断裂滑动速度对强震发生周期的影响——以东昆仑活动断裂带库赛湖断裂分段和西大滩断裂分段为例

2001年11月14日东昆仑断裂带库赛湖段发生8.1级大地震.事实上,库赛湖断裂分段大震的复发周期会受到其他分段运动行为的影响,尤其是临近的西大滩断裂分段.本文采用速度和状态依赖摩擦本构控制的一维弹簧滑块模型(BK模型)研究断裂分段滑动速度对强震复发周期的影响.以东昆仑活动断裂带库赛湖断裂分段和西大滩断裂分段作为实例进行研究,研究中将两断裂分段视为通过弹簧相连的滑块系统,其中模型参数的选择是以现有东昆仑活动断裂带库赛湖和西大滩分段的地质研究成果、历史地震和古地震资料直接给出,部分参数也采用了数值计算的方法.研究预测了两分段不同滑动速度对强震复发周期、断裂滑动速度及错动位移在未来0.5～0.6万年中随时间变化的影响.研究发现:在断裂分段之间的相互影响下,各断裂分段滑动速度与各段的强震发生周期没有规律性的关系;两断裂分段组成的系统中,某断裂分段滑动速度放慢(加快)会使该断裂分段未来强震发生的震级增大(减小),而对另外断裂分段的强震发生震级没有规律性影响;两断裂分段组成的系统中,某断裂分段滑动速度加快(放慢)会使另外的断裂分段在强震发生时错动的速度加快(放慢);同时,两断裂分段组成的系统中,某一断裂分段滑动速度上的变化对另一断裂分段强震复发周期的影响只有在较长时间跨度上才能体现.     

东昆仑活动断裂带库赛湖段破裂行为及影响因素的初步研究

2001年11月14日,青藏高原北部东昆仑断裂带库赛湖段发生了MS8.1地震。此次地震的发震断裂在地质史上具有高速左旋滑动的特征,特别是晚更新世晚期以来库赛湖断裂的平均滑动速率达(14.8±2.8)mm/a。库赛湖断裂不同的滑动速率可能会对其未来发生的运动行为产生影响,为此文中研究了东昆仑活动断裂带库赛湖段不同滑动速率和不同断裂面初始摩擦系数对断裂破裂行为的影响,建立了库赛湖断裂段对应的速度和状态依赖摩擦定律控制的单自由度弹簧滑块模型。为得到合理的模型参数,模拟中采用了断裂位错模型,考察了相关古地震研究资料、历史地震资料以及前人的相关研究成果。通过模拟库赛湖断裂段在不同滑动速率下未来6ka的破裂行为,发现断裂滑动速率快可使地震复发周期缩短,滑动速率慢会使地震复发周期延长。例如,若断裂以现今平均14mm/a的初始滑动速率运动时,地震复发周期为2.1ka;若以18mm/a的初始滑动速率运动,其对应地震复发周期为1～1.5ka;而滑动速率为8mm/a时地震复发周期为2.1～2.5ka,但断裂滑动速率对地震发生时断裂错动的位移和错动速度没有规律性影响;断裂面初始摩擦系数的大小对地震复发周期有影响,初始摩擦系数较大可能会使地震周期减小,初始摩擦系数小可能会使地震复发周期增加;同时,断裂面初始摩擦系数较小可能会使地震发生时断裂错动的位移和错动速度变大。     

鲜水河断裂带强震相互作用的动力学模拟研究

以鲜水河断裂带为研究区,首先依据断裂带的地震活动特征,确定整个断裂带的应变积累速率;然后根据GPS观测资料给出的水平应变率和地质给出的鲜水河断裂带断层分段及其相应各段的滑动分布,确定断裂带分段的应力、应变积累速率和强震复发间隔．在此基础上,采用三维有限元模型定量研究断裂带上1893年以来M6．7级以上地震的相互作用及其对断裂带强震复发的影响．研究结果表明,鲜水河断裂带上强震的发生有利于后续地震的发生．强震之间的相互作用不仅影响了断裂带各分段的强震复发间隔,还影响了整个断裂带上的强震活动特征．     

