), of Lesbos island (Aegean), for Patraikos-west Corinthiakos Gulfs, for Evoikos Gulf as well as for southern Bulgaria.The probability estimates based on the most recent large earthquakes, involve a number of basic physical assumptions and we would think that they provide a semi-stochastic approach to the problem of earthquake prediction in Greece.     

The time of occurrence and the magnitude of the largest aftershock over India

Summary The time of occurrence and the magnitude of the largest aftershock in relation to the main shock have been studied for India and its neighbourhood based on the USCGS data during the years 1963–1971. It is found that the largest aftershock occurs within 2 hours after the main shock in about 50% of the cases and frequency of occurrencen(t) of the largest aftershocks decreases hyper-bolically with the intervalt after the main event and could be represented by a law of the formn(t)=At ^–h whereA andh are constants. The probability of occurrence of the largest aftershock within 2 hours of the main shock is found to be higher over island are regions of the world. The difference (M ₀–M ₁) of the magnitude of the largest aftershockM ₁ to that of the main shockM ₀ as a measure of aftershock activity does not show any marked regional variation over India and its neighbourhood, as was reported by Mogifor Japan. Examination of the values ofM ₁/M ₀ and the constantb in Gutenberg-Richter's frequency magnitude relationship reveals a range of variation in both; high values ofM ₁/M ₀ have been found to be associated with high values ofb in many tectonic earthquakes and thus not, restricted to reservoir associated seismic activity.     

Seismogenic zones of the Transcaspian region: Characteristics of sources of the largest earthquakes. II. The Krasnovodsk and Kazandzhik earthquakes

An interpretation of the source origin of the largest Transcaspian Kazandzhik 1946 and Krasnovodsk 1895 earthquakes is proposed. The interpretation is based on the analysis of data on the geological structure of the Transcaspian region and the available evidence for coseismic effects of these events. Data on other earthquakes of the region and the results of focal mechanism determinations are taken into account. The Kazandzhik earthquake consisted of two shocks with separate sources. The source of the first, weaker shock, located in structures of the Greater Balkhan Ridge, was characterized by reversed-strike-slip motions. The 40–50-km-long source of the second, main shock, which determined the earthquake magnitude (M ～ 6.9–7.0), was located in the Kazandzhik basin, in the boundary zone between the Kopet Dagh foredeep and the Frontal anticlinal range. It was similar in type and coseismic effects to the source of the Ashkhabad earthquake of 1948. The Krasnovodsk earthquake source 100–120 km long, located in the crust, is associated with the development of the Balkhan foredeep. In accordance with the source size, the magnitude of the Krasnovodsk earthquake is M ～ 7.8–8.0. The three major earthquakes (Ashkhabad, Kazandzhik, and Krasnovodsk) in the Transcaspian region are associated with the general tectonic process of the presently continuing development of the Transcaspian Kopet Dagh and Balkhan foredeeps. This process forms the major Transcaspian seismogenic zone, possibly extending through the Caspian Sea up to the Black Sea coast. The Transcaspian seismogenic zone of a smaller size is associated with the continuing development of domelike structures of the Pribalkhano—Livanovskaya anticlinal zone in the Pribalkhanskaya depression. The generation of such earthquakes as the Kum Dagh 1983 and the Nebit Dagh (Burun) 1984 earthquakes is associated with this zone.     

新丰江地区部分地震的震源时间函数

广东省数字遥测地震台网建成以来积累了较丰富的数字化地震记录，作者利用这些数据开展震源研究，得到新丰江地区的部分地震震源时间函数的初步结果。得到结果的3组地震它们各自较大地震的震级分别为ML1．8、2．3和3．0级，对应的震源时间函数上升时间分别为0．07s、0．09s和0．11s，函数形态较为简单。     

蒙宁交界区地震震源深度的对比分析

选取内蒙古地震台网记录的2009~2015年蒙宁交界区103次ML≥2.5地震波形资料,采用震源深度测定的单纯型法、Hyposat法、双差法、PTD法重新测定震源深度,并将所获得结果进行对比分析。用CAP矩张量反演法重新测定了阿拉善左旗5.8级和4.2级地震的震源深度。最终获得用PTD法和双差法所得的震源深度结果与蒙宁交界区的构造特征比较吻合,单纯型法、Hyposat法效果不佳。同时得到蒙宁交界地震构造区的平均震源深度为13.32±8km。     

The optimum Bayesian probability procedure and the prediction of strong earthquakes felt in Mexico city

