The slip rate and strong earthquake recurrence interval on the Qianning-Kangding segment of the Xianshuihe fault zone

IntroductionLocated in the western part of Sichuan Province, China, the Xianshuihe fault zone is a notable strong earthquake zone in the eastern Tibetan Plateau. At its northwestern end, the Xianshuihe fault zone overlaps the Ganzi-Yushu fault in a left-stepping pattern. The fault zone extends southeastwards through Luhuo, Daofu, Kangding, and Moxi and disappears near Shimian, with a total length of 400 km. The fault trends N40(-50°W in the north, and N20(-30°W to the south of Kangdi…     

基于断裂两侧应变能积累的地震危险性参数估计—以1679年三河—平谷M8.0地震为例

本文基于断裂两侧应变能积累的概念,利用新夏垫断裂上探槽研究的古地震资料和1679年三河—平谷M8.0地震的历史资料,通过原地地震复发原则来评价指定断裂（段）在某一时段内的地震危险性,探讨其在未来一段时间内可能发生地震的最大潜在震级。由此说明现今应变能确定所面临的困难,而应用局部化应变（变形）与岩石-断裂系统局部失稳临界条件之间的联系,理论上可以由变形带的宽度减小率来预估未来地震的发生时间。      

Numerical simulation on the influences of Wenchuan earthquake on the surrounding faults

On 12 May 2008, the devastating Wenchuan earthquake struck the Longmenshan fault zone, which comprised the eastern margin of the Tibetan Plateau, and this fault zone was predominantly a convergent boundary with a right-lateral strike-slip component. After such a large-magnitude earthquake, it was crucial to analyze the influences of the earthquake on the surrounding faults and the potential seismic activity. In this paper, a complex viscoelastic model of western Sichuan and eastern Tibet regions was constructed including the topography. Based on the findings of co-seismic static slip distribution, we calculated the stress change caused by the Wenchuan earthquake with the post-seismic relaxation into consideration. Our preliminary results indicated that: (1) The tectonic stressing rate was relatively high in Kunlun mountain pass-Jiangcuo, Ganzi-Yushu, Xianshuihe and Zemuhe faults; while in the east Kunlun and Longriba was medium; also the value was less in the Minjiang, Longmenshan, Anninghe and Huya faults. As to the Longmenshan fault, the value was 0.28×10^-3 MPa/a to 0.35×10^-3 MPa/a, which is coincident with the previous long recurrence interval of Wenchuan earthquake; (2) The Wenchuan earthquake not only caused the Coulomb stress decrease in the source region, but also the stress increase in the two terminals, especially the northeastern segment, which is comparatively consistent with the aftershock distribution. Meanwhile, the high concentration areas of the static slip distribution were corresponding to the Coulomb stress reductions; (3) The Coulomb stress change caused by Wenchuan earthquake showed significant increase on five major faults, which were northwestern segment of Xianshuihe fault, eastern Kunlun fault, Longriba fault, Minjiang fault and Huya fault respectively; also the Coulomb stress on the fault plane of the Yushu earthquake was faintly increased; (4) We defined the recurrence interval as the time needed to accumulate the magnitude of the stress drop, and the recurrence interval of Wenchuan earthquake was estimated about 1 714 a to 2 143 a correspondingly.     

STUDY OF THE INFLUENCE OF STRONG EARTHQUAKE ON THE RECURRENCE BEHAVIOR OF MAJOR EARTHQUAKE ON ACTIVE FAULT-TAKING THE MIDDLE-NORTH SECTION OF XIANSHUIHE FAULT AS AN EXAMPLE