利用Virtual Quake地震模拟器研究鲜水河断裂带地震活动性与地震复发周期

2022年9月5日四川泸定6.8级地震发生在鲜水河断裂带磨西断裂上。本文依据鲜水河断裂带的断层几何形态、断层面物理力学参数、断层滑移速率等基础资料,构建断裂带三维模型,基于Virtual Quake地震模拟器开展鲜水河断裂带准静态数值模拟。对七条分支断裂独立模拟的结果显示模拟结果与历史地震的最大震级和复发周期具有较好的一致性。结果表明模型长度影响震级大小,滑移速率影响地震复发周期。断层面几何弯曲展布使得断层面应力分布不均匀,在弯曲处出现应力积累的现象,易触发地震,并出现了地震分段破裂现象,降低了几何弯曲断层的地震频次,为强震的孕育创造了条件。联合模拟的10000年时间内,鲜水河断裂带共发生了33次M≥7.0地震,最大震级为M7.6,地震活动性呈现一定的活跃期与平静期。断层系统地震间的相互应力作用和复杂的断层几何结构影响着地震迁移的复杂性。道孚断裂上相距40年发生两次M≥7.0地震,乾宁断裂北端相距5.8年发生M≥7.0双震,此类现象与历史地震有一定的相似性。     

鄂尔多斯地块北缘主要活动断裂晚第四纪强震复发特征

对鄂尔多斯活动地块北边界主要活动断裂的古地震研究、强震复发特征及异常分析,得到了晚第四纪的62次古地震,其中全新世期间33次.段落、断裂和断裂带3个层次的古地震复发特征有所差别,独立段落的强震序列多数遵循长短间隔复发的特征,而断裂和断裂带的随机或丛集特征更明显。“移动窗口测试”结果表明,色尔腾山山前断裂和乌拉山南缘断裂,随机偶合产生“异常接近/异常长间隔”的概率分别为64.4％和70％,各断裂的段落之间相互作用不明显;而整个断裂带,其概率为26.8％,断裂之间的相互作用明显。这种复发特征可能意味着地块整体运动对强震复发的影响。另外,色尔腾山山前断裂的乌句蒙口-东风村段和大青山山前断裂的土左旗-乌素图、呼和浩特段等3个段落离逝时间已超过平均重复间隔时间,是未来强震最可能发生的地点。     

鲜水河断裂带的地震模拟

本文运用由弹簧—滑块模型来模拟走滑断层的地震活动,讨论了模型中断层强度、断层滑块间弹簧强度、滑块与驱动盘之间片簧强度、滑块摩擦力的影响,以及初始条件敏感性。并以我国最为典型的一条走滑断层———鲜水河断裂带为例,运用试错法调整模型参数以使发生的地震最大限度地逼近实际发生的地震,并利用最终结果讨论了鲜水河断裂带今后的活动性。     

中国东部地区断裂的缜奏性活动

对中国东部地区断裂的节奏性活动进行了探讨,认为这种节奏性活动主要根据构造地貌进行鉴别,并可分为六种型式:稳定—蠕滑错动;稳定—急速错动;蠕滑—急速错动;交替型蠕滑错动;交替型急速错动和复式错动。地震活动周期与断裂的节奏性活动相关联。断裂活动产生强震的型式有单发式、对偶式和连发式,这三种形式分别出现在不同的断裂中,并取决于不同区域、不同断裂的活动特征。     

断层演化过程中的周期和非周期地震滑移及非地震滑移一维断层模型分析

本文首先根据Dieterich和Ruina提出的含速率和状态的摩擦定律(Dieterich-Ruina定律), 基于一维弹簧-滑块模型推导了地震复发周期的解析表达式, 然后将该近似解与数值模拟结果以及Barbot等的相关研究进行了对比分析． 此外, 本文还利用数值模拟与理论分析研究了断层周期和非周期演化的力学成因机制以及非地震滑移形成的另类力学机制, 并讨论了一维弹簧-滑块模型的优点及其局限性． 结果表明: ① 震后滑移和自加速/成核阶段的持续时间在整个演化过程中不能被忽略; ② 在修正后的复发周期模型中, 复发周期的长短除了与断层特征尺度、 作用于断层面上的有效正应力和远场加载速率相关外, 还受Dieterich-Ruina定律中摩擦参数的取值以及临界滑移距离的影响; ③ 当给定各个物理参数和几何参数时, 目前所得到的解析近似解可以很好地估计地震的复发周期, 其相对误差可小于5%; ④ 在断层演化过程中, 施加剪切应力加载会产生非周期的地震滑移, 而在自加速/成核阶段后期或震后滑移阶段早期, 施加较大的剪切应力加载, 则会出现非地震滑移．      

