1989, 11(4):1-13.
Abstract:From the point of view statistic physics and the renormalization group method, we studied the rupturing of a 1-D and a 2-D focal body, after the stress accumulation of the stress accumulation element in the combination model was into the nonlinear period. The critical value of the rupturing probability of the focal bodies is 0.2063, 0.1707 respectively. Using the rupturing critical value of the 2-D focal body, we got the critical ratio of the gap energy to the reference energy is 0.1872 for a seismic gap. The value 0.1872 was examined using ten seismic gaps from 1967 to 1980 and the seismic gaps (starting magnitude: ML=2, 3) from 1982 to 1986 in the eastern part of China. The results are satisfactory.
1989, 11(4):14-24.
Abstract:Fluctuation aggravation is a kind of critical phenomenon before suddenly phase cnange. In this paper we discuss premonitory fluctuation aggravation before strong earthquake at this point, such as small earthquake frequency, underground fluid, gas and earth stress and so on. The preliminary conclusions are as followss:
1. Before strong earthquake, the space distribution of small earthquakes which exceed average day active level in a large area is of the orderliness-the active belts of small earthquakes pass through the coming strong earthquake area. The intersecting area of two belts is the site of coming strong earthquake.
2. Before strong earthquake, most of the high frequency day of small earthquakes synchronize the time of the external causes, the external causes that are found at present include syzygy, solar term, magnetic storm exceeding middle level, and atmosphere pressure fall and so on. This kind of high frequency activity of small earthquakes usually appears a month or a day before the coming strong earthquakes.
3. The time of the premonitory fluctuation and the time of small earthquake frequency fluctuation are approximately synchronization, there are relations between them in the cause of formation.
Impending prediction indexes of earthquake as stated here are not only applicable to the many foreshork area, but also to few foreshork area. Because there are many times of premonitory fluctuation before strong earthquake, it is not possible to completely eliminate false for the time prediction of the strong earthquake.
1989, 11(4):25-36.
Abstract:In this paper, according to the geological structure, geomorphic feacture and the characteristics of seismic activity, the author: divided the loess region of the Northwest China into four subregions and studied their attenuation laws of seismic ground motion. The results show that the attenuation rate of intensity as well as seismic ground motion becomes slower from the western region to the eastern region with the increasing of the thickness of soil stratum. Before statistical analysis, the authors made linear interpolation of isoseismic contours to consider the uncertainty of attenuation. The authors also put forward a new thought, that is, using the Q value to adjust the parameters of attenuation law of seismic ground motion.
Lin Changyou , Wu Yuxia , Liu Xiaoling
1989, 11(4):37-45.
Abstract:In this paper, the conductive mechanism in situ of the high-resistive layer which is 10-25 km in the crust is discussed. It is indicated that the conductivity of the rock block in the layer mainly depends On the crack-porosity behaviour and distribution of porous water in it. Using the theory and numerical modeling of conductivity of partial melt, we can see that when the connection weight factor increases, the volume conductivity in situ of the layer sharply decreases. Analysing the characters of the strain with porous water in and around the focal region, we illustrate the precursory regionalization of the deep electrical change which probably appears during earthquake readiness, explain the characters of the regional volume resistivity and conductivity anistropy change, preliminarily diccuss the physical mechanism of the electrical change, and roughly estimate the possible values.
Shi Telin , Guo Daqing , Guo Xinduo , Liu Weihe , Yang Yuheng , Xiao Lizhu
1989, 11(4):46-54.
Abstract:The features of seismicity in the north area of Qinghai-Tibet Plateau are obtained:
(1) The active period of earthquake is about 230-250 years long, the tranquil period is about 130 to 150 years long.
(2) The seismicity has a relation to the seismic activity in the south area and the south edge of the Himalayas. After stronger earthquakes occurred in the south area of the Himalayas and the north area of Burma, there would be stronger earthquakes to occur in these areas with probability 87.5% and 66.7%, respectively.
(3) The earthquakes with M≥7 took place alternatively in several seismic zones. The first two earthquakes with M=6 would point out the furture location of next earthquake with M≥7.
(4) The medium earthquakes were not in active before the earthquakes whth M≥8, but were active before the earthquakes with M≥7. Generally, the medium earthquakes happen in north and west parts of Qinghai and southeast part of Gansu or in the edge of Gansu and Sichuan before the earthquakes with magnitude about 7.
According to above results, there may be an earthquake with M≥7 in the north area of Qinghai-Tibet Plateau in coming 10 years.
Li Jianguo , Shi Guimei , Wang Shengzu
1989, 11(4):55-63.
