大地震重复特征与平均重复间隔的取值问题

对延怀盆地及海原断裂古地震的详细研究表明,大地震的重复行为具有多样性。特征地震是大多数断裂活动的行为特征,但特征地震存在分级性,大地震的重复时间间隔存在分阶段性,以及断裂的相互作用会影响大地震的复发序列。因此,当大地震重复行为出现时间上的分阶段性,或特征地震分级现象导致不同强度的古地震间隔时间有明显差别时,用确定性或时间相依的概率方法评价大地震的危险性,需要分阶段或分级计算不同间隔阶段的平均值     

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     

龙门山断裂带晚第四纪的大地震活动——来自古地震研究的资料

2018年5·12汶川地震后,龙门山断裂带的大地震活动特征一直是倍受关注的科学问题.而探槽古地震研究是最直接揭示活断层带晚第四纪大地震活动规律的重要途径.本文通过系统总结龙门山断裂带近十年来探槽古地震研究成果,全面分析了龙门山断裂带不同段落的晚第四纪大地震活动与复发特征.结果显示：龙门山断裂带的大地震活动具有明显的分段性,北川—映秀断裂和江油—灌县断裂中段（包括小鱼洞断裂）是全新世以来,最为活跃的段落,约距今6000年以来,发生过3次位移量近似相等的事件,分别发生在5920—5730 cal BP和3300—2300 cal BP,大地震活动具有3000年左右的准周期复发特征;北川—映秀断裂的北段具有独立破裂的能力,该段汶川地震前一次事件发生在大约665—1030 AD,可能是历史上记载的942 AD地震事件,另一次事件发生在8240—7785 BC;江油—灌县断裂的南段（大川—双石断裂）发震能力明显弱于断裂带中段和北段.现有古地震数据表明,沿北川—映秀断裂,除汶川地震以外,并未显示出不同段落间在全新世期间存在级联破裂的证据,这可能意味着2008年汶川M8地震是龙门山断裂带上罕见的巨大地震事件.另外,青川断裂上探槽揭露的古地震变形事件不像是断裂直接位错的结果,更可能是被动响应北川—映秀断裂右旋位错的现象.     

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…     

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.      

Rupture segmentation and assessment of probabilities of seismic potential on the Xiaojiang fault zone

Spatial distribution of sources of strong and large earthquakes on the Xiaojiang fault zone in eastern Yunnan is studied according to historical earthquake data. 7 segments of relatively independent sources or basic units of rupture along the fault zone have been identified preliminarily. On every segment, time intervals between main historical earthquakes are generally characterized by “time-predictable” recurrence behavior with indetermination. A statistic model for the time intervals between earthquakes of the fault zone has been preliminarily established. And a mathematical method has been introduced into this paper to reckon average recurrence interval between earthquakes under the condition of having known the size of the last event at a specific segment. Based on these, ranges of the average recurrence intervals given confidence have been estimated for events of various sizes on the fault zone. Further, the author puts forward a real-time probabilistic model that is suitable to analyze seismic potential for individual segments along a fault zone on which earthquake recurrence intervals have been characterized by quasi-time-predictable behavior, and applies this model to calculate conditional probabilities and probability gains of earthquake recurring on the individual segments of the Xiaojiang fault zone during the period from 1991 to 2005. As a consequence, it has shown that two parts of this fault zone, from south of Dongchuan to Songming and from Chengjiang to Huaning, have relatively high likelihoods for strong or large earthquake recurring in the future. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 322–330, 1993.     

安宁河断裂带北段的最新地面活断层与地震潜在能力研究

从最新地面活断层的不连续性,断层滑动速率以及古地震研究的角度讨论安宁河断裂带北段的地震潜在能力,认为不连续的活断层可能成为各自独立的地震破裂单元,从而决定了地震的潜在能力,其中,野鸡洞破裂段的潜在地震能力最强,可达7级。上次地震至今的平静时间已接近古地震的平均重现间隔,因而具有高度的地震危险性     

强震孕育、发生及其复发循环过程的有限单元法模拟

强震孕育发生及其复发过程的定量研究对于预测预报地震有着重要的科学意义;合理连续地计算地震孕育、同震破裂过程及其复发循环特征将有助于我们更好地认识强震发生的时空分布规律.为此,本文基于Newmark隐式时间积分法,根据模拟孕震-同震循环过程的特殊要求,发展了一种新的有限单元计算方法.新方法具有以下特点:(1)在不改变时间...     

祁连山-河西走廊西段强震复发概率模型及强震潜势评估

祁连山-河西走廊西段构造区发育多条重要活动断裂,多年来已积累较丰富的古地震研究的成果.本文在前人研究基础上,结合历史地震数据等,从定量化强震复发间隔T与平均复发间隔Ta入手,将其比值(T/Ta)进行数学处理,借鉴NB模型的思路,建立祁连山-河西走廊西段构造区模型,进而对强震潜势进行评估.结果表明:祁连山-河西走廊西段构...     