两个自由度的滑块——弹簧模型中的幕式无震滑动

设想了一种两个自由度的滑块——弹簧模型，其中的2个滑块(滑块1和滑块2)由一根弹簧连接，并由一个慢慢移动的传动装置驱动。假设采用与速率和状态相关的摩擦定律，设定摩擦参数，使滑块1发生动态失稳。当摩擦参数接近稳定性转换点时，滑块2就会发生幕式无震滑动。在地震间隔期，当应力累积到大约稳态水平时，滑块2就开始缓慢滑动。随着振幅波动的衰减而成为稳态值，应力和滑动速度会发生准静态振荡。振荡衰减可能是自2001年以来日本东海地区观测到的幕式无震滑动的合理的产生机制。我们还在不同摩擦性质相互作用的双滑块模型的基础上，设想了板块边界上的各种滑动模式。     

两个自由度的滑块一弹簧模型中的幕式无震滑动

设想了一种两个自由度的滑块—弹簧模型,其中的2个滑块(滑块1和滑块2)由一根弹簧连接,并由一个慢慢移动的传动装置驱动。假设采用与速率和状态相关的摩擦定律,设定摩擦参数,使滑块1发生动态失稳。当摩擦参数接近稳定性转换点时,滑块2就会发生幕式无震滑动。在地震间隔期,当应力累积到大约稳态水平时,滑块2就开始缓慢滑动。随着振幅波动的衰减而成为稳态值,应力和滑动速度会发生准静态振荡。振荡衰减可能是自2001年以来日本东海地区观测到的幕式无震滑动的合理的产生机制。我们还在不同摩擦性质相互作用的双滑块模型的基础上,设想了板块边界上的各种滑动模式。     

川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究

利用1999—2007期和2009—2013期中国大陆GPS速度场数据,采用DEFNODE负位错反演程序估算了川滇菱形块体东边界——鲜水河—安宁河—则木河—小江断裂带在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征,讨论了汶川地震对该断裂系统的影响范围和程度,并结合b值空间分布和地震破裂时-空结果分析了断裂系统的强震危险段.结果表明,汶川地震前鲜水河断裂最南端为完全闭锁(闭锁深度25km),中南段地表以下10~15km深度为强闭锁状态,中北段基本处于蠕滑状态;安宁河断裂最南端闭锁很弱,其余位置闭锁深度为10~15km;则木河断裂除最南端闭锁较弱以外,其余位置基本为完全闭锁;小江断裂在巧家以南、东川以南、宜良附近、华宁以北等四处位置闭锁较弱,其余位置为强闭锁.10年尺度的GPS速度场反演所得断层闭锁程度所指示的强震危险段,主要为鲜水河断裂道孚—八美段、安宁河断裂中段、则木河断裂中北段、小江断裂北段东川附近、小江断裂南段华宁—建水段,该结果与地质尺度的断层地震空区和30年尺度的b值空间分布所指示的危险段落具有一致性.汶川地震后断裂带远、近场速度分布和块体运动状态发生变化,这种区域地壳运动调整使得负位错模型反演得到的断裂带闭锁情况发生一定变化.汶川地震前后川滇菱形块体东边界平行断层滑动亏损速率均为左旋走滑亏损,且在安宁河断裂北端、则木河断裂中北段滑动亏损速率最大;除鲜水河断裂中南段与最南端和小江断裂东川附近以外,其余断裂震后滑动亏损速率均有所增加.垂直断层滑动亏损速率既有拉张亏损也有挤压亏损,且鲜水河断裂最南端由震前挤压转变为震后拉张,其余断裂除了安宁河断裂和小江断裂中段与最北端存在挤压滑动亏损速率外均为拉张速率.     

