1990, 12(4):1-7.
Abstract:This paper introduces the fractal dimension into the analysis of seismic precursory sequence, discusses how the fraetal dimension of precursory sequence is determined and the minimum order parameter of the precursory sequence is determined further. Finally the authors discussed how useful information is obtained by the method of information entropy. The results show that the fractal dimension of water-level sequence(Heizi)is 1.7 and that of the crustal tilt sequence(Kuerle)is 2.1, meanwhile the three order parameters which describe the two sequences are 3. The results of information entropy show that in the range of 300km around the observation station some moderate-strong earthquakes occurred in the dropping process of entropy value.
Wu Borong , Zhu Zizheng , Yang Jianhui , Jia Dongyang
1990, 12(4):8-12.
Abstract:This paper introduces electromagnetic wave anomalies before some earthquakes observed at some observing points in Zhangye region, Gansu Province. These anomalies generally appeared a few hours, some days to more than ten days before earthquakes. The signals of electro-magnetic wave anomalies are low-frequency disturbances or continuous bidirectional strong pulses with higher frequency. The results observed show that electromagnetic wave anomaly can be regarded as a shortterm and imminent predicting index of earthquake.
He Genqiao , Chang Qiujun , Guo Yuying , Song Yulan
1990, 12(4):13-19.
Abstract:In this paper, the observational researches and results of fault gases at fixed points along some active faults since 1986 are introduced. The dynamic precursory variation of fault gases is observed before 5 earthquakes (Ms≥4.5)occurred in west Gansu Province since 1987. The dynamic precursors of fault gases before the earthquakes have following characteristics: variation range is wide; precursors immediately before events are prominent; the components of many kinds of gases change simultaneously, etc. For an about M=5 earthquake, its precursory range may reach 500 km. The authors consider that the method is suitable for monitoring immediately before event in seismic risk areas.
1990, 12(4):20-25.
Abstract:This paper deals with three synthetic fault plane solutions of weak earthquakes and P wave initial motion solutions of 23 earthquakes. It is pointed out that tension stress field with NW-NNW direction acts on Shanxi rift valley. Normal fault with dip slip and dip-strike slip are dominant.
1990, 12(4):26-29.
Abstract:This paper introduces a method calculating the relative fractal factor and has calculated the relative fractal factors(D2)of after-shock sequences of the Leipo earthquake(Ms=5.4), two Kangding earthquakes(Ms=5.2, 5.8)and the Dayi earthquake(Ms=6(1)/(4)), using this method. The D2 factors, for above mentioned four earthquakes, are 2.26982, 1.93915, 2.28738 and 1.5367 respectively. Relative coefficient and related departure of every D2 are calculated and given. The D2 factor of aftershock sequence in which the strong aftershock occurred is larger than that of aftershock sequence in which the strong aftershock did not occur.
1990, 12(4):30-35.
Abstract:In order to study the change characteristics of gouge size with fault displacement, a set of double direct shear apparatus was used in our experiments. According to the analysis of experimental results, an important fact was discovered, that is, the gouge grain size tended to a limit with the increasing fault displacement under a fixed normal stress. It was proved in this paper that the level of pressure during main fault gouge generation was obtained from the limit because there was a certain relation between the limit grain size and pressure.
1990, 12(4):36-43.
Abstract:Since 1900 the Asian intracontinental great earthquakes (M≥8.0) mainly have distributed in the three boundary zones of a vast triangle-shaped area, in addition, within this area the seismic activities are rather strong. The three boundary zones in turn are as follows: the Himalayas, the mountainous regions from Pamirs to West Mongolia, and the North-South Tectonic Belt in China. The author terms this area as the Asian Intracontinental Triangular Seismic Area (AITSA).
Based on the characteristics of the lithosphere thickness, the values of Vpn, the distribution of the upper mantle density, the isostatic gravity anomalies, the crustal structure, recent tectonic movement and seismic activities, the author infers preliminarily that, under the action of the gravity force, beneath AITSA there exists multi-diapirism from asthenosphere. Owing to this process of the upper mantle materials, the thinning of the lithosphere as result of erosion and the thickening of the crust clue to accretion may take place. the thickened crust is in a state of gravitational instability, resulting in the crustal materials flow, which controls the recent tectonic movements and the seismic activities within the crust.
According to this paper, the gravity may be the major one of the un-negligible tectonic driving forces in the AITSA.
Yao Zhengsheng , Wang Xiuqiong , Tang Kunling
1990, 12(4):44-48.
Abstract:The internal medium of the earth plays an important role in earth-quake process. In this paper we discuss the medium difference between the hypocenter and its surroundings based on the rigid features of the earth internal medium, and point out that the difference can be detected by seismic tomography. With some examples, we show that the seismic tomography can be used in determination of potential hypocenter.
Zhan Zhijia , Gao Jintian , Guo Qihua , Hu Rongsheng , Zhang Hongli , Zhao Congli , Shen Wenzhi
1990, 12(4):49-54.