It is of great significance to determine the factors and causes that affect the recurrence of major earthquakes. This paper introduces the influence of strong earthquake on the recurrence of major earthquakes according to elastic rebound theory, and then proposes to calculate the impact time Δt respectively from the effect of strong earthquakes on the same and surrounding faults on the major earthquake recurrence by using seismic moment release rate method and Coulomb stress change. In this paper, we studied the change amount of major earthquake recurrence by taking four earthquakes with magnitude greater than 6.5 occurring at different fracture sections of the Xianshuhe fault zone as an example, they occurred on Daofu, Changcu, Zhuwo Fault, respectively. We used seismic moment rate method to calculate the impact time Δt of strong earthquake on the recurrence of major earthquakes on the Daofu-Qianning Fault. We further discussed the effect of the Coulomb stress change due to the interaction between faults on the recurrence of subsequent major earthquakes. The co-seismic and post-seismic Coulomb stress changes caused by strong earthquake on the surrounding faults on the Ganzi-Luhuo Fault are calculated. With the fault interaction considered, the importance of the interaction between faults in the middle-north section of the Xianshuihe fault zone to change the recurrence of large earthquakes is retested and evaluated. The results indicate that the two strong earthquakes occurring along Xianshuihe Fault in 1904(M=7.0) and 1981(M=6.9) resulted in a delay of 80 years and 45 years of major earthquake recurrence on the Daofu-Qianning Fault respectively, and the M7.3 earthquake in 1923 and the M6.8 earthquake in 1967 resulted in an advance of 35 years of major earthquake recurrence on the Ganzi-Luhuo Fault.     

美国最近三代地震区划图中的断裂震源模型

活断层与古地震定量数据在美国近三代地震区划图中的应用基本上体现了各阶段活断层研究的最新成果,其中断裂震源模型起到了桥梁的作用,并不断得到完善。在1996年地震区划图中引入了特征地震模型与截断的G—R模型,用以表述断层的震级一频度分布关系。在2002年地震区划图中更明确地处理了参数的不确定性,并引入逻辑树概念,同时在特征地震模型中试用了多段破裂模型。在2008年地震区划图中引用了更为广泛的逻辑树来描述地震构造几何形态、地震震级和复发周期的不确定性,其中特征地震模型包括：单段破裂和多段破裂的特征地震模型,以及给定震级的浮动地震模型（或不固定分段模型）。这些经验值得在我国第五代地震区划图的编制工作中借鉴。     

交城断裂带北段最大潜在地震发震概率评估1

基于太原市目标区交城断裂带的定量研究,特别是对活动断裂上的古地震资料进行的系统、详细的分析与总结,建立了反映该断裂地震地质特点和运动学属性的复发模式和概率模型.引入震级-地表破裂长度、震级-震源破裂长度、震级-断层破裂面积以及震级-地震矩的经验关系进行震级估计,最后进行综合评估以确定交城断裂带北段潜在地震的最大震级.复发模式的建立兼顾了泊松和准周期两种模式,利用专家意见法组合相应的Poisson模型和BPT模型,计算活动断裂最大潜在地震的复发概率.结果表明,交城断裂带北段潜在地震最大震级为Ms7.2级,而未来50a、100a、200a发生Ms7.2级地震的概率分别为2.1％、4.0％和7.9％.     

Similarities between strike-slip faults at different scales and a simple age determining method for active faults

Abstract Several differently scaled strike‐slip faults were examined. The faults shared many geometric features, such as secondary fractures and linkage structures (damage zones). Differences in fault style were not related to specific scale ranges. However, it was recognized that differences in style may occur in different tectonic settings (e.g. dilational/contractional relays or wall/linkage/tip zones), different locations along the master fault or different fault evolution stages. Fractal dimensions were compared for two faults (Gozo and San Andreas), which supports the idea of self‐similarity. Fractal dimensions for traces of faults and fractures of damage zones were higher (D ～1.35) than for the main fault traces (D ～1.005) because of increased complexity due to secondary faults and fractures. Based on the statistical analysis of another fault evolution study, single event movements in earthquake faults typically have a maximum earthquake slip : rupture length ratio of approximately 10^?4, although this has only been established for large earthquake faults because of limited data. Most geological faults have a much higher maximum cumulative displacement : fault length ratio; that is, approximately 10^?2 to 10^?1 (e.g. Gozo, ～10^?2; San Andreas, ～10^?1). The final cumulative displacement on a fault is produced by accumulation of slip along ruptures. Hence, using the available information from earthquake faults, such as earthquake slip, recurrence interval, maximum cumulative displacement and fault length, the approximate age of active faults can be estimated. The lower limit of estimated active fault age is expressed with maximum cumulative displacement, earthquake slip and recurrence interval as T ? (d_max /u) · I(M).     