Finite element simulation of stress change for the MS7.4 Madoi earthquake and implications for regional seismic hazards

On May 22, 2021, the M_S 7.4 earthquake occurred in Madoi County, Qinghai Province; it was another strong event that occurred within the Bayan Har block after the Dari M_S 7.7 earthquake in 1947. An earthquake is bound to cast stress to the surrounding faults, thus affecting the regional seismic hazard. To understand these issues, a three-dimensional viscoelastic finite element model of the eastern Bayan Har block and its adjacent areas was constructed. Based on the co-seismic rupture model of the Madoi earthquake, we analyzed the co- and post-seismic Coulomb stress change caused by the Madoi earthquake on the surrounding major faults. The results show that the Madoi earthquake caused significant co-seismic stress increases in the Tuosuo Lake and Maqin-Maqu segments of the East Kunlun fault (>10 ?kPa), which exceeded the proposed threshold of stress triggering. By integrating the accumulation rate of the inter-seismic tectonic stress, we conclude that the Madoi earthquake caused future strong earthquakes in the Tuosuo Lake and Maqin-Maqu segments of the East Kunlun fault to advance by 55.6-623 and 24.7-123 ?a, respectively. Combined with the influence of the Madoi earthquake and the elapsed time of the last strong earthquake, these two segments have approached or even exceeded the recurrence interval of the fault prescribed by previous research. In the future, it is necessary to focus greater attention on the seismic hazard of the Maqin-Maqu and Tuosuo Lake segments. This study provides a mechanical reference to understand the seismic hazard of the East Kunlun fault in the future, particularly to determine the seismic potential region.     

郯庐断裂带鲁苏皖段地壳速度结构的分段特征及其地质意义

本文采用天然地震近震走时反演地壳三维速度结构的方法获得了郯庐断裂带鲁苏皖段及附近地壳(30°N—37°N,113°E—122°E)三维速度结构.对地壳内分层速度结构的分析发现,郯庐断裂带鲁苏皖段存在速度的分段特征.郯庐断裂带鲁苏皖段浅层35.3°N以北,34.5°N—35.3°N间,33°N—34.5°N间呈现的速度分段和地表出露地层有关,与地质上安丘段、莒县—郯城段,新沂—泗洪段三个破裂单元相对应,且和各段的地震活动相呼应,表明郯庐带新沂到泗洪段可能是断裂的闭锁段.郯庐断裂带鲁苏皖段地壳速度结构自浅至深分为三段,大体位置是:南段(32.5°N—33°N以南),中段(32.5°N—33°N至35°N—35.3°N),北段(35°N—35.3°N以北).上地壳分段与苏鲁超高压变质岩带的插入有关,中、下地壳速度分段则可能和火山岩滞留有关.地壳各层速度结构不同段的速度差异反映了构造块体的速度差异,表明各构造块体在地壳下部仍有差异,郯庐带西侧速度总体高于东侧,反映了不同构造块体的形成和组成差别,也说明了该断裂带可能延伸到莫霍面.而不同深度的分段性可能反映了不同地质演化过程.     

Seismicity simulation with a rate- and state-dependent friction law

The dynamic motions and stabilities of a single-degree-of-freedom elastic system controlled by different friction laws are compared. The system consists of a sliding block connected to an elastic spring, driven at a constant velocity. The friction laws are a laboratory-inferred friction law called the rate-and-state-dependent friction law, proposed by Dieterich and Ruina, and a simple friction law described by dynamic and static frictions. We further extend the solution to a one-dimensional mass-spring model which is an analog of a fault controlled by the rate-and-state-dependent friction law. This model predicts non uniform slip and stress drop along the rupture length of a heterogeneous fault. This result is very different from some earlier modelings based on the simple friction law and a slip weakening friction law. In those earlier modelings the stress and slip functions become smoother with time along the length of the fault rupture, owing to the interactions between fault segments during slip. Because of this smoothing process the number of small events will decrease with time, and the universilly observed stationary magnitude-frequency relation cannot be explained. The interaction between a fault segment and its neighboring segments can be measured when the post-slip stress on this segment is compared with the stress on an identical segment (represented by a block in this modeling) without neighboring segments. If the post-slip stress of the former is much higher than that of the latter, strong interaction exists; if the two are close, only weak interaction exists. The interaction is determined by the relative motion between fault segments and the time duration of interaction. Our new modeling with the rate-and-state-dependent friction law appears to show no such smoothing effect and provides a physical mechanism for the roughening process in the difference between the fault strength and stress that is necessary to explain the observed stationary magnitude-frequency relation. The noninstantaneous healing predicted by the rate-and-state-dependent friction law may be repsonsible for the recurring nonuniform slip and stress drop, and may be explained by the reduction of interaction among fault segments due to the low frictional strength during the fault stopping. The very low friction during slip stopping allows much longer times than does the higher friction due to instantaneous healing for the fault segments to adjust their motions from an upper-limit slip velocity to almost rest. According to newton's second law, a process with fixed masses and constant velocity changes involves low forces and weak interactions if it is accomplished in a long time period, and vice versa. Our modeling also indicates that the existence of strong patches with higher effective stress on a fault is needed for the occurrence of major events. The creeping section of a fault, such as the one along the San Andreas fault in central California, on the other hand, can be simulated with the rate-and-state-dependent friction law by certain model parameters, which, however, must not include strong patches. In this case small earthquakes and aseismic creep relieve the accumulating strain without any large events.     

