Complex Earthquake Cycle Simulations Using a Two-Degree-of-Freedom Spring-Block Model with a Rate- and State-Friction Law

Numerical simulations of complex earthquake cycles are conducted using a two-degree-of-freedom spring-block model with a rate- and state-friction law, which has been supported by laboratory experiments. The model consisted of two blocks coupled to each other and connected by elastic springs to a constant-velocity, moving driver. By widely and systematically varying the model parameters, various slip patterns were obtained, including the periodic recurrence of seismic and aseismic slip events, and several types of chaotic behaviour. The transition in the slip pattern from periodic to chaotic is examined using bifurcation diagrams. The model system exhibits typical period-doubling sequences for some parameter ranges, and attains chaotic motion. Simple relationships are found in iteration maps of the recurrence intervals of simulated earthquakes, suggesting that the simulated slip behaviour is deterministic chaos. Time evolutions of the cumulative slip distance in chaotic slip patterns are well approximated by a time-predictable model. In some cases, both seismic and aseismic slip events occur at a block, and aseismic slip events complicate the earthquake recurrence patterns.     

高原地区路基地震液化数值模拟研究

在青海玉树地震之后,有大量路基出现由于液化而导致的病害问题。以青海S308线结古—曲麻莱段公路路基变形为例,通过FLAC3D数值模拟软件还原该路基在地震中的变形破坏过程,得出如下结论:(1)无地下水情况下,边坡出现明显塑性屈服的振动强度是0.6g,塑性屈服首先发生在填土厚度较薄的路基两端。(2)若砂土完全饱水,随振幅的增加,饱和砂土层液化趋势逐渐增强。振幅小于0.3g时砂土层没有液化。振幅为0.4g时5s以后砂土层出现液化;振幅大于0.5g以后,从振动的开始就出现了液化。(3)下伏饱和砂土的路基动力破坏机理为:饱和砂土层近地表处屈服屈服区在饱和砂土层中向中部扩展饱和砂土层屈服贯通饱和砂土层完全屈服填土后部首先破坏填土破坏区在填土-砂土界面向下扩展填土后部地表屈服开裂破坏区在填土内扩展。至最终破坏时,填土中后部大范围开裂屈服,但填土前部依然保持完整。     

摩擦摆隔震支座理论分析与数值模拟研究

介绍了摩擦摆隔震支座的基本构成和隔震原理。利用力学平衡原理,对摩擦摆隔震支座进行了理论分析,推导了摩擦摆隔震支座的刚度和等效粘滞阻尼比,构造了摩擦摆隔震支座的滞回模型,并探讨了该支座的自回复能力,得到了其最大残余位移计算公式。采用有限元软件ABAQUS,对摩擦摆隔震支座进行实体单元建模,模拟低周反复荷载作用下,该支座的滞回特性与回复特性。研究结果表明：①理论分析和数值模拟结果吻合较好,验证了提出的滞回模型和最大残余位移计算公式的正确性;②摩擦摆隔震支座的滞回曲线饱满,具有良好的滞回性能;③摩擦摆隔震支座的刚度与球面半径成反比,可能的最大残余位移为摩擦系数和球面半径的乘积;④该支座的最大应力出现在支座处于设计位移的时刻,且一般位于滑块或支座板球铰面边缘。     

断层上的地震成核过程与前兆模拟研究

为了把握断层上地震的前兆规律,对连续介质中断层面上的地震成核过程进行了数值模拟研究。摩擦采用了速率及状态依赖怀本构关系,并考虑了正应力变化的影响。结果表明,在成核的后期阶段：①最大位移速率单调加速增加;②滑动热点（最大滑动速率处）在后期阶段开始自发性迁移,且在空间上③当最大滑动速率达到可以明显探测的量级时（高于加载速率一个数量级以上）,倒刘时间为２０小时或更长一些,这时的速率变化可作为临震预测标志     

Numerical Simulation of Earthquake Nucleation Process and Seismic Precursors on Faults

To understand precursory phenomena before seismic fault sliP,this work focuses onearthquake nucleation process on a fault plane through numerical simulation.Rate and statedependent friction law with variable normal stress is employed in the analysis.The resultsshow that in the late stage of nucleation process:(1)The maximum slip velocity ismonotonically accelerating;(2)The slipping hot spot(where the slip rate is maximum)migrates spontaneously from a certain instant,and such migration is spatially continuous;(3)When the maximum velocity reaches a detectable order of magnitude(at least one orderof magnitude greater than the loading rate),the remaining time is 20 hours or longer,andthe temporal variation of slip velocity beyond this point may be used as a precursoryindicator;(4)The average slip velocity is related to the remaining time by a log-log linearrelation,which means that a similar relation between rate of microseismicity and remainingtime may also exist;(5)when normal stress variation is taken int     

