The experimental study of acoustic emission during creep of rocks

Under normal temperature, the creep experiments with complete samples of Gabbro and Marble rocks are made under uniaxial compression. It is found that at the instantaneous creeping stage, AE activities increase with loading; at the steady creeping stage, large AE signals may appear at lower background of AE action, andm—value which shows the relationship between AE amplitude and frequency keeps stable on the low value or decreases; at the accelerate creeping stage, AE activities increase andm—value decreases quickly or decreases again after recovery. These experimental results are related to the quality of the samples. In this paper, AE activities during three stages of creeping process are connected with the seismic patterns (for exampleb—value, foreshocks). Finally, it is pointed out the possibility that the foreshock—mainshock—aftershock earthquake sequence has been formed by the mechanism of creep fracture of crustal rocks. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 104–112, 1991. This subject is sponsored by the Chinese Joint Seismological Science Foundation.     

Discussion on the feature of strong earthquake: Orderly distribution in time, space and intensity before the Western Kunlun Mountain Pass M =8.1 earthquake

In the paper, the feature of strong earthquake orderly distribution in time, space and intensity before the Western Kunlun Mountain Pass M=8.1 earthquake is preliminarily studied. The modulation and triggering factors such as the earth rotation, earth tides are analyzed. The results show that: the giant earthquakes with the magnitude more than 8 occurred about every 24 years and the earthquakes with the magnitude more than 7 about every 7 years in Chinese mainland. The Western Kunlun Mountain M=8.1 earthquake exactly occurred at the expected time; The spatial distance show approximately the same distances between each two swarms. The earth rotation, earth tide, sun tide and sun magnetic field have played a role of modulation and triggering in the intensity. At last, the conditions for earthquake generation and occurrence are also discussed. Foundation item: State Key Project of Science and Technology of China (2001BA601B01) and State 863 Plan of China.     

The effect of stress on pore pressure in rocks and the mechanism of water table anomaly before earthquakes

Triaxial compressive experiments of porous rock samples were carried out under various confining pressures and initial pore pressures without drainage; axial strain and pore pressure were observed versus differential stress. The results of such experiments show that pore pressure increases with increase of differential stress at low differential stress; pore pressure decreases with increase of differential stress at medium and high differential stress. Pore pressure also increases with large amplitude decrease of differential stress at high differential stress. Based on such experiments, it is suggested that water table anomaly before an earthquake reflects the change of differential stress in crustal rocks. The anomalous behavior of water tables in the epicentral and peripheral areas before the great Tangshan earthquake of July 28, 1976 are explained by such suggestion. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 88–95, 1991. This study is supported by the Chinese Joint Seismological Science Foundation. Professor Yongtai Che gave us much help in applying fund support and supplying earthquake case histories.     

The features of multiple fractures associated with the great Haiyuan 8.5 magnitude earthquake of 1920

It is deduced on the basis of field investigation that the total length of the stratigraphic fault associated with the great Haiyuan 8.5 magnitude earthquake of 1920 was 225 km. This fault was formed by 6 secondary faults with different geometric parameters, which align regularly inen echelon arrangement. Each secondary fault can be divided into three segments with different characteristics of deformation where the middle segment was mainly of the horizontal strike—slip fault while another two segments the vertical deformation as shown by the features of reverse or normal faults. It is also shown by the data of vertical and horizontal displacements that the horizontal displacement approached a maximum at the middle segment for each secondary fault and gradually decreased toward and finally disappeared at both ends of each segment while in contrast the vertical displacement was minimum at the middle and became large at both ends of the segment. The feature of the multiple peaks appeared in the deformation as shown by the earthquake displacements along the whole fault. This feature indicates that the 6 secondary faults associated with the great Haiyuan earthquake were the horizontal interrupted planes (i.e., dislocation surface) which were independent on each other, and hence each dislocation surface may represent an independent secondary fracture event of the earthquake. We thus think that the 6 relatively independent secondary events which occurred successfully might result in the great 8.5 magnitude Haiyuan earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 21–31, 1991. This project is sponsored by the Chinese Joint Seismological Science Foundation.     