Earthquake hazard in Marmara Region, Turkey

Earthquake hazard in the Marmara Region, Turkey has been investigated using time-independent probabilistic (simple Poissonian) and time-dependent probabilistic (renewal) models. The study culminated in hazard maps of the Marmara Region depicting peak ground acceleration (PGA) and spectral accelerations (SA)'s at 0.2 and 1 s periods corresponding to 10 and 2% probabilities of exceedance in 50 yrs. The historical seismicity, the tectonic models and the known slip rates along the faults constitute the main data used in the assignment. Based on recent findings it has been possible to provide a fault segmentation model for the Marmara Sea. For the main Marmara Fault this model essentially identifies fault segments for different structural, tectonic and geometrical features and historical earthquake occurrences. The damage distribution and pattern of the historical earthquakes have been carefully correlated with this fault segmentation model. The inter-event time period between characteristic earthquakes in these segments is consistently estimated by dividing the seismic slip estimated from the earthquake catalog by the GPS-derived slip rate of 22±3 mm/yr. The remaining segments in the eastern and southern Marmara region are also identified using recent geological, geophysical studies and historical earthquakes. The model assumes that seismic energy along the segments is released by characteristic earthquakes. For the probabilistic studies characteristic earthquake based recurrence relationships are used. Assuming normal distribution of inter-arrival times of characteristic earthquakes, the ‘mean recurrence time’, ‘covariance’ and the ‘time since last earthquake’ are developed for each segment. For the renewal model, the conditional probability for each fault segment is calculated from the mean recurrence interval of the characteristic earthquake, the elapsed time since the last major earthquake and the exposure period. The probabilities are conditional since they change as a function of the time elapsed since the last earthquake. For the background earthquake activity, a spatially smoothed seismicity is determined for each cell of a grid composed of cells of size 0.005°×0.005°. The ground motions are determined for soft rock (NEHRP B/C boundary) conditions. Western US-based attenuation relationships are utilized, since they show a good correlation with the attenuation characteristics of ground motion in the Marmara region. The possibility, that an event ruptures several fault segments (i.e. cascading), is also taken into account and investigated by two possible models of cascading. Differences between Poissonian and renewal models, and also the effect of cascading have been discussed with the help of PGA ratio maps.     

青藏高原东缘礼县-罗家堡断裂带晚更新世以来的活动性分析

礼县 -罗家堡断裂带晚更新世以来有过明显活动。在礼县—罗家堡段和天水镇—街子口段直接错断全新世地层。断裂沿线地表陡坎发育 ,水系被左旋位错。结合沿该断裂带广泛分布的地震滑坡、砂土液化等 ,认为礼县 -罗家堡断裂带是 1654年天水南 8级地震的发震构造。该断裂晚更新世以来的平均水平位错速率为 0 95mm/a ,平均垂直位移速率为 0 35mm/a ,垂直位移速率约为水平位移速率的 1/ 3。这个比值与一次断裂突发性垂直位错量 ( 1 9m)与水平位错量 ( 5 2m)的比值基本吻合     

Earthquake recurrence on whole active fault zones and its relation to that on individual fault-segments

IntroductionEarthquake recurrence models established on activity behaviors of strong earthquakes are the bases of long-term earthquake prediction, seismic risk zonation, and seismic hazard assessment. A lot of studies have been carried out on earthquake recurrence behaviors for specific seismogenic sources or fault-segments, and a series of empirical recurrence models have been proposed, such as the time-predictable model and the slip-predictable model for earthquakes repeated at the previous …     

Analysis of Paleoseismic Events of Dahuzhuang Trench at the Xiadian Fault

The Xiadian Fault is a very important concealed active fault in the Beijing Plain. It is the seismogenic fault of the Sanhe-Pinggu M_S8.0 earthquake in 1679. The ancient earthquake sequence in the long historical period is of great significance to understand accurately the activity characteristics of the fault and effectively reduce the earthquake disaster risk in Beijing. We have re-interpreted the Dahuzhuang trench, and identified three layers of buried paleosol, six collapsed wedges and one sand liquefaction event. Further, through the comparison with the landmark strata and paleo-earthquake events revealed by other trenches on the fault, an ancient earthquake sequence with a long historical period of the Xiadian Fault was established:since the 31ka, the Xiadian Fault has 11 occurrences of earthquake events (including the 1679 earthquake), and the average recurrence interval is about 2.8ka. The paleo-seismic sequence also shows that there is an ancient earthquake cluster period from 25ka to 15ka, and there are 5 strong earthquakes in the cluster period. The average recurrence interval is about 2.0ka, which reflects the phase difference of the Xiadian Fault activity.     

