2009, 31(2):103-109.
Abstract:The quasi-analytical method is a fast way used to solve integration equations about electromagnetic scattering problems, and is applicable to the strong scattering or large perturbation problems. In this paper the tensor quasi-analytical method for anomalous electric field which was introduced by Sun in 2005, is applied to the D. C. electrical field. The tensor quasi-analytical method about the anomalous spherite in the uniform field is studied, and the models which are approaching the reality are selected. The anomalous electric field caused by anomalous cube in the uniform field is calculated also. It is proved that the results is good and the method is precisional with high speed. It paves way for the quasi-analytical method using in forward and inverse modelings of 3D D.C. electrical field.
ZENG?Jin-yan , LI?Zi-hong , CHEN?Wen
2009, 31(2):110-114.
Abstract:The input parameters of bedrock includes depths of rock interface, rock shear wave velocity, earthquake motion intensity and so on. Through analyzing the result of site earthquake response that gained by selecting different rock interface depths, shear wave velocities and earthquake motion intensities, the conclusion is obtained: with different input parameters of bedrock, the peak values of acceleration and spectra of acceleration on the ground surface have great differences.
GAO?Guang-yun , PENG?Zheng-guang , ZHANG?Meng-fang , YANG?Cheng-bin
2009, 31(2):115-120.
Abstract:Thin layered method (TLM) is very efficient to study the wave propagation in layered media, and boundary element method (BEM) is very precise to solve infinite domain problems. After combining the advantages of two methods, the semi-analytical BEM model is erected by TLM based on the second shape function, on which the Green function is as fundamental solution of stratified half-space. This model can be effectively used to analyze the dynamic soil-structure interactions in layered ground. The effectiveness of passive vibration isolation by open trench in upper soft-layer and lower stiff-layer visco-elastic foundations is analyzed in detail. The results show that (1) in layered soils the deeper trenches are required to obtain the same effectiveness with screening isolation in homogeneous soils (soft-layer and lower stiff-layer in half-plane), and the amplitude reduction curve is obviously vibrated, (2) if the normalized depth of topsoil is less than 1.0, the normalized depth of open trenches should be greater than 1.3 in order to provide satisfactory screening effectiveness, (3) if normalized depth of topsoil is greater than or equal to 1.0 and less than or equal to 2.0, the normalized depth of open trenches should be greater than 1.8.
YUAN?Bing-xiang , CHEN?Wen-wu , LIANG?Shou-yun , LI?Jin-cheng
2009, 31(2):121-125.
Abstract:The Qinghai-Tibet Railway intersects with many active fault belts distributed on Qinghai-Tibet plateau. In this paper, the distribution laws of 29 active fault belts along the railway and geological hazards caused by the faults are studied. Through analysing the characteristics of geological hazards such as collapse, landslide, debris flow, and tipical sections of the route line, some principles for geological route selection in fracture zones are summurized as follows: the route should be arranged to pass across active fault segment with weaker activities and narrower width of the belt in right angle or higher angle, avoid as could as possible to build large and medium-size bridge, high bridge, tunnel, high-filling, deep-dugging which are difficult to be repaird after dammage. It has been proved that these principles are right and feasible for avoid or pass the active fault belts, and can be used in rebuild of Qinghai-Tibet Railway or other railway project.
WANG?Heng-zhi , SHI?Yu-cheng , LU?Yu-xia , LIU?Kun , QIU?Guo-rong
2009, 31(2):126-130.
Abstract:The target spectral fitting method is used to synthesize time-history of ground motion. The soil seismic response is analyzed by quantitalively changing the parameters of envelope, which could influence the site response in the process of artificial fitting ground motion time-history. In order to provide the basis for site fortification against earthquake, the influences of the time-history parameters are discussed. The results show that, when t1,t2 and c taking different values, the soil seismic response are greatly affected by the fitting ground motion time-history, and the influence degree is closely related to the soil structure.
SUN?Li-jian , ZHU?Yuan-qing , YIN?Ji-yao
2009, 31(2):131-135.
Abstract:Geostress measurement is a direct and effective way to get initial geostress. But initial geostress is disturbed in drilling, it exists the phenomenon of stress relief and stress redistributing after drilling, that makes the measuring value different from the actual value of the initial geostress. In this paper, the process of geostress measurement in borehole is simulated by using finite element method, the effects of rock property, stress border and fractures on geostress changes are studied, and the sensitive factors to initial geostress changes are summarized.