Conductivity structure of crust in the Tangshan seismic area and the possibility of exploring potential seismic sources by magnetotelluric method

It is shown by the result of digital magnetotelluric soundings in the Tangshan seismic area and its surrounding regions that the crust under the surface conductive sediments is divided into two layers,i. e., the resistive upper crust and the conductive lower crust. The upper crust wherein the Tangshan main shock and most of the aftershocks occurred is a convex lens-like body which is cut by faults at the east, south and west sides. The focus of the mainshock was located at the position of maximum thickness of the resistive upper crust while the spatial variation of Curie point isothermal surface and the deepest limit of the depths of aftershocks coincide with the downward depression of the bottom of the resistive upper crust. Thus, the Tangshan main shock and most of its aftershocks were related closely to the resistive upper crust from the view points of either vertical layering or lateral variations. And there were only a very few aftershocks in the conductive lower crust. The mechanical property of the rocks transforms from being brittle in the upper crust into ductile in the lower crust mainly due to the combination of different factors, e.g., increase of confining pressure, change in minerals, rise in temperature as well as stabilization of slips by high pore—pressure. A small amount of water and a rise in temperature may lead to a decrease of the electric resistivity within the rock while a change in the static pressure and mineral content within the rock causes very little change in the electric resistivity. Thus it is deduced that a resistive upper crust and a more conductive lower crust from the view points of either vertical or lateral variations are related to the brittle and ductile properties respectively. Hence it is possible that there is a relationship between the electric structure of the crust and zones of potential seismic hazard. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 354–363, 1991. The project is supported by the Chinese Joint Seismological Science Foundation, and the Swedish International Development Authority.     

The remote sensing observation in experiments of rock failure and the beginning of remote sensing rock mechanics

The remote sensing observational study for infrared radiation of rocks was proceeded during the loading on rocks until failure. The major instruments used in experiments were transient spectrum apparatus, intelligent spectrum apparatus, infrared radiation thermometer, infrared spectrum radiometer, and infrared thermal imaging system. The experiments for 26 kinds of rocks were made. The studies show that infrared radiation temperature of rocks increases along with increasing of stress. The amplitude of infrared radiation spectrum of rocks also increases along with increasing of stress. The observational results of infrared thermal imaging of rocks are consistent with infrared radiation temperature. Before formation of major faults for some rocks, the belt-shape thermal imaging of temperature anomaly displaies in position of future major faults. This study has led the new technology of remote sensing into rock mechanics and tend to establish a new field in rock mechanics — remote sensing rock mechanics (or remote sensing rock physics). The application of remote sensing rock mechanics in prediction of earthquake and rock burst, and in measurement of stress field in rock mass is expected. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 645–652, 1992. Jin-Shen HAO, Ji-Han LI, Xiao-Hong LIU, Yi-Qiao ZHI, Jin-Kai ZHANG, Yong-Hong Lü, Yi LIU, Yun-Shen YU, He ZHANG, Quan-Quan JI, Xiao-Fan ZHU and Ning CHEN took part in this work. This subject is supported by the Chinese Joint Seismological Science Foundation (91006). Work of Institute of Geophysics, SSB (93A0009).     

The stress field in the area from the west of Beijing to the Shanxi-Hebei-Nei Mongol border region

According to conditions of seismogeological structure and the data on seismicity in the area from the west of Beijing to the Shanxi-Hebei-Nei Mongol border region, the tectonic stress field and the seismic stress field in this area are studied by using the finite element method and the dislocation theory. In the light of the distribution features of these stress fields and the characteristics of recent activity of small earthquakes, it is inferred that there are two relative stress concentration zones in the area, they are (1) the zone which is bounded on the south by the Heishansi fault, on the west by the Niuxinchuan-Sihuizhuang fault and on the north by the Liangjiazhuang fault; and (2) the zone with a NW long axis, which is surrounded by the intersection zone of the Tianzhenbei, Jiucaigou-Huangtugudui, and Zhanggao faults. Of these, in the first relative stress concentration zone, a strong earthquake will be more probable to occur in future to the west of Huailai at the place where the Xiahuayuan, Hunjingdong and Sangganhe faults converge together but do not intersect, or in its surrounding area. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 307–318, 1991. The English version of this paper is improved by Dr. Zhixin Zhao.     

