Journal of Physics of the Earth
Online ISSN : 1884-2305
Print ISSN : 0022-3743
ISSN-L : 0022-3743
Volume 34, Issue Supplement
Displaying 1-22 of 22 articles from this issue
  • STATUS AND PROSPECTS
    Zhangli CHEN
    1986 Volume 34 Issue Supplement Pages S1-S11
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    The initial understandings about time and space distribution of major earthquakes and earthquake precursors, and prediction achieved for the past 18 years in China are summarized. Two major aspects of the fundamental understandings are: 1) Before most of the strong shocks, particularly those with magnitude over 7 occurring within an area under the detectability of a network, varieties of anomalous phenomena are observed. 2) Because of the complicated continental crustal structures, the temporal and spatial distributions of the continental seismicity in China are rather complex, but there are some regularities, and some unique dynamic patterns such as block-like, stripe-like, and diversified distributions of earthquakes.
    The problems of earthquake prediction are identified. They are mainly caused by 1) non-uniqueness of the relation between anomalous variations and earthquake precursors, 2) complexity of the relation between local and regional anomalies, and 3) diversity of possible earthquake precursors. And how to improve the level of earthquake prediction, topics to be further studied, and the key work to be carried out are also discussed. Efforts should be directed to 1) systematic evaluation and in-depth research of various prediction methods, 2) setting up the optimum monitoring network and appropriate data processing systems, 3) profound fundamental research, and 4) comprehensive research on earthquake precursors.
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  • Shaoxie XU, Yufen LIU
    1986 Volume 34 Issue Supplement Pages S13-S24
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Seismicity pattern represents the characteristics of a group of earthquakes. This paper describes several characteristic features of seismicity in China's mainland, especially in North China. They include block-like distribution of earthquakes, temporal correlation of seismic activities of given separate regions, repeat of certain seismicity pattern in space, etc. The spatial dimension of these patterns may reach hundreds or thousands of kilometers. Accordingly, the dynamic force causing earthquakes is suggested to act simultaneously on a large area. Earthquakes in China's mainland are mainly concentrated in a layer of 15-km thickness, i.e., the competent seismogenic layer. Because of the large difference between this thickness and the large horizontal dimension of seismicity pattern, the seismogenic layer can be considered as a thin shell. Since observed block-like seismicity pattern is very similar to the buckling pattern of a thin shell, we suggest that block-like pattern of seismicity is caused by the buckling of the seismogenic layer. The calculated dimension of the buckling pattern is about 500 km and it well agrees with the dimension of blocks.
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  • Zongjin MA
    1986 Volume 34 Issue Supplement Pages S25-S34
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    From the earthquake records of about 2, 000 years, it can be seen that North China, Korea, and Japanese Islands are associated with seismicity. During this period there are several seismically active periods of about 200 years, and each period can be subdivided into several seismically active episodes. In 1966, the seventh episode of the present active period was initiated and four strong earthquakes (MS≥7.0) have occurred in North China. Before or after these events, noticeable anomalies emerged at several places, which are called "regional stress windows." Eight "windows" (including six of seismicity, one of crustal deformation, and one of radon) are discovered. To our surprise, remarkable anomalies appeared at all the windows before the Japan Sea (or Akita-Oki) earthquake of 1983. It does not seem to be a mere coincidence. For a unified explanation of the phenomena of the episode and "windows, " the author presented the multiple stress concentration hypothesis in 1979. The locally stress-concentrated points would develop either into an earthquake focus or into a "window." There seems to be a close tectonic relation between the eastern China and the island arc system. In terms of geological and geophysical data, this region can be divided into several laths (long and narrow pieces of plate), stretching along a co-latitudinal direction. One of them is the North China-Korea-Honshu, Japan lath, which is a seismically active lath with large continental earthquakes. The configuration of the lath appears to be closely related to the geodynamic process.
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  • Zhizhen ZHENG
    1986 Volume 34 Issue Supplement Pages S35-S44
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
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  • Kinichiro KUSUNOSE, Osamu NISHIZAWA
    1986 Volume 34 Issue Supplement Pages S45-S56
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Acoustic emission (AE) was monitored during uniaxial compression of andesite and granite specimens, and their hypocenters were located with an accuracy of a few millimeters in a cylindrical sample of 10 cm in length and 5 cm in diameter. P-wave polarity data suggests that AE is radiated from a shear-type cracking. We expect that the stress field is monitored by the mechanism solutions. An AE gap that is very similar to a seismic gap of the second kind defined by Mogi in 1979, was observed prior to an extremely large AE in an andesite specimen under uniaxial compression of about 90% of the fracture strength. The focal mechanism solutions for the foreshocks and aftershocks of the large AE suggest that the local stress field changes by the main shock.