LIANG?Ming-jian , YUAN?Dao-yang , WANG?Ai-guo
2009, 31(2):136-141.
Abstract:Jiuxi basin, a compressional basin in western segment of Hexi Corridor, had developed several late Quaternary reverse faults and fold zones, and is a potential seismic source of strong earthquake in future. In this paper, taking Yumen potential seismic source zone as an example, the long-term seismic activity levels of 9 potential seismic sources near Jiuxi basin are compared. It is found that seismic activities of seismic sources in same magnitude grades are nearly in the same level respectively. Basing on the result, it is feasible that determination of the upper-bound magnitude of Yumen potential source is Ms7. 0. So, comparing seismic activities level in long term is a auxiliary measure for determination of potential seismic source zone.
HE?Li-jun , SHI?Yu-cheng , YANG?Hui-lin , HU?Ming-qing , XIN?Hai-liang
2009, 31(2):142-147.
Abstract:Two typical loess slopes along with highway in Gansu province are selected as research object. Using the finite element method, the stability of slopes with and without supports influenced by different ground motion are studied, and the efficiency Of supports to protect the slope body is analyzed as well. Results of calculation indicate that the safety coefficient reduces with increase of seismic peak acceleration, and the stability of slope depresses obviously. The supports for slope not only improve the stability of loess slope, but also enhance the aseismic behavior of slope for the design of support strength on the loess slop, it should be based on the maximum intensity of local ground motion, in order to advance the efficiency of the supports.
2009, 31(2):148-151.
Abstract:Up to now the fitting method used in seismic exploration technology is still 2-D method. In this paper, the 3-D seismic data are fitted by using the orthogonal polynomials and corehences of seismic data, with the method we can make full use of 3-D seismic data and improve the data processing efficiency.
2009, 31(2):152-156.
Abstract:Under the same geologicai environment, both slopes in a valley slide face-to-face, it could be called as "opposite-slide" landslide. In this paper taking the landslide in Yanjiagou valley of Zichang county, Shaanxi province, as example, the formation environment, development patterns, causes, mechanisms and the late evolution of deformation for the "opposite-slide" landslide are discussed. Based on the result for large number of " opposite-slide" landslids in northern Shaanxi province, some prevention countermeasures are put forword.
ZHANG?Jing-shu , GAN?Dan , MO?Yong , WANG?Er-chang , DUAN?Hui-jing
2009, 31(2):157-160.
Abstract:The analysis on the corner-overlap plane for frame structure tall building ,which is one of design not good for earthquake resistant, is maken. The result shows that the smaller the proportion of corner-overlap is, the less torsional rigidity of structure is, and the more torsional influence is. More stress concentrated on the corner-overlap floor in earthquake will cause serious deformation and fissures easily. In extra-limit determining, the corner-overlap plane should be considered as one of three or more extra-limit controling factors for unregular high building, but not be considered alone.
LI?Bao-kun , DIAO?Gui-ling , Avi?SHAPIRA , FENG?Xiao-dong
2009, 31(2):161-166.
Abstract:Comparison of the seismic sequences between Tonghai earthquake in 1970 and the Tangshan earthquake in 1976 indicates that the attenuation, number, intensity of aftershocks and shape of epicenter areas were different. In this paper, an interpretation is proposed that aftershocks reflect the adjustment process of the medium in seismic source after severe fracture. If the radio(a/b) from major axis length a and minor axis length b of the aftershock epicenter area is large, it implies the source volume being near to a plane and the adjustment process at the plane should be simple, so the aftershock attenuation is faster and strong aftershocks are less. In opposite case, with small a/b, the source volume is near to a cubic and the adjustment process is more complicated, so the aftershock attenuation is slower and strong aftershocks are more and stronger. It can be attempted to use the parameter a/b to estimate quickly that it the stronger aftershocks will be more or not, and the aftershock attenuation will be slow or not for the case that the aftershocks can be located immediately after the mainshock.
GAO?Shu-de , DU?Xue-bin , SU?Yong-gan , GAO?Yuan , PU?Xiao-wu , WANG?Jun-yan , YE?Yuan-yuan , CHEN?Yan-ping , MEI?Dong-lin , DI?Guo-rong , YANG?Fei
2009, 31(2):167-173.