Ultrasonic modelling research of earthquake response of underground lifeline engineering

Earthquake response of underground lifeline engineering is investigated by the method of ultrasonic model experiments in this paper. From general field conditions, two models of underground lifeline engineering, one for non-uniform field and the other for uniform field, are designed based on the similarity principle. Besides analysis of seismic phases, a series of analyses especially on particle vibration are carried out. The results show that: The shorter the epicentral distance, the greater are the intensity variation and the change rate of intensity variation of earthquake ground motion, so the more disadvantageous to underground pipelines. In soft covering layer, compressional waves mainly cause radial flexures deformation, but shear wave result in axial dilation deformation of the pipelines; when the thickness of the covering layer is smaller (less than seismic wave length), the rhythmic variation of the intensity of earthquake ground motion is controlled mainly by the wave length of seismic waves in the bedrock. The property of the covering layer has considerable effect on earthquake ground motion. For different covering layers, their effect on each component of earthquake ground motion is not the same. Owing to the effect of wave propagation, the ground is in different states of particle vibration at different times, and there is considerable difference in phase and intensity of particle vibration between two different covering layers near their junction line or surface. Because underground lifelines tend to vibrate with the particles of the earth around it, this results in different deformation of underground pipelines under different conditions. So, it is necessary to take corresponding anti-seismic countermeasures for pipelines according to their practical situations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 104–110, 1992. This paper is part of the research supported by Funds of Doctoral Faculty of National Education Committee.     

Regional variations in abrupt-change sequence of georesistivity and its application in earthquake prediction

Based on fracture mechanics, large amount of practically observed data is analyzed in this paper, and it is disclosed that seismically-anomalous earthquake resistivity sudden change sequence can be observed at the earth resistivity stations around the epicenter of a strong event. The maximum sudden change in the sequence tends to shift backward with the increase of epicentral distance, while it shifts forward with the increase of the magnitude of the earthquake. The maximum sudden change also expands from the epicenter to the peripheral areas. Therefore, the authors propose that it might be possible to predict the 3 key elements of a forthcoming earthquake by using the sudden change sequence, the frequency of the sudden change, the expansion velocity of the maximum sudden change and the time-distance product. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 176–185, 1993.     

新疆伽师地区地应力的GPS损伤模拟研究

采用几何损伤理论和方法推导了地壳存在不同方向和大小的断层时的有效应力的公式,讨论了利用几何损伤来分析和计算地壳中存在不连续断层的理论和方法,同时对中国新疆地区的地应力变化用几何损伤理论和方法结合该地区的GPS资料进行了数值计算研究,通过比较计算结果与1997年1月至1998年12月发生在该地区的Ms≥5．0地震活动可以看出,新疆南部的中强地震活动区主要在应力场变化激烈的地区。     

A visco-elastoplastic model for fault rocks and its application to earthquake research

In the light of the rheological properties of crustal rocks and some features of earthquakes, a rheological model for fault rocks is suggested in the paper and the possibility of applying the suggested model to the study of earthquake mechanism is discussed. The results show that it is reasonable to take the suggested model as a physical simplification of fault rocks and to apply it to the numerical calculation and simulation of 2-D problems. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 129–136, 1992.     