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  • Yutaka TANAKA
    1986 Volume 34 Issue Supplement Pages S57-S70
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    The purpose of this paper is to show, from the results of in situ stress measurements using the stress relief method, to what extent we can infer the state of tectonic stress in the upper crust. The three-dimensional stress state at a measuring site is expressed by the stereographic projection of maximum shear plane using the same technique as for fault plane solution, and by diameters of double circles indicating maximum shear and mean stress magnitudes. These illustrations can be used to discriminate sites which do not reflect real tectonic stress. Horizontal stress orientations coincide fairly well with the tectonic stress field estimated from fault plane solutions, crustal deformation, and orientation of active faults. Horizontal stress magnitudes at each site are therefore corrected to a depth of 300 m using the standard stress gradient with depth and then compared with the results at the hydrofracturing sites in the Kanto-Tokai area for examination of local stress magnitude. There is a tendency that shear stress values obtained by the hydrofracturing method are low compared with those by the stress relief method. The relation of shear stress to mean stress is also interpreted graphically to determine the present stress state, and compared with a critical fracture condition in the upper crust. Whether the measured stress values indicate the real crustal stress state or not, may be inferred from these methods which also enable us to compare the regional differences of stress state.
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  • Fangquan LI, Guangxun LIU
    1986 Volume 34 Issue Supplement Pages S71-S80
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    The stress state in the upper crust of the China mainland is discussed on the basis of in situ stress data measured by both hydrofracturing and overcoring techniques during the last ten years. From these measurements, it appears that the horizontal stresses are characterized by strong directionality, which varies from region to region. The maximum horizontal shear stress increases linearly with depth and its gradient varies with region. Both the vertical gradients of the maximum horizontal shear stress and the horizontal principal stress are much higher in West China than in East China. Many data show that the direction of the maximum horizontal principal stress, related to the geological structure and recent crustal deformation within the area, is almost uniform over vast regions.
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  • Hiroshi WAKITA, Yuji NAKAMURA, Yuji SANO
    1986 Volume 34 Issue Supplement Pages S81-S89
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Telemetered records of radon concentration in well water have been obtained from observation sites along the Pacific coast of Honshu, Japan, since as early as 1977. The accumulated data of two wells in the Tokai district indicate that no unique correlation exists between the water level and radon concentration changes. It is possible that changes in radon and water level are controlled by two different environmental factors, although the long-term trend between the two appears to be concordant. A stronger concordancy of the trend was found between borehole volume strain data and radon data. The concordancy suggests that radon emanation increases when the rocks are subjected to tensional stress.
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  • Zhengmeng LI
    1986 Volume 34 Issue Supplement Pages S91-S102
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Just before the large earthquakes in Bohai, Haicheng, Luhuo, Tangshan, and Songpan in northern and southwestern China, anomalous changes in radon content in groundwater from wells and springs were recorded at most of the observation stations. From the compilation of the records of radon anomalies, characteristic features of the imminent radon changes prior to a large earthquake are derived: (1) spike-like anomalous changes; (2) inhomogeneity of the spatial distribution of the anomalies around the epicentral area; and (3) migration and spatiotemporal evolution of anomalies. Understanding of the characteristics of radon anomaly is of importance and will contribute much to the prediction of an impending large earthquake.
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  • Noboru INOUYE
    1986 Volume 34 Issue Supplement Pages S103-S110
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
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  • Zusheng ZHANG, Shaofen YING, Yongjian SHEN
    1986 Volume 34 Issue Supplement Pages S111-S127
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
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  • Shoji SAKATA, Haruo SATO
    1986 Volume 34 Issue Supplement Pages S129-S140
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Borehole-type instruments have many advantages over the conventional instruments usually installed in vaults. The primary merit is that the location is not restricted by geomorphic conditions. This decisively helps us to establish an observation network in a plain field area for earthquake prediction. The borehole-type tiltmeter developed is, as a principle, a pendulum tiltmeter with an electric feedback circuit. Tiltmeters are usually installed in boreholes at depths of about 100 m. Now, we have 23 stations in operation in the Kanto-Tokai area, central Japan. The measuring range is 400 microradian, the resolution is 0.006 microradian, and the long-term stability is better than a few microradian per year. This observation system is expected to be very effective for detecting anomalous tilt changes of the order of 0.05 microradian per day with a time constant of from several hours to tens of days. Recently, an anomalous tilt change of up to 0.4 microradian was detected in the vicinity of the focal area preceding an earthquake of magnitude 6.0. The borehole-type three-component strainmeter invented has a dual cylinder of which the narrow clearance is equally divided into three chambers. Two sets of strainmeters of this type were installed in two boreholes at depths of 160 m at Yasato, Ibaraki-ken. They have often detected strain steps caused by big earthquakes. Detectable strain steps can be as small as 10-10. Strain steps observed by the two instruments agree with each other very well, and are in good harmony with the theoretical strain steps calculated on dislocation models. These facts have proven that instruments of this type have high credibility. Such high performances can be attributed to the fact that the whole system is free from solid friction and less affected by shock and vibration at the time of earthquakes. The future plan is to unify the tiltmeter and the three-component strainmeter to one unit which would be called the Integrated Borehole Observation System (IBOS).