2001年11月14日新疆-青海交界8.1级地震

简要介绍了2001年11月14日新疆－青海交界8．1级地震的预测情况，给出了中、美、日等对此次地震的震源参数测定和震源机制，以及余震的分布和加卸载响应比随时间的变化。进而对震区近期地震趋势进行预测。     

A Numerical Simulation of the Seasonal Cycle of Temperature, Salinity and Velocity Fields in Tokyo Bay

To understand when oxygen-depleted waters occur, how they develop and when they dissipate in inner Tokyo Bay, realistic simulations were attempted with fine spatial and temporal resolution by applying realistic time dependent external forcing. A 3D hydrodynamic model was driven by time-dependent external forcing factors/parameters such as solar radiation, air temperature, relative humidity, wind velocity, and fluvial discharge, under the open boundary conditions of 1995. A simulated time series of salinity and temperature agreed fairly well with observed data, except in summer. The model failed to reproduce the development of the surface mixed layer in summer. Several sensitivity analyses on the external forcing parameters such as wind velocity and vertical diffusivity were conducted to reproduce the mixed layer. However, changing these parameter values did not improve the model results.     

Simple Spring-mass Model Simulation of Earthquake Cycle along the Nankai Trough in Southwest Japan

— Along the Nankai trough in southwest Japan, due to the subduction of the Philippine Sea plate, great earthquakes have occurred repeatedly. The rupture zone is divided into five segments. Historical documents show the characteristic features of the past several earthquake cycles, such as almost simultaneous rupture occurrence in segments in spite of different convergence rates, the recurrence time of 90 to 150 years, the existence of segment pairing in earthquake ruptures and the different coseismic slip behaviors in respective segments. Based on the rate and state friction law, we simulate these features with a simple block-spring model to investigate the physical mechanisms of earthquake cycle. Considering the actual fault parameters related to the geometry and the kinematics of the convergent plate in five segments, we calculate the model parameters for the corresponding blocks in the simulation. The features of the observed earthquake cycle are successfully reproduced by assigning the other following model parameters; (1) the stick-slip periods are the same (more than 150 years) for non-interacting blocks, (2) the different pairs of frictional parameters a-b and D _c are assigned in each segment, (3) the interactions between segments are large, (4) the convergence rate in the eastern Tokai segment is about half of those in the other segments.     

A Discrete Element Analysis of the Sliding Friction Heat in High-Speed and Long-Runout Landslides

Earthquake is one of the main causes of high-speed and long-runout landslides. Generally, the heat generated in the sliding zone is significant in such devastating landslides. In this study, we establish a two dimensional slope model which includes 0.2 million elements to simulate the development of high speed and long-runout landslides using the discrete element software MatDEM. The model not only suggests that heat is produced by friction and fracturing, but also simulates the process of tension generation in cracks and the generation of a high heat zone near the sliding region. Besides, the heat field graph indicates a banded high heat belt that is related to the location of the thickest sliding body. The logarithms of the total calorific value and the highest value in the heat zone during the sliding process are linearly related to the logarithm of the landslide height.     

华北北部短临前兆场特征与震源过程的数值模拟

本文对华北２０多次Ｍｓ≥５的震例进行了研究，得到了华北北部地震的７项短临异常特征。同时，把短临地震阶段视为震源介质软化和断层蠕动的物理过程，利用各向异性非线性震源模型和有限元方法计算了震源及其周围地区特征点（假定观测点）上的平均应力、最大剪切力、体应变和孔隙压等物理量随时间的变化，通过对这些理论曲线的分析得到了短临地震前兆具有形态多样复杂、数量随时间指数型增长、异常从外围向震中迁移、异常相对集中于     

全球主要俯冲带处板块运动与地震各向异性及应力场的相关性讨论*

在全球板块的很多地方,包括俯冲带、大洋中脊、甚至大陆板块的内部等,地震各向异性都与板块绝对运动的图像存在一定的相关性,或者与板内应力场的优势取向一致。本文统计分析了全球9个包含主要俯冲带的板块边界内板块运动与地震各向异性及应力场的相关性,结果表明,板块的绝对或相对运动控制着板块边界的地震各向异性和应力场特征,尤其是板块的相对运动,在板块边界带处的影响十分明显;从计算结果可以看出,板块的相对运动方向与地震各向异性及应力场的相关性要好于板块绝对运动。在包含俯冲带的板块边界处,由于俯冲机理的复杂性和控制因素的多样性,使得俯冲带处两者的相关性较为复杂,不同深度来源的各向异性表现出不同特征,且应力状态受多种因素的控制,对于该区域两者的相关性则需进一步深入研究。     

3-D Simulation of Tectonic Loading at Convergent Plate Boundary Zones: Internal Stress Fields in Northeast Japan