Holocene activities of the Taigu fault zone, Shanxi Province, and their relations with the 1303 Hongdong M =8 earthquake

The Taigu fault zone is one of the major 12 active boundary faults of the Shanxi fault-depression system, located on the eastern boundary of the Jinzhong basin. As the latest investigation indicated, the fault zone had dislocated gully terrace of the first order, forming fault-scarp in front of the loess mesa. It has been discovered in many places in ground surface and trenches that Holocene deposits were dislocated. The latest activity was the 1303 Hongdong earthquake M=8, the fault appeared as right-lateral strike-slip with normal faulting. During that earthquake, the Taigu fault together with the Mianshan western-side fault on the Lingshi upheaval and the Huoshan pediment fault on the eastern boundary of the Linfen basin was being active, forming a surface rupture belt of 160 km in length. Moreover, the Taigu fault were active in the mid-stage of Holocene and near 7 700 aB.P. From these we learnt that, in Shanxi fault-depression system, the run-through activity of two boundary faults of depression-basins might generate great earthquake with M=8. Foundation item: Chinese Joint Seismological Science Foundation (201017). Contribution No. 2003A004, Institute of Crust Dynamics, China Earthquake Administration.     

The role of earth tide in crustal movement

The earth tide is usually ignored in orogenesis (geosynclinal activity) and magmatic activity. We believe that the role of earth tide in crustal movement should not be ignored. The elemental dynamic analysis of origin of magma chamber under dissipative tidal heating model and orogenic process driven by alternating earth tidal force is depicted. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 508–513, 1993. Xue-Min AI and Liang CHI also worked for this project. This work was supported by the Laboratory of Dynamical Geodesy, Academia Sinica. Translated from Chinese into English by Liang CHI.     

Electrical and thermal investigations of rocks and minerals under extremep,T-conditions

Summary For the discussion of the physico-chemical state and the phase transitions in the earth interior it is necessary to compare the results of geophysical field measurements with geophysical solid state investigations in the laboratory under extremep,T-conditions. In correspondence with the theoretical studies about the behaviour of the materials in the deep earth we investigated two groups of materials: (I) different types of rocks with reference to their elastic and thermal behaviour under extreme conditions, (II) simple compounds of elements which belong possibly to the representatives of the deep mantle and the earth interior. The method for measurement of the thermal diffusivity and the influence of anisotropy on the propagation of elastic waves in different rocks is described. The results of the dependence of the electric resistivity on pressure and temperature on synthetic and natural chalkogenides of the 3d-transition metals are discussed.Publication No. 474 of the Central Earth Physics Institute, Academy of Sciences, 15 Potsdam, Telegrafenberg, GDR.     

Internal structures and high-velocity frictional properties of a bedding-parallel carbonate fault at Xiaojiaqiao outcrop activated by the 2008 Wenchuan earthquake

This paper reports internal structures of a bedding-parallel fault in Permian limestone at Xiaojiaqiao outcrop that was moved by about 0.5 m during the 2008 M_W7.9 Wenchuan earthquake. The fault is located about 3 km to the south from the middle part of Yingxiu-Beichuan fault, a major fault in the Longmenshan fault system that was moved during the earthquake. The outcrop is also located at Anxian transfer zone between the northern and central segments of Yingxiu-Beichuan fault where fault system is complex. Thus the fault is an example of subsidiary faults activated by Wenchuan earthquake. The fault has a strike of 243° or N63°E and a dip of 38°NW and is nearly optimally oriented for thrust motion, in contrast to high-angle coseismic faults at most places. Surface outcrop and two shallow drilling studies reveal that the fault zone is several centimeters wide at most and that the coseismic slip zone during Wenchuan earthquake is about 1 mm thick. Fault zone contains foliated cataclasite, fault breccia, black gouge and yellowish gouge. Many clasts of foliated cataclasite and black gouge contained in fault breccia indicate multiple slip events along this fault. But fossils on both sides of fault do not indicate clear age difference and overall displacement along this fault should not be large. We also report results from high-velocity friction experiments conducted on yellowish gouge from the fault zone using a rotary shear low to high-velocity frictional testing apparatus. Dry experiments at normal stresses of 0.4 to 1.8 MPa and at slip rates of 0.08 to 1.35 m/s reveal dramatic slip weakening from the peak friction coefficient of around 0.6 to very low steady-state friction coefficient of 0.1-0.2. Slip weakening parameters of this carbonate fault zone are similar to those of clayey fault gouge from Yingxiu-Beichuan fault at Hongkou outcrop and from Pingxi fault zone. Our experimental result will provide a condition for triggering movement of subsidiary faults or off-fault damage during a large earthquake.     

