Variation of stress during the rupture process of the 1995 M_L=4.1 Shacheng, Hebei, China, earthquake sequence

Introduction An earthquake could be caused by the failure of focal material or fast slip on the pre-existed faults under the tectonic stress based on the understanding of the occurrence process of earth-quakes in which the stress change could play a key role. Therefore to examine the stress change is beneficial to understanding the physic process actually occurring in the source region deeply. The apparent stress is defined as the product of seismic efficiency and the average stress on the foc…     

Promoting effects of 1975 Haicheng foreshocks on theoccurrence of the mainshock

Ｐｒｏｍｏｔｉｎｇｅｆｆｅｃｔｓｏｆ１９７５ＨａｉｃｈｅｎｇｆｏｒｅｓｈｏｃｋｓｏｎｔｈｅｏｃｃｕｒｒｅｎｃｅｏｆｔｈｅｍａｉｎｓｈｏｃｋＸｉｎｇ－ＣａｉＬＩ（李兴才）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｔｉｓｍｏｌｏｇｉｃａ...     

Variation of stress during the rupture process of the 1995 ML=4.1 Shacheng, Hebei, China, earthquake sequence

According to the rupture dynamics of earthquakes, variations of the apparent stress and the difference between the static stress drop and the dynamic stress drop during the rupture of earthquakes are analyzed for the July 20, 1995 M _L=4.1 Shacheng, Hebei, China, earthquake sequence. Results obtained show that the apparent stress for main-shock is about 5 MPa, and the average apparent stress for aftershocks 0.047 MPa. During the rupture of the main-shock, the dynamic stress drop is approximately 1.6 times greater than the static stress drop with the difference of nearly 2.7 MPa. The dynamic stress drop is less than the static stress drop for all aftershocks with the average difference of −0.75 MPa. Therefore, when the mainshock occurs the final stress on the focal fault is higher than the dynamic frictional stress, corresponding to that the fault is abruptly locked. When the aftershocks occur the final stress on the focal fault is lower than the dynamic frictional stress, corresponding to that the fault overshoots. It can be seen from the above results that there could be some differences in the physic processes between the mainshock and the aftershocks. Contribution No. 05FE3013, Institute of Geophysics, China Earthquake Administration.     

2008年新疆于田MS7.3地震对后续 地震的完全库仑应力触发作用

在离散波数法基础上计算2008年3月21日新疆于田M_S7.3地震造成的近场区域完全库仑应力变化, 分析该变化对余震发生所产生的影响, 得到了此次地震在2008年10月5日乌恰M_S6.8地震震中处所产生的动态库仑破裂应力变化. 计算结果表明, 该地震近场区域库仑应力变化图像演化大概持续了60 s, 库仑应力变化对余震的触发率达到90%以上, 其中动态库仑应力变化图像更好地解释了余震的分布. 余震震中处的完全库仑应力变化计算结果表明, 其动态库仑应力变化远远大于静态库仑应力变化. 于田M_S7.3地震在乌恰M_S6.8地震震中处造成的最大动态库仑应力变化为0.12 MPa, 说明后者可能受到了于田M_S7.3地震的动态应力触发作用, 但不显著;而静态库仑应力则对其影响很小.      

Study on determination of stress level by seismic stress drops and the stress axis deflections before and after large earthquakes

Introduction The study of tectonic stress field, a major branch of the Earth science, plays an important role in geodynamics. The world stress map plan started from 1980s and was leaded by Zoback. Lots of scientists from many countries participated this plan. The plan collected global tectonic stress measurements and research results and established global stress database. The world stress map was edited based on the global stress database. The world stress map reflected feature of global li…     

Application of observed strain steps to the study of remote earthquake stress triggering

IntroductionModernseismologysuggeststhatearthquakesarecausedbyfaultslippingtriggeredbytec-tonicstressesaccumulatedtoacertainextent;andthefaultslip,inturn,releasesstresses.Infact,whenanintensivequakeoccurs,thefracturingoftheseismogenicfaultdoesnotleadtothereleaseofallthestressesbut,accordingtothegeometricrelationsamongthefaults,releasesstressesonsomeofthefaultstomakethemmorestable,whileaccumulatesstressesonotherfaultstomakethemtendtoslip.Asanapproximation,thestrengthofthefaulttobeysByerleylawby…     

