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Two great earthquakes of MS8.5 and MS8.3 determined by the China Earthquake Networks Center (CENC) occurred successively on September 12 and 13, 2007 in the sea area to the south of Sumatra, which is another group of large earthquakes after MS8.7 event on December 26, 2004 and MS8.5 event on March 29, 2005. The magnitudes of these earthquakes determined by the National Earthquake Information Center of USA (NEIC) are MW9.0 (26 December 2004), MW8.7 (29 March 2005), MW8.4 (12 September 2007) and MW8.1 (13 September 2007), respectively. Many researches about the two earthquakes of 2004 and 2005 have been developed (Chlieh et al, 2007; Ammon et al, 2005; ZHANG et al, 2005). XUE et al (2005a) studied the characteristics of seismic activity before the MW9.0 and make comparison between the two great earthquake sequences of 2004 and 2005 (XUE et al, 2005b). When analyzing spatial distribution of the two sequences, XUE et al (2005a) found a seismic gap with 400 km long and thought the seismic gap maybe a potential strong earthquake region taking historical earthquake activity there into account. It is interesting that the two earthquakes of 2007 just occurred in the seismic gap. Moreover the abnormal phenomena of the global and regional seismicity before the two earthquakes are similar to those before the large earthquake of 2004. In this paper, we will contrastively analyze the characteristics of seismic activity before the four large earthquakes and try to find the common features. The data used in this paper are from global earthquake catalog given by NEIC and the global earthquake catalog with MS≥7.0 obtained by CENC respectively. The earthquake catalog of NEIC can also cover earthquakes with M≥4.8 in Sumatra and its neighboring region (XUE et al, 2005a).

The seismogenic fault and the dynamic mechanism of the Ning’er, Yunnan Province MS6.4 earthquake of June 3, 2007 are studied on the basis of the observation data of the surface fissures, sand blow and water eruption, landslide and collapse associated with the earthquake, incorporating with the data of geologic structures, focal mechanism solutions and aftershock distribution for the earthquake area. The observation of the surface fissures reveals that the Banhai segment of the NW-trending Ning’er fault is dominated by right-lateral strike-slip, while the NNE-trending fault is dominated by left-lateral strike-slip. The seismo-geologic hazards are concentrated mainly within a 330°-extending zone of 13.5 km in length and 4 km in width. The major axis of the isoseismal is also oriented in 330° direction, and the major axis of the seismic intensity VIII area is 13.5 km long. The focal mechanism solutions indicate that the NW-trending nodal plane of the Ning’er MS6.4 earthquake is dominated by right-lateral slip, while the NE-trending nodal plane is dominated by left-lateral slip. The preferred distribution orientation of the aftershocks of MS≥2 is 330°, and the focal depths are within the range of 3∼12 km, predominantly within 3∼10 km. The distribution of the aftershocks is consistent with the distribution zone of the seismo-geologic hazards. All the above-mentioned data indicate that the Banhai segment of the Ning’er fault is the seismogenic fault of this earthquake. Moreover, the driving force of the Ning’er earthquake is discussed in the light of the active block theory. It is believed that the northward pushing of the Indian plate has caused the eastward slipping of the Qinghai-Tibetan Plateau, which has been transformed into the southeastern-southernward squeezing of the southwest Yunnan region. As a result, the NW-trending faults in the vicinity of the Ning’er area are dominated by right-lateral strike-slip, while the NE-trending faults are dominated by left-lateral strike-slip. This tectonic framework might be the main cause of the frequent occurrence of MS6.0∼6.9 earthquakes in the area.

In this study, a composite source model has been used to calculate the realistic strong ground motions in Beijing area, caused by 1679 M S8.0 earthquake in Sanhe-Pinggu. The results could provide us the useful physical parameters for the future seismic hazard analysis in this area. Considering the regional geological/geophysical background, we simulated the scenario earthquake with an associated ground motions in the area ranging from 39.3°N to 41.1°N in latitude and from 115.35°E to 117.55°E in longitude. Some of the key factors which could influence the characteristics of strong ground motion have been discussed, and the resultant peak ground acceleration (PGA) distribution and the peak ground velocity (PGV) distribution around Beijing area also have been made as well. A comparison of the simulated result with the results derived from the attenuation relation has been made, and a sufficient discussion about the advantages and disadvantages of composite source model also has been given in this study. The numerical results, such as the PGA, PGV, peak ground displacement (PGD), and the three-component time-histories developed for Beijing area, have a potential application in earthquake engineering field and building code design, especially for the evaluation of critical constructions, government decision making and the seismic hazard assessment by financial/insurance companies.