Study on Integrated Recurrence Behaviors of Strong Earthquakes Along Entire Active Fault Zones in the Sichuan-Yunnan Region, China

Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that recurrences of strong earthquakes in the 7 fault zones display near-random, random and clustering behaviors. The recurrence processes are never quasiperiodic, and are neither strength-time nor time-strength dependent. The more independent segments for strong earthquake rupturing a fault zone has, the more complicated the corresponding recurrence process is. And relatively active periods and quiescent periods for earthquake activity occur alternatively. Within the active periods, the distribution of recurrence time intervals between earthquakes has relatively large discretion, and can be modelled well by a Weibull distribution. The time distribution of the quiescent periods has relatively small discretion, and can be approximately described by some distributions as the normal. Both the durations of the active periods and the numbers of strong earthquakes within the active periods vary obviously cycle by cycle, leading to the relatively active periods having never repeated quasi-periodically. Therefore, the probabilistic assessment for middle- and longterm seismic hazard for entireties of active fault zones based on data of historical strong earthquakes on the fault zones still faces difficulty.     

Average slip rate,earthquake rupturing segmentation and recurrence behavior on the Litang fault zone,western Sichuan Province,China

The Litang fault zone (LFZ) is an important active fault within the northwestern Sichuan sub-block. To-gether with the Garzê-Yushu, Xianshuihe, and An-ninghe fault zones on its northern, eastern and south-eastern sides, the LFZ constitutes the lateral extrusion tectonic system in the southeastern part of the Qing-hai-Tibetan Plateau[1,2] (Fig. 1). According to instru-mental records, historical recordings and field investi- gation, an earthquake (Ms7.3) occurred on its middle to south se…     

Millennium recurrence interval of morphogenic earthquakes on the Qingchuan fault,northeastern segment of the Longmen Shan Thrust Belt,China

The 2008 M _w 7.9 Wenchuan produced a ～285–300-km-long coseismic surface rupture zone, including a 60-km-long segment along the Qingchuan fault, the northeastern segment of the Longmen Shan Thrust Belt (LSTB), Sichuan Basin, central China. Field investigations, trench excavations, and radiocarbon dating results reveal that (i) the Qingchuan fault is currently active as a seismogenic fault, along which four morphogenic earthquakes including the 2008 Wenchuan earthquake occurred in the past ca. 3500 years, suggesting an average millennium recurrence interval of morphogenic earthquakes in the late Holocene; (ii) the most recent event prior to the 2008 Wenchuan earthquake took place in the period between AD 1400 and AD 1100; (iii) the penultimate paleoseismic event occurred in the period around 2000 years BP in the Han Dynasty (206 BC–AD 220); (iv) the third paleoseismic event occurred in the period between 900 and 1800 BC; and (v) at least three seismic faulting events occurred in the early Holocene. The present results are comparable with those inferred in the central and southwestern segments of the LSTB within which the Wenchuan magnitude earthquakes occurred in a millennium recurrence interval, that are in contrast with previous estimates of 2000–10,000 years for the recurrence interval of morphogenic earthquakes within the LSTB and thereby necessitating substantial modifications to existing seismic hazard models for the densely populated region at the Sichuan region.     

川滇地区若干活动断裂带整体的强地震复发特征研究

我们根据历史地震资料，采用统计学方法研究了川滇地区7条活动断裂带整体的强地震复发特征。结果表明，这7条断裂带的强地震复发表现出趋于随机的、随机的、以及丛集的行为，复发过程不具有良好的准周期性，也不存在强度－时间或者时间－强度的相依性。组成断裂带的强震破裂段落的数量越多，复发过程就越复杂。相对的地震活跃期与平静期交替出现。其中，活跃期内地震复发间隔分布的离散性较大，可用Weibull分布近似描述；而平静期的持续时间分布的离散性较小，可用正态等分布近似描述。不同相对活跃期的持续时间及强震的数量差别很大，导致相对活跃期并非准周期重视。因此，基于断裂带整体强震复发间隔分布的中长期危险性概率评估仍然面临一定的困难。     

板内地震复发间隔对断层长度的标度关系研究及应用探索

虽然关于一些重要参数值仍然存在显著的不确定性，地学家们一致认为断层分布遵从幂律标度关系。本文我们把这些标度关系和地震分布的幂律标度关系结合起来获得了区域板内地震复发间隔对断层长度的标度关系式，再对其进行局部校准进而得到某一具体小地方的地震危险估计方法。小断层（未跨越孕震层与断４层）的标度资料表明地震复发间隔和断层长度的负幂成比例变化。由于最近认识到了大震标度中参数的不确定性，对于大断层（跨越孕震层的断层），其地震复发间隔是和断层长度的负幂还是和正幂成比例变化的问题是不确定的，这个问题对地震危险估计是至关重要的。