地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
37 巻, 4 号
選択された号の論文の16件中1~16を表示しています
  • ―広域の験震データの併合処理―
    海野 徳仁, 長谷川 昭, 高木 章雄, 鈴木 貞臣, 本谷 義信, 亀谷 悟, 田中 和夫, 澤田 義博
    1984 年 37 巻 4 号 p. 523-538
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    Precise focal mechanism study of earthquakes occurring in Hokkaido and northern Honshu is made by using 35 stations of microearthquake observation networks of Tohoku University and of Central Research Institute of Electric Power Industry.
    In the northern Honshu and at the junction between the Northeastern Japan Arc and the Kurile Arc, the upper seismic plane of the double-planed deep seismic zone is characterized by down dip compression and the lower seismic plane by down dip extension. The events occurring in the shallower part of the upper seismic plane (shallower than 60km in the northern Honshu and shallower than 70km at the junction) have low-angle thrust fault type.
    The upper seismic plane is not down dip compression but has various types of focal mechanisms beneath Hokkaido, the southwestern end of the Kurile Arc, although the shallower part of it has low-angle thrust fault type as the case of northern Honshu. This upper seismic plane disappears at the depths greater than about 120km. The lower seismic plane is characterized by down dip exension, which is the same as northern Honshu. In Hokkaido, the lower seismic plane with down dip extension type extends to the deeper part down to about 300km depth. On the contrary, in nortern Honshu, it is the upper seismic plane with down dip compression type that extends to the deeper part down to at least 200km depth.
    The characteristics of the double-planed deep seismic zone in the southwestern end of the Kurile Arc may suggest relatively strong slab pull force superimposed on the stress system generating the double-planed deep seismic zone.
  • 遠山 忠昭, 檀原 毅, 里村 幹夫
    1984 年 37 巻 4 号 p. 539-547
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    Although γ-ray surveys have often been carried out in order to research active faults, clear correspondence of γ-ray intensity to faults has not always been obtained. We examined over again the methods of γ-ray surveys and the following two points came up as important problems.
    (a) The hole to set the senser of γ-ray survey meter must be bored in the same radius and depth at each survey point.
    (b) Much attention must be payed to the difference of surface materials.
    In order to confirm the usefulness of the method in which the above two points are taken into consideration, the γ-ray surveys were carried out along a line across the Himenoyu fault. This fault was formed at the time of North-Izu earthquake in 1930, and its traces are yet clearly found. A clear peak of γ-ray intensity was obtained at the position on the fault.
    Next, this method was applied to the Ono fault whose precise position has not yet known, and we estimated the position of the fault by the results of γ-ray surveys.
  • 池田 隆司, 笠原 敬司, 伊藤 健治, 多田 堯
    1984 年 37 巻 4 号 p. 549-557
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    In order to obtain information on the underground structure around the Karasuyama-Sugaonuma fault, we carried out a temporary observation for artificial explosions which were blasted at four sites in Saitama and Ibaraki Prefectures in March 1982. Crossing the southern part of the fault, seven seismometers were deployed on an east-west striking observation line 30km long. For three of the explosions, good records were obtained at all the stations. Travel time analyses provided three layers; apparent p-wave velocities in the layers are 1.7km/sec, 2.8-3.1km/sec and 6.1km/sec from top to bottom. Travel times for the 6.1km/sec layer jump near Sashima-cho, Ibaraki Prefecture, where the western branch of the fault is supposed to lie. For the wave propagating through the topmost layer between the eastern and western sides of the north-south striking fault, a systematic difference in the wave form was observed. Those observed features strongly suggest that not only the basement layer (VP=6.1km/sec) but also upper layers are displaced or fractured by the Karasuyama-Sugaonuma fault.
  • 梅田 康弘, 飯尾 能久, 黒磯 章夫, 伊藤 潔, 村上 寛史
    1984 年 37 巻 4 号 p. 559-567
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    Many aftershocks (3.5≤M≤7.1) of the Mid-Japan Sea Earthquake (May 26, 1983, M=7.7JMA) were recorded at Fukaura by velocity type strong-motion seismometers. P-wave spectra of these aftershocks were obtained by band-pass filters and converted to the displacement spectra at a reference distance of 35km.