Numerical simulation of the earthquake generation process

A numerical algorithm is proposed for the simulation of the earthquake process during a seismic cycle. The algorithm is based on a heterogeneous discrete model of the fault plane and assumes there are two kinds of seismicity: background crack-like earthquakes and asperity-like events. An active zone of the fault contains an asperity distribution with a characteristic elementary area. The background seismicity randomly develops shear stress-free surfaces which tend to surround the asperities as in a 2D percolation process. The model parameters are taken from observations on the Vrancea (Romania) intermediate depth seismic region. The results emphasize the significant role of the geometry in the mechanism of the seismic failure. The algorithm predicts the nonlinear behavior in the frequency-magnitude distribution, the decrease of theb-slope associated with the asperity-like events, the magnitude range of major earthquakes, and their recurrence times.     

Earthquake probabilities and magnitude distribution (M ≥ 6.7) along the Haiyuan fault, northwestern China

Introduction Haiyuan fault is a major seismogenic fault in north-central China. One of the most devastat-ing great earthquake in the 20th century occurred near Haiyuan in northwestern China on Decem-ber 16, 1920. More than 220 000 people were killed and thousands of towns and villages weredestroyed during the devastating earthquake. A 230 km long left-lateral surface rupture zone wasformed along the Haiyuan fault during the earthquake with maximum left-lateral displacement of10 m. Pale…     

Co-seismic fault geometry and slip distribution of the 26 December 2004, giant Sumatra–Andaman earthquake constrained by GPS,coral reef,and remote sensing data

We analyze co-seismic displacement field of the 26 December 2004, giant Sumatra–Andaman earthquake derived from Global Position System observations,geological vertical measurement of coral head, and pivot line observed through remote sensing. Using the co-seismic displacement field and AK135 spherical layered Earth model, we invert co-seismic slip distribution along the seismic fault. We also search the best fault geometry model to fit the observed data. Assuming that the dip angle linearly increases in downward direction, the postfit residual variation of the inversed geometry model with dip angles linearly changing along fault strike are plotted. The geometry model with local minimum misfits is the one with dip angle linearly increasing along strike from 4.3oin top southernmost patch to 4.5oin top northernmost path and dip angle linearly increased. By using the fault shape and geodetic co-seismic data, we estimate the slip distribution on the curved fault. Our result shows that the earthquake ruptured *200-km width down to a depth of about 60 km.0.5–12.5 m of thrust slip is resolved with the largest slip centered around the central section of the rupture zone78N–108N in latitude. The estimated seismic moment is8.2 9 1022 N m, which is larger than estimation from the centroid moment magnitude(4.0 9 1022 N m), and smaller than estimation from normal-mode oscillation data modeling(1.0 9 1023 N m).     

Rupture model of the great AD 365 Crete earthquake in the southwestern part of the Hellenic Arc

An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismicity in this region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C., there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160 km and a seismic moment of 5.7 × 10²⁸ dyn·cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results showing low coupling for extensional strain of the upper plate.     

微震研究与应用进展

随着地震观测台站密度的不断增加以及地震检测技术的快速发展,微震研究受到了地震学界的广泛关注.与发震周期较长的大地震相比,微震复发周期短、发生频次高,可以获得更高分辨率的地壳内部介质物性和应力状态等变化信息.微震在许多领域具有广泛的应用,如研究断层几何形态、前震与地震成核的关系、余震时空演化特征及余震触发机理、远程动态触...     