In the paper, we introduce Allegre’s scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors (seismic spatial correlation length and coda Qc) associated with the earthquake (M=6.1) occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc.

This paper discusses the relation between two-step seismic design and the standard of probability of exceedance, and the relation of three-levels seismic ground motion parameters given by probability method and comprehensive probability method. The relative size relations of the ground motions with 2%, 10%, 63% probability of exceedance in 50 years, namely “large earthquake”, “moderate earthquake”, and “small earthquake”, are discussed through a practical example of seismic hazard analysis. The methods to determine seismic fortification criterion are discussed.

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed.

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of M L≥2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is proposed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.

During the period of 1999~2002, the Chinese seismologists made a serious of developments in the study on seismic sources including observations, experiments and theory. In the field of observation, the methods of the accuracy location of earthquake sources, the inversion of seismic moment tensor and the mechanism of earthquake source are improved and developed. A lot of important earthquake events are studied by using these methods. The rupture processes of these events are inverted and investigated combined with the local stress fields and the tectonic moment by using the measurements of surface deformation. In the fields of experiments and theory, many developments are obtained in cause of seismic formation, condition of stress and tectonics, dynamics of earthquake rupture, rock fracture and nucleation of strong earthquakes.

A great earthquake of MS=8.1 took place in the west of Kunlun Pass on November 14, 2001. The epicenter is located at 36.2°N and 90.9°E. The analysis shows that some main precursory seismic patterns appear before the great earthquake, e.g., seismic gap, seismic band, increased activity, seismicity quiet and swarm activity. The evolution of the seismic patterns before the earthquake of MS=8.1 exhibits a course very similar to that found for earthquake cases with MS≥7. The difference is that anomalous seismicity before the earthquake of MS=8.1 involves in the larger area coverage and higher seismic magnitude. This provides an evidence for recognizing precursor and forecasting of very large earthquake. Finally, we review the rough prediction of the great earthquake and discuss some problems related to the prediction of great earthquakes.

An M=6.0 earthquake occurred on February 23, 2001 in the western Sichuan Province, China. The macro seismic epicenter situated in the high mountain-narrow valley region between Yajiang and Kangding counties. According to field investigation in the region, the intensity of epicentral area reached VIII and the areas with intensity VIII, VII and VI are 180 km2, 1 472 km2 and 3 998 km2, respectively. The isoseismals are generally in elliptic shape with major axis trending near N-S direction. The earthquake destroyed many buildings and produced some phenomena of ground failure and mountainous disasters in the area with intensity VIII. This event may be resulted from long-term activities of the Litang fault and Yunongxi fault, two main faults in the western Sichuan. The movements between the main faults made the crust stress adjusted and concentrated, and finally the earthquake on a secondary fault in the block released a quite large energy.

Analysis of seismic data and seismicity characteristics in China, we gave a method to deal with seismic patterns by calculating density at grid nodes. Number of earthquakes and epicenter distribution are considered comprehensively in this method. Effect of datum accuracy is stressed on parameter confirmation. Seismic patterns from this method are stable and can reflect seismic characteristics reliably. These seismic patterns are the base of quantitative analysis of seismicity. It can be applied in seismic tendency analysis and medium-long term earthquake prediction, earthquake countermeasure and risk mitigation.

Earthquake activities in history are characterized by active and quiet periods. In the quiet period, the place where earthquake M S≥6 occurred means more elastic energy store and speedy energy accumulation there. When an active period of big earthquake activity appeared in wide region, in the place where earthquake (M S≥6) occurred in the past quiet period, the big earthquake with magnitude of 7 or more often occur there. We call the above-mentioned judgement for predicting big earthquake the “criterion of activity in quiescence”. The criterion is relatively effective for predicting location of big earthquake. In general, error of predicting epicenter is no more than 100 km. According to the criterion, we made successfully a middle-term prediction on the 1996 Lijiang earthquake in Yunnan Province, the error of predicted location is about 50 km. Besides, the 1994 Taiwan strait earthquake (M S=7.3), the 1995 Yunnan-Myanmar boundary earthquake (M S=7.2) and the Mani earthquake (M S=7.9) in north Tibet are accordant with the retrospective predictions by the “criterion of activity in quiescence”. The windows of “activity in quiescence” identified statistically by us are 1940–1945, 1958–1961 and 1979–1986. Using the “criterion of activity in quiescence” to predict big earthquake in the mainland of China, the earthquake defined by “activity in quiescence” has magnitude of 6 or more; For the Himalayas seismic belt, the Pacific seismic belt and the north-west boundary seismic belt of Xinjiang, the earthquake defined by “activity in quiescence” has magnitude of 7, which is corresponding to earthquake with magnitude of much more than 7 in future. For the regions where there are not tectonically and historically a possibility of occurring big earthquake (M S=7), the criterion of activity in quiescence is not effective.

