Abstract:There were three strong earthquakes to occur from July 12, 1995 to February 3, 1996 in the Yunnan province and its vicinity. These earthquakes formed a phenomenon of successive occurrence of multiple events. In this case, it is necessary that the precursor fields are formed by every earthquake to superpose mutually. The mixture precursor fields may be separated by the hierarchy method. And principle of separating mixture precursor fields is discussed. The results are following :(1)When precursors of different hierarchy of every earthquake meet each other, its synthetic amplitude becomes very big due to superposition. (2)When the appearing times of precursor of different hierarchy of every earthquake are near, the group of jump-like precursor appeared. (3)If an strong earthquake not only has obvious precursor, but also has obvious precursor-like after the earthquake, there will be other strong earthquakes to occur in the near future time. (4)If in the later period of the multiple source system, the anomalies muchmore become weak, it means that procedure of generating earthquake of the multiple source system is going to end

Abstract:According to the theory of greatest entropy, it is found that the most probable distribution of magnitude and interval time of earthquake are Weibull distribution. Using of K-S test and histogram test, actual seismic date about magnitude and interval time of earthquake of Tianzhu region, Gansu province from 1970 to 1990 are inspected with three models. The result obtained is identical with that by the theory.

Abstract:By using the single-link cluster method, precursor clustering features in time-space of the Tangshan and Datong earthquakes are studied. Time-space scanning to information entropy, average link length of the SLC frame and accumulation slide frequency of precursors of the two earthquakes is made. The results show that anomalies of the SLC frame before the earthquakes are very obvious, and can be divided into five periods. The anomalous magnitude is the largest from June, 1975 to June, 1976 (fourth period). The information entropy drops further, change of average link length is the same with that in the fourth period and accumulation slide frequency of the precursors increases one month before the earthquakes (fifth period).The change period of anomalies may be taken for the judging index of middle or short term prediction of earthquakes. Change process of information entropy from outside to area of coming earthquake epicenter may be used to judge the range of earthquake danger area.

Abstract:Seismicity feature of different scaled rectangles of Central-America and Beijing region is analyzed to study the hierarchical characteristic of spatial distribution of earthquakes. The result shows that the spatial distribution is hierarchical and scale-invariant. When the studied area is roughly divided into four small regions, the ratio between the number of earthquakes of the small region of which seismicity is high and the number of small region of which seismicity is low is 4 ～ 5. The earthquake distribution of smaller regions divided further possesses the same regularity. And this hierarchy is independent on time and magnitude. The hierarchy of crustal structure is the possible reason for the hierarchy of the earthquake spatial distribution.

Abstract:On the basis of data of 30 observation wells for the dynamic of groundwater and oil from 1973 to 1978, evolving process of anomalies of groundwater and oil dynamic before and after the Tangshan 7.8 earthquake is analyzed and studied. The results show the evolving process can be divided into four stages. The anomalies arise first in near epicentral area and then anomalous areas spread outward, showing several concentration point of anomaly. In middle-short stage, anomalous areas clearly contract and migrate from outer-ring to epicentral area. In the imminent stage, an anomalous concentration area with high value is formed in the epicentral area.

Abstract:The short-term and imminent earthquake prediction is the major difficult problem on earthquake prediction. It is dependent on good precursory measures and data processing method. Based on the viewpoint of the weak precursor information and by using the method for getting the information, the data observed from 31 stations or observation items such as radon in groundwater, water level, earth resistivity and ground stress in Gansu, Qinghai, Ningxia, Shaanxi are processed. The results show that there are weak precursor informations on about sixty five percent of the stations or items before the Gonghe M_S7.0 and Jingtai M_S6.2 earthquakes. It is quite evident that the method has higher capacity for distinguishing anomalies than other ways.

Abstract:Yueliangshan fault is the east segment of Haiyuan fault zone. The fault had ruptured during the Haiyuan M_S8. 5 earthquake in 1920. The recurrence behavior of palaeoearthquakes haven't been studied on the Yueliangshan fault. The preliminary study shows that there may be five palaeoearthquakes to occur on the fault at the early and late Holocene. The Haiyuan fault zone has the property of grade rupture. After studying the palaeoearthquake recurrence behavior of the whole fault zone, it is possible to determine whether the Yueliangshan fault is an independent rupture segment or a secondary segment influenced by other rupture segment.

Abstract:Model of artificial neural network (ANN)for evaluation of slope stability is established based on the basic principle of artificial neural network. The BP model adopted in this paper is studied and tested by choosing real examples of 70 slopes in Sichuan and Yunnan areas as studying samples. It is proved that the error back-propagation (BP)algorithm is advanced and the prediction model is accurate and useful in practice, for it is a new effective method.