23 October 2011 Van, Eastern Anatolia, earthquake (M W 7.1) and seismotectonics of Lake Van area

The 23 October 2011 Van earthquake took place in the NE part of Lake Van area, surprisingly on a fault (the Van fault) that is not present in the current active fault map of Turkey. However, occurrence of such a large magnitude earthquake in the area is not surprising regarding the historical seismicity of the region. The comparison of the damage patterns suggests that the earthquake is much likely a recurrence of the 1715 Van earthquake. The finite fault modelling of the earthquake using teleseismic broadband body waveforms has shown that the earthquake rupture was unilateral toward SW, was mostly reverse faulting, confined to below the depth of 5 km, did not propagate offshore, and was dominated by a failure of a single asperity with a peak slip of about 5.5 m. The total seismic moment calculated for the model is 4.6?×?10¹⁹ Nm (M _W ?≈?7.1). The finite fault model coincides with the field observations indicating blind faulting and the vertical displacements over the free surface estimated from it correlate well with the maximum reported uplift along the coast of Lake Van above the hanging wall. The possible offshore continuations of the Van fault and some other faults lying its south are also discussed by assessing a previous offshore seismic reflection study and the earthquake epicentres and focal mechanisms.     

Virtual California: Fault Model, Frictional Parameters, Applications

Virtual California is a topologically realistic simulation of the interacting earthquake faults in California. Inputs to the model arise from field data, and typically include realistic fault system topologies, realistic long-term slip rates, and realistic frictional parameters. Outputs from the simulations include synthetic earthquake sequences and space-time patterns together with associated surface deformation and strain patterns that are similar to those seen in nature. Here we describe details of the data assimilation procedure we use to construct the fault model and to assign frictional properties. In addition, by analyzing the statistical physics of the simulations, we can show that that the frictional failure physics, which includes a simple representation of a dynamic stress intensity factor, leads to self-organization of the statistical dynamics, and produces empirical statistical distributions (probability density functions: PDFs) that characterize the activity. One type of distribution that can be constructed from empirical measurements of simulation data are PDFs for recurrence intervals on selected faults. Inputs to simulation dynamics are based on the use of time-averaged event-frequency data, and outputs include PDFs representing measurements of dynamical variability arising from fault interactions and space-time correlations. As a first step for productively using model-based methods for earthquake forecasting, we propose that simulations be used to generate the PDFs for recurrence intervals instead of the usual practice of basing the PDFs on standard forms (Gaussian, Log-Normal, Pareto, Brownian Passage Time, and so forth). Subsequent development of simulation-based methods should include model enhancement, data assimilation and data mining methods, and analysis techniques based on statistical physics.     

甘孜-玉树断裂当江段地表破裂遗迹与1738年玉树西北地震的讨论

对历史记载的公元1738年玉树西北地震的震级及其发震构造目前仍存有争议。卫星影像解译和野外调查发现沿甘孜-玉树断裂当江段分布一条长约75km的左旋走滑地震地表破裂带,其最大同震水平位移约2.1m。综合分析该地表破裂带特征、探槽揭露信息、测年结果以及历史文献记载等资料,认为当江段应为1738年玉树西北地震的发震断层,基于震例类比和经验公式估算该次地震的震级为71/2级。沿甘孜-玉树断裂的历史地震破裂分布显示,玉树段在隆宝镇以西存在近50km长的破裂空段;当江段距1738年地震的离逝时间也可能已经接近其地震复发周期,上述两个段落未来均存在大震危险。     

鲜水河断裂带北西段不同破裂源强震震级（M≥67）及复发间隔研究

鲜水河断裂带是四川西部一条晚第四纪强烈左旋走滑活动的构造带，历史上发生多次强震. 它与西北侧的甘孜—玉树断裂带一起，构成青藏高原东部的侧向滑移构造系统中的川滇活动地块的北边界——羌塘地块的东北边界. 鲜水河断裂带北西段可以分成4个段落，每一段落均可作为一个独立的基本破裂单元而发生地震破裂，亦有可能发生不同尺度的多段联合瞧裂. 对鲜水河断裂带北西段不同尺度破裂的震级及复发间隔进行研究. 根据该地区的地质、地球物理、测量及地震等方面的资料，结合我国强震复发的特点，分析了拉分盆地内部的滑动速率分布，以确定各段落的等效长度和倾向宽度，从而建立适合我国大陆走滑断裂的面波震级与断裂发震面积的关系式；进而运用地震矩方法，考虑断层之间的相互作用，结合专家意见建立了该段的矩平衡断裂破裂模型；最后，给出了鲜水河断裂带北西段各破裂源特征化地震的复发间隔、震级大小和不确定性，以及他与中小地震的联合震级分布. 结果表明，鲜水河断裂带北西段较易发生单段破裂，复发间隔在100～150年左右.     