Abstract:Wudu seismic station is located in the boundary area between Gansu and Sichuan provinces. From 2003 to May 2008, before four moderate-strong earthquakes in this area, the observation data from Wudu station had significant precursor anomalies. It mainly showed as follows: the tensile stress in NS direction had been sustained increasing from 2001 to 2005, then turned to compression in four directions in 2007, and repidly increased. After this high-pressure stress kept seven months, the Wenchuang M8.0 earthquake occurred. The earth resistivity data showed the long trend of acceleration and changing, with increasing, descending etc. anomalies in a year scale. The annual variation ratio of the anistropic index S is two times in earthquake occurring years (anomaly years) than in quiet years. The variation of natural electric field had likeness, repeatability and similarity in imminent earthquake period.
LIU?Dai-qin , WANG?Xiao-qiang , LI?Jie , ZHU?Zhi-guo , FANG?Wei
2009, 31(2):174-178.
Abstract:Through analysing the mobile gravity measurement dada of last 8 times from 2005 to 2008 in Southern Tianshan area, Xinjiang Region, the spatial and temporal dynamic evolution characteristics of gravity field in this area are studied, the information related with seismisity is extracted, and relationship among the variation of gravity field, tectonic activity and seismic activity are discussed also. The result shows that the changes of gravitational field relate to the changes of tectonic environment. In the earthquake pregnant stage, some regional anomalies of gravity appear in a certain range. Earthquake often occurres near the zero line of gravity contours.
LUO?Guo-fu , ZHAO?Wei-ming , SHENG?Ju-qin , Ma?He-qing
2009, 31(2):179-185.
Abstract:The seismicity anomaly before strong and moderate-strong earthquakes in northern Qinghai--Tibet Plateau is common and credible, it is summarized and analyzed systematically in this paper. It is found that the precursor anomaly parameters of small and moderate earthquake activities before main-shock have a classificational characteristic relationship with the magnitude of main-shock. The result provides practicality and reference to earthquake prediction for this regione.
ZHA?Ling-yun , ZHANG?Hui , LIU?Xiao-feng
2009, 31(2):186-190.
Abstract:Since 2001, small -moderate seismicity has been increasing obviously in Pingliang area, Gansu province. In this paper, the focal depths are definited by the locating method based on genetic algorithm, the focal mechanism is calculated by the moment tensor inversion. According to seismic spatio-temporal distribution, seismic phase and regional geological structural environment, it is considered that the earthquakes in Pingliang area are mainly mining-induced earthquakes, and the kinds of initial mechanism are coal body compression, work face stretching and fault rockburst.
LI?Xing-jian , XU?Yu-hong , CHEN?Jian-jun , LI?Dong-sheng , LIU?Xiao-ming , WU?Yin , YIN?Liang
2009, 31(2):191-195.
Abstract:Using the Sato single scattering model, based on the near-field digital seismic records from Shandan seismic station of telemetry network of Gansu province, the change characteristics of coda Qc values of Minle--Shandan earthquake sequence, Gansu peovince, in 2003, are studied with loss time of 60 s. The relationship between the Qc values and frequency is obtained. For different center frequency points, the change from of Qc values are different. In develop stage of the frequency, Qc values changed with great fluctuations, and in early and late stages, the changes were weak.
NIE?Yong-an , YAO?Lan-yu , ZHAO?Guo-min
2009, 31(2):196-200.
Abstract:By investigating the various macro abnormal phenomena mainly before Haicheng earthquake in 1975, it is deduced that there are many rifts of different size underground in epicentral region before a great earthquake. These rifts can be found on the surface sometimes. Under the sustainable action of tectonic stress field, the expansion, dislocation and joint within or between these rifts will produce new rifts with greater size. The seismic fault, which was seen after the main shock, is the result of the last expansion, dislocation and joint of the rifts along the fault before the main shock. It is the expansion of these rifts and hot fluid moving up along them cause the various forms of macro abnormal phenomena before a great earthquake.
2009, 31(2):201-206.
Abstract:Through the analysis on type of earthquake and rupture features of Wenchuan Ms8.0 earthquake, the relationship of seismic activties between Longmenshan fault zone and Gansu province is discussed. Meanwhile the dynamic tracing process to Wenchuan earthquake sequence and how successfully predicting the aftershock activity in Gansu province are reviewed. Based on above, it is considered that we should obtain more physical informations from the process of earthquake pregnancy-developing-occurrence, and change the present earthquake prediction model which mainly depend on experience and statistics to a new model of physical earthquake prediction.
Sopyright:China Earthquake Engineering Journal