Based on seismic source spectrum solution by multi-station and multi-event coda method, applying Brune seismic source model, we have got the source factors and spectra of 48 small earthquakes occurred before and after the Douhe earthquake of October 6 in 1995. The seismic moments, corner frequencies and stress drops are estimated from the spectra, and their correlation and variation with time before and after the Douhe earthquake are discussed. The results indicate that the source factors show good stability, their peak frequencies and variation with frequency appear quite similar. Some events with higher stress drops occurred about one year before the Douhe earthquake. Taking into the account that the stress drop is calculated from seismic moment and frequency, as well as the correlation between them, we emphasis that the higher stress drop mentioned here just implies the higher corner frequency than the normal value.

By systematically studying seismic strengthening areas before 85 earthquakes with M≥6.0 in China, some results have been extracted. (1) Earthquake active strengthening area exists universally before strong shock or great earthquake; (2) The size of the strengthening area and its appearing time will increase when the earthquake magnitude increases; (3) The rate between the size of seismic strengthening area and the size of the source region decreases when earthquake magnitude increases; (4) The appearing time of the earthquake active strengthening region in the eastern part of China is longer than that in the western part of China. The above characteristics have been preliminarily explained qualitatively and half-quantitatively by applying the strong body earthquake generating model and the hard inclusion theory. Then applying the seismic strengthening area, we have obtained long-term predictions of 2 earthquakes, so the seismic strengthening area before strong earthquake or great earthquakes is a universal phenomenon, which has some mechanical base.

After analyzing systematically the dynamic variation of released H2 in Xiadian Fault during 1990–1996 and studying the whole data of earthquakes in the Beijing area during this period, we have found that the quantity of underground H2 release relates closely to earthquake activities. From the chart of annual frequency-magnitude of earthquake activities, the chart of H2 dynamic variation and release intensity, we have discovered that H2 release concerns with not only earthquake scale but also its frequency-magnitude. The higher earthquake scale and frequency-magnitude, the larger the released H2 quantity and its abnormal range.

In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi-empirical Green function, the period is up to 20 s. Such seismic waves can be used as a reference curve to test the strength of long period structures and their aseismic design. The long period part of seismic influence curve presented in "Architecture Aseismic Design Code" (GBJ11–89) is less than 3 s, and uncertainties exist in the effects of earthquake safety evaluation. This research will be able to eliminate these shortages.

On the basis of study results of deep sounding in the Yanqing-Huailai basin, the shallow active tectonics, palaeoseismic events, seismic activity, distribution of crustal stress field and other related data are combined to study the earthquake risk of the basin comprehensively. Meanwhile, the comparison of deep structures between the basin and some other earthquake regions such as the Xingtai area is made. It is thought that there is the background of deep structures for occurrence of moderate and strong earthquakes in the Yanqing-Huailai basin and its periphery, and the possibility for an M=7 earthquake to occur there cannot be excluded.

Based on a simplified media model of Gonghe area, the precursor characteristics of Gonghe M7.0 earthquake in 1990 are simulated in this paper by using the constitutive relationship of binary medium (solid and water). The results show that the simulated state distribution and extension variation of media are identical with the spatial and temporal distribution of reliable anomalies before Gonghe earthquake. The study also suggests that the development of the Gonghe earthquake has experienced a series of processes such as elastic deformation of large scale, early nonelastic dilatation, strain softening and elastic recovery in the neighbour region of Xining, nonelastic dilatation of high dense block near seismic source and earthquake occurrence. Therefore, it can be concluded that this earthquake development is neither a simple process for fissures developing and linking up with one another, nor a process of nonelastic volume expansion and water flowing into medium around seismic source, contrary, it is a complicated medium state changing process, and the style of such changing depends on geological structure environment of seismic source and its neighbour region. It is considered that different earthquakes are accompanied by different geological conditions, the spatial and temporal behavior of their precursors are certainly different.