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  • Jin MA, Yijun DU, Liqiang LIU
    1986 Volume 34 Issue Supplement Pages S141-S157
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    En-echelon cracks can be divided into two types: left lateral shear and left step or right lateral shear and right step (LL), and left lateral shear and right step or right lateral shear and left step (LR). The conditions of interaction and stability of two en-echelon cracks are analyzed by using the linear elastic finite element method and theory of fracture mechanics. Then, the fracturing process and precursors of the main fracture in the staggered region of en-echelon cracks are studied by a series of rock experiments. It is found that the geometrical factors of en-echelon cracks influence the interaction and instability of faults and precursors of the main rupture.
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  • Hiroshi ISHII, Satoshi MIURA, Akio TAKAGI
    1986 Volume 34 Issue Supplement Pages S159-S174
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Large-scale crustal activity before and after the Japan Sea earthquake with magnitude 7.7 on May 26, 1983 was investigated taking into account microearthquakes, crustal strain, crustal stress, and vertical movements and applying numerical experiments. It is found that about one month prior to the mainshock, anomalous microearthquake swarms took place at some points which were considered to be related to fracture zones. Short-term precursors were not recorded by extensometers and watertube tiltmeters deployed at distances more than 80 km from the epicenter of the mainshock. Observed strain steps explain computed steps based on an assumed fault model. Precursory uplift several years preceding the mainshock was found at the nearest Japan Sea coast to the epicenter by space-time analysis of repeated leveling surveys.
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  • Takeo MORIYA
    1986 Volume 34 Issue Supplement Pages S175-S192
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Tectonic relation between the colliding forearc and descending lithosphere beneath the Hokkaido transition zone is presented. Structure and state of stress inferred beneath Hidaka mountains and off Urakawa regions show a possibility that the crust of the northern Honshu forearc is downthrusting beneath Hidaka mountains-the southwestern end of the Kurile forearc. Urakawa-oki earthquake of 1982 (JMA magnitude 7.1) which occurred in the forearc-junction region is concluded to be a result of this colliding movement. The collision is inferred to be mainly ascribed to southwestward movement of the Kurile forearc which may be originated from oblique subduction of the Pacific plate beneath the Kurile forearc. To understand the tectonic relation between colliding structure of Hidaka mountains and off Urakawa regions, and configuration of intermediate-depth seismic zone, more than 4, 200 hypocenters were redetermined. To look through the configuration of the deep seismic zone in detail, the hypocenters were projected on vertical planes and on different slant planes perpendicular to the dipping deep seismic zone. Hypocenter distribution in the intermediate-depth seismic zone shows that the seismic zones of the northern Honshu and the Kurile arcs are overlapping beneath the transitional zone of the two arcs. It is inferred that the overlap is ascribed to anomalous southwestward migration of the obliquely subducted Pacific plate beneath the Kurile forearc.
    It is concluded that beneath the forearcs in the arc-junctions, crustal structure, geometry of the contorted plate and state of the stress may be significantly controlled by the direction of the oceanic plate motion.
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  • Shirong MEI
    1986 Volume 34 Issue Supplement Pages S193-S212
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Based on the re-examined precursory data of the Tangshan earthquake of July 28, 1976, the complexity and regularity shown by the pre-earthquake anomalies as well as the problems brought about to the practical prediction are analyzed. Three main points are discussed: 1) The diversity and three stages of the precursors of the Tangshan earthquake; 2) The synchronism as well as difference in time of the emergence and pattern changes of the precursors; 3) The relative concentration of the intermediate-term anomaly and the scattered distribution of the short-term and imminent anomalies in space. Furthermore, according to the research results achieved in recent years in China, the physical mechanisms of the precursors of the Tangshan earthquake are identified. The rock dilatancy of the focal body, aseismic fault creep, and mass movement are considered as the basic causes of the precursory complexity.