Frequency-domain array technique analysis for the rupture duration time and geometrical characteristics of the 2001 Kunlun Mountain Pass earthquake

In this paper, we briefly describe the principle of tracking energy radiation sources of large earthquakes using fre- quency-domain far-field array technique, present general steps of tracking energy radiation sources, and take the 2001 Kunlun Mountain Pass earthquake as an example to analyze key factors for setting parameters while pro- cessing data. Using broadband waveform data from a seismic array in Ethiopia and Kenya (EK Array), we obtain that the rupture initiation point of the 2001 Kunlun Mountain Pass earthquake is located in the east of Buka Daban Peak (35.92°N, 91.70°E), and the rupture duration time is less than 160 s, the rupture length about 520 km, with 180 km in the west of the initiation point and 340 km in the east, respectively. The western segment of the earth- quake fault bends towards southwest near Buka Daban Peak, which is in concordance with the surface rupture trace. The eastern segment apparently bends towards northeast near Xidatan, which is in agreement with the strike of Xidatan fault, but 30 km away from Xidatan fault. In addition, the results imply that the western segment of the earthquake fault appears erect while the eastern segment appears to be gradually dipping southwards.     

川滇菱形块体东边界库仑应力演化及强震发生概率估算

本研究基于分层黏弹介质模型,考虑强震或大地震同震位错、震后黏滞松弛及主断层段震间构造应力加载三方面效应,给出1480年以来,川滇菱形块体东边界鲜水河断裂带、安宁河断裂带、则木河断裂带和小江断裂带共20个断层段由三方面效应引起的累积库仑应力变化随时间的演化,分析强震间相互作用和强震发生的应力累积背景,定性分析各断层段的地震危险性.同时,分别采用现今台网地震目录和川滇菱形块体东边界各断层段强震复发间隔两种资料,定量计算2030年各断层段的强震发生概率;并基于摩擦本构理论,将周边强震引起的库仑应力变化量作为应力扰动,修正强震发生概率的计算结果.各断层段累积库仑应力演化的结果表明,鲜水河断裂带中部八美段、色拉哈段及南部磨西段、安宁河断裂带冕宁-西昌段、小江断裂带北部巧家-东川段和南部建水段的累积库仑应力显著增加.修正的强震发生概率计算结果显示,鲜水河断裂带中部八美-色拉哈-康定一带、安宁河断裂带冕宁-西昌段、小江断裂带南部华宁-建水一带强震发生概率较高,地震危险性值得关注.本研究基于库仑应力演化计算定性分析强震危险性的同时,基于摩擦本构律理论,结合地震引起的应力扰动和强震发生背景,定量计算修正的强震发生概率,为川滇菱形块体东边界强震危险地点及中长期发震紧迫程度判定提供方法和依据.     