The evidence of east-west compression in northeast Japan has been reported by many investigators on the basis of geodetic, geologic and geomorphic data, but its origin still remains far from understood. In the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones, and demonstrated its validity through the numerical simulation of internal stress fields in northeast Japan with realistic 3-D geometry of plate interfaces. At convergent plate boundary zones, in general, a part of plate convergence is consumed by steady slip along plate interfaces, and the remaining part by inelastic deformation (seismic faulting, aseismic faulting, and active folding) of overriding plates. Such a plate boundary process to be called ``partial collision' can be quantitatively described by introducing a collision rate defined as c = 1 − steady slip rate at plate interfaces/plate convergence rate. By this definition, we can simply represent the mechanical process of partial collision, which includes total subduction (c = 0) and total collision (c = 1) as two extreme cases, in terms of steady slip rates at plate interfaces. On the basis of elastic dislocation theory, first, we numerically computed the internal stress fields in northeast Japan produced by the total subduction of the Pacific plate beneath the North American plate, however the computed stress pattern was opposite in sense to observations. Then, we computed the internal stress fields by taking c = 0.1 on average, and succeeded in reproducing the observed east-west compression in northeast Japan. This indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading.     

1927年古浪8级地震的破裂习性及破裂机制的数值模拟

1927年古浪8级地震是继1920年海原8．5级地震之后发生在海原一祁连山断裂带上的另一次特大地震。对这次地震的破裂习性，前人的研究结果存在较大分歧。本文在多探槽揭露和地面追踪调查基础上，结合相关的历史资料分析后，认为本次地震是由构成古浪推覆体的天桥沟一黄羊川断裂、皇城双塔断裂冬青顶断裂段以及武威一天祝隐伏断裂等共同作用的结果。对古浪推覆体平面和剖面变形机制的有限元数值模拟结果显示，其应力和应变的集中区主要分布在天桥沟一黄羊川断裂西段、皇城一双塔断裂冬青顶一带以及武威一天祝隐伏断裂和古浪一双塔断裂所在的古浪峡一带，这与地震地表破裂带的展布是一致的，同时也进一步说明了1927年古浪8级地震是该推覆体整体活动的结果。     

台湾地震对华南及华东地区应力场影响的数值模拟研究

台湾是我国地震发生最为频繁的一个地区,一些地震学者研究过中国周边地区地震与中国大陆地震活动的关系,有研究认为台湾地区强震活动与大陆中强地震活动具有同期活跃的特点,这种板内地震与板缘地震同步活跃的特点表明,二地区可能具有同一个动力来源,可能是由于板缘地震所引起的应力调整对板内地震孕育所作出的贡献.     

3-D Modelling of Plate Interfaces and Numerical Simulation of Long-term Crustal Deformation in and around Japan

— We developed a 3-D simulation model for long-term crustal deformation due to steady plate subduction in and around Japan by incorporating viscoelastic slip-response functions into a realistic 3-D plate interface model, constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes. The lithosphere-asthenosphere system is modelled by an elastic surface layer overlying a Maxwellian viscoelastic half-space. Kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across the interfaces. With this model, giving the steady slip rates at plate interfaces calculated from NUVEL-1A, we simulated long-term crustal deformation due to steady plate subduction in and around Japan. The simulated crustal deformation pattern is characterized by steep uplift at island arcs, sharp subsidence at ocean trenches and gentle uplift at outer rises. The numerical results show the strong dependence of the deformation pattern on the 3-D geometry of plate interfaces.     

Rupture Property of the 1927 Gulang Ms8.0 Earthquake and Numerical Simulation of Rupture Mechanism

INTRODUCTIONThe1927GulangMS8.0earthquake is a severe earthquake followed the HaiyuanMS8.5earthquake of1920inthe Qilian Mt._Hexi Corridor earthquake zone.The most severely hit region wasaround Gulang and Liangzhou(the present Wuwei)of Gansu Province,with a…     

Simulation of Frictional Strength and Steady Relaxation Using the Rate and State Dependent Friction Model

In this paper, frictional strength of hard solids, such as rock–rock sliding surfaces, is studied as a function of waiting time and shearing velocity. A one dimensional spring–mass sliding system is numerically simulated under the quasistatic condition using the rate and state dependent friction model. It is established that frictional strength varies linearly with the logarithm of waiting time (also known as time of stationary contact or relaxation time, etc.) as well as logarithm of shearing velocity. Analytical expression developed for frictional strength is found to be valid only in the case of high stiffness of the connecting spring. In the steady relaxation simulation, a steadily sliding mass is suddenly brought to zero velocity and relaxation of the interfacial stress and corresponding velocity at the sliding interface is studied as a function of relaxation time in the velocity strengthening regime of friction. A mathematical relation is derived between state variable and waiting time using the concept of steady relaxation. The relaxation model is also compared with the experimental data from the literature. Finally, the present study enables one to unify the slide–hold–slide friction experiments.