汶川M_S8.0地震发震断裂大地震原地重复现象初析

在历史记录中,成都和龙门山地区没有发生过类似汶川MS8.0地震强度的地震。那么,在地质记录中是否会存在类似震级的古地震遗迹?作者分别在中央和前山断裂中段的地表破裂带上4个地点开挖了探槽4个和剖面1个,并进行了断错地貌面的实测。文中从几个地点新老地貌面累计变形量、探槽揭露的古地震遗迹等方面讨论汶川地震发震断裂大地震原地重复现象存在的基本事实。结果表明:无论在中央断裂的小鱼洞、擂鼓镇还是前山断裂的白鹿镇、汉旺等地,汶川5.12地震之后Ⅱ级阶地断层陡坎与Ⅰ级阶地陡坎高度基本呈倍数关系,探槽揭露Ⅱ级阶地标志地层(黄砂土层)在断裂两盘的位差也是5.12地震的约2倍,显示在龙门山地区区域Ⅱ级阶地形成之后,汶川5.12地震发生之前,存在一次与汶川MS8.0地震地表变形规模相当的地震事件     

Earthquake probabilities and magnitude distribution (<Emphasis Type="Italic">M</Emphasis>≥6.7) along the Haiyuan fault,northwestern China

In recent years, some researchers have studied the paleoearthquake along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on this paleoseismological information, the recurrence probability and magnitude distribution for M≥6.7 earthquakes in future 100 years along the Haiyuan fault can be obtained through weighted computation by using Poisson and Brownian passage time models and considering different rupture patterns. The result shows that the recurrence probability of M _S≥6.7 earthquakes is about 0.035 in future 100 years along the Haiyuan fault.     

南北地震带北段近期强震趋势研究

2008年5月12日汶川8.0级地震后,南北地震带可能进入新一轮的强震活跃期.从汶川8.0级地震以来ML≥5.0地震活动空间分布特征来看,近期南北地震带北段与中、南段存在较大差异.由南北地震带强震前孕震区中强地震活动特征,并结合当前5级地震活动情况,认为应同时关注南北地震带中、南段和北段的强震危险性.甘东南地区出现的4级地震空区被2011年2月23日迭部-岷县交界ML4.4地震打破后,2011年11月1日空区周边又发生了青川Ms5.4地震,表明该空区及周边地区的地震活动增强.类比1990年共和7.0级地震前的空区演化过程,认为甘东南地区存在发生7级地震的可能.结合对甘东南地区主要大型断裂7级地震复发周期的综合分析认为,需关注南北带北段毛毛山断裂和金强河断裂、香山-天景山断裂东段、黄河断裂灵武段、西秦岭北缘断裂、六盘山-宝鸡断裂和东昆仑断裂东段玛沁-玛曲段发生7级地震的可能.     

基于广义帕累托分布的地震震级分布尾部特征分析

极值理论在地震危险性分析中有着重要应用, 发震震级超过某一阈值的超出量分布可以近似为广义帕累托分布. 基于广义帕累托分布给出了若干地震活动性参数的估计公式, 包括强震震级分布、 地震复发周期和重现水平、 期望重现震级、 地震危险性概率和潜在震级上限等; 以云南地区震级资料为基础数据, 讨论了阈值选取、 模型拟合诊断和参数估计; 在此基础上计算了该地区的地震活动性参数. 结果表明, 广义帕累托分布较好地刻画了强震震级分布, 通过超阈值(POT)模型计算的复发周期与实际复发间隔统计基本一致, 高分位数估计在一定阈值范围内表现稳定, 为工程抗震中潜在震级上限的确定提供了一种途径.