    The spectra thus obtained were added to the seismic spectral data of other regions previously obtained by the same method. From the total spectra, scaling of seismic spectra was produced by earthquakes with the magnitude range of 0_??_M_??_7.5. The seismic spectra of small or micro-earthquakes have only one peak, but most spectra of large earthquakes have two peaks at low- and high-frequencies. The low- and high-frequency spectral peaks vary with different slopes of f-3 and f-9, respectively for various magnitudes.
    For the large earthquakes, the low- and high-frequency spectral peaks correspond to the coherent movement of main fault and small ruptures, respectively. Clear separation of the observed two spectral peaks for a large earthquake implies that the dimension of small rupture element is not arbitrary but limited.
  • 古瀬 慶博, 河野 芳輝
    1984 年 37 巻 4 号 p. 569-578
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    Isostasy over central Honshu area is examined by the following four methods.
    (1) Cross-spectrum technique is applied to analyse a correlation between Bouguer anomalies and topographic relief over the area. Admittance functions derived from this technique for the area show good agreement with those for stable continents.
    (2) Residual Bouguer anomalies (R. B. A.) over the area are calculated by subtracting a gravity effect of the subducting Philippine sea plate from the observed Bouguer anomalies. The relationship between the R. B. A. and topographic releaf shows a higher correlation than that between the observed Bouguer anomalies and topographic relief.
    (3) Theoretical Bouguer anomalies calculated by using the admittance functions in central Honshu and topographic relief in stable continents are in good agreement with the R. B. A. over the area.
    (4) Hydrostatic pressure at the Moho along the Atsumi-Noto explosion seismological observation line satisfies the empilical rule between depth of Moho and pressure at it, which was found in tectonically stable continental and oceanic areas.
    It is shown from these results that the isostatic state is achieved over central Honshu as it does over stable continents, though the area is tectonically quite active.
  • 近畿地方中北部の微小地震活動について
    前田 直樹, 渡辺 晃
    1984 年 37 巻 4 号 p. 579-598
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    In the middle and northern parts of Kinki District, microearthquakes are occurring almost stationarily. In order to investigate their activity in relation to the tectonic structure and also to simulate the occurrence of larger events, a telemetry network of observation stations was spread densely over these areas. The data, thus acquired, were analyzed and filed with a data processing system.
    By using these data of about seven thousand events (1976 to 1981), we got a most detailed spatial distribution of microearthquakes and compared it with the fine tectonic structure in this region.
    As the result of analyses, it is clarified that microearthquakes are not distributed uniformly over the tectonic lines or the active faults, but they form some arrays or clusters systematically along a north-south direction. It may be possible to conceive of the shape and direction of arrays or clusters being provided apriori under a tectonic field of northsouth direction. An earthquake family, then, seems to be composed of microearthquakes belonging to an arrays, because the cutoff value (M=4-5) in the frequency distribution of magnitude corresponds well to the size of the array.
    Next, the time series of microearthquake activity is examined by applying the Weibull distribution. The mode of activity is divided into two portions, having respectivedly the successive and random properties, at a certain value of time interval of earthquake occurrence. This characteristic value varies among the earthquake families, and also has a negative correlation to the Gutenberg-Richter's b value. The value, therefore, seems to be a parameter that indicates the state of medium and/or the temporal concentration of tectonic stress.
    Thus, we intend to obtain more data to deduce a local concentration of tectonic stress or a change of pattern of stress field through detailed studies on the spatial and temporal distributions of microearthquakes in stationary states.
