• Volume 8,Issue 1,1986 Table of Contents
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    • STUDY ON THE SOURCE PROCESS OF THE SONGPAN GREAT EARTHQUAKE

      1986, 8(1):1-10.

      Abstract (559) HTML (0) PDF 682.91 K (1026) Comment (0) Favorites

      Abstract:Based on the viewpoint that there must be adjustment elements of stress at the ends of earthquake source region and medium of the source region is stronger than that in the neighbour.This paper,by means of the modulated small earthquake method,analyses the source process of the Songpan earthquake (M=7.2).The temporal-spatial pattern of small earthquakes indicates that the source process has three stages.
      1.The first-stage (1970-May 7,1973)
      In this stage,a gap appeared in the seismic pettern by the modulated small earthquakes,but no modulated small earthquakes still took place in the gap.It indicates that the homogeneity and the strength of source region are greater than those in its outside part.The background of source region is formed in this stage.
      2.The second stage (May 8,1973-Dec.1974)
      During this time,in the seismic pattern,non-modulated small earthquakes disappear in the source region,hut more active for strong and moderate earthquakes in the northern end of the source,which shows that the hypocentral area has been formed and stress is being accumulated.
      3.The third stage (Jan.1975-Aug.15,1976)
      In this stage,the junction regions of the modulated small earthquakes belts are formed at the ends of the Songpan source region.The non-modulated small earthquakes began to be active again in the source,which shows that the adjustment elements at the ends of the source have been formed.In this time,the source region has provided the conditions for the occurrence of earthquakes.
      4.During a few months (about half a year) before the 1976 Songpan earthquake,in the epicentral area and its periphery (about 300×200sq.km),there an anomalous ratio of modulated small earthquakes,which means that there is a very high stress in the source and its periphery.By this we can judge the strong earthquake is coming.
      5.There appeared peaks of small earthquakes on June 27,July 13 and Aug.15 in a large scale of the middle part of North-South earthquake belt before this earthquake,the first two of which are synchronized with solid tide,the last of which happened on the day before eanthquake.Such a synchronization means that a large earthquake is impending to occur.

    • DISCUSSION ON THE MEETING OF EARTHQUAKE COMMENCEMENT FAULTS AND STATIC FAULTS

      1986, 8(1):11-23.

      Abstract (588) HTML (0) PDF 909.53 K (919) Comment (0) Favorites

      Abstract:It is very common for a dynamic earthquake commencement fault to meet a static fault when earthquake happens This paper divides such a meeting into four types and gives the mechanical models of their own respectively.By mechanical analysis and mathematical analogy,the consquence resulted possibly from every kind of type of the fault meeting is discussed with the earthquake events in this paper.
      1.The earthquake commencement fault is arrested by static fault;
      2.Strong aftershock happens in the meeting area where commencement fault has been arrested;
      3.Breaking through static fault,commencement fault runs on,and on until a conjugate earthquake maybe arises.
      The above discussion may be useful to the prediction of magnitude and strong aftershock.

    • DISCUSSION ON THE RELATIONSHIP BETWEEN FOCAI FAULT LENGTH AND FACAL FAULT DISLOCATION

      1986, 8(1):24-40.

      Abstract (610) HTML (0) PDF 1.11 M (919) Comment (0) Favorites

      Abstract:F.F.L.and.F.F.D.* are two important quantities of the earthquake source parameters.It is important for earthquake prediction to find indicated scales of them before earthquake occurs.The special value between F.F.L.and F.F.D.represents the harmonic property in dis ocation procedure of fault at depth.This property is helpful for us to understand source circumstance.
      In this paper,we have collected the fault data of great earthquakes occurred in regions of China,Japan and the United States,then analysed and processed these data,and obtained approximate linear relationship between F.F.L.and F.F.D.,the former of which is 10-5 order of magnitude larger than the latter.
      In addition to the above-mentioned,depending on the harmonic relationship between F.F.L.and F.F.D.in the earthquake procedure,we discuss the problem whether the earthquake fault before the 1976 Tangshan earthquake creeped or not,and whether the slippage in the Tanlu fault can do or not for handred kilometers of horizontal offset.

    • THE STUDY OF THE RELATION BETWEEN B VALUE AND CRUSTAL STRESS RELAXATION

      1986, 8(1):41-52.

