1998, 20(3):1-8.
Abstract:The fluctuation aggravation,critical slow-down and macroscopic ordering exhibited by the complex system in the fluctuation intensification stage are critical indexes before abrupt events in the modern statistical physics.The indexes are used in the short-impending prediction study of medium and strong earthquakes.The results indicate that the indexes also exist in the seismicity data in short-impending stage.To use the former two indexes can predict several possible occurrence dates of main shock and to use the latter index can determine the main shock epicenter.
ZHANG Fanmin , LI Qinghe , RONG Dailu
1998, 20(3):9-15.
Abstract:The characteristics of shear wave splitting before and after the Yongdeng MS5.8 earthquake on July 22,1995 are studied by using the digital seismic records from 1990 to 1995 of Lanzhou station in CDSN network and the several records of Langsuo station which was established jointly by China and France.The time-delays of splitting shear waves and the polarization directions of fast shear waves are determined quantitatively by using Maximum-Eigenvalue (ME) method,Wave Distinguish Factor (WDF) method and Maximum-Likelihood (ML) method.The results show that the time-delay of splitting shear waves began to increase about one year before the earthquake,the polarization direction of fast shear waves turned from NE to NW-before the event,and that the time-delay of splitting shear waves and the polarization direction of fast shear waves became normal very fast after the earthquake.The variations in the time-delay are similar to the results from Peacock (1988) and the variations in polarization direction of fast shear waves are similar to that before and after the Sunan earthquake (1990).
1998, 20(3):16-21.
Abstract:Using the analytical methods of anomaly frequency accumulation and change velocity,evolution character of ground fluid group anomalies with time before and after moderate and strong earthquakes in proper areas is studied.The results show that the ground fluid anomaly frequency accumulation curve and change velocity curve before and after earthquake exhibits three processes:stable (zero value fluctuation)-accelerating (successive positive value)-recovering (successive negative value).The changes of anomaly accelerated before earthquake.By using this method,anomaly character of ground fluid can be judged quantitatively in certain degree.The method also may be applied to judge anomaly nature of other kinds of precursory observation items.
ZHANG Suxin , WANG Jiyi , ZHENG Yunzhen
1998, 20(3):22-26.
Abstract:Characteristics of time-space evolution of dynamic pattern of radon content in groundwater are discussed. Isograms of monthly variation rate of radon content in groundwater are drawn, which is dynamic pattern of the variation rate. The result shows that anomaly characteristic region appeared around the epicenter in which variation rate of radon content is over 0.06 before the Tangshan earthquake.Area of the characteristic region expanded first and then narrowed with time, showing two stages.
JIANG Zhiping , WANG Zanjun , YAN Ying
1998, 20(3):27-32.
Abstract:Monthly departure curves of Outgoing Longwave Radiation (OLR) at the intersections of latitude and longitude in a range of 32°~40°N and 89°~105 °E from July,1989~Dec.,1996 are drawn.Analysing these curves,variation characteristics of OLR before strong earthquakes are studied.The results show anomalous variations with opposite direction or oscillation of the OLR curves appear 1~4 months before strong earthquake at the intersections around the epicenter.Anomalous intersections are distributed in the shape of the belt before some earthquakes.
CHANG Qianjun , ZHANG Yu , ZHOU Zhiyu
1998, 20(3):33-38.
Abstract:The observation data by water tube tiltmeter,quartz horizontal extensometer and quartz pendulum tiltmeter at Lanzhou deformation station during 1994-1996 are analysed.The results show that anomaly of the tidal factors of M2 wave appeared before the Yongdeng MS5.8 earthquake on July 22,1995 and the Tianzhu MS5.4 earthquake on June 1,1996.Accelerating anomalous change with rate greater after earthquake than before earthquake in tide daily average values are obvious before and after the two earthquakes.
CHEN Yuhua , ZHANG Min , ZHANG Xiaoqing , ZHU Deyu , XIAO Zhenmin
1998, 20(3):39-43.
Abstract:Seismogenic structure of the Gonghe MS7.0 earthquake on Apr.26,1990 in Qinghai province is studied by using data on geology,seismology and deformation.It is possible that the Wayuxiangka-Lagan blind thrust fault with trend of NW-NWW is the seismogenic fault for the Gonghe MS7.0 earthquake in 1990.Ground deformation by the Gonghe earthquake is fold-up-heaval mainly.Therefore,the Gonghe earthquake is a typical "blind fault-folding earthquake".
ZHANG Yuansheng , LI Qinghe , XU Guoming
1998, 20(3):44-51.
Abstract:Damped least squares method is used in combined inversion for three-dimensional crustal velocity structure and hypocenter parameters. Used data are travel-time difference between P wave and S wave, and two-dimensional velocity structure from deep seismic sounding data is regarded as restricting condition of three-dimensional velocity model. And by using earthquake data, quasi-2-D velocity profiles are constituted for building initial model. Based on travel time inversion, waveforms of several earthquakes are inverted applying genetic algorithm s. The crustal velocity model from travel time inversion result has been revised. An area of 34°~42°N and 94°~112°E is selected as research area and gathered many travel-time difference between P wave and S wave from 1986 to 1995, seven two-dimensional velocity profiles from deep seismic sounding and seismic waveform records in three components of several earthquakes from two digital stations in the area. The velocity tomographies of different sections in depth of 0~25 km are obtained, and the results are discussed.