  • 飯尾 能久
    1984 年 37 巻 4 号 p. 599-606
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    A micro-fracture with a magnitude of about -2 occurred at a depth of about 700m in the Nakatatsu mine after about 48 hours from the latest explosion for excavation. The location of the micro-fracture was obtained at a distance of about 15m from the newly excavated face. The micro-fracture was accompanied with many aftershocks. The linear dimension of the aftershock area was obtained to be about 1m. The number of aftershock per unit time decreased hyperbolically with the time elasped after the main shock, similar to those of large, moderate and small earthquakes. The p-value in the modified Omori's formula was obtained to be 0.84. The m-value in the Ishimoto-Iida's formula for the aftershocks was obtained to be 2.01. These statistical properties of the aftershocks of the micro-fracture are the same as those of earthquakes. In a rock test, large AE events are also accompanied with aftershocks. The number of the aftershocks of large AE events decreases hyperbolically with time, similar to those of earthquakes. It may be concluded that the fracture in rock is accompanied with aftershocks and that the number of aftershocks decreases hyperbolically with time out of relation to its rupture size.
  • 渡辺 偉夫
    1984 年 37 巻 4 号 p. 607-619
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    The purpose of this paper is to study statistical features on tsunami occurrence in and near Japan, used revised tsunami table of WATANBE (1983).
    Obtained results are as follows.
    1) Recent occurrence number becomes two and one forth (2 1/4) times for more one step of tsunami grade magnitude m and five times for the more two steps.
    2) Only the Chile and Kurile-Kamchatka tsunamis have given effective damage in the Japanese coast.
    3) HATORI'S grade magnitude mH is equal or more to m off northeastern Japan and equal or less to m off southwestern Japan. This depends on a locality of wave damping.
    4) The equation mH=2.25Mt-18.26 (Mt: ABE'S tsunami magnitude) has the smallest standard error among four relation between (m, M), (m, Mt), (mH, M) and (mH, Mt).
    5) Earthquake origin depth H is not so effective for tsunami occurrence.
    6) Log S is better linear relation with Mt than m, mH and M.
    7) In general, tsunamigenic earthquakes have pressure and tension axes of east-west direction and reverse fault of dip-slip type.
  • 瀬川 爾朗
    1984 年 37 巻 4 号 p. 621-632
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    This paper claims that ‘Gravity disturbance’ instead of free air anomaly should be used for deriving the subterranean structure of the earth from gravity anomalies. The free air gravity anomaly is affected not only by the underground density anomaly but by the undulation of geoid which is also caused by the same density anomaly. The gravity disturbance is a kind of free air anomaly reduced to the surface of the normal earth ellipsoid which is the reference surface to estimate the geoidal height. The geoid undulation that is caused by the disturbing potential is also affected by the reference surface on which the disturbing potential is evaluated. This effect has been examined, leading to a conclusion that the effect is apparent, but that its amount is negligible from the viewpoint of the influence on the density structure.
    Bouguer reduction which is to be applied to gravity disturbance is also discussed. ‘Bouguer disturbance’ thus newly defined can be obtained by conducting the Bouguer reduction while replacing the elevation by the height measured above the normal ellipsoid in the case of land, or replacing the depth of sea by the depth minus the geoidal height in the case of sea.
    Comparison between the free air anomaly and the gravity disturbance in and around the Japanese islands shows that the differences which are the averages within grids 1°×1° range from -0.3mgal to +14.5mgal. In order to examine how the density structure of substratum would change if the gravity disturbance is used instead of the free air anomaly the 2 dimensional structure across the northeast Honshu along a parallel 39°45′N that had been obtained by Segawa and Tomoda (1976) was reexamined. The result shows that the density of crust may change by the amount of +0.01g/cm3, and that the density of the low velocity zone in the upper mantle inferred to exist beneath the Sea of Japan may change by the amount of +0.0009mgal. The difference of the density obtained by reestimation seems to be small, suggesting that the difference between the free air anomaly and the gravity disturbance might not be so important. However, the author is of the opinion that the gravity anomaly that can be used equivalently to the height of geoid is not the free air anomaly but the gravity disturbance, and that even the minor difference in density estimated here would become more important in future when better information in the other field of geophysics becomes available.
  • 卜部 卓, 平田 直
    1984 年 37 巻 4 号 p. 633-645
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    An automatic playback system for direct analogue tape recordings from an ocean bottom seismograph (OBS) network was developed. The system utilizes a mini-computer equipped with a high speed A-to-D converter. In the direct analogue recording method, ground motion is recorded continuously for 10 to 25 days in a compact-cassette tape and is reproduced at several hundred times recording speed.