Abstract:To search for the obvious noise of geomagnetic interference occurred near the Beijing observatory round about March of 1988, we set up 8 sites in Sujiatuo-Wolonggang area. The special experimental observation of the geomagnetic interference noise was carried out with the model G-816 and G-826 proton precession magnetometers. The results show that the geomagnetic interference noise mainly originated from the electromagnetic interference in the Xiangshan region, and subsequently from the subway in the Beijing City. The geomagnetic inter-ference noise occurred at 06h-23h (the Beijing time)each day. Its dominant spectrum is at short-period(T=2-4m). The method of the observation and research in this paper has practical application value for monitoring the environmental condition of geomagnetic observatory (site) and for correcting the contaminated data of geomagnetic field.
1990, 12(4):55-59.
Abstract:In this paper, we make a numerical and simulant calculation of coupled stress and rock strength weakening caused by water seeping after reservoir impounding, using the theory of two-phase porous medium. The results show that due to water seeping, pore pressure in rock increases and coupled stress decraeses, so the effective stress in rock decreases and the shear strength should decrease. The decreasing increment is comparable to the value of the shear stress drop on seismic fault surface. Finally, some possible mechanisms about reservoir earthquake caused by water seeping are discussed.
1990, 12(4):60-68.
Abstract:The dynamic shear modulus and damping ratio are important parameters in earthquake engineering and other dynamic analyses. In this paper, the experimental research on dynamic shear modulus and damping ratio of loess with the DJC-240 triaxial test apparatus was introduced by statistic method and the accuracy of the parameters was improved. The revisionary formula for calculating dynamic shear modulus based on physical properties of soil was presented. The authors have pointed out the obvious influence of damping ratio due to different consolidation ratio and consolidation pressure. The essential correlation between damping ratio and the construction of loess was found.
1990, 12(4):69-75.
Abstract:This paper deals with the application of deformation simulations and gravity analogy in the study of characteristic formation of graben system in the western part of North China. Experiments disclose that principal stress of the modern tectonic stress field of these graben systems is NEE-SW horizontal compression, and it is accompanied by additional vertically uplifting force from the lower crust and the upper mantle. The experimental results have confirmed that these graben systems are formed mainly due to the occurrences of tensile stress and shear stress on the axis of upheaval region of round edge of the Erdos block.
In this paper, the seismicity here is analysed and studied, and the relation between the formation of graben system and seismicity is simulated using model experiment of laser holography photoelasticity.
1990, 12(4):76-79.
Abstract:In this paper, a computer program for determining near earthquake time and space parameters is designed, on the basis of memory gradient method for unconstrained optimization. As long as the computer gets the recorded data from more than three stations, it can run. The recorded major phases(P, S, Pn, Sn) all can be used in the program. The program is applicable to determine the parameters of near earthquake in or out of the network of stations. Even if the earthquake is far from the network, the precision of the results determined with this program is not lower than that with the method of intersection.
1990, 12(4):80-83.
Abstract:With the movement of Indian plate northward in the swaying way, a pair of rotational shear belts formed in front of Pamir arc and Asam arc, which are two projecting points of Indian plate. And M≥7 strong earthquakes occur alternately from one belt to another in period of every 90 years.
After a swaying movement, due to the elastic reaction of Himalayan arc, a moderate strong earthquake zone causally formed in the middle of Qinghai-Xizang plateau adjacent to 90°E, at the both sides of the vertical line to Himalayan arc.
1990, 12(4):84-87.
Abstract:然界是一个复杂的有序的整体系统。在这个系统中各个部分彼此关联。近几年发展起来的系统科学中的新三论,即突变理论、耗散理论和协同论(包括混沌动力学和分数维理论),正是人们对自然界的整体性认识的重要进展。
1990, 12(4):88-92.
Abstract:近年来,在我国西部地震活动水平明显增强的形势下,河西走廊地区开始出现中强地震活动。如1980年肃北5.9级地震及1986年青海门源北6.4级地震等。
1990, 12(4):93-94.
Abstract:近年来,不少专家、学者都在探讨震群与大地震的关系。有人认为霍山震群是预报华北强震的“窗口”。但是作者研究认为,霍山震群活动与华东地区发生的强震有较好的对应关系。
Li Liuyu , Jin Ming , Jiang Xuyuan
1990, 12(4):95-96.
Abstract:波速比和振幅比的变化都是孕震区介质性质的变化引起的,因此研究它们的变化特征对于地震预报具有一定的意义。但是目前人们仅限于用小尺度样品研究它们的变化特征,用大尺度样品研究较少。为此,我们对大尺度混凝土样品中波速比和振幅比的变化特征进行了实验研究。
1990, 12(4):97-99.
Abstract:带头地震是异年倍九律时间系列中的头一个地震,其震级较大。在它发生后几百年内附近200-300公里范围的6级和6级以上地震与它的发生日期往往呈倍九天的关系,其月份范围在带头地震发生日期前后2-3个月内。已发现的带头地震有1679年三河平谷大震,1668年郎城大震,1624年扬州大震,1604年泉州东大震。另外还发现在中国西部也有不少带头地震。带头地震和随后的被带地震其间的倍九律关系可能是具有倍九天可公度的外因调制地下过程的结果。在前兆观测的基础上用带头地震有助于选择发震日期。
Sopyright:China Earthquake Engineering Journal