Abstract:A new method for analysis of slop stability to earthquake is presented. The method combines finite element method (FEM)with traditional slip surface method, and is divided into two steps: first, based on the FEM, the effective stresses in slop are determined by solving dynamic equilibrium equation at some time; second, determining the most dangerous slip surface and its factor of safety at this time by using the effective stresses calculated in the preceding step. The method not only can consider behavior of stressstrain of soil, but also can determine the most dangerous slip surface and its factor of safety at any time. The detailed algorithm of the method is also given.

Abstract:The methods, technology and the applied range of shear wave exploration are summarized. The importance of shear wave exploration in engineering seismology and engineering geophysics is pointed out. According to need of actual works, some improvement measures are proposed for the problems of some methods. The applied effects of various methods are introduced through actual examples. The results show that the methods are practical and effective in the exploration.

Abstract:The real process of digital measure of radon is simulated by flow through radon gas source. The experimental study on the instrument standardization and each procedure of digital measure of radon is made. It was found that count rate reduces while gas flowing rate increases. This fact can be explained by the lasting time of gas in the scintillation chamber. Some conclusions are drawn: instrument of the digital measure of radon must be standardized and only standardized by flow through radon gas source; gas flux of entering the scintillation chamber should be controlled or measured in the process of digital measure of radon. In addition, the radio contamination in scintillation chamber is analyzed.

Abstract:Dynamic change of regional stress field before and after the Datong-Yanggao earthquake is inverted by using data of well water level. In the inversion, the method inverting stress change in water bearing system in reference [1] is used. The results show that the zero value line of stress field crosses epicentral regions of the Datong M_S6.1 and M_S5.8 earthquakes. The stress field of periphery of the epicentral region transformed from positive stress into negative stress, and the value of the positive stress increased gradually before the earthquakes. After the earthquakes, the stress field is slow in change.

Abstract:The deep environment of strong earthquake preparation in the region of Gansu, Ningxia and Qinghai is analyzed and discussed based on more than two hundred MT measurement data and six artificial seismic sounding profiles, combined with gravitational and geothermal fluid observation data. It is suggested that strong earthquakes often develop and prepare in the top of thick lower resistivity layer, above the lower velocity layer and in the media with dramatic lateral variation electrically and mechanically. The nature of these conditions implies that under the affects of stress, the easiest place for stress concentration is the place where vertical and horizontal deformations of crust layers are inconsistent.

Abstract:The 9 years gravity informations measured from 1991 to 1999 in Lanzhou-Wudu-Tianshui area are analyzed and compared. The relationship of gravity with the Yongdeng M_S5.8 earthquake on July 22, 1995 and Tanchang M_S3.9 earthquake on Nov. 18, 1998 is discussed by considering geologic structures. The results show that there were obvious gravity changes near the epicenters before and after the two earthquakes.

Abstract:On the basis of magnetotelluric sounding practice in northwestern China since many years, arrangement condition of observation point is discussed from observation instrument, topography and interference factor. The arrangement pattern of electrode in field observation is analysed. Analysing the difference between observation data in mountain area and that in basin, some suggestions on arrangement condition of the observation points are made. The data disturbed by electromagnetic noises of two observation points are showed. Observing effect at the point which is reselected distant from interference source is better. It is considered if frequency of interference signal is close to that of magnetotelluric sounding signal, it will be difficult for instrument to restrain the interferences by oneself because resistance of the instrument to interferences is limited.

Abstract:A detailed analysis on development process of regulated current supplies in earth resistivity measuring system is made. Technical indices and function of 2A, WL-5 and WL-5N regulated current supplies are evaluated. Detailed analysis and discussion on some technical problems in further development of the supplies are made. It is believed that the technique of high frequency switching supply ought to be applied in design of regulated current supply for measurement of earth resistivity. A main circuit of high frequency switching regulated current supply is given.

Abstract:On the basis of studies of predecessors, a new method--providing current in varying period is proposed. Basic principle of the method and its use in Terrameter are analyzed. Effect of removing stochastic error of the method is simulated by the test in laboratory and computer. The results show that the method is better in removing stochastic error.

Abstract:Data of artificial earthquake sounding, interpretation of gravity, geology, aeromagnetic detection, telluric electromagnetic sounding, seismic activity and geochemistry are used to study relationship between the 1920 Haiyuan M_S8. 6 earthquake and geologic structure. The result shows that the Haiyuan fault is an overlap fold-fault taking the shape of the shovel with depth less than 10 km, which bears no relation to occurrence of the 1920 Haiyuan earthquake because the focal depth of the earthquake is 15 ～ 20 km.The Haiyuan earthquake relates to both NS and EW structures extending to the top of the asthenosphere and the movement of the material of the asthenosphere. The ground deformation of all kinds along the Haiyuan fault are induced by the earthquake.

Abstract:The conception and the significance of the soil structure are presented. The history of soil structure study is retrospected and the classification of the approach to quantitatively express the soil structure is made. On the basis of analysis of the domestic and foreign status quo of the study, it is proposed that the soil mechanics method is the most actual and effective for quantitative study of the soil structure.