Study on the Genesis of the Yongsheng Earthquake with Ms6.0 on October 27, 2001

On October 27, 2001, a large earthquake with Ms6.0, named the Yongsheng earthquake, occurred along the Jinshajiang segment of Chenghai fault in Yongsheng County, Yuunan Province. It is the largest event to occur along the Chenghai fault in the last 200 years. The seismo-geological survey shows that the seismogenic fault, which is the Jinshajiang segment of Chenghal fault, takes left-lateral strike-slip as its dominant movement pattern. According to differences in vertical motion, motion time, landforms and scales, the Chenhai fault can be divided into eight segments. The Jinshajiang segment has a vertical dislocation rate of 0.4mm/a, far lower than the mean rate of the Chenghai fault, about 2.0 mm/a. It‘ s deduced that the two sides of Jinshajiang segment “stuck“ tightly and hindered the strike-slip of the Chenghai fault. The strong earthquake distribution before this event shows that the Jinshajiang segment was in the seismic gap. The Chenghai fault, as a boundary of tectonic sub-blocks, makes the Northwest Yunnan block and the Middle Yunnan block move clockwise, and their margins move oppositely along the Chenghai fault. In the motion process of the Chenghai fault, structural hindrance and the seismic gap of strong earthquakes are propitious to the concentration and accumulation of structure stress. As a result, the Yongsheng Ms6.0 earthquake occurred. The Sujiazhuang-Shangangfu segment is similar to the Jinshajiang segment with a low vertical motion rate of 0.3 mm/a and in the seismic gap. So it‘s postulated that the segment may become a new structure hindrance, and the Yongsheng Ms6.0 earthquake may trigger the occurrence of future large earthquakes along this segment.     

2001年10月27日永胜6.0级地震的成因探讨

2001年10月27日云南永胜发生6．0级地震，笔者先后参加了地震现场灾害损失评估和震后野外科学考察。考察表明，这次地震发生在程海断裂金沙江段上，断裂以左旋走滑活动为主。程海断裂分为8段，各段的垂直差异运动不均匀，金沙江段中更新世以来的垂直位错速率为0．4mm/a，远远低于程海断裂的垂直位错平均速率(2．0mm／a)，从而使金沙江段成为断裂左旋走滑活动的构造障碍段。永胜6．0级地震之前，金沙江段处于程海断裂带上强震活动的“空段”内。程海断裂控制下的次级块体——滇西北块体与滇中块体的边界沿程海断裂作相向运动。在此运动过程中，程海断裂有全线贯通无阻的趋势，构造障碍段和强震活动的围空段有利于构造应力集中、积累，从而孕育和发生了永胜6．0级地震。苏家庄—山岗辅段垂直位错速率仅为0．3mm/a，同时也处于强震活动的围空段内，在程海断裂的贯通过程中成为新的构造障碍段，极有可能成为未来M≥6．0地震的危险地段。     

景泰-天祝断裂单元与多重特征地震的危险性概率评估

基于景泰 -天祝断裂的大比例活动构造填图资料 ,建立了合理的破裂分段地质模型。在此基础上 ,采用地震危险性分析的“实时模型”并考虑断层段之间的相互作用 ,对景泰 -天祝断裂的大震危险性概率作了定量评估。所得结果认为 ,景泰 -天祝断裂的下次大震很可能是毛毛山与金强河两个单元破裂段的组合破裂 ,震级约MS7 5。未来 10 ,2 0 ,5 0 ,10 0a内最可能的发震概率分别是 14%、2 7%、5 6 %和 81%     

Recurrence characteristics of late-quaternary strong earthquakes on the major active faults along the northern border of Ordos block

Through study on trenches, analysis of recurrence characteristics and recurrence interval cluster/gap of strong earthquakes along the major active faults on the northern border of Ordos block, we found 62 paleoearthquakes that occurred in the late Quaternary, including 33 earthquakes occurring in the Holocene. The recurrence characteristics of the paleoearthquakes are different at three levels, segments, faults, and fault zones. The strong seismic sequence on the independent segments is mostly characterized by long- and short-interval recurrences, while that on the faults and in fault zone is characterized clearly by random and cluster recurrences. Results of the moving window test indicate that the probabilities of "temporal cluster or gap", caused by random coincidence as opposed to intersegment contagion, are 64% and 70% for the Serteng piedmont fault and for the south-border fault of Wula Mountains, respectively, no clear interaction among the segments of each fault; while the probability is 26.8% for the whole fault zone, suggesting a clear interaction among the faults of this fault zone. These recurrence characteristics may imply an effect of the entire block motion on the recurrence of strong earthquakes. Moreover, the elapsed time for the Wujumeng Pass-Dongfeng Village segment of Serteng piedmont fault and the Tuzuo Banner-Wusutu and the Hohhot segments of Daqingshan piedmont fault has exceeded the average recurrence interval, hence these three segments may be the possible places for future strong earthquakes.