1998, 20(3):52-58.
Abstract:Based on a research for a great number of loess landslides caused by earthquakes in the northwest China,several factors which have an effect on stability of loess landslides are analysed,especially analysing the effect of earthquake.The mechanism of loess landslides to occur and geometric feature of sliding surface in loess slope are discussed.A fundamental approach forecasting the most dangerous sliding surface in loess slope by traditional random scouting method and genetic algorithm is introduced.A new method forecasting loess landslides in a region by using scouting analysis is suggested and it is proved to be effective and practical in test of Huihui Chuan landslides.
HOU Kangming , DENG Qidong , LIU Baichi , HAN Youzhen
1998, 20(3):59-65.
Abstract:Based on calculating of numerical simulation,the reason why the length of the surface rupture caused by the 1927 Gulang MS8 earthquake is much short was further interpreted theoretically.Distribution pattern of seismic intensity,impeded processes of surface rupture,decline process of displacement vector,fault deformation and distribution characteristics of the maximum shearing stress were studied.Results show the NNW-trending faults are a kind of "barrier structure" which impeded propagation of the seismic rupture toward east and west,and resulted in a short rupture length.
SHI Yucheng , CAI Hongwei , SUN Chongshao
1998, 20(3):66-72.
Abstract:In accordance with the achievements of seismic microzonation and earthquake geotechnical engineering of cities or important engineering sites in loess areas of western China, the characteristics of wave velocity and nonlinearity of loess are summed up.In connection with the typical instance,the factors influencing on ground motion parameters for loess areas are discussed.
YUAN Zhixiang , DI Xiuling , DING Yunyu
1998, 20(3):73-78.
Abstract:The 2 051 earthquakes are relocated and their focal depths are determined by using Powell scanning method and time difference of P and S wave from earthquake data observed from 1984 to 1993 at 79 local seismic stations in the zone of 103°~113°E, 31°~39°N in Shaanxi,Shanxi, Henan, Hubei, Gansu and Ningxia provinces.The maps of distribution of present earthquake epicenters,spatial distribution of present earthquake sources,isogram distribution of average focal depths and longitudinal and latitudinal sections of focal depths of present earthquakes in and around the Weihe downfaulted basin are drawn. On the basis of above-mentioned works the regularity of spatial distribution of earthquake sources are studied. The results show that the non-uniform spatial distribution of earthquake sources in and around the Weihe downfaulted basin basically reflects the differences of seismicity level of the region and closely related to the difference of geotectonics and heterogeneity of crustal velocity structure of the region.
1998, 20(3):79-82.
Abstract:A three dimensional combination model has been put forward by means of adding an adjustment element under the fault in the combination model. The under adjustment element is composed of ductile material. It doesn't accumulate but transfers stress to the over accumulation element before earthquake,quits the boundless propagation of rupture by it's viscosity during earthquake,and controls the aftershock activity with dependence of it's deformation on time after earthquake.The acts of under adjustment element can be partly examined by creep curve of seismic fault.
1998, 20(3):83-87.
Abstract:By contrasting and studying the abnormal variation characteristics of b and C(n) values before six moderately strong earthquakes in the west China,it is found that the shape,appearance time from beginning to end,duration time,combination forms,and so on of abnormality of the two indexes can be used to predict the possible occurrence time of future event.In addition,respectively suitable ranges of the two indexes are discussed.
1998, 20(3):88-88.
Abstract:梯度——波扰效应是我们最近提出来的.其含义是:在梯度环境中,如质点有向某方向运动的趋势,则在波扰动该环境时,质点更有利于沿原来有利的方向运动.这个效应的物理机制是波动引起的后果逆于梯度和顺于梯度时是不同的.
WANG Jinbao , DAI Huaguang , DING Boyang , ZHAO Rei , ZHENG Mingjun
1998, 20(3):92-94.
Abstract:主要根据调查资料及电测深、钻探资料论述了孔家崖断裂的展布以及第四纪以来不同地质时期活动特征.早更新世以来该断裂的平均倾滑速率为0.17~0.21mm/a,全新世以来平均倾滑速率为0.2mm/a.根据该断裂的展布及活动特征对某场区的工程建设提出了一些建议.
XING Chengqi , LIANG Xiaopeng , ZHANG Jie , DONG Zhiping
1998, 20(3):95-104.
Abstract:This is a methodological research on the chronology of soil development with the view of dating active structures in the piedmont of the Yumushan mountains of the Hexi corridor,China. Based on chemical analyses of soil samples systematically collected from test pits dug on terraces of different periods and 14C and thermoluminescence dating of these terraces,the authors made a detailed study on the primary physical and chemical features of soil development in this region related to the new fault activities,as well as their evolution law with time. The quantitative relations of the content and accumulation index value of CaCO3 in soils to ages of soil development were established preliminarily. Examination and contrastive analysis show that the established formulae are applicable to the active fault dating in similar areas.
Sopyright:China Earthquake Engineering Journal