Focal mechanisms and tectonic stress field of the Xinfengjiang earthquake

Altogether 83 events were recorded clearly by all the 8 sub-seismometric stations of the telemetrered seismic network in the Xinfengjiang area during the period from October 1st 1983 to April 30th 1987. Based upon the difference of the initial motion of P waves, the authors divided the 83 earthquakes into 37 pattens. Combining similar pattens, we have got 5 types of focal mechanism solutions. The recent tectonic stress field of the Xinfengjiang region is discussed. The characteristics of the stress axis and the nodal planes are different from which our predecessors got earlier; but the present results is similar to which put forward by the authors in 1981. This paper shows that the tectonic stress field is clearly characterized by a compression in the N-S direction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica 13. 462–476, 1991.     

An Overview of the Study on Stress Magnitude

Crustal stress field holds an important position in geodynamics research, such as in plate motion simulations, uplift of the Qinghai-Xizang (Tibet) Plateau and earthquake preparation and occurrence. However, most of the crustal stress studies emphasize particularly on the determination of stress direction, with little study being done on stress magnitude at present. After reviewing ideas on a stress magnitude study from geological, geophysical and various other aspects, a method to estimate the stress magnitude in the source region according to the deflection of stress direction before and after large earthquakes and the stress drop tensor of earthquake rupture has been developed. The proposed method can also be supplemented by the average apparent stress before and after large earthquakes. The stress direction deflection before and after large earthquakes can be inverted by massive focal mechanisms of foreshocks and aftershocks and the stress drop field generated by the seismic source can be calculated by the detailed distribution of the earthquakes rupture. The mathematical relationship can then be constructed between the stress drop field, where its magnitude and direction are known and the stress tensor before and after large earthquakes, where its direction is known but magnitude is unknown, thereby obtaining the stress magnitude. The average apparent stress before and after large earthquakes can be obtained by using the catalog of broadband radiated energy and seismic moment tensor of foreshocks and aftershocks and the different responses to stress drops. This relationship leads to another estimation of stress magnitude before a large earthquake. The stress magnitude and its error are constrained by combining the two methods, which provide new constraints for the geodynamics study.     

江苏及邻区现代应力场空间分布特征分析

利用１９８０年１月至１９９１年２月间江苏及邻区天然地震的Ｐ波初动符号，按不同深度分层计算平均节面解，分析江苏及邻区现代应力场空间分布特征。在不同深度上表现出中、深部层应力方向较一致。     

Preliminary analysis on the tectonic stress level in the source region of Tangshan earthquake

Introduction Analyzing tectonic stress field based on focal mechanism data is an important way to the study tectonic evolvement of lithosphere and associated dynamic process. Such studies growrapidly in China and abroad (Zoback, 1992; Plenefisch, Bonjer, 1997; XU, 1985; CUI, XIE, 1999). At present most of the studies focus on the inversion of focal mechanism data for the direction and relative magnitude of stress tensor, and few on absolute stress. Using focal mechanism and fault scratch,…     

1989年12月25日侯马4.9级地震的应力异常

叙述了1989年12月25日侯马市发生4.9Ms地震前距震中约100km的赵城观测站地应力出现的异常情况,指出只要埋设环境、安装方法、观测程序符合规范要求,简易地应力对一定范围内的较大地震是有监测能力的。     

Application of mechanical and statistical models to the study of seismicity of synthetic earthquakes and the prediction of natural ones

Based on a cellular automata model, which obeys rules produced by a spring-damper-slider model of fault network, a synthetic earthquake catalog of deterministic chaos can be produced. It is a challenge to inverse the model parameters and predict the synthetic earthquakes from the synthetic catalog. We apply an improved statistical model of coupled stress release to the synthetic catalog, it does successfully inverse the stress evolution of the system, but effectively prediction of the earthquakes from the stresses remains a problem. This research is partially supported by the Chinese Joint Seismological Science Foundation and Asian 2000 Foundation of New Zealand.     