Study of the characteristics of earthquake precursory anomalies of He and H2 Beijing No. 2 Cotton Mill well and their relation with earthquakes

This paper systematically summarized the relation of the abnormal change of He and H₂ dissolved gasses in deep hot-water well at Beijing No. 2 Cotton Mill and their relation with seismicity of the region. An empirical formula for the relation of the precursory anomaly of He and H₂ gasses with the magnitude and occurrence time of earthquake has been derived. Two events of magnitude greater than 5 in North China had been successfully predicted by using this formula. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 490–497, 1993.     

Study on a gravity precursor mode of the Ms=7.0 Lijiang earthquake

To study the seismogeny process or the precursory behavior of the 1976Ms=7.0 Lijiang earthquake,we analyze the repeat gravity data with high precision from the Westem Yunnan Earthquake Prediction Experiment Area(WYEPEA)and the relted results of geology and geophysics survey in this paper.Considering the gross errors caused by observation data and model difference,we have firstly inverted the slip distribution of the main active faults with time based on the robust Bayesian least squares estimation and multi-fault dislocation model.The re-sults show that the slip changes of the faults with time from 1990to 1997obviously reflect the preparation process of the Lijiang earthquake.The images of main precursor mode have the characteristic of main shock-after shock type,which is agreement to the model of coupling movement tetween crust density and crust deformation(DD mode of coupling movement).     

松原5.7级地震震中区土壤氢气变化特征

2018年5月28日吉林松原发生5.7级地震,为了探究地震对断层气的影响以及震后断层气变化特征,震后在震中区进行了多期土壤氢气浓度观测工作,得到了震中区氢气浓度的最大值、背景值等多项指标。结合地震前后氢气浓度数据,分析震中区震前、震后氢气浓度趋势性变化情况,结果显示:在此次地震活动中,氢气浓度变化有"震前缓慢升高—临震下降—震后迅速升高—强余震前再次骤升"的现象;氢气浓度变化与地震活动间有很好的映震关系,主震对氢气浓度的上升起主要作用,而余震则起诱发作用,余震的活动会使赋存在地下岩石裂隙的氢气释放量增大,表明氢气对余震活动的响应较灵敏;另外,震后某一时刻空气中的氢气浓度也会升高,这可能与区域断层中的氢气逸散到大气中有一定关系。     

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.     

Method of prediction of earthquake by using seismisity

The method of prediction of earthquake by using seismisity (MPES) is to make use of the message of earthquakes (including large, middle, small) in pre-period to predict large earthquake in post-period. Some better methods are presented in this paper which are selected among many means used in our country recent years. These methods are classified into six sets: 1. Method of spatial pattern; 2. Method of time process; 3. Method of seismic sequence; 4. Method of earthquake correlation; 5. Method of parameters of seismic source and medium; 6. Comprehensive method. Prediction effects of each method are evaluated with unique score. The value of each method, scoreR, are generally in a range between 0.3 and 0.6. This value only represents internal consistency, however, the ability of actual prediction belongs to the extensional effect, which is generally lower than the value of internal consistency. If the ability of actual prediction could be evaluated withR = 0.3, the ability of prediction of earthquake by seismicity will be stated as following: If most of earthquakes must be predicted, the warning time needs to take seventy percent of whole time period of prediction; If half earthquakes must be predicted, the warning time needs to take twenty percent of whole time period of prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 239–252, 1993.