      Abstract (580) HTML (0) PDF 913.67 K (700) Comment (0) Favorites

      Abstract:This paper deals with the influence of temperature,pressure,water and chemical composition on crustal rock's relaxation time and the influence of some factors,besides average stress of earth crust on b value.It is believed that the less the average relaxation time of crustal medium is,or the more heterogeneous crustal medium is,or the more slowly crustal medium is stressed,the greater b value is.

    • A DISCUSSION ON THE PROBLEM OF SEISMIC WAVE PROPAGATING THROUGH VERTICAL INHOMOGENEOUS MEDIA

      1986, 8(1):53-61.

      Abstract (521) HTML (0) PDF 700.02 K (686) Comment (0) Favorites

      Abstract:The synthetic seismograms of head waves are computed,which propagate through the medium with a high velocity layer in it.1t is seen that interference head waves will occur if the high velocity layer becomes thinner until a certain extent.The limitation of ray theory is proved in a flank.Analyzing the energy conservation relation of reflection and refraction coefficients of seismic wave,it has been noticed that the probability of reflection and refraction coefficients is greater than one.A numeral method of computing synthetic seismogram,finite difference method is introduced,which can be used to calculate Lamb problem in vertical inhomogeneous media.

    • THE INVERSION OF SEISMIC SURFACE WAVE DISPERSION AND THE STRUCTURE OF UPPEK CRUST IN QINHAI AREA

      1986, 8(1):65-74.

      Abstract (575) HTML (0) PDF 586.97 K (841) Comment (0) Favorites

      Abstract:The inversion of seismic surface wave dispersion is one of the important methods for exploring the structure of the earth's interior,in this paper,problems on inversion calculation are discussed in detail and the upper crustal structure of Qinghai area is inversed by using the information of Gansu Seismic network.

    • THE CHARACTERISTICS AND THE CAUSE OF THE FORMATION OF THE GOUGE FROM HAIYUAN ACTIVE FAULT ZONE AND ITS EFFECT ON THE SLIDING BEHAVIOR OF THE FAULT ZONE

      1986, 8(1):75-90.

      Abstract (497) HTML (0) PDF 3.99 M (499) Comment (0) Favorites

      Abstract:This paper makes a systematic study for all kinds of the characteristics of the gouge from Haiyuan active fault zone.The kinds of the small-sized faults in the gouge zone have been investigated.The implication of the organic geochemistry of the composition of the gouge is approached.A combination of various SEM micro-surface textures on quartz fragments in gouges caused by mechanical movements of faults is advanced through ihe study in contrast with each of the combinations in eight enviroments.The combination in gouges is regarded as a sigh to determine an active fault.The SEM micro-surface dissolved textures on quartz fragments in the gouge are classified into five types.The age and the state of the active faults are analysed on the based of five types.The types of the SEM micro-textures in the gouge are discovered.The relations between the active faults and the micro-textures and the distribution of grain size in the gouge are analysed.The formation and the evolution of the gouge are discussed.The effect of the gouge on the sliding behavior of the fault zone in Holocene Epoch and the relation between the gouge and the earthquakes are studied.

    • THE QUATERNARY STRUCTURAL ACTIVITIES AND SEISMICITY ON THE NORTHEASTERN SECTOR OF THE NORTH FRINGE FAULT ZONE OF AERJIN MOUNTAINS

      1986, 8(1):91-99.

      Abstract (568) HTML (0) PDF 688.70 K (541) Comment (0) Favorites

      Abstract:The north fringe fault zone of Aerjin mountains is an important fault in Aerjin fault system (Altyn Tagh fault system).It might have existed in Late Proterozoic and became the boundary fault between Talimu Plateform and paleo-ocean plate in Paleozoic.In the neotectonic movement it has had very intense activities particularly left-lateral strike-slip movement.In this paper its notheastern sector is studied.
      On this sector of the fault zone a thick fault gouge belt and a wide cataclastic rock belt were observed.The plane distribution of the fault zone often exhibits an echlon or oblique connexion pattern.The deformation and some specific geomorphic features caused by strike-slip movement of fault are given.
      According to a great deal of data of the displacement distance on water system and other geomorphic unit we obtained four average slip rates from diffirent times in late Quaternary to today.They are 5.8mm/yr.from Middle Pleistocene,3.4-4.0mm/yr.from the lntersadial of middle Pleistocene,4.0-4.5mm/yr.from Late Pleistocene,and 8.0mm/yr.from Holocene.Based on C14 dating,the rate is more than 3.6mm/yr.from late Holocene.
      In the northeastern sector we found some paleoseismic traces and afresh paleoearthquake deformation belt in Lucaogo,where we estimatedthat the earthquake occurred about 300 years ago and M=7.0-7.5 according to the slope of fault scarps and length of fracture belt.The relationship between recent seismicity and the fault zone,the seismic risk and great earthquake recurrence are discussed.