    First, the output of the analogue tape from an OBS is rectified, low-pass-filtered, then digitized continuously at a relatively slow sampling rate of 13Hz (samples per seismic second) and stored in a magnetic disk. In the digitized record, the events satisfying a specified criterion are detected and put on a list for each OBS. Non-seismic events are eliminated by cross-referencing the lists of all OBS's in the network. Secondly, portions of the listed earthquakes are digitized again from the analogue tapes at a fast sampling rate of 60 to 150Hz. The re-digitizing is done automatically according to the schedule made from the lists of earthquakes. The sampling rates of the digitized earthquake data files are unified with reference to each OBS clock by numerical resampling. The earthquake data files from all the OBS's are assembled and edited for each earthquake to make a multi-station data file in which the records of all the stations are referred to a common time axis like telemetered network data. It is visualized by a D-to-A converter and a chart recorder. This format of visual records facilitate picking up earthquake phases for hypocenter determination because the correlation of the waveforms among those obtained at different stations are apparent. This leads to more accurate measurement of arrival times than by the conventional method; reading a single-station record. The digitized data files are preserved in magnetic tapes.
    Although the system is intended primarily to process earthquakes network data, it is also applicable to other kinds of data such as those by explosion experiments. This system has automated and speeded up the OBS data processing significantly.
  • 小玉 一人
    1984 年 37 巻 4 号 p. 647-654
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    I propose a simple model to evaluate the possible mechanical and topographical effects that might be caused when an oceanic plate is subducted beneath the continental plate. The model will focus on the effects caused by perturbations such as oceanic ridges, seamounts and plateaus on the oceanic plate. The model consists of the two-dimensional Newtonian viscous fluid over the rigid basement with all the oceanic elements moving with a constant velocity. Applying Fourier transform analysis to the basic solutions for harmonic basal undulations, the basal shear stress and topographic profile caused by subducting oceanic ridges, seamounts, or plateaus were calculated. Assuming reasonable values for such physical constants as viscosity (1022 poise), density (3g/cm3), thickness of overriding plate (20km), height of ridge or seamount (1km), and subducting velocity (10cm/yr), the resultant surface profile varies asymmetrically from the top of 316m down to -260m, and the shear stress from -570bar up to 1270bar. The results from these calculations allow us to make quantitative estimates of the geological consequences of the past ridge subduction beneath island arcs but also give possible explanation for some of the uneven seismic activities found around present subduction zones.
  • 小山 順二, 鄭 斯華, 鈴木 次郎
    1984 年 37 巻 4 号 p. 655-669
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
    A spectral analysis has been developed to obtain an approximate spectrum of short-period waves with nearly random phases. The analysis method has been applied to more than 900 short-period seismograms of recent great earthquakes in the world. Short-period seismic moment M1, which represents an estimate of earthquake source spectrum at a period of about 1 to 2 seconds, has been evaluated for 79 earthquakes covering the range of seismic moment M0 from 7.5×1029 to 7.5×1024 dyne·cm. It has been shown that seismic moment M0 is approximately in proportion to the square of short-period seismic moment M1 in the above dynamic range. A relation between short-period seismic moment and bodywave magnitude mb* redetermined from maximum trace amplitudes of P-wave trains has been obtained;
    logM1=1.24mb*+17.9.
    The former relation would give constraint to understand the rupture mechanism of irregular faults and the latter would give a quantitative measure to evaluate the overall excitation of short-period seismic waves due to large earthquakes.
  • 鵜川 元雄, 藤縄 幸雄, 杉山 四朗, 小沢 美喜男
    1984 年 37 巻 4 号 p. 671-674
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 菊池 真市
    1984 年 37 巻 4 号 p. 674-676
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 浅田 敏, 綱川 秀夫, 山本 芳孝
    1984 年 37 巻 4 号 p. 677-678
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 越川 善明
    1984 年 37 巻 4 号 p. 679-680
    発行日: 1984/12/25
    公開日: 2010/03/11
    ジャーナル フリー
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