Bayes' theorem has possible application to earthquake prediction because it can be used to represent the dependence of the inter-arrival time (T) of thenext event on magnitude (M) of thepreceding earthquake (Ferraes, 1975;Bufe et al., 1977;Shimazaki andNakata, 1980;Sykes andQuittmeyer, 1981). First, we derive the basic formulas, assuming that the earthquake process behaves as a Poisson process. Under this assumption the likelihood probabilities are determined by the Poisson distribution (Ferraes, 1985) after which we introduce the conjugate family of Gamma prior distributions. Finally, to maximize the posterior Bayesian probabilityP(/M) we use calculus and introduce the analytical condition .Subsequently we estimate the occurrence of the next future large earthquake to be felt in Mexico City. Given the probabilistic model, the prediction is obtained from the data set that include all events withM7.5 felt in Mexico City from 1900 to 1985. These earthquakes occur in the Middle-America trench, along Mexico, but are felt in Mexico City. To see the full significance of the analysis, we give the result using two models: (1) The Poisson-Gamma, and (2) The Poisson-Exponential (a special case of the Gamma).Using the Poisson-Gamma model, the next expected event will occur in the next time interval =2.564 years from the last event (occurred on September 19, 1985) or equivalently, the expected event will occur approximately in April, 1988.Using the Poisson-Exponential model, the next expected damaging earthquake will occur in the next time interval =2.381 years from the last event, or equivalently in January, 1988.It should be noted that very strong agreement exists between the two predicted occurrence times, using both models.     

中强震对地壳应力场的影响——以盈江地区5次中强震为例

为了研究中强震对震源区应力场的影响,本研究以盈江地区2008—2014年间发生的5次中强震为例,深入研究这5次中强震对盈江地区地壳应力场的时空影响.为了探究中强震对应力场的时空影响,我们对盈江地区地壳应力场进行了以下研究：根据5次中强震发生时间,分时段反演应力场以考察应力场在时间上是否存在变化;根据震源机制解的空间分布,将研究区分为南部和北部反演应力场,以确定应力场是否存在空间差异;随机抽取震源机制解反演应力场以便确定应力场是否存在时空差异.研究结果表明：(1) 5次中强震对盈江地区应力场产生的扰动较小,没有引起盈江地区应力场在时间上的显著变化;(2) 在研究时段内,盈江地区地壳应力场在时空上可以视为均匀应力场;(3) 盈江地区的地壳应力场为走滑型,最大主应力轴呈NNE-SSW向,最小主应力轴呈SEE-NWW向,最大和最小主应力轴倾角近水平,中间主应力轴倾角近直立.

     

Investigation of historical earthquakes in the northeastern Fujian area

Taking the northeastern Fujian area as an example, we provide some new technological ideas and contents for the historical earthquake investigation of significant engineering construction sites. ① Make sure the integrity of earthquake materials with reference to the regional histories of culture and disasters; ② Evaluate the influence of historical earthquakes on the basis of actual records, review and identify the epicenter location and magnitude of destructive earthquakes. The research by the new technological ideas will endue the investigation of historical earthquakes with new meanings in the cultural phylogeny and credible time domain, so as to make the results of historical earthquake research more scientific. The aim of the paper is to improve the level of historical earthquake investigation for a better service to the engineering construction.     

强震对大地震发生率的影响研究及在鲜水河断裂带的应用

根据弹性回跳理论,有些断层上的大地震复发具有准周期性.强震的发生会对断层上大地震的复发周期产生影响.利用布朗过程时间（BPT）模型能够定量计算出一次强震对同一断层上大地震复发的延后时间.本文对断层上的强震对大地震发生率的改变量进行了研究,并以鲜水河断裂的几次地震为例,将由BPT模型计算的强震对大地震发生率的改变量与由库仑破裂应力计算的结果进行了比较.本文的研究表明,对于强震对大地震发生时间的延后幅度,使用BPT模型和库仑破裂模型计算的结果差别不大.周边强震对断层状态的加载使大地震复发时间的提前幅度可由BPT模型和库仑破裂模型计算,模型计算结果与现实震例相符.2014年11月22日康定M6.3级和M5.8级地震使鲜水河断裂带乾宁-康定段的大地震复发期望时间延后了36年,使磨西断裂的大地震复发期望时间提前了9年,从公元2086年提前至公元2077年.     

冕宁大桥水库诱发地震的监测

冕宁大桥水库是目前国内唯一处于强震多发地区和地震高烈度区的大Ⅱ型水库。对该水库进行了有关地震安全性评价，建设了水库地震监测系统，完成了水库地震对策研究。2002年3月3日大桥水库诱发Ms4．6级水库地震，根据所获得的水库地震监测资料，在这次水库地震的半年以前，我们认为会在不太长的时间里在库区及其邻区有可能发生4级左右的地震。     

四川长宁地区宽频带数字近震记录特征

通过对2008年1月至2013年10月四川省长宁地区ML≥3.5的20个近震重新进行分析后发现,在ML≥4.0时,该地区近震面波发育,ML震级略大于MS震级;100~160 km以内的部分台站即可清晰记录到上地壳绕射波Pb,也可清晰记录到下地壳反射波Pm P;在研究时间段内,该地区仅发生1次ML≥5.0地震,用波形记录测定出有两个不同的破裂点。