    • AGE OF FAULT-SCARPS AND EARTHQUAKE RECURRENCE INTERVALS ON CHANGMA FAULT

      1986, 8(1):100-106.

      Abstract (643) HTML (0) PDF 546.28 K (932) Comment (0) Favorites

      Abstract:Based on authers' field investigations, using geological methods, in the paper we have mainly discussed the fault-scarp features and displacement features in eastern Changma fault zone, some paleoseismic evidences along the fault zone, including the faults formed in Holncene Epoch, ancient slump, drumlin and fault cliff and coarsely ascertained the displacement rates of the NEE fault, the age of the fault-scarps and earthquake recurrence intervals along the faul zone.
      The studied results show that the active properties of the NEE fault have transformed themselves from extrusion, into left-lateral shear-tension Since Holocene Epoch and the left-lateral shear-tension activity of the fault did form the fault-scarps.
      An earthquake (Ms=7.5) probably once occurred along Changma fault zone about A.D.104. The recurrence intervals for magnitude 7-7 (1)/(2) earthquake are 2620 years when creep rate is considered, and 1500 years when creep rate is not considered. The strike displacement rate of the fault is 4.5mm/Yr during 12760 years, and 6.5mm/yr during 1880 years. A ratio of strike displacement to the dip is 4.7.

    • THE SIMULATED TEST ON THE RELATION BETWEEN THE TECTONIC STRESS FIELD IN THE NORTHERN PART OF NORTH-SOUTH SEISMIC BELT AND THE EPICENTRAL MIGRATION

      1986, 8(1):107-113.

      Abstract (533) HTML (0) PDF 1.36 M (547) Comment (0) Favorites

      Abstract:The modern characteristics of distribution of the tectonic stress field in the northern part of North-south Seismic Belt are studied in this paper with distortion analogy,ordenary optic elastics and the simulated test of optic elastics of laser holography under various force sources.The paper deals with the principal compression stress,the main tension stress and their directions in this region.The isorithm of the principal compression stress in the region is given in this paper as well.Thus it can be known from the test mentioned above the stress value in the action of unified stress field in every segment of this region.With Moll strength theory,the seismicity here is made an analysis and a research is conducted to the.relation between the modern features of distribution of the tectonic stress field and epicentral migration.

    • A NEW VIEWPOINT ON THE CAUSE FOR RESERVOIR EARTHQUAKES-A MODEL OF WEAKENED AND IMAGE FORCE

      1986, 8(1):114-119.

      Abstract (593) HTML (0) PDF 372.99 K (699) Comment (0) Favorites

      Abstract:以前的水库地震成因学说大多是认为地下断层积累了较高的应力,难以错动,当水库蓄水后,水通过裂隙渗透到断层面上,从而降低了断层面上的有效正压力或摩擦系数,导致断层的快速错动形成地震。然而这个学说对解释极浅源地震是有困难的。根据模拟实验,产生粘滑要有一定的正应力,否则仅能产生稳滑。在地下几公里的深度上围压比较小,因之在这样的深度是否存在粘滑条件还值得商榷。在这种情况下,用水去帮助断层错动更没有必要了。本文作者认为水库地区坚硬介质中大量小裂缝的接通是某些水库发生大量小震的原因。水进入裂缝后可加强裂纹的蠕滑,它使裂纹端部形成应力集中,有利于诸裂纹间的接通,而不是水进入断层后使断层本身发生错动而形成地震。当大量小裂缝互相接通时,即大量水库小震发生后,水又进一步渗透到小震活动区,使这一软弱区的范围(面积和深度)进一步扩大,形成应力调整区。如果在库区下方较深处有隐伏的蠕滑断层(走滑或倾滑),这可成为水库区另一个调整单元。它们之间相对完整的介质区即为应力积累区——震源区。在区域应力场的作用下,隐伏的蠕滑断层端部有剪应力集中,另外水库弱化区下方也有应力集中,这就使两个调整单元有接通的趋势,当积累单元的应力达到极限值时,这种接通就必然产生,并形成较大水库地震。另外,水库弱化区的下界面对蠕滑断层端部还有象力作用,它也有使该断层向弱化区传播的趋势,从而导致较大的水库地震。本模式说明,如果建水库前对未来诱发的地震进行预测时,应注意库区更深部是否有隐伏断层存在。

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