龙首山地区构造应力场初步探讨

讨论了沟谷成因与构造应力场的关系,利用沟谷资料计算了龙首山地区的主压应力方向,结果表明,主压应力为北东向。新构造应力场、现代构造应力场、地震应力场趋于一致。认为晚第三纪以来,龙首山地区地壳构造应力场相对稳定,应该是青藏地块与阿拉善地块相互作用的结果。     

地震应力产生传递与集中机制的研究

讨论得出地震应力是随着“双向应变结构”的形成而产生的;地震应力主要有压缩应力、拉疏应力及剪切应力的复杂性;地震应力的传递与集中,在本质上就是应变的迁移与应变的转换;地震应力与区域构造应力有生成关系上的联系,也有作用对象与作用目的不同的区别。     

西藏羊八井-康马地区现今地应力测量结果与应力状态分析

本文给出了西藏羊八井-康马地区不同地点的现今地应力实测值的大小和方向. 为了解青藏高原现今地应力状态,结合青藏铁路工程的需要,我们在羊八井-康马地区进行了现场地应力测量. 测量方法采用压磁应力解除法,测点分别布置在羊八井、拉萨、曲水和康马等四个不同的构造部位,测量深度为11～18m. 测量结果表明,本区最大水平主应力方向以NW-NNW为主,最大水平主应力值一般为33～104MPa,但在板块缝合带上的曲水测点最大水平主应力值为23MPa. 与其他地区相比较,本区属中高应力区. 而在曲水应力值属中等偏小,可能反映了板块缝合带现今处于应力释放状态,板块缝合带附近应力具有复杂性.     

巴塘6.7级地震和雅江6.0级地震前后三叉口地区重力场变化情况

三叉口地区在1989年巴塘6.7级地震和2001年雅江6.0级地震前的重力场变化显示该地区的地应力呈聚集状态,能量的释放较少;在震后重力场变化显示该地区的地应力呈释放状态,有较大的能量释放。     

CBT型钻孔倾斜传感器振动时效预老化系统试验研究

CBT型钻孔倾斜传感器是我国地倾斜测量的重要仪器，只有保证倾斜传感器的高灵敏度和高自身稳定性，才能获得优质的观测数据。以往采用热处理和自然时效的方式消除传感器残余应力，进行预老化处理，提高传感器自身稳定性。该处理方法虽行之有效，但周期较长，难以满足日益增加的台站建设需要。为此，本文构建实验室倾斜传感器整机预老化系统，开展倾斜传感器快速消除残余应力试验，并跟踪传感器样品在阿图什台站的安装使用效果。通过实践证明，振动时效预老化工艺可有效消除传感器残余应力，有利于倾斜传感器的快速稳定。     

科里奥利力对断层作用的统计研究

首先给出了分解到已知断层面法向和切向上的断层错动科里奥利应力(简称为科里奥利法向应力和切向应力)表达式,然后从哈佛大学矩心矩张量目录中选取主余震资料进行分析,按断层分类研究了科里奥利法向应力和主震震级与其最大余震震级差及主震地震矩与余震地震矩总和之差的折合矩震级间的关系.研究结果显示:地震断层错动过程中虽然产生了使断层两盘相互拉离(或挤压)的科里奥利法向应力,它降低(或增加)了断层错动时断层面上的摩擦阻力,但是应力量值太小(科里奥利法向应力估计最大不到0.1MPa,即不到一个大气压),不足以对断层错动及主震能量释放产生影响,从而影响余震的最大震级和总体水平.     

Recent crustal movements and earthquakes in the area of the Tornquist Zone

Summary The present state of knowledge on recent crustal movements, stresses and earthquakes around the Tornquist Zone has been collected. It is found that the Tornquist Zone is neither geodetically nor seismically active, but it separates regions of different earthquake activity.Members of the working group on recent crustal movements around the Tornquist Zone: H. Lykke Andersen, M.C. Oncescu, V. Mocanu, E. and P. Bankwitz, G. Grünthal, and S. Gregersen.     

雁列断层应力场影响因素数值模拟分析

利用有限元法,建立具有黏弹性力学参数的断层接触对,采用对比分析的方法,通过改变雁列断层的几何间距和黏滞系数,分析影响雁列断层构造应力场的因素和分布状态,模拟出雁列断层在失稳过程中,地震所产生的应力降和应力应变等以及第一、第二、第三主应力与断层之间的角度关系等。