The occurrence process of the Xingtai earthquake (1996) is discussed on the basis of evolution of small scale ground temperature fields on the background of large ground temperature field. It point out that the merging and strengthening of GHV is one of the basic reasons for triggering the Xingtai earthquake. It is worthy to pay attention that the earthquake precursors (for example ground temperature …) does not clear with the shorter distance from the epicenter. It is an urgent task for earthquake prediction to strengthen the supervision of some spatial-temporal continuous elements (such as G.T, geomagnetism, ground tilt field, gravity, etc.) and carry out comprehensive analysis.

With the orthogonal design and the finite element methods, the outside stresses acting on the boundary and the inside tectonic stress field before the 1911 Honghai Bay earthquake are obtained. Under these stress fields, the dislocation patterns of the faults are consistent with the observed ones. Using the softening unstabilization model for elastoplastic media to simulate the process of the earthquake occurrence, 5 moderate and strong earthquakes in these areas in this century are simulated. The results show that the moderate or strong earthquake happened only at the sections of the faults whose fault safety degree is zero. According to the present distribution of the fault safety degree, the authors predict the seismic risk zones there.

Based on the research of computer model on unified seismogenic process of grouped earthquakes in tectonic block under tectonodynamic force, some characteristics of seismic activity and some features of earthquake precursory field have been studied, including activity of grouped earthquakes, the relationship between earthquake activity and earthquake precursors, the cause of earthquake precursors and so on. By comparing research between the results of theoretical model and practical earthquake cases, some physical explanation for seismogenic process, some characteristics of earthquake activity, and the features of earthquake precursory field have been given.

Based on the observations of many years, it has been found that “small earthquake modulation windows” exist in the situation of some special geological structures, which respond sensitively to the variations of regional stress fields and the activities of earthquake swarms greater than moderate strong magnitude, and can supply some precursory information. More than two “small earthquake modulation windows” can also provide a general orientation of the first main earthquake of a earthquake cluster. Compared with “seismic window” based on frequency it is no doubt that the “modulation-window” has an unique characteristic of applicational significance to medium-term earthquake prediction with a time scale of two or three years.

In this paper, we propose the principle, methods and calculating formulas for determining the certainty factors of earthquake precursory anomaly evidences CF(E). Based on the guidebooks for earthquake prediction, we give the methods of determining the CF values of 22 evidences (including seismic gap, belt,b-value,c-value, velocity ratio, strengthen of anomalous activities, quiet of anomalous activities, seismic window, earthquake swarm, earthquake sequence, coda wave, initial motion of P wave, stress drop, geoelectricity, geomagnetism, stress, ground tilt, ground water level, radon and hydrochemistry, gravity, space environment and macroscopic anomalies), and show three examples. The purposes are to use the Expert System for Earthquake Prediction (ESEP) further.

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.

To actually reflect the seismic temporal-spatial inhomogeneity of intra continental strong earthquakes of North China in seismic hazard analysis, several seismological and geological characteristics have been selected and quantized to describe the seismicity features in time and space of every magnitude interval with the thought of dividing the interesting magnitude range into several intervals and using of spatial probability distribution function. A component analysis method with orthogonal transformation is introduced to avoid the repeated use of the same element and the subjective effects in determining the annual earthquake occurrence rates of earthquake. By passing synthetic fuzzy judgement on the nonintercorrelated new characteristics, the annual occurrence rates of every magnitude interval of each potential source area are obtained associated with the adjustments of earthquake reducing process after the occurrence ofM>7 quake. An intensity map of the Beijing-Tianjin-Zhangjiakou area is calculated as an example which shows a close coincidence with the seismic temporal-spatial inhomogeneity of North China.

Based on the cognizance of the temporal-spatial inhomogeneity of seismicity in North China, adopting the results of earthquake prediction in the past two decades and the currently used methods of seismic hazard analysis, and after some zonation trials in North China, some improvements on the zonation principle and methodology were made: 1. Seismic zones were taken as statistic units where seismicity parameters were obtained. Tendency analysis was introduced. Earthquake annual average occurrence rates were estimated corresponding to the seismicity level in the future period; 2. Average annual earthquake occurrence rates for a given magnitude interval of a specific seismic zone were assigned to potential sources considering the relative risk level among these sources. Thus, the risk of great earthquakes can be estimated. 3. The probabilistic spatial distribution function under the condition of magnitude interval was suggested to reflect the temporal and spatial inhomogeneity of seismicity. 4. An orientation function in the seismic hazard analysis model was adopted, which reflects the real condition of earthquake foci in China.