Abstract:The rupture process and instability mode of step-like asperity located on sliding plane in granite specimen were studied under triaxial compression at confining pressures of 300-500 MPa. The main experimental results are as follows:
when differential stress (σ1-σ3) reaches 0.15-0.17 (σ1-σ3)c, where(σ1-σ3)c is the peak stress level of the first event of stickslip, macroscopic fracture takes place along the base of step-like asperity and the linear relation between stress and displacement is kept; with increasing stress level fracture propagates and cuts through the original asperity at (σ1-σ3)≥0.3(σ1-σ3)c, and in the meanwhile, some new lower asperities are formed; as (σ1-σ3)≈(σ1-σ3)c, the sliding plane originally with asperity has been flattened relatively, and after that, the sudden instability with large stress drop and violent shock occurs.
The results indicate that the failure of asperity can only cause micro-or fore-shocks and acoustic emission, and the main shock of earthquake is induced by stick-slip along a flattened fault zone. In other words, the mechanism of strong earthquake is not the fracturing of asperities, but the unstable sliding along relatively flatten fault zone.
1989, 11(4):64-70.
Abstract:In this paper, 16 items of 4 factors used in distinguishing magnitude interval related to maximum event that might happen every year are chosen, and the earthquake sequences of Ms≥4.0 (in exception of aftershock) occurred in North China from 1960 to 1986 are dealt with. Fuzzy relation equation of magnitude decision containing 3 magnitude intervals, Ms≤6.0, 6.0
Gui Xietai , Guan Huaping , Dai Jing'an
1989, 11(4):71-75.
Abstract:This paper introduces the observations at Changii, Hebei Province and Wudu, Gansu Province geoelectric stations (△≤100km) for two major earthquakes (Tangshan earthquake on July 28, 1976 and Songpan earthquake on August 16, 1976). The results of short-term and imme diate precursors were carefully checked and compared with each other. We got a similar precursory phenomenon which was not contingency. The similarity suggests that the similar anomalous phenomenon is objective; the electrical method (apparent resistivlty) is a hopeful methodfor earthquake prediction.
1989, 11(4):76-82.
Abstract:In this paper, we have discussed the temporal-spatial distribution of seismicity, "window effect" of stress field and the feature for small in magnitude but high in intensity in Hechi region, Guangxi. A qualitative interpretation for the mechanism of earthquakes occurred in this region has been done using some results of rock experiment.
The region is situated in two intersecting faults and it is sensitive to stress. The research result shows that the seismicity attributed to stick slip of existing fracture under low stress in very inhomogeneous medium. Special geological setting can not compose a condition preparating great earthquakes and the seismicity can not constitute a threat to Longtan reservior region nearby.
Zhao Congjun , Zhang Jian , Shen Hao , Tian Xiaoyan
1989, 11(4):83-90.
Abstract:Based on the splaying features of surface structure, the background of gravity field and magnetic field, and the basement structure features from aeromagnetic survey, the crustal structure, tectonic stress field and potential focal region in the southern Sichuan Basin and the adjacent areas of Yunnan and Guizhou provinces are discussed. The results show that the tectonic stress field of these areas is of multidirectivity and multiperiodicity. In Palaeozoic era the direction of principal compression stress was about SN, and now about EW. The deep fault activity in EW is not obvious, only has a few of microearthquakes. But the areas Which EW deep faults intersect other direc tional faults often occur earthquakes. And the areas which the basements, of different rock feature border on are also the seismic prone areas.
Sun Chengde , Wang Bangben , Liu Yonglan
1989, 11(4):91-94.
Abstract:笔者通过对大量地电资料的分析,发现深埋电极进行地电观测,能够排除表层干扰,突出地震异常。本文利用深埋电极的地电观测资料,总结了1983年菏泽5.9级地震前地电异常特征。
1989, 11(4):95-100.
Abstract:根据自由振荡理论,质量负荷作用下的地球形变平衡方程[1]形式为。
Xu Yongjian , Li Anran , Han Xiaoguang
1989, 11(4):101-104.
Abstract:丹江口水库自1967年11月开始蓄水。1970年1月起,库区一些特殊地段开始出现了明显的地震活动,并分别于1972年4月3日和1973年11月29日发生了林茂山3.5级(Ms)地震和宋湾4.7级(Ms)震群活动。
1989, 11(4):105-116.
Abstract:Migrations of seismic activity observed after large earthquakes which occurred in and near the Japanese Islands are investigated, A common feature of migrational phenomena in the six cases which are studied in this paper is that migration occurred along geological tectonic zones, Sometimes existence of active tectonic zone is reconfirmed by the appearance of migrational phenomena, Analogizing to plate boundary regions where seismic activity is known to migrate or diffuse along mechanically coupled plane, we can consider that inland active tectonic zones correspond to mechanically interacting boundaries of crustal blocks. It is likely that more than one type exist in miqrational phenomena. In the cases we investigated following characteristics are observed that velocity of migration is about several km/year, seismic gaps remain between focal regions of large earthquakes, and there are seismically active periods in each seismic belt. A possible mechanism of migration is successive break down of asperities in which tectonic stress concentrates by relative movement of crustal blocks.
Sopyright:China Earthquake Engineering Journal