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  • Deyi FENG, Mingzhou LIN, Chun JIANG, Ronghua CHENG
    1986 Volume 34 Issue Supplement Pages S213-S221
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    This paper presents a direct method for fuzzy recognition of earthquake precursors and a method of fuzzy clustering analysis of temporal seismicity patterns for earthquake prediction. The direct method for fuzzy recognition of earthquake precursors is based on their fuzzy description by use of membership functions. If we use a suitable membership function, the abnormal features of a precursor can be more clearly recognized. The membership function proposed by Feng et al.. in 1981 is applied to reported changes in VP/VS, resistivity, and radon content. The basic idea of application of fuzzy clustering analysis to earthquake prediction is that time intervals with different sizes of the largest earthquake can be classified on the basis of fuzzy similar relations according to the various kinds of statistical indices of seismicity. The method based on the fuzzy equivalent relation includes the following steps: obtaining a fuzzy resemblance relation between samples, transforming it into a fuzzy equivalent relation, and classifying the original samples. The statistical indices of seismicity used by Feng et al. in 1984 is employed for clustering analysis of seismicity in the North-South Seismic Belt of China.
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  • Xuezhong SHAO, Jiru ZHANG, Qiyuan LIU, Siya ZHANG
    1986 Volume 34 Issue Supplement Pages S223-S239
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    This work deals with the deep structure of the earth's crust and the uppermost mantle as revealed by a method using P-SV converted waves from earthquakes in Beijing-Tianjin-Tangshan and some large-earthquake areas of the North China Plain. During the last ten years a series of seismic profiles have been completed in the studied region with a total length of about 2, 000 km. The comparison of deep structure with the distribution of earthquakes indicates that most strong earthquakes are located at the boundary of fault-blocks and especially at the intersection of deep-seated fault zones where the depth of deep boundaries changes discontinuously. Some common features of the deep structure have been revealed in Tangshan and other large-earthquake areas of the North China Plain. These include shallow crystalline basement, deep Moho discontinuity, thick crystalline crust, and intersection of deep-seated faults with different trends. By way of structural comparison, some areas with deep structures similar to those of large-earthquake areas have been established in the northern part of the North China Plain, which could be considered the areas with potential risk for strong earthquakes.
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  • Toshikatsu YOSHII, Shuzo ASANO, Susumu KUBOTA, Yoshimi SASAKI, Hiroshi ...
    1986 Volume 34 Issue Supplement Pages S241-S248
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    Under the Fourth Earthquake Prediction Project of Japan starting from 1979, the Research Group for Explosion Seismology conducted a series of explosion seismic experiments to reveal detailed structure of the shallow crust. In this paper, results from two experiments in the Izu Peninsula are shown. Structure of the shallow crust in the peninsula is very complex and is quite valuable for the other geophysical and geological investigations. For example, time terms of the basement layer show a good correlation with Bouguer anomalies when we assume a reduction density of about 2.7 g/cm3. A layer with a velocity of about 4.1 km/s observed in the whole Izu Peninsula may correspond to the Yugashima Group. Our structural models are also useful for discussion of abnormal crustal uplift and seismic activities observed around the Izu Peninsula in recent years. We believe that the middle-size seismic experiment like these Izu experiments may be the most appropriate one in geologically complex regions such as Japan.
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  • Wucheng SUN, Wen FAN, Songlin LI
    1986 Volume 34 Issue Supplement Pages S249-S264
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
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  • Guoyu DING
    1986 Volume 34 Issue Supplement Pages S265-S278
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    A fundamental problem of carrying out earthquake prediction lies in the correct identification of a potential active area of strong earthquake activity. To attain this goal, it is necessary to study the state of a recent crustal rupture field related to strong earthquake activity. Large amounts of data have been acquired on historical earthquakes, active faults, surface faults associated with earthquakes, isoseismal lines, and source mechanisms in China. All these data outline objectively the principal pattern of recent crustal ruptures related to strong earthquake activity in China. It shows that this kind of crustal rupturing is characterized by rupturing in zones and regions. Four such major zones could be outlined. They are the Central Asian zone, the North-South zone, the North China zone, and the Southeastern Coast zone. Studies on the distribution, characteristics of activity, and mechanisms of the rupture zones, and recurrence interval of strong earthquakes in these zones have become of considerable significance for strong earthquake prediction.
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  • Qitong LI
    1986 Volume 34 Issue Supplement Pages S279-S291
    Published: 1986
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    This paper reviews seismic investigation of nuclear power plant siting in China, according to the present practices of nuclear power plant siting. Various kinds of seismic investigation are required for nuclear power plant siting, such as seismic and geologic investigation (mainly active fault research), earthquake prediction study (mainly the identification of potential seismic source), and earthquake engineering investigation (mainly earthquake hazard analysis). Finally, several problems associated with nuclear power plant siting are put forward for further investigation.
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